2Na+2H2O=2NaOH+H2↑ 2.3g金属Na=0.1mol
0.1 0.1 0.1 0.05
4g 0.1g
反应后溶液总质量是102.3-0.1=102.2g
NaOH质量分数是 4g/102.2g=3.91%