Chemistry Notes
HSC Core Topic 1
The Identification and Production of Materials
Humans have always exploited their natural environment for all their needs including food, clothing and shelter. As the cultural development of humans continued, they looked for a greater variety of materials to cater for their needs.
The twentieth century saw an explosion in both the use of traditional materials and in the research for development of a wider range of materials to satisfy the specialist needs of space travel and the information technologies. Added to this was a reduction in the availability of the traditional resources to supply the increasing world population.
Chemists and chemical engineers continue to play a pivotal role in the search for new sources of traditional materials such as those from the petrochemical industry. As the fossil organic reserves dwindle, new sources of the organic chemicals presently used have been found. In addition, chemists continually searching for compounds to be used in the design and production of materials to replace those that have been deemed no longer satisfactory for needs.

1. Fossil fuels provide both energy and raw materials such as ethene, for the production of other substances.
•

Identify the industrial source of ethene from the catalytic cracking of some of the fractions from the refining of petroleum.

Ethene is obtained from refined petroleum via catalytic cracking (use of catalyst to break larger chains into smaller ones, to meet demand) NOTE that ethene is a by-product of cracking used to produce other alkanes.
(1) When an alkane is cracked,
H H H H H

H C
H
(2) there are 2 more hydrogens required where bond was broken therefore, 1 hydrogen moves from one cracked part to the other
(3) the one missing 2 Hs will form a double bond, to make an alkane and an alkene •

C
H

C
H

C
H

C H
H

H
H C

H
C

H
C

H
C

H
C H

H

H

H

H

H

H
C
H

H
C
H

H

H
C
H

H
C
H

H
C H
H

Explain that catalytic cracking is an example of an industrial process that involves surface reactions with inorganic catalysts.

The catalysts in the industrial process of catalytically cracking petroleum are structured aluminosilicate called zeolites. This structure causes zeolites to have large surfaces. The cracking reaction occurs on the inner surfaces of the catalysts, thus a surface reaction.
Since the zeolites are solid and the reactants are liquid/gas, this reaction is heterogeneously catalysed. Example:
Decane

zedite catalyst
500°C

ethene

+

2-methylheptane

•
•

Explain the relationship between the properties of alkanes and alkenes and their non-polar nature and weak dispersion forces between molecules.
Identify data, plan and perform a first-hand investigation to compare the reactiveness of appropriate alkenes with the corresponding alkanes in bromine water in solution.

Since alkanes and alkenes are non-polar and only have weak dispersion forces between their molecules, they have similar (low) boiling points and melting points, as well as similar solubility (in non-polar solvents, not soluble in water). Short chains (1-4) are gases, and higher are liquids.
Alkenes are much more reactive than alkanes. While alkanes are useful since they burn in air, alkenes react much more readily with halogens (and decolourise Cl, Br, I). Alkanes require
UV light and undergo a substitution reaction, while alkenes allow addition reactions by easily breaking their double bonds.
C 6 H 14 (l) + Br 2 (soln) --> C 6 H 13 Br(soln) + HBr(aq)
Hexane + Bromine --> 1-Bromohexane + Hydrogen bromide
CH 3 –CH 2 –CH=CH-CH 2 –CH 3 + HCl --> CH 3 –CH 2 -CH 2 -CH-CH 2 -CH 3
|
Cl
3-Hexene + Hydrogen chloride --> 3-chlorohexane
Alkanes
• Saturated hydrocarbons of the general formula C n H 2n+2 (where n = 1, 2, 3…)
• Commonly called paraffins (Latin: little reactivity) because of their relative unreactivity • They are non-polar molecules, single covalent bonds linking carbon atoms with hydrocarbon chain. Dispersion forces exist between