WAEC Chemistry 2022 Objective — Question 14
Question 14 of 50 from the West African Examinations Council (WAEC) Chemistry 2022 Objective paper, with the correct answer and a full explanation.
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A colourless gas with a pungent smell is evolved when dilute hydrochloric acid is added to a sample of a salt. The gas evolved could turn
- A. acidified K2Cr2O7 solution colourless
- B. acidified KMnO4 solution colourless
- C. Fe(NO3)2 solution green
- D. Pb(NO3)2 paper blackCorrect
Explanation
The gas described is hydrogen sulphide (H2S). H2S reacts with Pb(NO3)2 on paper to give PbS, which has a black colour: H2S + Pb(NO3)2 → PbS + 2HNO3.
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