Calculations
If you understand what solubility expressions mean, you should be able to solve problems involving the expressions. Have a look at the example calculation below.
Morphine Sulphate is soluble in 21 parts of water. You have a saturated solution of Morphine Sulphate in water. Assuming that the solubility is correct, how many millimoles of Morphine Sulphate (RMM 758.8) are dissolved in 147 ml of water? Answer to 3 significant figures.
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9.23 millimoles of Morphine Sulphate are dissolved in the water.
- The solubility parts expression indicates that:
1 gram of Morphine Sulphate dissolves in 21 ml of water.
The solution is saturated and the solubility is assumed to be correct.
Thus 21 ml of water contains 1 g of Morphine Sulphate
Thus 147 ml of water contains 147/21 x 1 g = 7 g of Morphine Sulphate - Find the moles of Morphine Sulphate present:
Moles of Morphine Sulphate = Mass / RMM = 7 / 758.8 moles = 0.009225 moles
Millimoles of Morphine Sulphate = 1000 x 0.009225 mmoles = 9.225 mmoles
Millimoles of Morphine Sulphate = 9.23 mmoles to 3 sig figs