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JAMB Chemistry 1978 Question 47

Question 47

Qualitative Analysis

You are provided with five gas jars containing SO2, CO2, H2, CO and NO respectively. Select a test from A to E which will identify ANY ONE of the gases completely

  1. A.pass each gas into lime water
  2. B.pass each gas into water and test with litmus paper
  3. C.pass each gas into concentrated sulphuric acid
  4. D.expose each gas to atmospheric air
  5. E.expose each gas to fumes of hydrogen chloride.
Show the answer and explanation

Answer: D (expose each gas to atmospheric air)

Explanation

Nitrogen(II) oxide reacts with oxygen in air to form brown nitrogen(IV) oxide: 2NO + O2 → 2NO2. None of the other gases changes colour in air, so this test picks out NO for certain. (Lime water fails because both SO2 and CO2 turn it milky.)