Question

1.9g of sample dissolved in 29 mL 100C hot water, what is the maximum of the crystals when the solution cooled to 0C and recrystallized? And, how much remains in the filtrate?

the solubility in 100mL water is

0.17g/100mL at 0C

6.8g/100mL at 100C

Answer 1

Boiling water has a solubility of 6.8 g/100 mL.

Cool water ( at 0 deg Celsius) has a solubility of 0.17 g/ 100 mL

Here 1.9 g dissolved in 29 ml at 100 deg c

Weight of compound dissolve in 29 ml of cooled water at 0 deg C

We have 0.17 g dissolve in 100 ml at 0 deg C

So in 29 ml cold water

Weight of compound dissolves = 29 x 0.17 g / 100 = 0.049 g

So after cooling to 0 deg c, 0.049 g dissolves in cold water and balance crystallize out

So weight of crystallized compound is 1.9 g – 0.049 g = 1.851 g

The weight of the compound remains in the filtrate ( or dissolved in water) = 0.049 g