Bài 4:
\(Mg+2HCl\to MgCl_2+H_2\\ MgCO_3+2HCl\to MgCl_2+H_2O+CO_2\uparrow\\ CO_2+Ca(OH)_2\to CaCO_3\downarrow+H_2O\\ n_{CaCO_3}=\dfrac{10}{100}=0,1(mol);n_{H_2}=\dfrac{2,8}{22,4}=0,125(mol)\\ \Rightarrow n_{Mg}=n_{H_2}=0,125(mol);n_{MgCO_3}=n_{CO_2}=n_{CaCO_3}=0,1(mol)\\ \Rightarrow m_{Mg}=0,125.24=3(g);m_{CaCO_3}=0,1.84=8,4(g)\\ \Rightarrow \%_{Mg}=\dfrac{3}{3+8,4}.100\%=26,32\%\\ \Rightarrow \%_{MgCO_3}=100\%-26,32\%=73,68\%\)