\(\begin{array}{l}
3)\\
N{a_2}C{O_3} + CaC{l_2} \to CaC{O_3} + 2NaCl\\
nN{a_2}C{O_3} = nCaC{l_2} = nCaC{O_3} = \frac{{20}}{{100}} = 0,2\,mol\\
CMN{a_2}C{O_3} = \frac{{0,2}}{{0,2}} = 1M\\
C\% CaC{l_2} = \frac{{0,2 \times 111}}{{200}} \times 100\% = 11,1\% \\
4)\\
a)\\
BaC{O_3} + 2HN{O_3} \to Ba{(N{O_3})_2} + C{O_2} + {H_2}O\\
Ba{(N{O_3})_2} + N{a_2}S{O_4} \to BaS{O_4} + 2NaN{O_3}\\
b)\\
Ca{(N{O_3})_2} + N{a_2}C{O_3} \to 2NaN{O_3} + CaC{O_3}\\
CaC{O_3} + C{O_2} + {H_2}O \to Ca{(HC{O_3})_2}\\
Ca{(HC{O_3})_2} + 2HCl \to CaC{l_2} + 2C{O_2} + 2{H_2}O
\end{array}\)
