解：設(shè)參加反應(yīng)的碳酸鈣的質(zhì)量為?$x。$?
?$\mathrm {CaCO}_3+2\mathrm {HCl}\xlongequal[ ]{ }\mathrm {CaCl}_2+\mathrm {H}_2\mathrm {O}+\mathrm {CO}_2↑$?
100 44
? $x$? 4.4g
?$\frac {100 }{x }=\frac {44 }{4.4\mathrm {g} }，$?解得?$x=10\mathrm {g}$?
則貝殼中碳酸鈣的質(zhì)量分?jǐn)?shù)為?$\frac {10 \mathrm {g}}{25 \mathrm {g}}×100％=40 ％ $?
答：貝殼中碳酸鈣的質(zhì)量分?jǐn)?shù)為?$40\%。$?
