You are required to prepare 100g of potassium nitrate crystals from its saturated solution at 75 degree Celsius. If the solubility of potassium nitrate at 75 degree Celsius is 155g and 20 degree Celsius is 31g, find the weight of potassium nitrate solution at 75 degree Celsius to achieve.

Answer 1

I'm somewhat confused on how the solubility is being measured; however, this is what I would do. I suspect this is NOT what your prof wants.
I would take the 75 C saturated solution. I assume the solubility is 155 g/100 g H2O so that solution will weigh 255 g and contain 155 g KNO3.
That is (155/255)*100 = 60.8% KNO3.

Then 0.608 x ? = 100 g and ? = approx 164 grams. Weigh out that much, and evaporate the water. What is left is 100 g KNO3. I have done exactly what the problems asks us to do BUT I suspect the prof want you to go through the solubility and have it crystallize from the 20 C solution.