a) Mg+2HCl---->MgCl2+H2
Chất rắn C là Cu
%m Cu=\(\frac{2,5}{12,1}.100\%=20,66\%\)
%m Mg=100-20,66=79,34%
b)n Mg=\(\frac{12,1-2,5}{24}=0,4\left(mol\right)\)
Theo pthh
n H2=n Mg=0,4(mol)
m H2=0,8(g)
m dd sau pư=12,1+200-2,5-0,8=215,4(g)
Theo pthh
n MgCl2=n Mg=0,4(mol)
m MgCl2=0,4.95=38(g)
C% MgCl2=\(\frac{38}{215,4}.100\%=17,64\%\)