tion:So, you know that potassium nitrate, KNO3 , has a solubility of 155 g per 100 g of water at 75∘C and of 38.0 g at 25∘C .What that MEANS is that at 75∘C , you can dissolve as much as 155 g of solid potassium nitrate in water without the solution becoming saturated.Once you hit that 155 g mark, the solution becomes saturated, which means that the solution can't dissolve any more solid.Now, the same thing can be SAID for the solution at 25∘C . At this temperature, dissolving less than 38.0 g of potassium nitrate per 100 g of water will result in an unsaturated solution.At the 38.0 g mark, the solution will become saturated.Now, take a look at how the solubility graph for potassium nitrate looks likeSo, you are starting with 100 g of saturated solution at 75∘C . Mind you, you have 100 g of solution that contains as much dissolved potassium nitrate as possible.This solution will contain100.0g solution⋅155 g KNO3(155+100)g solution=60.78 g KNO3Now, potassium nitrate's solubility is given per 100 g of water. Calculate how much water you have in this initial solutionmwater=100.0 g−60.78 g=39.22 g Next, DETERMINE how much potassium nitrate can be dissolved in 39.22 g of water at 26∘C in order to make a saturated solution, i.e. have the maximum AMOUNT of dissolved potassium nitrate possible39.22g water⋅38.0 g KNO3100g water=14.9 g KNO3This means that when the initial solution is cooled from 75∘C to 25∘C , the amount of water that it contained will only hold 14.9 g of dissolved potassium nitrate.The rest will crystallize out of solutionmcrystallize=60.78 g−14.9 g=45.9 g