Question

有40g5%的NaCl溶液，若要將其質(zhì)量分?jǐn)?shù)增加到10%，可采取的方法是（　　）

• A、將溶劑蒸發(fā)掉一半
• B、加入40g15%的NaCl溶液
• C、將溶液質(zhì)量蒸發(fā)掉一半
• D、加入2gNaCl固體

Answer 1

分析：分析溶液改變后溶液組成的改變，利用溶質(zhì)質(zhì)量分?jǐn)?shù)的計(jì)算公式，計(jì)算出所得溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)．

解答：解：A、將溶劑蒸發(fā)掉一半，溶質(zhì)質(zhì)量不變，仍為40g×5%=2g；蒸發(fā)后溶液中溶劑質(zhì)量=

40g-40g×5%

2

=19g；則所得溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)=

2g

2g+19g

×100%≈9.5%
B、加入40g15%的NaCl溶液，所得溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)=

40g×5%+40g×15%

40g+40g

×100%=10%
C、將溶液質(zhì)量蒸發(fā)掉一半，所得溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)=

40g×5%

40g 2

×100%=10%
D、加入2gNaCl固體，所得溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)=

40g×5%+2g

40g+2g

×100%≈9.5%
故選BC

點(diǎn)評(píng)：要使溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)增加一倍，可采取蒸發(fā)相當(dāng)于原溶液質(zhì)量一半的溶劑的質(zhì)量．