WAEC Chemistry 2025 Theory — Question 35

Question 35 of 70 from the West African Examinations Council (WAEC) Chemistry 2025 Theory paper, with the correct answer and a full explanation.

3(c)(ii). What mass of oxygen would react with 9.0g of aluminium? [O = 16.0, Al = 27.0]

Model answer

From 4Al + 3O2 -> 2Al2O3: 4(27)g Al reacts with 3(32)g O2, i.e. 108g Al reacts with 96g O2. For 9g Al: x = (9 x 96)/108 = 8.0g of O2.

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