About Engineering

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1) Fossils fuels provide both energy & raw materials such as ethylene, for production of other substances Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum Catalytic cracking is the process whereby high molecular weight fractions are broken down to low molecular weight ones. This process is used in petroleum refineries where crude oil is broken down to smaller alkenes and alkanes, until ethene, propene, (or both) are formed. Catalytic Cracking allows greater output of high-demand products.

Identify that ethylene, because of the high reactivity of its double bond, is readily transformed into many useful products Ethylene, because of the high reactivity of its double bond, can form many useful products, such as plastics (polyethylene). For example, ethene can react with water to form ethanol, with a H3PO4 catalyst at 300oC. Ethene can react with oxygen in the presence of an Ag catalyst and at 250oC, to form ethylene oxide, which is further treated with dilute acid solution to form ethylene glycol. Ethene can also react with oxygen, with a copper chloride catalyst and at 150oC, to form vinyl chloride (chloro-ethene)

Identify that ethylene serves as a monomer from which polymers are made Ethylene is the monomer which is converted into the polymer polyethylene by the process of polymerisation (chemical reaction where many small identical molecules join together to form one large molecule).

Identify data, plan and perform a first-hand investigation to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water and iodine in solution Alkanes burn in air to form CO2 and H2O, and liberate large amounts of heat in the process. Alkanes also react with (or decolourise) Cl, Br, and I, very slowly, in the presence of ultra-violet light. However without UV-light no rxn occurs. However, alkenes are much more reactive, as, when they react, their double bond opens allowing the formation of single bonds, which allow alkyl groups to be attached. Therefore, a good test to determine alkanes from alkenes is to add bromine water (HOBr) which is brown. If the solution decolourises then it is an alkene and if not it is an alkane.

Identify polyethylene as an addition polymer and explain the meaning of this term Polyethylene is an addition polymer; that is, it forms by molecules adding together without the loss of any atoms. Basically, each double bond opens out to form single bonds with the neighbouring molecules.

Outline the steps in the production of (poly) ethene as an example of a commercially and industrially important polymer Two processes used:
An older gas phase process, which uses high-pressure (1000 to 3000 atm), high temperatures (300oC) and’initiator’ organic peroxide). This process leads to significant chain branching (addition of alkyl groups) and therefore reduces density. Hence, this process is used for low-densitypolyethylene. The newer process, (called the Ziegler-Natta process) uses pressures of only a few atmospheres and temperatures of about 60oC and uses a catalyst which is a mixture of titanium (III) chloride and a trialkylaluminium compound. This product is more crystalline, with less branching, hence high-density. Therefore, this process is used for high-density polyethylene.

Identify the following as commercially significant monomers (pp 15): – Vinyl chloride
– Styrene; by both their systematic and common names

Describe the uses of the polymers made from the above monomers in terms of their properties Polyvinyl Chloride (PVC)- rigid because the chlorine side group is larger than hydrogen. This makes it stiff and reduces flexibility. It is used for sewerage pipes, down pipes, guttering because of its strength. Low Density Polyethylene- Has chain branching meaning that chains can’t get close to one another, so it has low density. Soft and flexible. Used for wrapping plastic...
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