30.50ml=0.03050l,4.25ml=0.00425l,25.00ml/250ml=1/10
CaO质量分数
0.02mol/l*0.03050l=0.00061mol
0.00061mol*56.08g/mol＝0.0342088g
0.0342088g*10=0.342088g
0.342088/0.5=0.684176=68.4176%
Fe2O3质量分数
0.02mol/l*0.00425l=0.000085mol
0.000085mol*(1/2)*159.7g/mol =0.00658725g
0.00658725g*10=0.0658725g
0.0658725/0.5=0.111745=11.1745%