Question

7．計(jì)算在80克質(zhì)量分?jǐn)?shù)為15%的硝酸鈉溶液里含有硝酸鈉多少克？在這種溶液里加入20克水后，所得溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)變?yōu)槎嗌伲?

Answer 1

分析 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%，則溶質(zhì)的質(zhì)量=溶液質(zhì)量×溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)．

解答 解：由于溶質(zhì)的質(zhì)量分?jǐn)?shù)=$\frac{溶質(zhì)質(zhì)量}{溶液質(zhì)量}$×100%，則80g質(zhì)量分?jǐn)?shù)為15%的NaNO₃溶液里溶質(zhì)的質(zhì)量為：80g×15%=12g．
由于在該溶液中加入20克水后，溶質(zhì)的質(zhì)量并沒(méi)有發(fā)生變化，故所得溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)為：$\frac{12g}{80g+20g}$×100%=12%．
答：含有硝酸鈉12克．在這種溶液里加入20克水后，所得溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)變?yōu)?2%．

點(diǎn)評(píng) 本題的難度不是很大，主要考查了有關(guān)溶質(zhì)的質(zhì)量分?jǐn)?shù)的有關(guān)計(jì)算及用水稀釋溶液的有關(guān)計(jì)算，加深學(xué)生對(duì)溶質(zhì)質(zhì)量分?jǐn)?shù)的理解，從而培養(yǎng)學(xué)生解決問(wèn)題的能力和計(jì)算能力．