Chemistry Questionnaire

Only available on StudyMode
  • Download(s) : 194
  • Published : October 24, 2012
Open Document
Text Preview
ST ANDREW’S JUNIOR COLLEGE

JC 2 Preliminary Examination
CHEMISTRY

9647/03

Higher 2

13 September 2010

Paper 3 Free Response

2 hours

Candidates answer on separate paper.
Additional Materials: Answer paper, Graph Paper, Data Booklet

READ THESE INSTRUCTIONS FIRST
Write your name and civics group on all the work you hand in. Write in dark blue or black pen on both sides of the paper.
You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions.
A Data Booklet is provided.
You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together.

2
This question paper consists of 10 printed pages.
SAJC 2010 P3 – Answer any four questions.
1

(a) Hydrolysis of a lipid (containing multiple ester linkages) produced the following fatty acids.
Structure I

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH

Structure II

CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH

(i) In an experiment, hot acidified potassium manganate(VII) was used to oxidise Structure I. Write the structural formulae of all organic products formed during the oxidation.
(ii) What is meant by the term cis-trans isomerism? How many cis-trans isomers are present in Structure I? Draw any 2 possible cis-trans isomers. (iii) State the physical state of this lipid at room temperature. Explain your answer.

[9]

(b) Suggest a possible identity for each of the organic compounds A-E below. Explain your reasoning and write balanced equations for the reactions involved where possible. (i) A, C11H14O2 is a neutral compound. Hydrolysis of A gives B, C7H6O2 which is a white precipitate and C, C4H10O which does not decolourise acidified potassium manganate(VII) on heating.

(ii) D, C4H10O2 reacts with 2 moles of sodium metal, but not with solid sodium carbonate. On boiling under reflux with aqueous potassium manganate(VII), D gives a compound, E, C4H6O3.

E reacts with alkaline aqueous iodine to give a yellow

precipitate and evolves carbon dioxide when solid sodium carbonate is added. [11]

3
[Total:
20]

2

(a) Explain each of the following observations as fully as you can. (i) Phenylalanine, C6H5CH2CH(NH2)COOH, is readily soluble in water whereas phenylamine is insoluble.

(ii)

Trimethylamine, (CH3)3N, has a lower boiling point than dimethylamine, (CH3)2NH.

(iii)

An aqueous solution of trimethylamine is more basic than phenylamine. [9]
(b) When 20.0 cm3 of a solution of trimethylamine was titrated against 0.0300 mol dm -3 hydrochloric acid, the following pH readings were obtained:
Volume / cm3
0
5
10
15
20
25
28
30
32
34
35
40
45
50

pH
12.4
10.6
10.2
10.0
9.7
9.4
9.2
8.9
8.5
3.4
3.0
2.5
2.3
2.2

(i) Plot a graph of these results with pH on the y axis and volume of hydrochloric acid added on the x axis. Label and comment on the shape of the curve before, at and after neutralisation.

(ii) Label the equivalence point on your graph for b(i) and suggest a suitable indicator from the following list. Explain your choice.
Indicator
Methyl orange
Methyl red
Bromothymol blue
Phenol red

pH at which colour changes
3.2 – 4.4
4.8 – 6.0
6.0 – 7.6
6.8 – 8.4

4
Phenolphthalein

8.2 – 10.0

[7]
[Turn over
2

(c) A sodium salt of glutamic acid, monosodium glutamate (MSG), is a flavour enhancer. O
H2 N

CH

C

OH

C H2
C H2
C
OH

O

Glutamic acid

(i) Draw structural formulae of the products of the reactions between glutamic acid and

I

aqueous NaOH

II

aqueous HCl

(ii) Draw the structural formula of a dipeptide formed between glutamic acid and phenylalanine, showing the ionic form in which it would exist at pH 10. [4]
[Total:
20]

5

3

(a) Iron(III) chloride is a dark...
tracking img