Question

When 1.00 g of a strong acid is dissolved in 100 mL of water the pH of the solution is 0.908. Assuming no change in volume when the solution is formed. Calculate the molar mass of the unknown acid?

• A. 20 g $ \text{mo}{{\text{l}}^{-1}} $
• B. 36 g $ \text{mo}{{\text{l}}^{-1}} $
• C. 63 g $ \text{mo}{{\text{l}}^{-1}} $
• D. 81 g $ \text{mo}{{\text{l}}^{-1}} $

Answer 1

Answer: (D)

$ pH=0.908=-\,\log \,[{{H}^{+}}] $ $ [{{H}^{+}}]=0.1235\,M=[Acid] $ $ m $ mol of acid = 12.35 Molar mass $ =\frac{1000}{12.35}=80.97\approx 81\,g\,mo{{l}^{-1}} $