(1)4克NaOH ===> 0.1mol(2)n(NaOH) : n(H2O) == 1:49(3)n(H2O) == 0.1*49/1== 4.9mol(4)这种烧碱溶液中溶质的质量分数== 4/(4+18*4.9)*100% == 4.34%