Question

A saturated solution of KNO3 at 60C was cooled to 30C. How many grams of KI will come out of the solution as solid and settle at the bottom of the solution undissolved? Hints: Take the solubility of KNO3 at both temperatures and find the difference.

Answer 1

• About 48 g of KNO₃ per 100 g of water.

Step-by-step explanation:

See the graph attached with the solubility curves for KNO₃. I have marked the solubilities of interest.

The question, obviously has a typo. You need to find how many grams of KNO₃ will come out of the solution as a solid and settle at the bottom of the solution undissolved.

You can see that the solubility of KNO₃ at 60ºC is about 106g per 100 g of water, and the solubility of the same substance at 30ºC is about 58 g per 100g o f water. You cannot tell with precision because the divisions value 10 g/100 g of water.

A saturated solution contains the maximum amount of solute that the solvent can dissolve at that temperature.

Then, when the solutions is cooled, the amount of solute that cannot be dissolved will precipitate.

You just must subtract:

• 106 g of KNO₃/ 100 g of water - 58 g of KNO₃ per 100 g of water = 48 g of KNO₃ per 100 g of water.