Na2CO3+2HCl→2NaCl+H2O+CO2
x---------------------------------------------x
CaCO3+2HCl→CaCl2+H2O+CO2
y----------------------------------------y
=>Ta có :\(\left\{{}\begin{matrix}126x +120y=36,6\\x+y=0,3\end{matrix}\right.\)
=>x=0,1 mol , y=0,2 mol
=>m Na2SO3=0,1.126=12,6g