Deduce the two acids and their conjugate bases in the following reaction:

${\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{NH}}_3\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{OH}}^{-}\left(\mathrm{aq}\right)+{\mathrm{NH}}_4^{+}\left(\mathrm{aq}\right)$

Explain why the following reaction can also be described as an acid–base reaction.

${\mathrm{F}}^{-}\left(\mathrm{g}\right)+{\mathrm{BF}}_3\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{BF}}_4^{-}\left(\mathrm{s}\right)$

When these $1.0 \mathrm{mol} {\mathrm{dm}}^3$ acidic solutions are arranged in order of increasing strength (weakest first), what is the correct order?

Acid in solution X : ${\mathrm{K}}_{\mathrm{a}}=1.74\times {10}^{-5} \mathrm{mol} {\mathrm{dm}}^{-3} \mathrm{at} 298 \mathrm{K}$ 

Acid in solution Y : ${\mathrm{K}}_{\mathrm{a}}=1.38\times {10}^{-3} \mathrm{mol} {\mathrm{dm}}^{-3} \mathrm{at} 298 \mathrm{K}$ 

Acid in solution Z : ${\mathrm{K}}_{\mathrm{a}}=1.78\times {10}^{-5} \mathrm{mol} {\mathrm{dm}}^{-3} \mathrm{at} 298\mathrm{K}$

Ammonia, ${\mathrm{NH}}_3$ , is a weak base. It has a ${\mathrm{pK}}_{\mathrm{b}}$ value of $4.75$.

Calculate the pH of a $1.00\times {10}^{-2} \mathrm{mol} {\mathrm{dm}}^{-3}$ aqueous solution of ammonia at $298 \mathrm{K}$.