Question

You have a 35.5 g of a saturated solution of potassium nitrate at 80oC which you cool to
40oC, what mass of potassium nitrate will precipitate out of solution?

@80 degrees C solubility is 160g solute/100g H2O
@40 degrees C solubility is 60g solute/100g H2O

Answer 1

normally, solubility would be read from a graph.

you dont have 100g aolution, you have 35.5/100 th, so at 80C, you have 35.5/100*160 grams in solution, which is 56.8g KNO3
now at 40C, you can only have 60*(35.5/100) grams in solution,or 21.3 grams in solution.
How much came out of solution?
56.8-21.3=....