Organic Chemistry
8 marks · NormalThe hydrocarbon octane, C8H18, is a major component of gasoline (petrol). Gasoline is mainly used as a fuel in cars.
State what organic chemistry is the study of.
Name the homologous series to which octane belongs.
Explain how the name 'octane' shows the number of carbon atoms in each molecule, including the code used for the chain length.
Complete the equation for the complete combustion of octane (C8H18). State the formulae of all products.
State one typical use of gasoline and explain why its properties make it suitable for this use.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Organic chemistry is the study of the compounds of carbon (except simple oxides, carbonates, and carbides) or the chemistry of carbon compounds.
(b) Alkanes
(c) The prefix 'oct-' in 'octane' indicates that each molecule contains a chain of 8 carbon atoms. This is because the code 'oct' means eight carbons. The suffix '-ane' shows that it is an alkane with only single bonds.
(d) 2C8H18 + 25O2 → 16CO2 + 18H2O
(e) Petrol (gasoline) is used as a fuel in cars. Its hydrocarbons combust easily to release a large amount of energy, making it suitable for powering engines.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States that organic chemistry is the study of carbon compounds.
B2 (b) · 1 mark · Correctly identifies alkanes as the homologous series.
M1 (c) · 1 mark · Mentions that 'oct-' means eight carbon atoms (reference to chain length coding).
A1 (c) · 1 mark · States that '-ane' shows it is an alkane (single bonds only).
M2 (d) · 1 mark · Writes balanced formula for octane and oxygen as reactants, correct product formulae for either product.
A2 (d) · 1 mark · Completes and balances the equation correctly as 2C8H18 + 25O2 → 16CO2 + 18H2O.
B3 (e) · 1 mark · States that gasoline is used as a fuel in cars.
E1 (e) · 1 mark · Explains why petrol/gasoline is suitable (releases a large amount of energy on combustion, suitable for engines).
Worked solution
a) Organic chemistry is the study of carbon compounds (except simple oxides of carbon and some carbonates and carbides).
b) Octane belongs to the alkane homologous series.
c) The prefix 'oct-' indicates that the molecule has eight carbon atoms in its chain. This code is used to show chain length. The suffix '-ane' tells you that it is an alkane, having only single bonds between the carbon atoms.
d) The products are carbon dioxide and water.
e) Gasoline is used as a fuel for cars because its hydrocarbons combust easily and release a large amount of energy, which is useful for running car engines.