设金属Na质量x
2Na + 2H2O = 2NaOH + H2
2*23----------------2*40----------------2
x
生成H2质量=x/23
生成NaOH质量=40x/23
x+24-x/23=31.2
x=7.53g
NaOH质量13.1g
溶解度s
s/100=13.1/(31.2-13.1)
s=72.38g