将4.6g金属钠投入到95.4g水中,所得溶液中溶质的质量分数为(  ) A.等于4.6% B.等于8.0% C.小于8.0% D.大于8.0%

问题描述:

将4.6g金属钠投入到95.4g水中,所得溶液中溶质的质量分数为(  )
A. 等于4.6%
B. 等于8.0%
C. 小于8.0%
D. 大于8.0%

将4.6g钠投入到95.4g水中,发生2Na+2H2O=2NaOH+H2↑,则
2Na+2H2O=2NaOH+H2
46g       80g   2g
4.6g   m(NaOH) m(H2
m(NaOH)=

4.6g×80g
46g
=8.0g,
m(H2)=
4.6g×2g
46g
=0.2g,
则w(NaOH)=
8.0g
(4.6g+95.4g−0.2g)
×100%=8.02%>8%,
故选D.