WAEC Chemistry 2014 Theory — Question 3

Question 3 of 38 from the West African Examinations Council (WAEC) Chemistry 2014 Theory paper, with the correct answer and a full explanation.

1(b). Determine the oxidation number of sulphur in Na₂S₂O₃.

Model answer

Let oxidation number of S = x. Na=+1, O=-2. 2(+1)+2(x)+3(-2)=0 ⟹ 2+2x-6=0 ⟹ 2x=4 ⟹ x=+2. The oxidation number of sulphur in Na₂S₂O₃ is +2.

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