What is Ampholyte?

Example 10.13 (Ethanoic acid and ammonia)

Mix $0.10\,\mathrm{mol}$ of ethanoic acid and $0.10\,\mathrm{mol}$ of ammonia in $1.0\,\mathrm{L}$. The strongest acid is $\ce{CH3COOH}$, the strongest base $\ce{NH3}$: $\ce{CH3COOH + NH3 <=> CH3COO- + NH4+}$, $K = 10^{9.25 - 4.76} = 10^{4.49}$, quantitative. The equivalent solution contains $0.10\,\mathrm{mol}/\mathrm{L}$ of $\ce{CH3COO-}$ and of $\ce{NH4+}$. Its predominant reaction, $\ce{NH4+ + CH3COO- <=> NH3 + CH3COOH}$, has the small constant $10^{-4.49}$ and keeps $[\ce{NH3}] = [\ce{CH3COOH}]$, whence, as for an ampholyte, $\mathrm{pH} = \frac12(4.76 + 9.25) = 7.01$.