Question

5．向100g溶質(zhì)質(zhì)量分?jǐn)?shù)為20%的NaCl溶液中加入3gNaCl固體和12g水．完全溶解后，所得溶液溶質(zhì)質(zhì)量分?jǐn)?shù)為（　�。�

• A． 20%
• B． 10%
• C． 15%
• D． 22.5%

Answer 1

分析 根據(jù)溶質(zhì)的質(zhì)量分?jǐn)?shù)=$\frac{溶質(zhì)質(zhì)量}{溶液質(zhì)量}×$100%，結(jié)合題意進(jìn)行分析解答．

解答 解：方法一、向100g質(zhì)量分?jǐn)?shù)為20%的NaCl溶液中加入3gNaCl固體和12g水，使其完全溶解，所得溶液中NaCl的質(zhì)量分?jǐn)?shù)是$\frac{100g×20%+3g}{100g+3g+12g}×$100%=20%．
方法二、3gNaCl固體和12g水，溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)為$\frac{3g}{12g+3g}×$100%=20%；故向20%NaCl溶液中，再加入相同溶質(zhì)質(zhì)量分?jǐn)?shù)的溶液，所得溶液溶質(zhì)質(zhì)量分?jǐn)?shù)仍為20%．
故選A．

點(diǎn)評(píng) 本題難度不大，掌握溶質(zhì)質(zhì)量分?jǐn)?shù)的有關(guān)計(jì)算并能靈活運(yùn)用即可正確解答本題．