1. Metals have been extracted and used for many thousands of years
* Outline and examine some uses of different metals through history, including contemporary uses, as uncombined metals or as alloys.
Contemporary Uses of common metals
Metal | Uses | Iron and Steel (an alloy with <2% carbon)Good tensile strength, cheap, rusts (corrodes) | - Railways, bridges, buildings- motor cars bodies, ships and trains- Engine blocks, fire hydrants, drainage pipes, and gates- Reinforcing in concrete (roads, bridges, high rise buildings)- Refrigerators, washing machines and other domestic appliances- Heavy machinery in industry- Containers (drums and tin cans)- pipes, nails, nuts and bolts | Aluminium - low density, light weight, good tensile strength, and high resistance to corrosion | - Buildings (window and door frames, paneling)- Aeroplanes- Motor car parts (cylinder heads, radiator cores)- High voltage transmission lines- Domestic pots and pans and wrapping foil- Drink containers- Electric wiring over long distances (long distance power lines) | Copper | - Electrical wiring (household and street cables)- Pipes and plumbing fittings
- Electroplating, jewellery and household decorations | Zinc | - Galvanizing iron (surface coating)- Protective paints and electroplating- Diecast alloys (car carburetors) and brass- Casing for dry cells (batteries) | Lead | - Car batteries- Plumbing (flashing) and in solder- In crystal glass and as glaze for pottery |
Different Metals Throughout History and their uses:
The first metal to be extracted from an ore was copper. This occurred in the Middle East in about 6000 B.C. Copper oxide was heated with charcoal (mainly carbon) and globules of copper resulted. This copper was used to make domestic utensils and possible some types of ornaments. Working copper, however, was difficult as the melting point needed was too great for wood fires to achieve. Furthermore, the finished products of copper were fairly soft as pure copper is an extremely soft metal. Therefore, copper tools did not replace the stone ones currently in use. In Cyprus, around 3000 B.C. copper was actively mined.
As time progressed, it was discovered that heating copper and tin ores with charcoal produced a much harder metal alloy – Bronze. Bronze has a much lower melting point than copper and so could be melted, moulded and worked much more easily in wood fires. Around 2000 B.C., bronze had become prominent and used for tools and weapons throughout the European and Asian continents. This led to a technological difference between societies with bronze and those without it; simply put – nations that first developed methods of mining and using Bronze as weapons were able to conquer less developed nations.
Tin mines were available in Cornwall around this period as well. Bronze was the most prominent metal used for weapons and tools from about 2000 B.C to 1000 B.C. That is why this era is known as the Bronze Age.
In order to extract iron from iron oxide, using wood-fires (charcoal) you must generate a temperature higher than that of copper extraction. It was not until 1200 B.C. that humans developed a method of generating these higher temperatures and also the ability to forge iron into tools and weapons. It was necessary to blow air into the fire to get a sufficiently high temperature, and then it must be softened in order to forge it. However, iron as a substance had been known to exist at least thousand years before this (2500 B.C.) because it had been found in nearly pure form in meteorites.
The technology for extracting, processing and moulding rapidly spread out throughout Europe and Asia. Iron is a much harder metal than bronze, and therefore most weapons and tools were made of iron instead. Systematically, the period from about 1000 B.C. to 1.C.E is called the Iron Age.
Anthropologists and historians end the Iron Age at 1 C.E and like to call the era to present the Modern Age. Throughout the Modern Age, the technologies for producing iron and steel rapidly improved, and quantities being used increased markedly (Especially after the Industrial Revolution of the eighteenth century).
However, there was no significant move towards the use of new alloys or metals until the late nineteenth century. This is despite metals such as cobalt, zinc, nickel tungsten, manganese, chromium and titanium being isolated in the eighteenth century, and magnesium, sodium, cadmium, aluminium as well as vanadium being isolated in the nineteenth.
Alloy steels were developing from about the late 1880’s and were developed in the following order:
* Tungsten steel (for cutting tools) * Manganese steel (for railway lines and digging tools) * Silicon steel (electromagnets and transformer cores) * Chromium steel (Safes, files, ball bearings) * Nickel steel (used for scientific instruments + used for telecommunication) * Vanadium steel (Cars since low density, lightness + high tensile strength)
Stainless steel was manufactured and came into use after about 1920.
Metals that have come into common use in the last 100 years include aluminium, tungsten, magnesium and tungsten.
Aluminium and steel both require electricity in order to produce them. This explains why they were only manufactured in the last 100 years – because electricity only became prominent around 100 years ago.
Aluminium – The commercial use of aluminium began towards the end of the nineteenth century and has expanded rapidly ever since. Aluminium has displaced iron and steel for many uses for which it was better suited. Aluminium is often alloyed with copper manganese, magnesium and titanium.
Tungsten – Although tungsten had been used in steel alloys from the 1880s, its use as a pure metal for filaments in light bulbs (and later in television picture tubes) did not begin to be used markedly because of its difficulty to be turned into wires (because of its high melting point).
Magnesium – Prominent during WWII, as it was the major components of alloys for aircraft bodies and cares. Still used in mobiles, computers, though it has been mainly replaced by aluminium
Titanium – Highest strength to weight ratio of any metal; very hard and very resistant to corrosion. Alloyed with aluminium and vanadium it is even stronger and harder. It is used in aerospace industry, for medical impacts and for bicycles and other sporting appliances.
Note: “The least reactive metals were the easiest to isolate and were the first metals to be widely used, and that it is only in modern times that industry has become sufficiently skilled to isolate and refine metals such as aluminium, and the metals that are added to iron to make steel.”
* Describe the use of common alloys including steel, brass and solder and explain how these relate to their properties.
Contemporary Uses of Different types of alloys
Type of Steel | Composition | Particular Properties | Uses | Carbon Steels | Mild Steel | <0.2% Carbon | Soft, Malleable which allows it to be manipulated into different shapes easily | Car Bodies, Pipes, nuts, bolts and roofing. | Structural Steel | 0.3 to 0.6% Carbon | High tensile strength, Hard. Allows for it to be used in situations where extreme strength is necessary. | Beams and girders, railways and reinforcing | High-Carbon Steel | 0.6 to 1.5% Carbon | Very Hard makes it useful in cutting. | Knives and tools such as drill bits, chisels hammers | Alloy Steels | Chrome Steel | 2 to 4% Chromium | Hard + Shock resistant which makes it suitable for security devices | Safes, files, ball bearings | Tungsten Steel | 10 to 20% tungsten0 to 5% Chromium and Vanadium | Hard at high temperatures- good for cutting because it doesn’t melt and stays hard | Cutting and grinding tools | Silicon Steel | 2 to 5% Silicon | Easily magnetized and demagnetized | Electromagnets and transformer cores | Stainless Steels | Stainless Steel | 10 to 20% Chromium5 to 20% Nickel | Hard, resist corrosion. Good for cutting as well as situations that require the tool to be resistant to corrosion. | Food processing machinery, kitchen sinks and appliances, cutlery, surgical and dental instruments, some razor blades |
Contemporary Uses of non-ferrous alloys
Alloy | Composition | Special Properties | Uses | Brass | 50 - 60% copper with zinc | Lustrous gold appearance, hard but easily machined which allows it to be shaped easily but it is also attractive. | Plumbing fittings, musical instruments, decorations | Bronze | 80 – 90% copper with tin | Hard, resists corrosion, easily cast which allows for it to resist damage but can be easily machined. | Ships’ propellers, casting statues | Duralumin | 95% Aluminium, 4% copper, 1% manganese | Low density, very strong makes it light and strong so good for aircrafts + bikes | Aircraft parts, racing bicycles | Solder | 30-60% tin with lead | Low melting point adheres firmly to other metals when molten. Easy to melt, therefore good adhesive. | Joining metals together, particularly in plumbing and electronics. | Copper-nickelCoinage alloy | 75% copper with nickel | Silvery appearance resists corrosion. Therefore long lasting, which is essential for the coins | 5, 10, 20, 50 cent coins | “Gold” coinage alloy | 92% copper, 6% Aluminium, 2% Nickel | Gold appearance resists corrosion. Therefore long lasting, which is essential for the coins | 1 and 2 dollar coins | 18 Carat Gold9 Carat Gold | 75% Gold37.5% Gold | Harder than pure gold
(24 Carat). Pure gold is too soft to be used in Jewellery; the additions make the alloy harder which increases the durability of the jewellery. Also very attractive and lustrous. | Jewellery |
Note: For both, balance is roughly equal amounts of silver and copper.
* Explain why energy input is necessary to extract a metal from its ore.
“A mineral is a pure (or nearly pure) crystalline compound that occurs in the Earth’s crust.
An ore is a compound or mixture of compounds from which it is economic (or commercially profitable to extract a desired substance such as a metal.”
For almost every metal a chemical reaction is used to extract the metal from its ore. Every chemical reaction involves either the release or absorption of heat which is one of the most common forms of energy.
Some chemical reactions that involve the extraction of a metal from its ore absorb or use heat (endothermic), while in other reactions heat is released (exothermic).
Numerous examples of each type of reaction are available including:
* Extracting Iron from Iron (III) oxide with carbon in a blast furnace releases heat in an exothermic reaction. * Extracting Aluminum from alumina absorbs large amounts of heat in an endothermic reaction * Extracting copper from copper sulfide ores releases huge amounts of heat in an exothermic reaction * Extracting Nickel involves crushing and flotation that concentrates the ore, which is then roasted. Here the chemical reaction is endothermic and exothermic as large amounts of heat is absorbed and released. * Extracting copper from chalcopyrite, CuFeS2, is an endothermic reaction where large amounts of heat is absorbed to extract the metal and is also an exothermic reaction since large amounts of heat energy is released.
Energy input is essential to extract a metal from it’s ore for the following reasons:
* Many ores contain metal oxides. These oxides are much more stable than the actual metals themselves. Therefore a significant amount of energy is essential in order to break the metal – oxygen bond in the metal oxide. Only then can the metal be released in its elemental form, thus energy input is necessary to extract a metal from its ore. * Ions are the main component of an ore (because they are reactive); pure substances remain as is (due to their stability). The metal (product of the chemical reaction) contains more energy than the reactant (the ore). Therefore energy must be added, which will result in the reduction (and decomposition) of the ore. The energy causes the breaking down of intermolecular bonds within the ore, causing new substances to be formed. The reaction is usually endothermic. * Energy is not only involved in the extraction reaction. That is only one part of the total amount of energy used. Energy is also used to mine the ore, purify or concentrate the ore, maintain the high temperatures that are necessary for the extraction reactions and also to purify the raw metal or to form useful alloys (such as steel, brass and bronze).
* Identify why there are more metals available for people to use now than there were 200 years ago.
There are three main reasons why there are more metals available for people to use now than there were 200 years ago:
I) Technology has improved rapidly since the 1800’s. Humans have learnt how to create a high-temperature environment (such as a blast furnace) that has allowed them to extract metals that couldn’t be extracted previously. Furthermore, with the introduction of electricity, the method of electrolysis was produced. This allowed for the most reactive metals (such as aluminium) to be extracted from there ores. 200 years ago these technologies were not present and therefore there was no method of extracting these metals as heating carbon did not provide sufficient energy to extract those metals.
II) Over the past 200 years, the improvement of metallurgical skills for making and testing new alloys led to the incorporation of a wider range of metals into everyday products. The improvement led to the increasing amount of alloys being produced. Due to this, scientists began to experiment with different metals to determine the outputs if two metals were combined. An example of this is titanium. Titanium is the seventh most abundant metal in the Earth’s crust but is extremely difficult to extract from its ores. Titanium was not widely used on it’s own as a metal but when it was discovered that when titanium is combined with limited amounts of other metals, it becomes extremely hard, has high-tensile strength and is very light, its use expanded rapidly. Titanium alloys became the back-bone of modern jet and aircrafts. With the improvement of metallurgical skills to create new alloys, a wider range of metals are available for people to use now than 200 years ago.
III) Money. In the past it was very expensive to extract metals from their ores. An example of this can be seen with aluminium. The major cost in extracting aluminium is the electricity used for the electrolysis and for keeping the electrolyte molten. During the twentieth century the price of electricity fell steadily and this improved the competitive position of aluminium relative to steel, so it became used more prominently. Thus the reducing cost of extracting the metal is another reason why more metals are available for people to use now.
Currently there are many more metals available for people to use than there were 200 years ago. Before the 19th Century (1800) only ten prominent metals were in use: tin, iron, lead, copper, silver, zinc, gold, platinum and bismuth. These metals were either naturally occurring in the Earth as uncombined elements (Gold, Silver, Platinum) or could be easily extracted by heating with carbon.
However, currently there are at least another twelve or more metals in widespread industrial use (such as aluminium, titanium, magnesium, uranium, cadmium, molybdenum, vanadium, chromium, nickel, cobalt, manganese, tungsten) whereas about another twenty-five metals have specialised uses. Some of these metals include gallium, rubidium, sodium, strontium, calcium, beryllium and zirconium.
There are two main criteria which determine the availability of metals for commercial or industrial use:
- Abundance of metal in the Earth’s crust
- Ease of extracting the metal from its ore * Gather, process, analyse and present information from secondary sources on the range of alloys produced and the reasons for the production and use of these alloys. Alloy | Reasons for production | Uses | Alnico 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, and the balance is Fe. | Alnico alloys make strong permanent magnets, and can be magnetized to produce strong magnetic fields. They were produced to create a magnetic field upto three times that of the Earth’s. This phenomenon allowed scientists to use the alloy in many magnetic applications. | - Magnet applications - electric guitar pickups- microphones- sensors- loudspeakers - cow magnets | MagnaliumAluminium with 5-50% Magnesium | It provides greater strength, greater resistant to corrosion and a lower density than pure aluminium. Also more workable and easier to wield than aluminium. However, too much magnesium eg >50% makes the alloy brittle and susceptible to corrosion. | - Pyrotechnics since when large amounts of Mg is present, the powder is flammable so used as a metal fuel.
- Aircraft and Vehicle components due to low density and high strength. | Vitallium 60% cobalt, 20% chromium, 5% molybdenum and other substances. | Developed by Albert W. Merrick in 1932.It has a very low in density, is lightweight and resists corrosion. Furthermore it is also a thermal resistor. Also does not react in the body with any substance like other metals do (inert). This makes it suitable for medical purpose | - Dentistry because it is light weight and resists corrosion.
- Medical surgery as the substance is inert to any body fluid under any condition.- Turbocharger components because of thermal resistance | Gunmetal88% Copper, 10% Tin and 2% Zinc | It is very resistant to corrosion from water, steam and salt water. Its composition varies based on why it is produced but copper, tin and zinc are the three major components. Also withstands atmospheric corrosion. | - Guns- Valves, pump parts and steam fittings as it is resistant to corrosion from steam/salt water.- Machinery brushes- Gears and bearings subjected to heavy loads + low speeds. | Galinstan68.5% Ga, 21.5% In, 10% Sn | Galinstan is commercially used as a mercury replacement due to its nontoxic properties. Has high reflectivity and lower density, and is produced as a regular replacement for mercury in astronomy.
It is also a promising coolant, but is costly and aggressive, however ongoing experiments are being conducted. | - Thermometers due to its nontoxic properties, but inner tube must be coated with gallium oxide to prevent the alloy from wetting the glass surface.- Liquid mirror telescopes for astronomy -It is also a promising coolant. |
* Analyse information to relate the chronology of the Bronze Age, the Iron Age and the modern era and possible future developments.
Stone Age – up to about 3000 B.C.
The Stone Age refers to a period of time in human prehistory, all the way back from the first primate tool making more than 2.6 million years ago to about 3000 BC, when metallurgy in the form of smelting copper ore was developed.
The Stone Age refers to the time period in which man made its tools from stones, such as flint. The Stone Age was participated in by at least nine species of the genus Homo. They lived in small tribes leading a hunter-gatherer lifestyle, until the very end of the Stone Age.
Common Stone Age products included the mortar and pestle, arrowheads, spearheads, stone scrapers, and most famously, hand-axes. Pottery came at the very end. Bone needles and straw textiles were also made. After the basics of Stone Age tools were developed, very little refinements came for thousands of years after. Advanced darts, harpoons, the fishhook, the oil lamp, rope, and the eyed needle all appeared in the ensuing periods.
Copper Age – 3200 to 2300 B.C.
The Copper Age was the transitional period between the Stone Age and the Bronze Age in which an introduction of native copper took place while stone was still the main resource utilized. Copper is the eighth most abundant metal in the earth crust, available all over the world and one of the few that can appear in pure state. Furthermore it is not complicate work with it, bare hammering can transform a nugget into a bead. Additionally, the eye-catching look of the native copper makes it easy to recognize and even more attractive if converted into jewellery.
Copper can be found in over 160 different minerals. Ones of the most commonly exploited minerals are the Cuprite, Malachite, Azurite, Chalcopyrite, Chrysocolla and Tennantita, e.g. malachite was found in Rudna Glava (Serbia) or Cabrierés (France).
In locations such as Cyprus or Crete, collecting the mineral was once as easy as simply picking it up from the ground. The treatment of this native mineral was also uncomplicated through cold-hammering. This permitted the production of only a limited range of artifacts like awls, pins, or beads as in larger objects, the metal cracks when it is cold-hammered.
Heating the metal on an open fire reduces its hardness considerably and increases malleability. This permits the confection of slightly more sophisticated objects like bracelets.
In time, native copper became hard to fine so copper ore was used. This was a very significant development as it was the beginning of metallurgy, as the mineral has to be smelted to separate the copper from the gangue. Thus, technology was required to do so, showing how over time, humans began to learn new tehcniques and technology increased allowing them to take advantage of resources like copper.
Bronze Age – 2300 to 1000 B.C.
The Bronze Age refers to a period of time where metallurgy had advanced to the point of making bronze from natural ores.
The Bronze Age primarily took place between 2300 BC and 1000 BC and resulted in the gradual improvement of sophisticated metallurgy which culminated in the discovery of iron working around 1000 B.C.
The Bronze Age began 4000 years ago in the present-day areas of Turkey, Iran, and Iraq. The birthplace of metallurgy is usually taken to be Anatolia, Turkey.
The Bronze Age was important because it allowed for the creation of more durable tools and artifacts for productive use. Bronze knives, axes, armor, pottery, or artwork are harder and longer-lived than stone or copper making it a more preferable resource. A more durable resource enhances the potential for sustained economic activity, but more importantly - warfare.
During the Bronze Age, much of humanity was segmented into thousands of warring tribes. Those that had mastered the art of making Bronze weapons and tools were likely to dominate their not yet advanced neighbours.
Iron Age – 1000 B.C. to 1 C.E.
The Iron Age was the period of time when iron metallurgy was the most sophisticated. Iron-working is preferable to bronze because is had a much higher durability and is available more readily in the form of iron ore. An iron sword would be able to break a bronze sword with a vigorous blow. This shows that civilizations that first developed the art of iron metallurgy had a significant advantage over their developing neighbours – especially when it came to warfare.
Systematic production of iron originated in Anatolia (modern-day Turkey), and simultaneously spread to all parts of the world – East and West.
Products from the Iron Age were similar to that of the Bronze Age, but they were much more durable: swords, pottery, chains, farming tools, etc. lasted significantly longer than their bronze predecessors.
Modern Era – 1 C.E to present
As time passed on technology improved and as a result an increasing amount of metals and alloys were produced. This allowed for the construction of many tools, technologies and structures.
The most common metals in use today are iron and aluminium. Iron, however, is rarely ever used in its pure elemental state, but rather it is used as an alloy of steel for construction purposes. Aluminium is one of the Earth’s most abundant metals. Therefore it is used for a variety of purposes ranging from saucepans, foil, aircraft and drink cans.
The future (possible future developments):
The latest trend in metallurgy is in recent years has been the use of knowledge to predict unusual properties of alloys, which may have considerable value in engineering and industry applications.
The following are four points that are likely to be possible in the not so distant future:
I. Specialised mills and units with maximum automation of all production purposes will be present in new highly developed plants. In the future the productivity of these plants will increase and the demand for steel may reach 12 – 15 million tonnes per year per plant.
II. The blast furnace industry will increase the volume of their active blast furnaces and new super high-capacity furnaces will be available, all containing improved technological equipment.
III. Furthermore, the process of smelting iron will be intensified: the preparation process will be improved, gas pressure will be increased, and natural gas in combination with cold technological oxygen will be used in the furnace. This will not only raise the production of iron but also raise its quality.
IV. Further improvement and development of oxygen-converter and electrosteel processes will be likely.
1. Metals differ in their reactivity with other chemicals and this influences their uses
• Describe observable changes when metals react with dilute acid, water and oxygen
Metals vary in their reactions with certain substances. Some are very reactive whereas others are extremely unreactive to the same substance.
Reaction with Oxygen:
All metals except silver, platinum and gold react with oxygen to form oxides:
- Li, Na, K, Ca, Ba react rapidly at room temperature.
- Mg, Al, Fe, Zn react slowly at room temperature but burn vigorously if heated in air or pure oxygen.
- Sn, Pb, Cu react slowly and then only if heated.
All the oxides formed are ionic compounds.
Those metals which burn in air or oxygen form crystalline white solids that have none of the physical properties of the original metal (lustre, strength etc.)
When metals slowly react at room temperature, they lose their shiny lustrous appearance. Some, such as Al, become coated with a dull layer of tightly adhering oxide, which prevents further reaction. However, others like iron, form a powdery surface layer of oxide which does not impede further reaction.
For example when magnesium is heated in air, large amounts of heat and light energy are given off in the exothermic reaction. The initial shiny silver metal turns into a white powdery substance known as Magnesium oxide.
2Mg(s) + O2(g) 2MgO(s)
Reaction with water:
Not all metals react with water/steam:
Li, Na, K, Ca, Ba react with water at room temperature.
Mg, Al, Zn, Fe react with steam at high temperatures.
Sn, Pb, Au, Ag, Cu do not react at all.
When a reaction occurs with water the products formed are hydrogen gas and the metal hydroxide.
2Na(s) + H2O(g) 2NaOH(s) + H2(g)
When calcium is dropped into water, bubbles of colourless gas form. Furthermore, a suspension of insoluble calcium hydroxide forms.
When a piece of freshly cleaned magnesium ribbon is held near steam, a white deposit of MgO forms on the ribbon. With steam, however, the product is oxide, not hydroxide.
Note: Refer to prac/theory to see reactions of Mg with all three substances.
Water is more energetically stable than dilute acids, thus less metals react with it in comparison to acid
Reaction with Dilute Acid:
Acids are substances which in solution produce hydrogen ions, H+. Most metals react with dilute hydrochloric and sulfuric acids to from hydrogen gas and a metal salt.
For example Magnesium:
Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)
As can be seen, a metal salt along with hydrogen gas is produced. In a physical sense, vigorous bubbles are seen to arise from the hydrochloric acid (which we know is hydrogen gas), furthermore we notice a clear solution forms (which we know is magnesium chloride). Also, the container gets hot.
Extra: Remember: OILRIG
When an atom loses one or more electrons we say that it has been oxidized.
If an atom gains one or more electrons we say that it has been reduced. Redox reactions are where reduction and oxidation occur simultaneously in the same reaction.
Half Equations: These are reactions that describe the oxidation and reduction process separately in terms of electrons lost or gained.
Metals that react vigorously with dilute acids also react vigorously with water and oxygen, and are called active metals. (Eg. Magnesium)
Metals that react less vigorously with dilute acids also react less vigorously with water and oxygen, and are less active metals. (Eg. Zinc)
Metals that do not react with dilute acids also don’t react with water and oxygen, and are called inactive metals. (Eg. Gold)
* describe and justify the criteria used to place metals into an order of activity based on their ease of reaction with oxygen, water and dilute acids
Metals vary in their reactivity. Reactive metals will react with oxygen, whereas those that are inactive will not, placing them lower on the activity series. A highly reactive metal with react with cold water, whereas metals that don’t react with cold water may react with hot water and are lower on the activity series. Metals that don’t react with water, need to be tested in dilute acid to test their reactivity. Thus metals that react vigorously are deemed to be more reactive than those that react less vigorously or only with concentrated acids.
The reason for this procedure is that metals that react with oxygen will react more vigorously with water and then acids. Thus by determining where each metal will react, we can make up an activity series which is a list of metals based on their order of reactivity.
The activity series of the common metals goes as follows:
K, Na, Li, Ba, Ca, Mg, Al, Zn, Fe, Sn, Pb, Cu, Ag, Pt, Au * identify the reaction of metals with acids as requiring the transfer of electrons
Acids are substances which in solution produce hydrogen ions, H+. It is the hydrogen ions which react with the metals. These ions result in the transfer of electrons between the substances involved.
Metals reacting with acids are redox reactions. Another name for these reactions is electron-transfer reactions. For example when Magnesium reacts with dilute hydrochloric acid, the net ionic equation is: Mg(s) + 2H+(aq) Mg2+(aq) + H2(g)
As can be seen the Magnesium has been oxidized while the H+ has been reduced.
* outline examples of the selection of metals for different purposes based on their reactivity, with a particular emphasis on current developments in the use of metals
Some situations where the choice of metal is based heavily upon the chemical reactivity: * Roof Guttering for Houses: Non-reactive aluminium is one option but it is extremely expensive. On the other hand galvanized iron is available which is significantly cheaper but eventually corrodes. * Water pipes: Non-reactive, expensive copper or cheaper, corrodible iron.
* Electrical contacts for replaceable circuit boards in computers / other electronic equipment: Cheaper copper (which slowly forms a non-conducting oxide layer) or expensive gold which will not react to oxygen.
* Body Implants: Extremely expensive and inert titanium alloys of less expensive, but over the long term corrosion susceptible stainless steel.
Metals currently used for different purposes include:
* Lithium: used in pace-makers, cameras and button cells due to the energy of electrons transferred from lithium anode and the high reactivity of lithium
* Magnesium: used as a component in fireworks, military and emergency purposes and inside boilers. This is due to its relatively high reactivity and the fact it burns bright when heated with air
* Aluminium: lack of reactivity means it can be used as drink cans, food wraps, aircraft bodies, in automobiles and in window frames
* Titanium: used as artificial joints, aircraft and ship bodies, pipes. Its relevant properties are a low reactivity, stable, resistance to corrosion and chemically inert nature in the human body
* outline the relationship between the relative activities of metals and their positions on the Periodic Table
By inspecting our activity series it is possible to determine certain trends between them and the periodic table:
The activity series shows that Group 1 metals are the most reactive, followed by Group 2 metals. Group 3 (Al) comes next in reactivity followed by some transition metals (Zn, Fe) and then the metals of group 4. At the end of the series are more transition metals (Cu, Ag, Pt, Au).
Furthermore, the activity series also shows that in groups 1 and 2 reactivity increases from top to bottom. * Identify the importance of first ionization energy in determining the relative reactivity of metals.
The relative reactivity of metals correlates with a physical property known as first ionisation energy.
First Ionisation energy of an element is the energy required to remove an electron from a gaseous atom of the element.
Ionisation energy is commonly measured in kJ / mol. Where a mole is a particular number of atoms (6.023 x 10^23).
The first ionisation energy measures the ease of removing an electron from a metal atom: the lower the ionisation energy, the easier ir is to remove an electron.
The reactivity of metals increases as their ionisation energy decreases.
As we go from left to right across the activity series, metal ions become easier to reduce to metal atoms. Due to the fact that metal ions are present in ores, it can be said that the further to the right in the activity series a metal is, the more easily it can be extracted from its ores.
K, Na, Li, Ba, Ca, Mg, Al
All require electrolysis of molten ionic compounds in order to be extracted from their ores.
Zn, Fe, Sn, Pb
Reduction of oxides with carbon or carbon monoxide
Cu, Ag – roast sulfides in air
Pt, Au – occur naturally as free metals.
A superoxide is an anion with the chemical formula O2- . It is important product of the one electron reduction of dioxygen (O2), which occurs widely in nature. With one unpaired electron, the superoxide ion is a free radical.
3) As metals and other elements were discovered, scientists recognised that patterns in their physical and chemical properties could be used to organise the elements into a periodic table. * Identify an appropriate model that has been developed to describe atomic structure
The current model of the atomic structure is an adaptation of the original atomic structure outlined by Ernest Rutherford. In 1911, he suggested that the atom consisted of a small, dense core of positively charged particles in the centre (or nucleus) of the atom, surrounded by a swirling ring of electrons.
He concluded through his experiments and the experiments of others that the nucleus was extremely dense (because in his experiment the alpha particles would bounce off of it) but the electrons were extremely small, and spread out at large distances (since the alpha particles would pass right through this area of the atom).
Rutherford's atom resembled a tiny solar system with the positively charged nucleus always at the centre and the electrons revolving around the nucleus. The positively charged particles in the nucleus of the atom were called protons. Protons carry an equal, but opposite, charge to electrons, but protons are much larger and heavier than electrons. Ernest Rutherford interpreted results obtained by Giger and Marsden, when they exposed a thin film of gold foil to a beam of alpha particles. He concluded that all of the positive charge and most of the mass of an atom was concentrated in an extremely small region at its centre. Which we today know is correct.
Atoms are electrically neutral since the number of protons balances the number of electrons, thus giving an overall net charge of zero. The size of the atom is irrelevant as the number of protons and electrons will always be the same in an atom.
Thus an appropriate model of the atomic structure is that of Ernest Rutherford’s as it demonstrates a positively charged nucleus and a cloud of revolving electrons. However some essential refinements were necessary to this model and these were incorporated as they were discovered. For example the discovery of neutrons in 1932 by James Chadwick explained why the dense nucleus of the atom was able to stay together as it did. Also the discovery of numerous other things, such as subshells and valence electrons were essential and were basically added to the same atomic structure proposed by Ernest Rutherford
The Rutherford Model contained a number of errors, but it provided scientists with a base that an atom is more than just a singular particle, it is made of protons, neutrons and electrons.
:Rutherford Model of a Lithium Atom
* Outline the history of the development of the Periodic Table including its origins, the original data used to construct it and the predictions made after its construction.
History of the Periodic Table:
Contributor | Date | What was Contributed | Comment | Aristotle | ~330 BC | Four Elements – Fire, Air, Earth, Water | | Antoine Lavoisier | ~ 1770 - 1789 | Wrote the first list of the 33 elements currently known and also distinguished between metals and non-metals | Some of these elements were later found to be compound and mixtures. | Jöns Jakob Berzelius | 1828 | Developed a table of atomic weights and also introduced letters to represent the elements rather than full names. | | Johann Döbereiner | 1829 | Developed groups of three elements known as triads. These elements had similar properties. Some examples of his triad include: Lithium, Sodium and Potassium formed a triad. Calcium, barium and Strontium formed a triad.
Chlorine, bromine & iodine also formed a triad. | He was the first man to bring forward the notion of groups. He proposed that nature contained triads of elements the middle element had properties that were an average of the other two members when ordered by the atomic weight. (Law of Triads) | Alexandre-Emile Béguyer de Chancourtois | 1862 | Alexandre Béguyer de Chancourtois was the first person to list the known elements in order of increasing weight of their atoms. But due to the complicated nature of his proposed graph, his ideas were shrouded in less read journals. His graph was so complicated that most French experts still had trouble interpreting it. It was not until after Mendeleev that his work was credited. | | JohnNewlands | 1864 | At this stage over 60 elements were known to exist. Newlands arranged these elements in order of atomic weights and realised that the properties of the first and ninth elements, second and tenth elements etc. were very similar. Due to his he proposed the “Law of Octaves” which was simply that ‘if the chemical elements are arranged according to increasing atomic weight, those with similar physical and chemical properties occur after each interval of seven elements.’ | Newlands’ Law of Octaves identified that many of the elements had similarities but his law required similarities where none actually existed. However he was unable to comprehend that some elements had not been discovered and therefore did not leave any gaps for those elements. He was the first person to initiate the notion of periods. | Lothar Meyer | 1869 | He was able to compile a periodic table containing 56 elements. He arranged the elements based on the periodicity of properties such as molar volume when it was arranged in the order of atomic weight. Meyer’s contribution was his ability recognises periodic behaviour. A repeating pattern of atomic volume. When atomic volume of an element was plotted against its atomic weight a clear pattern existed. Meyer realised that due to the graph, atomic volume rapidly peaks and then falls considerably. | Dmitri Mendeleev and Lothar Meyer both produced their own Periodic tables at the same time, but Mendeleev is still considered to be the father of the Periodic table.Meyer is also recognised for identifying periodic behaviour which allowed for the development of groups and periods. | Dmitri Mendeleev | 1869 | He also produced a periodic table based on atomic weights like Lothar Meyer, but he arranged them ‘periodically’ with elements that had similar properties arranged under each other. He also left certain gaps for elements that he believed had not been discovered yet. Furthermore, he was able to predict the properties of those elements. We know those elements to be gallium, scandium and germanium. Additionally, Mendeleev also re-arranged the order of the elements if their properties dictated it. For example: Tellurium is heavier than iodine but it comes before iodine in the periodic table. | The periodic law allowed for the properties of the elements to be estimated. Properties of the elements vary according to their atomic weights. | William Ramsay | 1898 | He was able to discover the noble gases which allowed for the inclusion of six more elements into the periodic table. We know these gases are in their own separate group and are also highly unreactive. | “In 1894 Ramsay removed oxygen, nitrogen, water and carbon dioxide from a sample of air and was left with a gas 19 times heavier than hydrogen, very unreactive and with an unknown emission spectrum. He called this gas Argon. In 1895 he discovered helium as a decay product of uranium and matched it to the emission spectrum of an unknown element in the sun that was discovered in 1868. He went on to discover neon, krypton and xenon, and realised these represented a new group in the Periodic Table.” | Henry Moseley | 1914 | He was able to determine the atomic number of each of the elements discovered at the time. He was also able to modify the “Periodic Law” to ensure the properties of the elements vary periodically according to their atomic numbers. | Moseley’s modified Periodic Law puts the some of the elements in the right order compared to what they were previously. For example, Argon and Potassium as well as Cobalt and Nickel were placed in their correct order. | Glenn Seaborg | 1940 | He was able to discover and also synthesise elements that occurred after uranium in the periodic table, known as the lanthanides and actinides or the transuranic elements. | “In 1940 uranium was bombarded with neutrons in a cyclotron to produced neptunium (Z=93). Plutonium (Z=94) was produced from uranium and deuterium. These new elements were part of a new block of the Periodic table called Actinides. Seaborg was awarded a Nobel Prize in 1951”. |
What data was used to construct the periodic table and what predictions could be made after every stage of its construction?
Obviously a necessary task when constructing the periodic table is to firstly discover the individual elements. Gold, silver, tin, copper, mercury and lead had been known for ages gone but the first actual discovery of an element did not occur until 1649, when phosphorous was discovered. Over the next 200 years or so, an increasing number of elements and knowledge about them were unravelled. By 1869, 63 elements were discovered and as knowledge about these elements grew scientists began to recognise patterns in their properties and this led to their classification.
The first person to really recognise a pattern between the elements was Johann Döbereiner (see table) who noticed that some groups of three elements possessed very similar properties and furthermore that the middle element was the average of the outer two elements (when the elements were arranged by atomic weight). Thus he developed the “Law of Triads”. As scientists expanded their knowledge these triads began to groups of four and five, showing that the relationships extended beyond Döbereiner’s Law. However, research in these areas was restricted due to the lack of accurate values.
The first attempt at designing a periodic table was done by French geologist A. E. Béguyer de Chancourtois (see table). He transcribed a list of elements onto a cylinder so that 16 mass units were written on the cylinder for every turn and so that closely related elements with similar properties could be lined up vertically. He was the first to recognise the reoccurrence of elemental properties after every seven elements. He was able to predict the stoichiometry of metallic oxides His chart however contained certain ions and compounds which reduced accuracy of some of his predictions.
The next major step that occurred was the development of the Law of Octaves by John Newlands (see table). This law allowed for the prediction of elemental properties especially between elements that were separated by seven others.
Lothar Meyer and Mendeleev both in 1869 simultaneously constructed their own periodic tables. Meyer released an abbreviated version of his periodic table in 1864 but by the time he extended and released his full version (1870), Dmitri Mendeleev had released his own (1869). Mendeleev was able to organise the elements into families with similar properties. After this he arranged the metallic elements according to their valency or combining power. However he came to challenges with certain metallic elements displaying variable valencies. Mendeleev also noticed patterns in the properties and atomic weights of the halogens, alkali metals and alkaline earths. In an effort to extend this pattern, he created a card for each of the 63 known elements of the time. When Mendeleev arranged the cards in the order of ascending atomic weight, he realised that he was able to group elements of similar properties together. Thus the periodic table was formed. The major advantage of Mendeleev’s table over previous attempts of other scientists was that he was able to exhibit similarities horizontally, vertically and diagonally. Mendeleev was so confident in his own periodic table that he knew that the atomic masses of certain elements were incorrect. He changed the atomic mass of beryllium from 14 to 9 and also changed the weights of 17 other elements. However even after the re-measurement of atomic weights, some elements were still placed out of atomic weight order.
Here is where Mendeleev’s true genius was shown to the world. He predicted that certain elements had not been discovered so he left gaps in his periodic table for them. Also, he predicted the properties of those elements (such as eka-aluminium, eka-boron and eka-silicon which we now know to be germanium, scandium and gallium) and when they were found, their properties almost matched those predicted by Mendeleev.
Comparison of the properties of germanium:
Property | Predicted by Mendeleev | Actual (as observed in 1886) | Atomic weight | 72 | 72.3 | Density | 5.5g/mL | 5.47g/mL | Melting point | Very high | 960 degrees Celsius | Specific heat capacity | 0.31 J K-1 g-1 | 0.32 J K-1 g-1 | Formula of oxide | RO2 | RO2 | Density of oxide | 4.7 g/mL | 4.70g/mL | Formula of chloride | RCl4 | GeCl4 | Boiling point of Chloride | 100 degrees Celsius | 86 degrees Celsius |
The periodic law outlined by Mendeleev was that the properties of the elements vary with their differing atomic weights. There were certain errors in his periodic table and he incorrectly identified some relationships but he was the first person to provide a sophisticated outline for the arrangement of the elements known as the Periodic Table. The next major discovery was that of the Noble gases by William Ramsay in 1898, who was able to discover argon. He discovered that these elements had a zero valency so named it group zero. Due to these factors, he was able to accurately predict the discovery of neon and also predicted its properties before its discovery.
Scientists of the twentieth century were able to coin the term atomic number and due to the discovery of isotopes it was noted that the periodic law was dependant on atomic number rather than atomic weight. One of these scientists was Henry Moseley who was responsible for determining what we know as the atomic number. He proposed that it, rather than atomic weight, was the basic feature which determined properties. He proposed a modified periodic law: Properties of the elements vary periodically with their atomic numbers. This allowed for the correct allocation of argon, potassium, cobalt, nickel, tellurium and iodine.
The last major change to the periodic table resulted from Glenn Seaborg’s research in the middle of the twentieth century. He was able to discover plutonium in 1940 and was then able to discover all the transuranic elements (from 94 to 102). He then re-arranged the periodic table by placing the lanthanide series above the actinide. Thus with this final arrangement, the modern periodic table was complete. Now scientists were able to predict the reactions between certain elements, the composition of the compounds, reactivity of certain elements, ions and compounds and also the ionisation of elements. These were now predictable due to the work done from the time of Aristotle to the final stages of Seaborg’s research.
* Explain the relationship between the position of the elements in the Periodic Table, and:
- Electrical conductivity
- Ionisation energy
- Atomic radius
- Melting point
- Boiling point
- combining power (valency)
The reactivity of a metal associates well with its first ionisation energy: the lower the first ionisation energy, the greater the reactivity of the metal. This is due to one sole reason: that both reactivity of a metal and ionisation energy are related to the ease with which the metal will lose its electrons. Therefore the logical comparison can be made that:
“For metallic elements reactivity decreases from left to right across a period of the table (for example Na, Mg, Al) and increases from top to bottom down a group (Be, Mg, Ca, Sr).”
This is simply because the more left and down you proceed in the periodic table, the easier it is for the electrons to be removed, thus resulting in higher reactivity.
However, the case for non-metals is not as simple as it is for metals. This is mainly due to the fact that there are a minimum of two types of reactivity for non-metals. There is the formation of ions (anions) and also the formation of covalent compounds.
Generally in both cases the reactivity increases as you go from left to right across a period. Furthermore, the reactivity decreases as you go from top to bottom down a group. This is simply because the farther to the right and up you proceed in the periodic table, the higher the electronegativity, this results in a more forceful exchange of electrons.
First Ionisation Energy is the energy required to remove an electron from the outermost shell of an element when it is gaseous state. Ionisation energy is measure in kJ/mol. Each element has several ionisation energies and the energies always increase per ionisation level. This is simply because it requires more energy to remove a negative electron from a position ion than it does from a neutral species. This is fully due to the electrostatic attraction between the positive nucleus and the negative electron cloud. After the first electron is removed, there is extra electrostatic attraction on the remaining electrons making them harder to remove.
Ionisation energies provide strong evidence towards periodic law. Furthermore they also provide significant confirmation that the atoms want to have “noble gas configuration”. As can be seen from the graph above, when first ionisation energies are plotted against atomic number a clear trend is seen. The minimum values are all captured by the alkali metals (group 1 – Li, Na, K, Rb, and Cs) showing that it is easy to remove an electron from these elements. On the other hand the maximum values are captured by the noble gases (He, Ne, Ar, Kr, Xe, Rn) showing that a large amount of energy is needed to remove an electron from these stable elements.
“Elements with low ionisation energies readily form positive ions and therefore such elements form ionic compounds (Na+1, Ca+2, Al+3).”
As you go across any period of the periodic table, the first ionisation energy increases, indicating that when you move from left to right, the tendency to lose electrons deceases. When you go down any group of the periodic table, the ionisation energy decreases. This indicates that elements lose electrons less readily as we move from left to right. This is because elements on the right hand side of the periodic table wish to gain electrons to form an octet, whereas the ones on the left would rather lose those electrons. Also elements more readily lose electrons as we go down a group. This is because the increasing number of shells in the atom allow for the easier removal of the outermost electrons.
When atomic radius is plotted against atomic number, the curve shows a distinctly periodic nature. The atomic radius passes though a set of maximum’s which corresponding directly to the group 1 metals (also known as the alkali metals). There is also a set of minimums which occur in the last group of the periodic table known as the noble gases. Thus the relationship between the position of elements in the Periodic table and their atomic radius is that the atomic radius decreases from left to right across any period of the table. This is because of the stronger attractive forces in atoms between the opposite charges in the nucleus and electron cloud cause the atom to be contracted in slightly. Furthermore the atomic radius also increases in going down any group of the table. This is because of the increasing size of the nucleus as you move down a group. Also, new energy levels of electrons are added to the atom, each making the atom significantly larger in both mass and volume.
When a substance melts, some of the forces that hold the particles together are broken or loosened so that the particles can move freely but are still together. The stronger the attraction forces (intermolecular bonds), the more energy is needed to break them, and thus they have higher melting points.
When the melting points of the elements are plotted against their atomic numbers a periodic behaviour occurs, as the curve passes a series of minimums which correspond to the noble gases. The maximums do not appear in such a simple pattern however. The maximum melting points occur approximately half-way between the minimums.
When a substance boils, the majority of the remaining attractive forces between the molecules (intermolecular forces) are broken so that the particles can freely and far apart (because of their gaseous state which results in rapid translational movement). The stronger the intermolecular bonds (attractive forces), the more energy is required to overcome them, thus giving them a higher boiling point.
When the boiling points of the elements are plotted against atomic numbers, the graph that is produced is similar to the graph on the previous page which showed the melting points of the elements plotted against their atomic numbers. The boiling point graph undergoes a similar series of minimums which correspond to the atomic numbers of the noble gases. Furthermore, the maxima occur approximately half-way between the minimums.
“The electronegativity of an element is a measure of the ability of an atom of that element to attract bonding electrons towards itself when it forms compounds.
If the difference in electronegativities of two elements is greater than 1.5, the elements will form an ionic compound; otherwise the compound will be covalent.”
The electronegativity increases as we move from left to right across a period. This is because elements situated on the left of the table have one or two valence electrons and would give those electrons away to achieve an octet. Accordingly, they have a low electronegativity. On the other hand, elements situated on the right of the table only require a few electrons to complete a full octet, so they want to grab other elements electrons, thus giving those elements high electro-negativity.
The electronegativity deceases as we move down a group. This is because electrons situated at the top of the able have minimal electrons that they want to preserve. Thus they have a stronger desire to acquire more electrons. Elements situated on the bottom of the table have a large amount of electrons and therefore losing some is not an issue. This is mainly due to the electron shells. Electrons in the outer electron shells are not as tightly bound to the atom and are thus easily lost, whereas internal electrons (those closer to the nucleus) have much more electrostatic attraction and are thus tightly bound.
Combining power (valency)
The most common valency of an element is its group number (if it is in groups one to four) or eight minus its group number (if it is groups five to seven).
The noble gases are situated in group eight (also known as group eighteen or group zero) because they have no valence electrons and therefore are very unreactive and rarely form compounds.
It is not possible to determine some of the valencies of the elements situated outside the general groups (one to eight). These elements are known as the transition metals and have varying valencies. For example copper may have a valency of one or two, iron may have a valency of two or three, chromium may have a valency of two or three etc. However most of these transition elements from cations with a positive two charge.
The position of an element determines its valency which hence determines its combining power. If an element is situated in group eight it has zero valencies and thus will have limited combining power. If an element is situated in any other group of the periodic table it will have a number of valence electrons meaning that it will have a significant combining power. Generally the most reactive metals are located to the bottom left of the periodic table (due to their low electronegativity) whereas the most reactive non-metals are situated towards the top-right (due to their high electronegativity). These elements have the greatest combining power but the lowest valencies. I.e. therefore it could be said that the lower the valency the greater the combining power.
Metals are good conductors of electricity, non-metals are not good conductors of electricity rather they are electrical insulators.
This means that all the elements situated on left hand side of the periodic table (except hydrogen) all the way to group three have good electrical conductivity. This is mainly because of their metallic nature and structure. (I.e. they have metallic bonding which means there is a sea of delocalised electrons which can move freely and this allows for the conduction of electricity).
The elements on the right hand side of the periodic table (the non-metals) are electrical insulators because they do not have free moving electrons. They usually form diatomic covalent bonds and this means that the electrons are tightly bound within the molecules and therefore no electricity can be conducted since no free electrons. This is with the exception of carbon, which despite being classified as a non-metal displays excellent electricity conductivity when in the form of graphite.
All semi-metals are able to conduct electricity but Silicon, Germanium, Boron Tellurium which display high levels of resistance when it comes to electrical conductivity.
4) For efficient resource use, industrial chemical reactions must use measured amount of each reactant.
* Define the mole as the number of atoms in exactly 12g of carbon-12 (Avogadro’s Number).
The mole is simply a number. Like a dozen is a group of 12 some-things, a mole is 6.02 x 10^23 some-things. So if you have a mole of people, you would have 6.02 x 10^23 people. In chemistry it will usually refer to the number of atoms or molecules within a particular mass.
Eg: How many moles of Carbon dioxide, in 2.30g?
Note: The relative atomic mass (or atomic weight) of an element is the average mass of the atoms present in the naturally occurring element relative to the mass of an atom of the carbon-12 isotope taken as exactly 12.
Note: It is essential to realise that the relative atomic mass (or atomic weight) of an element is NOT the mass of an atom of that element. It is just a relative mass – relative to the mass of a carbon atom.
Note: Relative atomic mass and atomic weight are the same terms
The relative molecular mass (or molecular weight) of a compounds is the mass of a molecule of the compound relative to the mass of an atom of the carbon-12 isotope which is taken as exactly 12.
The molecular weight of a compound is the sum of the atomic weights of the atoms as given in the molecular formula.
The relative formula mass (or formula weight) of a compounds is the sum of the atomic weights of the atomic species given in the stated formula of that compound.
Note: If for any element we take the mass which in grams is numerically equal to the atomic weight, then it contains 6.02 x 10^23 atoms.
The Avogadro constant (for which the symbol is NA) is the number of atoms in exactly 12 grams of the carbon-12 isotope.
The molar mass is the mass of a mole of the substance. It can used for both elements and compounds.
Note: When we use gaseous elements it is important to understand that elements in a gaseous state may be diatomic. For example oxygen. Here it is important to identify wether or not the question wishes the molar mass of oxygen atoms (which is 16) or the molar mass of oxygen gas (which is 32).
It is relatively easy to convert between mass, moles and the number of atoms/molecules.
To change from mass to moles: n = m/M (where n is the number of moles, m is the mass of the substance, M is the molar mass of the substance).
To convert from moles to number of atoms/molecules:
Number of atoms/molecules = number of moles x the Avogadro constant * Compare mass changes in samples of metals when they combine with oxygen.
Note: In order to calculate the percentage composition of a particular element within a substance, use the following formula:
In the compound of formula AwByCz:
w x (atomic weight of A) x 100
%A= ________________________ molecular weight of AwByCz
Look At Attached example mole Questions.
* Describe the contribution of Gay-Lussac to the understanding of gaseous reactions and apply this to an understanding of the mole concept.
* Recount Avogadro’s law and describe its importance in developing the mole concept
In 1808, a man by the Name of John Dalton proposed a theory which we know as Dalton’s atomic theory.
The three postulates of Dalton’s atomic theory were:
* Matter is composed of tiny, invisible particles called atoms * All atoms of the one element are identical, but different from the atoms of all other elements * Chemical reactions consist of combining, separating or rearranging atoms in simple whole number ratios.
This theory led to the use of symbols, formulae and equations, and also the concept of relative atomic mass.
However, formulae and atomic weights were the grey area. It was Gay-Lussac and Avogadro who provided the answer.
After studying the volumes in which gases reacted, Gay-Lussac, in 1808, proposed the law of combining volumes:
“When measured at a constant temperature and pressure, the volumes of gases taking part in a chemical reaction show simple whole number ratios to one another.”
(1) For example: 100 mL of hydrogen reacts with 100 mL of chlorine to form 200mL of hydrogen chloride (one “volume” reacts with one “volumes” to form two “volumes”)
Avogadro noted the similarity between Gay-Lussac’s statement and the third postulate of the atomic theory. Thus he proposed the following:
“When measured at the same temperature and pressure, equal volumes of gases will contain the same number of molecules”.
This became known as Avogadro’s Law
By applying this law to statement (1), we can deduce that one molecule of hydrogen combines with one molecule of chlorine to form two molecules of hydrogen chloride.
One MOLE of hydrogen gas reacts with one MOLE of chlorine gas to produce two MOLES of hydrogen chloride.
Gay-Lussac’s law of combining volumes along with Avogadro’s law allowed for the use of results from quantitative analysis in order to determine formulae for compounds and hence their relative atomic masses.
Because the existence of formulae and atomic weights, and hence the ability to write chemical equations, are essential for the concept of moles, it can be concluded that the work of Gay-Lussac and Avogadro was critically important in developing the mole concept.
Avogadro’s law can be rearranged to read:
“Equal numbers of molecules of different gases occupy the same volume (at the same temperature and pressure).”
In this form Avogadro’s law allows us to convert statement about numbers of molecules in chemical equations into statements about volumes. BUT ONLY FOR GASEOUS REACTANTS AND PRODUCTS.
Note: The study of quantitative aspects of formulae and equations is called stoichiometry. The calculations involved are stoichiometric calculations.
* Distinguish between empirical formulae and molecular formulae.
The empirical formula of a compound is the formula that tells us the simplest ratio in which the atoms are present in the compound.
The molecular formula of a compound is the formula that tells us how many of each type of atom are present in a molecule of the compound.
Molarity is the concentration of solute within a solution.
- The concentration of solution is the amount of solute dissolved in a given amount of solution - The amount of solute is the number of moles of solute - The amount of solution is the volume of solution in Litres - The Molarity of a solution is defined as the number of moles of solute in one litre of solution. - Molarity = (moles of solute) / (volumes of solution in litres) - c = n / V (where c is the Molarity of the solution in mol/L) - The symbol M is used for Molarity. 1M means a Molarity of one mole/litre. - Square brackets  around a symbol indicate the “concentration of”.
[Na+] means the concentration of sodium ions in moles per litre.
5) The relative abundance and ease of extraction of metals influences their value and breadth of use in the community.
* Define the terms mineral and ore with reference to economic and non-economic deposits of natural resources.
A resource is something that we need or want to use. Natural resources are freely available in nature (naturally occurring). Synthetic Resources are man-made and do not occur naturally in nature.
A economic resource is a resource through we which we are able to gain profit.
Metals make up one of our most precious natural resources. Metals are non-renewable because when we have consumed them all, they are unable to be replaced and we cannot make any more.
A rock is a mixture of minerals.
An ore is a compound or mixture of compounds from which it is economic (or commercially profitable) to extract the desired substance such as a metal.
A mineral is a pure (or nearly pure) crystalline compound that occurs in the Earth’s crust.
Haematite is a mineral; it is the common ore of iron. The ore of aluminium is bauxite; it is a mixture of compounds, mainly the minerals gribbsite and boehmite, iron (III) oxide, silica and various clays. There are various minerals called alumino-silicates but these minerals are not ores of aluminium because it is not economic to extract aluminium from them. Thus showing that the term “ore” is coined to a deposit where the metal mined has a profitable yield.
* Describe the relationship between the commercial prices of common metals, their actual abundances and relative costs of production.
Factors which affect the price of the metal are:
* The abundance and location of ores of the metal (less abundant ores will generally attract higher royalties and so will be more expensive) * The cost of extracting the metal from the ore (aluminium and titanium are much more expensive to extract than iron or copper) * The cost of transporting the metal or its ores to the required location (rare metals or their ores may need to be shipped from remote locations, while for abundant metals conveniently located ore deposits can be used) * The world-wide demand for the metal; if demand is high, the price rises; if it slumps, price falls: the supply and demand factor.
Element | O | Si | Al | Fe | Ca | Na | K | Mg | Abundance
(% by mass) | 49.2 | 25.7 | 7.5 | 4.7 | 3.4 | 2.6 | 2.4 | 1.9 |
Resource | Approximate Known Reserves | Aluminium | 1000000000 (1x10^9) | Copper | 300000000 (3x10^8) | Iron | 90000000000 (9x10^10) |
It is likely prediction that copper will be the first one to run out.
Factors that will affect how long these metals will last: Rate of use, new discoveries of ores, new developments, replacement materials.
Based on present rate of usage, these reserves of aluminum, copper and iron are expected to last approximately 30, 20 and 90 years respectively. As these three metals are used extensively by our society, a shortage of any of them will have vast consequences.
If Aluminium supplies were to reach shortage levels, these would be the consequences: * Lower abundance – Higher costs * Economic consequences. * Alternative products (eg plastics) – higher environmental consequences eg. Pollution * Greater amount of recycling
There are a number of ways scientists can help make these reserves last longer including: * Increase recycling * Develop new methods of extracting metals * Metal protection – new methods * Develop alternatives for metals.
Commercial prices and cost of production of metals vary considerably. The following table provides some approximate estimates for comparison.
Metal | Price ($A/Tonne) | Production ($A/Tonne) | Relative Abundance | Aluminium | 2000 | 1600 | 1st | Iron | 1100 | 900 | 2nd | Magnesium | 5300 | 4200 | 8th |
* Explain why ores are non-renewable resources
Metal ores are non-renewable resources. They were formed when the Earth was formed and there is now way of forming any more of them. While we are unlikely to use up all the known reserves of metal ores in the short term, we nevertheless should use them as sparingly as possible so as to make them last for as long as possible.
Simply put, the main way of doing this is through recycling. There are four advantages of recycling metals:
1) Less energy used in recycling metals than in extracting metal from virgin ore
2) Finite natural resources (ores) are conserved.
3) Less rubbish has to be disposed of. This is a major concern in big cities where sites for garbage dumps are becoming hard to find.
4) Recycling may lead to lower prices for metals.
The problem with any form of recycling is that the used material has to be collected from very scattered locations. The ore comes from a confined location (the mine site); it is processed into metal and then into usable products are quite specific placed or factories; but then as the products are sold and used, they are scattered very widely throughout our communities. Collecting used material for recycling is a major money and energy cost of recycling.
* Describe the separation process, chemical reactions and energy considerations involved in the extraction of copper from one of its ores.
Ore: Chalcopyrite (CuFeS2)
Separation Process + Chemical Reactions:
1) Mining, crushing and grinding:
The mined ore is placed in a crusher and converted into pebbles. The pebbles and then ground to liberate the mineral crystals from the rock.
Using the process of froth flotation the Chalcopyrite mineral is separated from the gangue of silicate minerals. The Chalcopyrite mineral sticks to the froth and are removed. The froth is pumped to the smelter, whereas the gangue is disposed.
3) Roasting and Smelting
The roasting process converts the sulfide mineral into an oxide. Smelting is an industrial process in which a furnace provides high temperatures to produce molten materials for chemical reduction. Chemical Reduction involved converting a metallic compound to a metal. The copper is released from the mineral because the iron and sulfur atoms combine more readily with oxygen to from stable compounds.
Sand and calcium carbonate are added to the smelter. Oxygen rich air is also blown in, and the Chalcopyrite undergoes a complex series of reactions until copper is finally formed.
Overall Reaction: 2CuFeS2(s) + 5O2(g) 2Cu(l) + 2FeO(s) + 4SO2(g)
Sand and calcium carbonate combine to form calcium silicate. The iron oxide combines with the silicate to form a slag which floats on the melted copper. The ‘slag’ of iron silicate can be readily removed.
FeO(s) + CaSiO3(l) FeSiO3(l) + CaO(s)
Sulfur is removed as sulfur dioxide gas by blowing air through the molten copper at 1200 degrees. This is converts some copper sulfide into copper oxide and these react to finally produce copper.
Roasting: 2Cu2S(s) + 3O2(g) 2Cu2O(l) + 2SO2(g)
Smelting: 2Cu2O(l) + Cu2S(l) 6Cu(l) + SO2(g)
The melted copper is run off into moulds and cast into blocks for further refining. The cast copper is called “Blistered copper” because of the bubbled surface caused by escaping sulfur dioxide gas. It contains 2-3% impurities of other metals such as gold, silver and nickel.
Electro-refining of copper
In order to refine the blister copper produced, electrolysis is necessary. Electro-refining involves the oxidation of the blister copper (this forms the anode in the electrolytic cell) and the reduce of the copper ions so formed back to metallic copper at the negative electrode (cathode).
Overall Electrolytic cell reaction:
Cu(s) + Cu2+ Cu2+ + Cu(s)
Impure Anode Pure deposit on Cathode
A significant amount of energy is required to undergo the extraction of copper from Chalcopyrite. It is estimated that 2470kJ is the minimum amount of energy required to produce 1kg of pure metal in this extraction process.
Note: In general, the more active a metal, the greater the energy required to extract it from its ores.
However, the energy involved in the extraction reaction is the only part of the total energy budget of the extraction process. Energy has to be supplied in order to: * mine the ore * purify or concentrate the ore * maintain high temperatures needed to make the extraction reactions go * purify the raw metal or form it into useful alloys.
* Recount the steps taken to recycle aluminium
The steps in recycling aluminium are:
* Collect the used products from homes, shopping centers, factories etc. * Transport the collected material to a central processing plant * Separate the aluminium from the impurities such as dirt, labels etc. * Re-smelt the metal into ingots * Roll ingots into sheets of aluminium * Transport these sheets to product manufacturers.
In recent years, more attention is given to the recycling of aluminium drink cans as they are readily used by the community and widely dispersed, thus they can be recycled in order to reduce the cost of manufacturing new products.
Recycling aluminium requires only 5% of the energy and produces only 5% of the CO2 emissions as compared with primary production and reduces the waste going to landfill.
* Discuss the importance of predicting yield in the identification, mining and extraction of commercial ore deposits.
The percentage composition and mass-mass calculations are widely used in the mining and minerals industries to calculate the yields of materials from their ores.
The yield of a metal from a particular mineral or ore is the mass of metal that can be obtained from a particular mass of the mineral/ore.
Yield if often expressed as a percentage.
While we can use formulae to calculate (or predict) yields of metals from particular minerals (pure compounds), for ores we have to measure them experimentally. This is because ores are mixtures of the required mineral and unwanted material, and, being mixtures, they have variable composition (from one location to another).
Measurement of the yield from a particular ore body is extremely important in the mining and minerals industry because it determines whether extraction of the metal from that ore is profitable or not. Whenever a new ore body is found, samples are analysed to see if the yield of the metal is enough to make mining the ore, economically profitable.
Another factor is considering yield, is that the yield produces in large factories is less than that of a laboratory.
The Percentage yield of a chemical reaction is the amount of product obtained expressed as a percentage of the amount expected from the chemical equation.
Some reasons why yields are often less than 100% are:
* There are physical losses (such as spillages or leakage) * Some of the product / reactant may be lost through vaporisation * Sometimes all of the reactants may not react. * Rate of reaction may be too slow. (premature analysis) * There may be certain side reactions which consume parts of the reactants.
[ 1 ]. Table is directly from: Smith, Ronald. Conquering Chemistry - Preliminary Course Australia: McGraw-Hill, 2004
[ 2 ]. Direct quote: UNSW, SCHOOL OF CHEMISTRY, HSC TEACHERS' WORKSHOP. “8.3 Metals” - November 1999 URL: http://www.chem.unsw.edu.au/highschool/files/metals.pdf
[ 3 ]. Direct Quote: Smith, Ronald. Conquering Chemistry - Preliminary Course Australia: McGraw-Hill, 2004
[ 4 ]. Direct Quote: "law of octaves." Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 03 Jun. 2009 URL: http://www.britannica.com/EBchecked/topic/424834/law-of-octaves
[ 5 ]. Direct Quote: Aus-e-tute- “History of the Periodic Table of Elements” – Date Visited: 04-06-2009
[ 6 ]. Direct Quote: Aus-e-tute- “History of the Periodic Table of Elements” – Date Visited: 04-06-2009
[ 7 ]. Table is Directly from: Smith, Ronald. Conquering Chemistry - Preliminary Course Australia: McGraw-Hill, 2004
[ 8 ]. Direct Quote: Smith, Ronald. Conquering Chemistry - Preliminary Course Australia: McGraw-Hill, 2004
[ 9 ]. Direct Quote: Smith, Ronald. Conquering Chemistry - Preliminary Course Australia: McGraw-Hill, 2004
[ 10 ]. Direct Quote: Smith, Ronald. Conquering Chemistry - Preliminary Course Australia: McGraw-Hill, 2004
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