Question

今有未知溶質(zhì)質(zhì)量分?jǐn)?shù)的鹽酸50 g，與7.8 g鋅充分反應(yīng)后，鋅有剩余，然后再加入20 g7.3%的鹽酸，恰好與剩余的鋅完全反應(yīng)，求：（1）第一次反應(yīng)時(shí)所用鹽酸中溶質(zhì)的質(zhì)量分?jǐn)?shù)．（2）反應(yīng)后所得溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)．

Answer 1

分析：計(jì)算第一次反應(yīng)時(shí)所用的鹽酸中溶質(zhì)的質(zhì)量分?jǐn)?shù)時(shí)，應(yīng)先計(jì)算出加入20 g7.3%的鹽酸時(shí)消耗的鋅的質(zhì)量，才能得出第一次所消耗的鋅的質(zhì)量，才能得出結(jié)果．反應(yīng)后所得溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)計(jì)算時(shí)，先計(jì)算出兩次反應(yīng)后所得溶質(zhì)的質(zhì)量，然后確定出所得溶液的質(zhì)量．

解答：解：設(shè)與20 g7.3%的鹽酸反應(yīng)的鋅的質(zhì)量為X，反應(yīng)后生成的氫氣質(zhì)量為a₁，生成ZnCl₂質(zhì)量為b₁
Zn+2HCl═ZnCl₂+H₂↑
65  73
X 20 g×7.3%

65

73

=

X

20g×7.3%

X=1.3g
Zn+2HCl═ZnCl₂+H₂↑
73      136
20 g×7.3%  b₁

73

136

=

20 g×7.3%

b1

b₁=2.72g
Zn+2HCl═ZnCl₂+H₂↑
73         2
20 g×7.3%     a₁

73

2

=

20 g×7.3%

a1

a₁=0.04g

設(shè)第一次反應(yīng)時(shí)所用鹽酸中溶質(zhì)的質(zhì)量分?jǐn)?shù)為Y，反應(yīng)后生成的氫氣質(zhì)量為a₂，生成ZnCl₂質(zhì)量為b₂

Zn+2HCl═ZnCl₂+H₂↑
65   73  136   2
7.8 g-1.3g   50 gY b₂a₂

65

73

=

6.5g

50gY

Y=14.6%
Zn+2HCl═ZnCl₂+H₂↑
65        136
7.8 g-1.3g       b₂

65

136

=

6.5g

b2

b₂=13.6g
Zn+2HCl═ZnCl₂+H₂↑
65             2
7.8 g-1.3g     a₂

65

2

=

6.5g

a2

a₂=0.2g
反應(yīng)后所得溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)為

2.72g+13.6g

50g+20g+7.8g-0.04g-0.2g

×100%=21.0%
答：第一次反應(yīng)時(shí)所用鹽酸中溶質(zhì)的質(zhì)量分?jǐn)?shù)為14.6%；反應(yīng)后所得溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)為21.0%．

點(diǎn)評(píng)：在確定反應(yīng)后溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)時(shí)，一定要確定好反應(yīng)后的溶質(zhì)和溶液，否則就會(huì)得到錯(cuò)誤結(jié)果．