Question

有一瓶溶質(zhì)質(zhì)量分?jǐn)?shù)為10%的溶液，當(dāng)蒸發(fā)掉60g水后，溶質(zhì)質(zhì)量分?jǐn)?shù)變?yōu)?0%，則原溶液中溶質(zhì)的質(zhì)量是

1. A.
   12克
2. B.
   60克
3. C.
   120克
4. D.
   無法確定

Answer 1

A
分析：溶液蒸發(fā)水沒有析出固體，溶劑質(zhì)量減小60g溶液質(zhì)量也減小60g而溶質(zhì)質(zhì)量不變，溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)增大；利用蒸發(fā)前后溶質(zhì)質(zhì)量相等，計(jì)算出原溶液的質(zhì)量；最后利用溶液質(zhì)量×質(zhì)量分?jǐn)?shù)=溶質(zhì)質(zhì)量，計(jì)算原溶液中溶質(zhì)質(zhì)量．
解答：設(shè)10%的溶液的質(zhì)量為x，則蒸發(fā)60g水后溶液質(zhì)量為（x-60）g
x×10%=（x-60）g×20%
x=120g
120g溶質(zhì)質(zhì)量分?jǐn)?shù)為10%的溶液中溶質(zhì)的質(zhì)量=120g×10%=12g
故選A．
點(diǎn)評：蒸發(fā)溶液質(zhì)量一半的水時，蒸發(fā)后所得溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)為原溶液溶質(zhì)質(zhì)量分?jǐn)?shù)的2倍．