Question

Calculate the $pH$ of a solution (nearest integer) obtained by mixing $100ML$ of an acid of $pH=3$ and $400mL$ solution of $pH=1$. Both contain strong acids.

Answer 1

pH 3 corresponds to hydrogen ion concentration of ${10}^{-pH}={10}^{-3}=0.001M$.
pH 1 corresponds to hydrogen ion concentration of ${10}^{-pH}={10}^{-1}=0.1M$
Hence, the hydrogen ion concentration of the resulting solution is $\frac{100\times 0.001+400\times 0.1}{100+400}=0.0802$
Hence, the pH of the resulting solution is $pH=-log\left[H^{+}\right]=-log0.0802=1.096$.
Hence, the pH of the solution is 1.096.