Question

1. The solubility of a substance in 100g water is 50g at 25oC. 55 g of the substance is dissolved in 100g water at 40oC and cooled to 25oC, no crystals appear. A glass rod touches the surface of this solution and crystals appear. How many grams of the substance remain in solution?

2. The solubility of a substance is 15g in 100g water. If 54g of the substance is mixed in 200g water, how many grams of the substance will remain in solid state?

Answer 1

Ans 1.

The solubility of the substance in 100 g water is 50 g at 25^o C.

Now when 55 g of the substance is dissolved at 40^oC , it has 5 g more of the substance as compared to the solution that may contain the substance at 25^oC.

Now when the glass rod touches the solution , this 5 g crystals appear , as the temperature is now lower (25^oC) , where the solubility is 50 g / 100 g of water.

So the grams od substance remaining in the solution will be 55 - 5 = 50 grams .