Alternative to Practical Paper

A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

Look up the following tests for cations, anions, gases, hydrocarbons etc. if necessary:
Identify Cations
Identify Anions
Collect and Identify Gases
Identify Hydrocarbons and Others

Questions
Solid E was analysed. E was an aluminium salt. Some of the observations are shown below.
Appearance of solid E - white crystalline solid.
Test 1:
A little of solid E was heated in a test-tube - colourless drops of liquid formed at the top of the tube.
(a) A little of solid E was dissolved in distilled water.
The solution was divided into four test-tubes and the following tests were carried out.

Complete the observations for tests 2 and 3.
(i) Test 2:
Drops of aqueous sodium hydroxide were added to the first test-tube.
observations ________________________[1]
(ii) Excess sodium hydroxide was then added.
observations ________________________[1]
(iii) Test 3:
Drops of aqueous ammonia solution were added to the second test-tube. Excess ammonia solution was then added.
observations ______________ [2]

Two further tests are carried out and the following observations made.
tests on solution of E observations
Test 4:
To the third test-tube of solution, dilute hydrochloric acid was added, followed by barium nitrate solution - no reaction
Test 5:
To the fourth test-tube of solution, aqueous sodium hydroxide and aluminium foil were added.
The mixture was warmed carefully - effervescence, pungent gas given off, gas turned damp litmus paper blue
(b) What does test 1 tell you about solid E? __________[1]
(c) Identify the gas given off in test 5. __________ [1]
(d) What conclusions can you draw about solid E? __________ [2]
(e) Test 5 states that the mixture should be warmed carefully.
In terms of safety, explain why it is necessary to warm carefully _________ [2]

Answers

• Show Answers

  (a) (i) white precipitate [1]
  (ii) precipitate dissolves in excess; [1]
  (iii) white precipitate; [1]
  no change / precipitate remains; [1]
  (b) contains water / hydrated [1]
  (c) ammonia, not: ammonium [1]
  (d) Any two from:
  nitrate;
  hydrated salt / contains water;
  it is not a sulfate; [2]
  (e) sodium hydroxide is hazardous / irritant / caustic; [1]
  allow: toxic
  boiling causes mixture to spit / blow-out; [1]

Questions
E-numbers identify chemicals which are added to foods.
(a) E210 is benzoic acid. How could you show that a solution of benzoic acid is a weak acid?
test
result __________ [2]
(b) E110 is Sunset Yellow.
Outline a method you could use to show the presence of E110 in a food colouring.
You may draw a diagram to help answer the question. [4]

Answers

• Show Answers

  (a) Universal indicator / pH paper; [1]
  pH of 4–6 / yellow / orange; [1]
  note: any suitable test with appropriate result
  (b) Any four from:
  chromatography;
  description of applying food colouring to paper;
  use of solvent;
  results / number of spots;
  compare results to known sample / reference to Rf value; [4]
  marks can be obtained from a labelled diagram

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