WAEC Chemistry 2018 Theory — Question 19
Question 19 of 24 from the West African Examinations Council (WAEC) Chemistry 2018 Theory paper, with the correct answer and a full explanation.
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4.(a)(i) Draw and label a diagram for the laboratory preparation of a dry sample of Sulphur (IV) oxide. (ii) Write a balanced chemical equation for the reaction in 4(a)(i). (iii) State the precaution that must be taken in the preparation of the gas stated in 4(a)(i). (iv) Give a reason why the precaution stated in 4(a)(ii) must be taken.
Model answer
(i) The apparatus consists of a dropping funnel of concentrated hydrochloric acid added to sodium thiosulphate in a flask, gently heated, with the gas dried and collected as shown in the diagram. (ii) 2HCl + Na₂S₂O₃ → 2NaCl + H₂O + SO₂. (iii) The gas (SO₂) must be prepared in a fume cupboard. (iv) This precaution is necessary because the gas is poisonous.
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