1) SO2+H2O-->H2SO3
2) HNO3+NaOH-->NaNO3+H2O
3) 2Fe(OH)3-->Fe2O3+3H2O
4) 2Al+3H2SO4-->Al2(SO4)3+3H2
дано
m(H2SO4)=4.9g
-----------------------
m(BaSO4)-?
4.9g Xg
H2SO4+BaCL2-->BaSO4+2HCL
98 233
M(H2SO4)=98 g/mol , M(BaSO4)=233 g/mol
4.9/98 = X/233
X=11,65 g
ответ 11.65 г