1.
State what is meant by a hydrocarbon.
[1 mark]
- compound of H and C only
JD SCIENCE
Unit 6 answers — Organic chemistry and fuels
Indicative marking points. Award marks for equivalent scientific or mathematical wording. Do not issue this sheet with the student worksheet.
2.
State what is meant by an alkane.
[1 mark]
- saturated hydrocarbon CₙH₂ₙ₊₂
3.
State what is meant by an alkene.
[1 mark]
- unsaturated hydrocarbon CₙH₂ₙ
4.
State what is meant by fractional distillation.
[1 mark]
- separating crude oil by boiling point
5.
State what is meant by cracking.
[1 mark]
- breaking long alkanes into shorter alkanes and alkenes
6.
State what is meant by complete combustion.
[1 mark]
- hydrocarbon + O₂ → CO₂ + H₂O
7.
State what is meant by incomplete combustion.
[1 mark]
- produces CO and/or C
8.
State what is meant by a polymer.
[1 mark]
- long chain of monomers
9.
State what is meant by a functional group.
[1 mark]
- the reactive part of a molecule
10.
State what is meant by an ester.
[1 mark]
- from alcohol + carboxylic acid
11.
Owain is asked about a hydrocarbon in a WJEC Chemistry paper.
(a) [2 marks]
- alkanes and alkenes
(b) [3 marks]
- crude oil is a mixture of hydrocarbons
12.
Owain is asked about an alkane in a WJEC Chemistry paper.
(a) [2 marks]
- single C–C bonds only
(b) [3 marks]
- used as fuels
13.
Owain is asked about an alkene in a WJEC Chemistry paper.
(a) [2 marks]
- contains C=C
(b) [3 marks]
- bromine water decolourises
14.
Owain is asked about fractional distillation in a WJEC Chemistry paper.
(a) [2 marks]
- fractionating column
(b) [3 marks]
- larger molecules have higher BP
15.
Owain is asked about cracking in a WJEC Chemistry paper.
(a) [2 marks]
- high T and catalyst
(b) [3 marks]
- meets demand for petrol and alkenes
16.
Owain is asked about complete combustion in a WJEC Chemistry paper.
(a) [2 marks]
- blue flame
(b) [3 marks]
- plenty of oxygen
17.
Write the formula of the alkane with 9 carbons.
[3 marks]
- Final answer: C9H20
18.
Balance C₃H₈ + O₂ → CO₂ + H₂O
[3 marks]
- Final answer: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
19.
Mr of C₂H₄ (C=12, H=1)
[3 marks]
- Final answer: 28
20.
A 100 cm³ sample of alkene decolourises bromine water. What does this show?
[3 marks]
- Final answer: C=C present / unsaturated
21.
Percentage of C in CH₄
[3 marks]
- Final answer: 75%
22.
Moles of CO₂ from 2 mol C₂H₆ complete combustion (2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O)
[3 marks]
- Final answer: 4 mol
23.
Owain carries out a WJEC-style required practical linked to organic chemistry and fuels. This is a typical WJEC required-practical style question.
(a) [2 marks]
- Independent: the independent variable for this topic
- Dependent: the measured outcome
(b) [2 marks]
- keep all other variables constant
- so the test is fair / only one variable is changed
(c) [2 marks]
- repeat and calculate a mean / use a tighter method
24.
Owain carries out collecting valid data for organic chemistry and fuels. This is a typical WJEC required-practical style question.
(a) [2 marks]
- Independent: a chosen factor
- Dependent: a quantitative measurement
(b) [2 marks]
- calibrated instrument
- so the test is fair / only one variable is changed
(c) [2 marks]
- systematic error from zero error
25.
Owain carries out drawing a graph for organic chemistry and fuels. This is a typical WJEC required-practical style question.
(a) [2 marks]
- Independent: x-variable
- Dependent: y-variable
(b) [2 marks]
- same scale / same apparatus
- so the test is fair / only one variable is changed
(c) [2 marks]
- not drawing a line of best fit through the trend
26.
Owain carries out evaluating a method about organic chemistry and fuels. This is a typical WJEC required-practical style question.
(a) [2 marks]
- Independent: method change
- Dependent: precision / accuracy
(b) [2 marks]
- same sample size
- so the test is fair / only one variable is changed
(c) [2 marks]
- too few repeats
27.
Compare a hydrocarbon with an alkane.
[4 marks]
- compound of H and C only
- saturated hydrocarbon CₙH₂ₙ₊₂
- give one linked difference
28.
Compare an alkane with an alkene.
[4 marks]
- saturated hydrocarbon CₙH₂ₙ₊₂
- unsaturated hydrocarbon CₙH₂ₙ
- give one linked difference
29.
Compare an alkene with fractional distillation.
[4 marks]
- unsaturated hydrocarbon CₙH₂ₙ
- separating crude oil by boiling point
- give one linked difference
30.
Compare fractional distillation with cracking.
[4 marks]
- separating crude oil by boiling point
- breaking long alkanes into shorter alkanes and alkenes
- give one linked difference
31.
Apply your knowledge of incomplete combustion to this situation: yellow flame
[3 marks]
- yellow flame
32.
Apply your knowledge of a polymer to this situation: addition polymers from alkenes
[3 marks]
- addition polymers from alkenes