Question

The pH of a 2 M solution of a weak monobasic acid (HA) is 4. What is the value of the Van’t Hoff factor?

(a) 0.00005

(b) 1.005

(c) 1.0005

(d) 1.00005

I have been asked this question by my school teacher while I was bunking the class.

Asked question is from Abnormal Molar Masses topic in portion Solutions of Chemistry – Class 12

Answer 1

The correct answer is (d) 1.00005

The best I can explain: pH = 4 means [H^+] = 10^-4 M

HA     ⇌ H^+    +     A^–

Initial

C mol L^-1

0

0

After dissociation

C – Cα

Cα

Cα

Total = C (1+α)

Thus, [H^+] = Cα, i.e., 10^-4 = 2 x α or α = 5 x 10^-5 = 0.00005

i = 1 + α = 1 + 0.00005 = 1.00005.