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Secondary 4 Pure Chemistry Organic Chemistry Quiz

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Secondary 4 Pure Chemistry Quiz - Organic Chemistry

Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 45

Duration: 45 minutes
Total Marks: 45

Instructions:

Answer all questions.
Write your answers in the spaces provided.
The number of marks is given in brackets [ ] at the end of each question or part question.
You may use a periodic table and a calculator.

Section A: Hydrocarbons and Crude Oil (Questions 1–5)

1. Crude oil is separated into fractions by fractional distillation.
(a) State the physical property on which this separation depends. [1]
........................................................................................................................................

(b) Explain why the fraction collected at the top of the fractionating column is more flammable than the fraction collected at the bottom. [2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................

2. The table below shows some properties of two hydrocarbons, P and Q.

Hydrocarbon	Molecular Formula	Boiling Point (°C)
P	$C_3H_8$	-42
Q	$C_8H_{18}$	126

(a) To which homologous series do P and Q belong? [1]
........................................................................................................................................

(b) Explain, in terms of intermolecular forces, why Q has a higher boiling point than P. [2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................

3. Ethene ( $C_2H_4$ ) is an important industrial chemical.
(a) Describe the test for unsaturation using bromine water. Include the colour change observed. [2]
........................................................................................................................................
........................................................................................................................................

(b) Ethene reacts with steam to form ethanol. State the catalyst and temperature used in this industrial process. [2]
Catalyst: ....................................................................................................................
Temperature: ..............................................................................................................

4. Complete the equation for the complete combustion of propane. [2]
$C_3H_8 + 5O_2 \rightarrow \text{__________} + \text{__________}$

5. Which of the following statements about alkanes is incorrect? [1]
A. They are saturated hydrocarbons.
B. They undergo substitution reactions with chlorine in UV light.
C. They decolourise bromine water rapidly in the dark.
D. Their general formula is $C_nH_{2n+2}$ .

Answer: ________

Section B: Alcohols, Acids, and Esters (Questions 6–12)

6. Ethanol can be manufactured by fermentation or by the hydration of ethene.
(a) State one advantage of manufacturing ethanol by fermentation rather than by hydration of ethene. [1]
........................................................................................................................................

(b) State one condition required for fermentation. [1]
........................................................................................................................................

7. Ethanol is oxidised to ethanoic acid using acidified potassium manganate(VII).
(a) What colour change is observed during this reaction? [1]
From ____________________ to ____________________

(b) Draw the structural formula of ethanoic acid, showing all atoms and bonds. [2]

8. Ethanoic acid reacts with ethanol to form an ester.
(a) Name the ester formed. [1]
........................................................................................................................................

(b) Write the balanced chemical equation for this reaction, including state symbols. [2]
........................................................................................................................................

(c) State the catalyst used in this reaction. [1]
........................................................................................................................................

9. A student investigates the rate of reaction between magnesium ribbon and two different acids:

Acid A: 1.0 mol/dm³ hydrochloric acid
Acid B: 1.0 mol/dm³ ethanoic acid

(a) Predict which acid will react faster with magnesium. [1]
........................................................................................................................................

(b) Explain your answer in terms of ionisation. [2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................

10. Methanol ( $CH_3OH$ ) is a member of the alcohol homologous series.
(a) Draw the structural formula of methanol. [1]

(b) Methanol burns in excess oxygen. Write the balanced equation for this reaction. [2]
........................................................................................................................................

11. Which reagent can be used to distinguish between ethanoic acid and ethanol? [1]
A. Aqueous sodium chloride
B. Aqueous sodium carbonate
C. Limewater
D. Universal indicator paper only

Answer: ________

12. Esters are used as food flavourings.
(a) State two physical properties of esters. [2]

............................................................................................................................
............................................................................................................................

(b) Why are esters used in perfumes? [1]
........................................................................................................................................

Section C: Polymers and Macromolecules (Questions 13–17)

13. Poly(ethene) is an addition polymer.
(a) Draw the structure of the monomer used to make poly(ethene). [1]

(b) Draw the structure of the repeating unit of poly(ethene). [1]

14. Nylon is a condensation polymer.
(a) Name the two types of monomers used to make nylon. [1]
........................................................................................................................................

(b) What small molecule is eliminated when nylon is formed? [1]
........................................................................................................................................

15. Terylene is another condensation polymer.
(a) Identify the functional group present in the Terylene chain. [1]
........................................................................................................................................

(b) Explain why Terylene is suitable for making clothing fibers. [1]
........................................................................................................................................

16. Disposal of plastics is an environmental issue.
(a) State one problem caused by non-biodegradable plastics in landfills. [1]
........................................................................................................................................

(b) Suggest one method to reduce plastic waste other than recycling. [1]
........................................................................................................................................

17. Which of the following polymers is formed by condensation polymerisation? [1]
A. Poly(propene)
B. Poly(chloroethene)
C. Nylon
D. Polystyrene

Answer: ________

Section D: Isomerism and Synthesis (Questions 18–20)

18. Butene ( $C_4H_8$ ) has several isomers.
(a) Define the term isomers. [1]
........................................................................................................................................

(b) Draw the structural formula of but-1-ene. [1]

19. A compound X has the molecular formula $C_4H_{10}O$ . It reacts with sodium to produce hydrogen gas.
(a) Identify the homologous series to which X belongs. [1]
........................................................................................................................................

(b) Draw the structural formula of one possible isomer of X. [1]

20. The following scheme shows the conversion of ethene to ethanoic acid.
$\text{Ethene} \xrightarrow{\text{Step 1}} \text{Ethanol} \xrightarrow{\text{Step 2}} \text{Ethanoic Acid}$

(a) Name the reagent used in Step 1. [1]
........................................................................................................................................

(b) Name the type of reaction occurring in Step 2. [1]
........................................................................................................................................

(c) If Step 2 is incomplete, a mixture of ethanol and ethanoic acid remains. Describe how you could separate ethanoic acid from this mixture using a chemical method (not distillation). [2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................

End of Quiz

Answers

Secondary 4 Pure Chemistry Quiz - Organic Chemistry (Answer Key)

Total Marks: 45

Section A: Hydrocarbons and Crude Oil

1.
(a) Boiling point [1]
(b) The fraction at the top has smaller molecules / shorter carbon chains [1]. These have weaker intermolecular forces of attraction, requiring less energy to overcome, making them more volatile and flammable [1].
(Note: Accept "lower boiling point" as part of the explanation for volatility, but must link to flammability/volatility).

2.
(a) Alkanes [1]
(b) Q has a larger molecular size / longer carbon chain / higher relative molecular mass than P [1]. Therefore, Q has stronger intermolecular forces of attraction (van der Waals forces) which require more heat energy to overcome [1].

3.
(a) Add bromine water (orange/brown) to the ethene [1]. The solution decolourises (turns colourless) [1].
(b) Catalyst: Phosphoric(V) acid / $H_3PO_4$ [1].
Temperature: 300°C [1].

4.
$C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$
[1] for $3CO_2$ , [1] for $4H_2O$ .

5.
C [1] (Alkanes do not react with bromine water in the dark; alkenes do).

Section B: Alcohols, Acids, and Esters

6.
(a) Uses renewable resources / sugar cane / corn / does not rely on crude oil [1].
(Do not accept "cheaper" as it depends on oil prices).
(b) Any one: Temperature around 30-40°C / Anaerobic conditions (no oxygen) / Yeast present [1].

7.
(a) Purple [1] to Colourless [1].
(b)

      O
      ||
H - C - C - O - H
    |   |
    H   H

[1] for correct C-C bond and functional group arrangement, [1] for all atoms and bonds shown correctly.

8.
(a) Ethyl ethanoate [1].
(b) $CH_3COOH(l) + C_2H_5OH(l) \rightleftharpoons CH_3COOC_2H_5(l) + H_2O(l)$ [1] for correct formulae, [1] for state symbols and equilibrium sign (accept arrow if balanced).
(c) Concentrated sulfuric acid / $H_2SO_4$ [1].

9.
(a) Acid A (Hydrochloric acid) [1].
(b) Hydrochloric acid is a strong acid and is fully ionised in solution, producing a higher concentration of $H^+$ ions [1]. Ethanoic acid is a weak acid and is partially ionised, producing a lower concentration of $H^+$ ions [1]. Higher $[H^+]$ leads to a faster rate of reaction.

10.
(a)

    H
    |
H - C - O - H
    |
    H

[1]
(b) $2CH_3OH + 3O_2 \rightarrow 2CO_2 + 4H_2O$ [1] for formulae, [1] for balancing.

11.
B [1] (Sodium carbonate reacts with acid to produce effervescence/ $CO_2$ , but not with alcohol).
(Note: D is partially correct as acid changes colour, but B is a definitive chemical test for the acid group producing gas).

12.
(a) Any two: Volatile / Sweet smell / Neutral / Insoluble in water [1] each.
(b) They have pleasant/fruity smells [1].

Section C: Polymers and Macromolecules

13.
(a) Ethene:

    H   H
    |   |
    C = C
    |   |
    H   H

[1]
(b) Poly(ethene) repeating unit:

    H   H
    |   |
-- [ C - C ] --
    |   |
    H   H

[1] (Must show bonds extending outside brackets).

14.
(a) Diamine and Dicarboxylic acid [1].
(b) Water / $H_2O$ [1].

15.
(a) Ester linkage / -COO- [1].
(b) It is strong / durable / resistant to stretching [1].

16.
(a) Takes up space / Does not decompose / Releases toxic gases if burned [1].
(b) Reusing plastics / Using biodegradable plastics / Reducing consumption [1].

17.
C [1]

Section D: Isomerism and Synthesis

18.
(a) Compounds with the same molecular formula but different structural formulae [1].
(b) $CH_2=CH-CH_2-CH_3$ [1].
(c) 2-methylpropene:

      CH3
      |
CH2 = C - CH3  (Incorrect valency in text, see structure below)

Correct structure:

      H
      |
H2C = C - CH3
      |
      H

Wait, 2-methylpropene is $CH_2=C(CH_3)_2$ .
Structure:

No, that is but-1-ene isomer? No.
Isomer of $C_4H_8$ : 2-methylpropene.

      H
      |
H - C - H
      |
H2C = C
      |
      H

Let's draw 2-methylpropene clearly:
Central C double bonded to $CH_2$ , single bonded to two $CH_3$ groups.
[1] for correct branched structure with double bond.

19.
(a) Alcohols [1].
(b) Butan-1-ol or Butan-2-ol or 2-methylpropan-1-ol etc.
Example (Butan-1-ol):

H H H H
| | | |
H-C-C-C-C-O-H
| | | |
H H H H

[1]

20.
(a) Steam / Water [1].
(b) Oxidation [1].
(c) Add sodium carbonate / sodium hydrogen carbonate [1]. Ethanoic acid will react to form a soluble salt (sodium ethanoate) and release $CO_2$ . Ethanol will not react. The mixture can then be separated (e.g., by distillation or extracting the salt) [1].
(Note: The question asks for a chemical method to distinguish/separate conceptually. Reacting with base converts acid to salt, changing its physical properties).