解：根據(jù)質(zhì)量守恒定律，反應(yīng)生成氧氣的質(zhì)量為?$108.8 \mathrm {g}+2.0 \mathrm {g}-110.0 \mathrm {g}=0.8 \mathrm {g}。$?
設(shè)參加反應(yīng)的?$\mathrm {H}_2\mathrm {O}_2$?的質(zhì)量為?$x。$?
?$2\mathrm {H}_2\mathrm {O}_2\xlongequal{\mathrm {MnO}_2}2\mathrm {H}_2\mathrm {O}+\mathrm {O}_2↑$?
68 32
? $x$? 0.8g
?$\frac {68}{32}=\frac x{0.8 \mathrm {g}}$?
?$x=\frac {68×0.8 \mathrm {g}}{32}=1.7 \mathrm {g}$?
答：參加反應(yīng)的?$\mathrm {H}_2\mathrm {O}_2$?的質(zhì)量為?$1.7 \mathrm {g}。$?
