Question

1．實(shí)驗(yàn)室有80g硝酸鉀溶液，溶質(zhì)質(zhì)量分?jǐn)?shù)為20%
①加入20g水，所得硝酸鉀溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)是多少？
②加入20g硝酸鉀，所得硝酸鉀溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)是多少？
③要使所得硝酸鉀溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)是40%，要加入多少克硝酸鉀？
④要使所得硝酸鉀溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)是40%，要蒸發(fā)多少克水？

Answer 1

分析 根據(jù)溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)=$\frac{溶質(zhì)質(zhì)量}{溶液質(zhì)量}$×100%，進(jìn)行解答．

解答 解：原溶液的溶質(zhì)質(zhì)量為：80g×20%=16g．
①加入20g水，所得硝酸鉀溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)是$\frac{16g}{80g+20g}×100%$=16%；
②則加入20g硝酸鉀后溶質(zhì)質(zhì)量為：16g+20g=36g．
故所得溶液的質(zhì)量分?jǐn)?shù)為：$\frac{36g}{80g+20g}$×100%=36%．
③要使所得硝酸鉀溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)是40%，設(shè)要加入硝酸鉀質(zhì)量為x
$\frac{16g+x}{80g+x}×100%$=40%
x=26.7g
④要使所得硝酸鉀溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)是40%，設(shè)要蒸發(fā)水質(zhì)量為y
$\frac{16g}{80g+y}×100%$=40%
y=40g
故答案為：①16%；②36%；③26.7g；④40g．

點(diǎn)評(píng) 本題難度不大，掌握溶質(zhì)質(zhì)量分?jǐn)?shù)=$\frac{溶質(zhì)質(zhì)量}{溶液質(zhì)量}$×100%，并能靈活運(yùn)用是正確解答本題的關(guān)鍵