WAEC Chemistry 2025 Theory — Question 65

Question 65 of 70 from the West African Examinations Council (WAEC) Chemistry 2025 Theory paper, with the correct answer and a full explanation.

Alternative A, Q1(b)(iv). Calculate the percentage purity of NaHCO3.

Model answer

% purity = (mass concentration of pure NaHCO3 / mass concentration of impure NaHCO3) x 100%. Impure B: 250cm3 contains 4.0g, so 1000cm3 contains (1000x4)/250 = 16.0 g/dm3. % purity = (5.59/16.0) x 100% = 34.94%.

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