解：设得到$\mathrm {NH}_4\mathrm {Cl}$的的质量为$x。$
$\mathrm {NaCl}＋\mathrm {NH}_3＋\mathrm {CO}_2＋\mathrm {H}_2\mathrm {O}\xlongequal[ ]{ }\mathrm {NaHCO}_3↓＋\mathrm {NH}_4\mathrm {Cl}$
58.5 53.5
65t×90% $x$
$\frac {58.5 }{53.5 }=\frac {65\mathrm {t}×90\% }{x }，$解得$x=53.5\mathrm {t}$
答：同时得到$\mathrm {NH}_4\mathrm {Cl}$的质量至少是$53.5\mathrm {t}。$
