\(n_{Na_2SO_3}=\dfrac{12,6}{126}=0,1\left(mol\right)\\ 1,PTHH:Na_2SO_3+2HCl\rightarrow2NaCl+H_2O+SO_2\uparrow\\ \Rightarrow n_{HCl}=2n_{Na_2SO_3}=0,2\left(mol\right)\\ \Rightarrow m_{CT_{HCl}}=0,2\cdot36,5=7,3\left(g\right)\\ \Rightarrow m_{dd_{HCl}}=\dfrac{7,3}{20\%}=36,5\left(g\right)\\ 2,n_{H_2O}=n_{SO_2}=0,1\left(mol\right);n_{NaCl}=0,2\left(mol\right)\\ \Rightarrow\left\{{}\begin{matrix}m_{H_2O}=0,1\cdot18=1,8\left(g\right)\\m_{SO_2}=0,1\cdot64=6,4\left(g\right)\\m_{CT_{NaCl}}=0,2\cdot58,5=11,7\left(g\right)\end{matrix}\right.\\ \Rightarrow m_{dd_{NaCl}}=12,6+36,5-1,8-6,4=40,9\left(g\right)\\ \Rightarrow C\%_{NaCl}=\dfrac{11,7}{40,9}\cdot100\%\approx28,61\%\)
