11.2 Alkanes, Set A To print: Ctrl + P, paper A4, margins Default.
Learners' AlleyDesigned by Khow Willard
11.2

Alkanes

Set AFoundations
Name
Time 1 hour
Total 31 marks

A Data Booklet may be used.

A

From the lesson

13 marks
1
Name CH3CH(CH3)CH(CH3)CH3.
[1]

Source: Learners' Alley, Alkanes slides

2
Common10 cm3 of a gaseous hydrocarbon needs exactly 50 cm3 of O2 for complete combustion and gives 30 cm3 of CO2. Find its formula.
[3]

Source: Learners' Alley, Alkanes slides

3

CommonFind the statistical ratios of

(a)
1-chloropropane : 2-chloropropane from propane
[1]
(b)
the two monochloro products of 2-methylpropane
[1]

Source: Learners' Alley, Alkanes slides

4
CommonWhy does pentane boil higher than 2,2-dimethylpropane?
[2]

Source: Learners' Alley, Alkanes slides

5
Write the two propagation steps for CH4 + Br2.
[2]

Source: Learners' Alley, Alkanes slides

6
What conditions favour monosubstitution?
[1]

Source: Learners' Alley, Alkanes slides

7
Why are alkanes insoluble in water?
[2]

Source: Learners' Alley, Alkanes slides

B

Practice

18 marks
8

CommonExcess pentane was reacted with bromine in the presence of UV light. Assuming that only mono-bromination takes place and the reaction occurs at the same rate at all carbon atoms, what is the ratio of the products formed?

1-bromopentane2-bromopentane3-bromopentane
A132
B312
C123
D321
A
B
C
D
Answer [1]

Source: VJC 2012 Prelim P1 Q18, via EJC Alkanes Topical Revision, Q4

9

CommonAlkanes differ in their boiling points. Four alkanes are given below.

1C4H102CH3(CH2)3CH33CH3C(CH3)2CH34CH3CH2CH(CH3)2

Which of the following shows the correct sequence of the boiling points of the four alkanes given?

A1 < 2 < 3 < 4
B1 < 3 < 4 < 2
C2 < 3 < 4 < 1
D2 < 4 < 3 < 1
Answer [1]

Source: CJC 2013 Prelim P1 Q15, via EJC Alkanes Topical Revision, Q5

10

Name the following compounds.

(a)
CH3C(CH3)2CH2CH3
[1]
(b)
CH3CH(C2H5)CH(CH3)CH3
[1]

Source: RJC H2 Chemistry Tutorial 11 (Alkanes), Q1(a) and (b)

11
CommonArrange the following hydrocarbons in order of increasing boiling point, giving your reasons: (a) 2-methylhexane, (b) heptane, (c) 3,3-dimethylpentane, (d) hexane, (e) 2-methylpentane.
[4]

Source: RJC H2 Chemistry Tutorial 11 (Alkanes), Q2

12
30 cm3 of an alkane is completely burnt in 340 cm3 (excess) of oxygen and the volume of residual gases is measured at room temperature and pressure. These are then shaken with aqueous sodium hydroxide solution. Once again, the volume of gas is measured. The volume of residual gas before shaking with NaOH is 250 cm3 and after shaking with NaOH is 100 cm3. Calculate the relative molecular mass, Mr, of the alkane. Draw and name all the possible isomers of the alkane.
[3]

Source: RJC H2 Chemistry Tutorial 11 (Alkanes), Q4

13

ChallengeBromination of 3-methylpentane produces a mixture of four different monobromoalkanes. One of them is compound X.

(a)
Name and describe the mechanism of the reaction between 3-methylpentane and bromine to form compound X. You may use the formulae R–CH3 and R–CH2Br to represent the structures of 3-methylpentane and compound X respectively.
[3]
(b)
Use your mechanism from (a) to suggest why the bromination can be carried out with yellow light (which has lower energy) but chlorination requires blue or ultraviolet light (which has higher energy).
[1]
(c)
Draw the structures of the other three monobromoalkanes that were formed together with compound X. Hence suggest the relative proportion in which the four monobromoalkanes are formed.
[3]

Source: EJC Alkanes Topical Revision, Section B Q8(b)(i) to (iii)