Question

Formic acid has a concentration of 0.1M and Ka is 1.77 x 10^-4. What is the value of degree of dissociation?

(a) 4

(b) 4.2

(c) 0.42

(d) 42

I got this question in a national level competition.

My question is based upon Equilibrium topic in division Equilibrium of Chemistry – Class 11

Answer 1

The correct answer is (b) 4.2

Easy explanation: The dissociation constant K = [H^+][HCOO^–]/[HCOOH] = x^2/0.1 – x = 1.77 x  10^-4; x = [H^+] = 0.0042M. The percent of dissociation is x/0.1 = (0.042M)100% = 4.2. Therefore the value of degree of dissociation is 4.2