If a mixture of two or more substances in solution is allowed to crystallize by decreasing the temperature of the solution, the crystals will contain more of the least soluble substance CRYSTALLIZATION – A method of separating substances based on differences in solubility EX7-1 (of 13)

EX7-2 (of 13)

35 g A, 5 g B 100 g H2O at 100°C Dissolved Crystallized EX7-3 (of 13)

70 g A are soluble at 100ºC, so all 35 g A will dissolve 50 g B are soluble at 100ºC, so all 5 g B will dissolve EX7-4 (of 13)

35 g A, 5 g B 100 g H2O at 100°C Dissolved Crystallized 35 g A, 5 g B nothing 100 g H2O at 0°C Dissolved Crystallized EX7-5 (of 13)

5 g A are soluble at 0ºC, so 5 g A will dissolve  the rest of the A (35 g - 5 g) will crystallize out 10 g B are soluble at 0ºC, so all 5 g B will dissolve EX7-6 (of 13)

85.7% of A has crystallized out 35 g A, 5 g B 100 g H2O at 100°C Dissolved Crystallized 35 g A, 5 g B nothing 100 g H2O at 0°C Dissolved Crystallized 5 g A, 5 g B 30 g A 85.7% of A has crystallized out The crystals are 100% A EX7-7 (of 13)

What if only half the water is used? EX7-8 (of 13)

35 g A, 5 g B 50 g H2O at 100°C Dissolved Crystallized EX7-9 (of 13)

35 g A are soluble at 100ºC, so all 35 g A will dissolve 25 g B are soluble at 100ºC, so all 5 g B will dissolve EX7-10 (of 13)

35 g A, 5 g B 50 g H2O at 100°C Dissolved Crystallized 35 g A, 5 g B nothing 50 g H2O at 0°C Dissolved Crystallized EX7-11 (of 13)

2.5 g A are soluble at 0ºC, so 2.5 g A will dissolve  the rest of the A (35 g – 2.5 g) will crystallize out 5 g B are soluble at 0ºC, so all 5 g B will dissolve EX7-12 (of 13)

92.9% of A has crystallized out 35 g A, 5 g B 50 g H2O at 100°C Dissolved Crystallized 35 g A, 5 g B nothing 50 g H2O at 0°C Dissolved Crystallized 2.5 g A, 5 g B 32.5 g A 92.9% of A has crystallized out The crystals are 100% A EX7-13 (of 13)