Question

A solution is prepared from 20mL of 0.10M HNO3 and 30mL of 0.05M H2SO4. If the H2SO4 completely ionises, the pH of the solution would be:
A. +1 B. +3 C. –log 0.02 D. –log 0.07

Answer 1

$$n_1(H^+) = c(HNO_3)V_1 = 0.10M*0.02L = 0.002mol$$

$$n_2(H^+)=2c(H_2SO_4)V_2 = 2*0.05M*0.03L = 0.003mol$$

$$n_{total} = 0.002mol+0.003mol = 0.005mol$$

$$V_{total} = 0.02L+0.03L = 0.05L$$

$$c(H^+) = n/V = 0.005mol/0.05L = 0.10M$$

$$pH = -logc(H^+) = +1$$

Answer: A +1