Na2O + H2SO4 = Na2SO4 + H2O
Na2SO3 + H2SO4 = Na2SO4 + H2O + SO2
nSO2=0,025 mol
=>nNa2SO3= 0,025 mol => m=3,15 g
=> mNa2O=0,62 g
bảo toàn Na => nNa2SO4 = nNa2O + nNa2SO3 = 0,025+0,01=0,035 mol
=> m muối=4,97g
mdd sau =3,77+200-0,025.64=202,17 g
=> C%=2,46%