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JAMB Chemistry 1987 Question 16

Question 16

Solubility and Solutions

The solubility of Na3AsO4(H2O)12 is 38.9 g per 100 g H2O. What is the mass percentage of Na3AsO4 in the saturated solution? [As = 75, Na = 23, O = 16, H = 1]

  1. A.87.2%
  2. B.38.9%
  3. C.19.1%
  4. D.13.7%
Show the answer and explanation

Answer: D (13.7%)

Explanation

The hydrate has M = 424, of which Na3AsO4 is 208. So 38.9 g of hydrate holds 38.9 × 208/424 = 19.1 g of Na3AsO4 in 138.9 g of solution: 19.1/138.9 × 100 = 13.7%.