Question

A,B and C have the following solubilities in 100 mL of water at 25°C, respectively: 15g, 35 g and 65 g. If 75 g of each are added to 200 mL water, which will completely dissolve? How much of each will remain undissolved?

Answer 1

Answer:

Only C can dissolve in water because its solubility is greater than 0.375 g/mL

C dissolves completely

22.5 g of A remain undissolved in 100 mL of water

2.5 g of B remain undissolved  in 100 mL of water

Explanation:

Solubility : The amount of salt that can be dissolved in a given volume of solvent at a particular temperature .

$Solubility = \frac{mass}{volume}$

For each salt the solubility of 75 g in  200 mL water is

$Solubility = \frac{75}{200}$

0.375 g/mL

This mean 1 ml of water has 0.375 g of A , B and C

100 mL of water contain = 37.5 g of each salt A , B,C

In the question , the solubility of A , B and C in 100 are given as :

A =  15 g : It means maximum 15 g of A can dissolve in 100 mL

$Solubility = \frac{15}{100}$ = 0.15 g/mL

B = 35 g  : It means maximum 35 g of B can dissolve in 100 mL

$Solubility = \frac{35}{100}$ = 0.35 g/mL

C = 65 g : It means maximum 65 g of A can dissolve in 100 mL

$Solubility = \frac{65}{100}$ = 0.65 g/mL

Since ,Solubility of A and B is less than 0.375 g/mL

So A and B  can't dissolve in water at 25°C

A is excess by 37.5 - 15 = 22.5 g

B is in excess by 37.5 - 35 = 2.5 g

Hence 22.5 g of A remain undissolved

Hence  2.5 g of B remain undissolved

Only C can dissolve in water because its solubility is greater than 0.375 g/mL