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