calculez masa de acid din solutie
c=mdx100/ms---> md= 800x31,5/100 g=252g HNO3
calculez moli acid, stiind M,HNO3= 63g/mol
niu= m/M= 252g/63g/mol= 4molHNO3
calculez moli si masa carbonat din ecuatia chimica
1mol.........2mol
MgCO3 +2HNO3---> Mg(NO3)2 +CO2+H2O
x............4mol
x= 2mol MgCO3
M,MgCO3=84g/mol
m=niuxM= 2X84 g=......................CALCULEAZA !!!