设纯Na2SO4质量x
Na2SO4+BaCl2=2NaCl+BaSO4↓
142````````````````````````233
x``````````````````````````3.2g
142:x=233:3.2g
解得x≈1.95g
因此杂质质量分数约为(2g-1.95g)/2g=2.5%