The concentration of the nitric acid solution was 5.6 M.
Start by writing the balanced chemical equation for your reaction
Notice that you have a
Use magnesium carbonate's molar mass to determine how many moles were present in the 8.2-g sample that completely reacted
This means that the nitric acid solution had
Molarity is defined as moles of solute, in your case nitric acid, divided by liters of solution. Since you know the volume of the nitric acid solution and how many moles of solute it contained, you can solve for its molarity by
Rounded to two sig figs, the number of sig figs you gave for the mass of magnesium carbonate, the answer will be