Question

將一瓶80g 10%的NaCl溶液分為2等份，每份溶液中溶質(zhì)的質(zhì)量分數(shù)為________；若將其中的一份溶液中溶質(zhì)的質(zhì)量分數(shù)減小一半，應(yīng)加水________g，若將另一份溶液中溶質(zhì)的質(zhì)量分數(shù)增大一倍，應(yīng)加入NaCl________g．

Answer 1

10%    40    5
分析：溶液具有均一性，把溶液分成兩等份，其中每一份溶液的質(zhì)量分數(shù)與原溶液的溶質(zhì)質(zhì)量分數(shù)相同；
根據(jù)加水稀釋時溶液中溶質(zhì)質(zhì)量不變，由稀釋前溶液中溶質(zhì)質(zhì)量與稀釋后溶液的溶質(zhì)質(zhì)量分數(shù)計算稀釋后溶液質(zhì)量，稀釋前后溶液質(zhì)量差即加入水的質(zhì)量；
隨著溶質(zhì)氯化鈉質(zhì)量的增加溶液的質(zhì)量分數(shù)變大，根據(jù)增大一倍后溶液中溶質(zhì)質(zhì)量為原溶液中溶質(zhì)質(zhì)量與所加入氯化鈉的質(zhì)量和，計算出所增加溶質(zhì)質(zhì)量．
解答：根據(jù)溶液的均一性，每份溶液的質(zhì)量分數(shù)均為10%；
溶液中溶質(zhì)的質(zhì)量分數(shù)減小一半時溶液的質(zhì)量==80g，則加入水的質(zhì)量=80g-40g=40g；
設(shè)增加氯化鈉質(zhì)量為x時使溶液的溶質(zhì)質(zhì)量分數(shù)增大，（40g+x）×20%=40g×10%+x，解得x=5g；
故答案為：10%；40；5．
點評：對溶液進行加水稀釋時，若加入水的質(zhì)量與溶液質(zhì)量相等，則稀釋后溶液的溶質(zhì)質(zhì)量分數(shù)為原溶液溶質(zhì)質(zhì)量分數(shù)的一半．