Question

An acid $HA$ is $40\%$ dissociated in an aqueous solution. The hydronium ion concentration of its $0.2M$ solution would be:

• A. $0.08M$
• B. $0.4M$
• C. $0.2M$
• D. none of these

Answer 1

Answer: (A)

$0.08M$

Acid -base reaction is as follows:

$HA+H_{2}O\to H_3{O}^{+}+A^{-}$

Given, degree of dissociation $\left(\alpha \right)=40\%=0.4$

For weak acid, hydronium ion concentration is

$\left[H_3{O}^{+}\right]=C\alpha =0.2\times 0.4=0.08$

So, the correct option is $A$