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JAMB Chemistry 1985 Question 8

Question 8

Volumetric Analysis

3.0 g of a mixture of potassium carbonate and potassium chloride were dissolved in a 250 cm3 standard flask. 25cm3 of this solution required 40.00 cm3 of 0.1 M HCl for neutralization. What is the percentage by weight of K2CO3 in the mixture (K = 39, O = 16, C = 12).

  1. A.60
  2. B.72
  3. C.82
  4. D.89
  5. E.92
Show the answer and explanation

Answer: E (92)

Explanation

HCl used = 0.040 × 0.1 = 0.004 mol, which reacts with 0.002 mol of K2CO3 (K2CO3 + 2HCl). The whole 250 cm3 holds 0.02 mol × 138 g = 2.76 g, and 2.76/3.0 × 100 = 92%.