2.1. MMgCl2=24+2*35.5=95g/mol
raport de masa==>MgCl2=24g:71g
raport atomic==>MgCl2=1:2
%Mg=mMg/M*100=24/95*100=25.263
%Cl2=mCl2/M*100=71/95*100=74.736
2.2.
MH2O=18g/mol
n=m/M=90/18=5 moli H2O
1 mol H2O.............18g
5mol......................90g
1mol HCl..............36g
x=2.5 moli...........................90g
MHCl=36.5g/mol
n=m/M==>m=n*M=2.5*36.5=91.25g HCl