Question

THE SOLUBILITY OF BENZOIC ACID IN THE WATER IS 6.80 g PER 100 ML AT 100 C AND 0.43 g PER 100 ML AT 25 C.

1) calculate the minimum volume of water needed to dissolve 1.00 g of benzoic acid at 100 c.

2) calculate the maximum theoretical percent recovery from the recrystallization of 1.00 g of benzoic acid from 15 ml of water, assuming the solution is filltered at 25 c.

Answer 1

Ans :

1 ) Since 6.80 g of benzoic acid can be dissolved in 100 mL of water at 100 degrees C

The minimum amount of water required to dissolve 1.00 g benzoic acid at 100 degrees C will be (1 .00 x 100 ) / 6.80

= 14.70 mL

2 ) At 25 Degrees C only 0.43 g of benzoic acid can be dissolved in 100 mL of water

So amount of it present in 15 mL water in its dissolved state will be (15 x 0.43) / 100 = 0.0645 g

The amount recrystallised will be 1.00 - 0.0645 = 0.9355 g

Theoretical percent recovery = ( 0.9355 / 1.00) x 100

= 93.55 %