An industrial chemist treats solid \(\mathrm{NaCl}\) with concentrated
\(\mathrm{H}_{2} \mathrm{SO}_{4}\) and obtains gaseous \(\mathrm{HCl}\) and
\(\mathrm{NaHSO}_{4}\). When she substitutes solid NaI for \(\mathrm{NaCl}\), she
obtains gaseous \(\mathrm{H}_{2} \mathrm{~S},\) solid \(\mathrm{I}_{2},\) and
\(\mathrm{S}_{8},\) but no \(\mathrm{HI}\).
(a) What type of reaction did the \(\mathrm{H}_{2} \mathrm{SO}_{4}\) undergo
with NaI?
(b) Why does NaI, but not \(\mathrm{NaCl}\), cause this type of reaction?
(c) To produce HI \((g)\) by reacting NaI with an acid, how does the acid have
to differ from sulfuric acid?