O LevelChemistryCambridge (CIE)Exam Questions11. Organic Chemistry11.7 Carboxylic Acids

Carboxylic Acids (Cambridge (CIE) O Level Chemistry): Alternative to Practical Questions

Exam code: 5070

3 hours35 questions

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11.7 Carboxylic Acids

1a
2 marks

A student oxidises ethanol to ethanoic acid.

The ethanol is placed in a boiling tube and acidified aqueous potassium manganate(VII) is added. The boiling tube is then stood in a beaker of hot water.

Explain why the boiling tube is stood in a beaker of hot water rather than heated directly with a Bunsen burner flame.

How did you do?

1b
1 mark

State the colour change seen in the boiling tube as the reaction takes place.

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1c
2 marks

The student adds the acidified aqueous potassium manganate(VII) drop by drop, and stops when the colour of the added solution remains in the mixture after swirling.

Explain what this shows.

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1d
2 marks

The student repeats the experiment using ethanoic acid in place of ethanol.

The colour of the acidified aqueous potassium manganate(VII) does not change.

Explain why.

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2a
2 marks

A student compares the reaction of magnesium with dilute ethanoic acid and with dilute hydrochloric acid.

Both acids have a concentration of 0.1 mol / dm3.

In each experiment, 50.0 cm3 of the acid is added to an excess of magnesium ribbon. The volume of hydrogen collected is measured every 30 seconds.

time / s

0

30

60

90

120

150

180

volume of hydrogen with hydrochloric acid / cm3

0

38

54

59

60

60

60

volume of hydrogen with ethanoic acid / cm3

0

14

27

38

47

55

60

State which acid reacts faster.

Give one piece of evidence from the table that supports your answer.

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2b
2 marks

Explain why the final volume of hydrogen collected is the same for both acids.

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2c
2 marks

Name two variables that the student kept the same in the two experiments.

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2d
2 marks

Suggest one improvement to the method that would make the comparison more reliable.

Explain why it would help.

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3
6 marks

Vinegar is a dilute solution of ethanoic acid in water.

A student has two samples of vinegar, P and Q. One sample contains a higher concentration of ethanoic acid than the other.

Plan an investigation to find out which sample contains the higher concentration of ethanoic acid.

Your plan must use common laboratory apparatus, the two samples of vinegar and solid calcium carbonate. No other chemicals should be used.

Your plan must include:

  • the apparatus needed

  • the method to use and the measurements to take

  • the variables to control

  • how the results are used to decide which sample is more concentrated

You may draw a diagram to help answer the question.

How did you do?

4a
1 mark

A student investigates the temperature change when dilute ethanoic acid is neutralised by aqueous sodium hydroxide.

25.0 cm3 of dilute ethanoic acid is placed in a polystyrene cup and its temperature is measured. Aqueous sodium hydroxide is then added in 5.0 cm3 portions. The highest temperature reached after each addition is recorded.

volume of sodium hydroxide added / cm3

0

5.0

10.0

15.0

20.0

25.0

30.0

highest temperature reached / °C

20.0

22.5

25.0

27.5

26.5

25.5

24.5

State the volume of aqueous sodium hydroxide needed to neutralise the ethanoic acid.

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4b
2 marks

Explain why the highest temperature reached falls when more than this volume of aqueous sodium hydroxide is added.

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4c
2 marks

Explain why a polystyrene cup is used rather than a glass beaker.

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4d
2 marks

The student used a thermometer with 1 °C divisions.

Suggest a more suitable thermometer for this investigation.

Justify your choice.

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5a
1 mark

A student makes an ester from ethanoic acid and ethanol.

A few drops of an acid catalyst are added to a mixture of the two liquids in a boiling tube. The boiling tube is stood in a beaker of hot water for several minutes. The mixture is then poured into a beaker of aqueous sodium carbonate.

Suggest why the mixture is warmed.

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5b
2 marks

State how the student could tell that an ester has been formed.

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5c
2 marks

Suggest why the mixture is poured into aqueous sodium carbonate at the end of the experiment.

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5d
2 marks

State one safety precaution the student should take when handling the acid catalyst.

Explain why it is needed.

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