What is the $pH$ of a $0.005 \ M$ $Ba(OH)_2$ solution?

Five solutions of $KOH$ are prepared as follows: $1st \to 0.1 \ mol$ in $1 \ L$,$2nd \to 0.2 \ mol$ in $2 \ L$,$3rd \to 0.3 \ mol$ in $3 \ L$,$4th \to 0.4 \ mol$ in $4 \ L$,$5th \to 0.5 \ mol$ in $5 \ L$. What is the $pH$ of the resulting mixture?

Given that the dissociation constant for $H_2O$ is $K_w = 1 \times 10^{-14} \ mol^2/L^2$. What is the $pH$ of a $0.001 \ M$ $KOH$ solution?

When $100 \ mL$ of $0.1 \ M$ $NaOH$ is added to $50 \ mL$ of $0.2 \ M$ $HCl$ at $25 \ ^oC$,the $pH$ of the resulting solution will be:

The hydroxyl ion concentration of $10^{-2} \ M \ HCl$ is:

Calculate the $pH$ of $1.0 \times 10^{-8} \ M \ NaOH$ solution.