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JAMB Chemistry 1998 Question 17

Question 17

Solubility and Solutions

90.0g of MgCl2 was placed in 50.0cm3 of water to give a saturated solution at 298K. If the solubility of the salt is 8.0 mol dm−3 at the same temperature, what is the mass of the salt left undissolved at the given temperature? [Mg = 24, Cl = 35.5]

  1. A.52.0g
  2. B.58.5g
  3. C.85.5g
  4. D.88.5g
Show the answer and explanation

Answer: A (52.0g)

Explanation

Molar mass of MgCl2 = 95. 50 cm3 dissolves 8.0 × 0.050 = 0.40 mol = 38 g. Undissolved = 90 − 38 = 52 g.