Question

The degree of hydrolysis of salt of a weak acid and weak base in its 40.1M solution is found to be 50%. If the molarity of the solution is 0.2M, the percentage hydrolysis of the salt should be
(A) 100%
(B)50%
(C)25%
(D)none of the above

Answer 1

Hint: The hydrolysis of any substance is independent of its concentration of the substance and would remain the same if the concentration of the substance is given and it depends only on the equilibrium constant i.e. $K_H$. Now, solve it.

Complete step by step solution:
-By the term molarity, we simply mean the no of moles of the solute dissolved in 1000 ml of the solution and it is generally expressed as M.
-Before proceeding further we should know first what is the degree of hydrolysis. The extent to which the hydrolysis of any substance can be carried out when it has attained the equilibrium is called the degree of the hydrolysis of that very substance i.e.
$$\text{h=}\sqrt{K_H}$$
Here, h is called a degree of hydrolysis and $K_H$ is called the equilibrium constant of that hydrolysis. And is totally independent of the concentration of that substance.
So, now from the numerical;
As we know that, the molarity of the solution= 40.1 M (given)
Then, the Percentage of hydrolysis =50%(given)
Now, if the molarity of the solution = 0.2 M(given)
Then, the percentage of hydrolysis is also the same i.e. the 50% because the degree of the hydrolysis is independent of the concentration.
Hence, the percentage hydrolysis of the salt is 50%.

So, option (B) is correct.

Note: Don’t get confused in the term’s molarity and molality. Molarity may be defined as the no of moles of the solute in 1000ml of the solution whereas the molality is the no of moles of the solute in 1000g of the solvent.