Find solubility of $$\mathrm{PbI}_2$$ if its solubility product is $$7.0 \times 10^{-9}$$.

What is the $$\mathrm{pH}$$ of a solution containing $$2.2 \times 10^{-6} \mathrm{M}$$ hydrogen ions?

What is the concentration of $$\left[\mathrm{H}_3 \mathrm{O}^{+}\right]$$ ion in $$\mathrm{mol} ~\mathrm{L}^{-1}$$ of $$0.001 ~\mathrm{M}$$ acetic acid $$(\alpha=0.134)$$ ?

A buffer solution is prepared by mixing 0.2 M sodium acetate and 0.1 M acetic acid. If pK$$_a$$ for acetic acid is 4.7, find the pH.