Topics: PH, PH indicator, Acid Pages: 6 (1568 words) Published: March 11, 2013

Differences between acids and bases
An acid-base reaction is based on the reaction involving the ionization of water H2O -> H+ + OH-
This means that water can break apart into a hydrogen ion and a hydroxide ion. These two ions can also join together to form a water molecule. When a strong acid is placed in water, it will ionize completely, and break down into its constituent ions in which one of it a hydrogen ion. When a strong base is placed in water, it will ionize completely and dissociate into its constituent ions in which one of them is a hydroxide ion. Based on their reactions in water, we can effectively define what an acid and a base is and distinguish between the two. The first modern definition of an acid and a base was proposed by Arrhenius. According to his theory, Arrhenius stated that an acid is a substance that dissociates in water to form hydrogen ions (H+) and increases the concentration of H+ ions in an aqueous solution and that a base is a substance that dissociates in water to form hydroxide ions (OH-) and increases the concentration of OH- ions in an aqueous solution. His definitions were however limited to aqueous solutions. A major problem with the Arrhenius acid-base concept is that certain substances such as ammonia, (NH3), produce basic solutions and react with acids, yet contain no hydroxide. In 1923, J. N. Bronsted and T. M. Lowry dependently proposed a new way of defining acids and bases in aqueous solutions. According to the Bronsted-Lowry concept of acids and bases, acids are hydrogen ion donors and bases are hydrogen ion acceptors. An acid can donate an H+ ion (proton) to another substance while a base can accept an H+ ion from another substance. The term proton means the species H+ (the nucleus of the hydrogen atom) rather than the actual hydrogen ions that occur in various solutions. The definition thus shows that reaction is independent of the solvent. The use of the word species rather than substance or molecule implies that the terms acid and base are not restricted to uncharged molecules but apply also to positively or negatively charged ions. This extension is one of the important features of the Bronsted-Lowry definition. Based on these definitions, the properties of an acid can be distinguished from that of a base. An acid react with most metals to form hydrogen gas, have a sour taste, frequently feel sticky and are usually gases or liquids. Vinegar and grapefruit juice are too harmless acids. Hydrochloric acid is much more dangerous and may cause severe burns. A base on the other hand feels slippery because the skin dissolves a little when it comes in contact with them, have a bitter taste, react with grease and oil, and frequently solids.

Discussion of indicators
An indicator is a chemical compound that is added in small amounts to an aqueous solution so that the pH of that solution can be determined visually. An acid-base indicator is either a weak acid or a weak base. An indicator does not change color from pure acid to pure alkaline at specific hydrogen ion concentration, but rather, the color change occurs over a range of hydrogen ion concentrations. This range is termed the color change interval. It is expressed as a pH range. Some examples of indicators include thymol blue, methyl yellow, methyl orange, bromphenol blue, bromcresol green, methyl red, bromthymol blue, phenol red, neutral red, phenolphthalein, thymolphthalein, alizarin yellow, nitramine, and trinitrobenzoic acid. In this experiment phenolphthalein is the indicator used in the titration process.

Discussion of terms
Titration is the process of determining the quantity of a substance A which is the acid by adding measured increments of substance B which is the base, with which it reacts (almost always as a standardized solution called the titrant) with provision for some means of recognizing (indicating) the end point at which essentially all of the acid has reacted using an...
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