What mass of nitric acid solution, mass fraction = 7%, must be spent on the reaction with 5 mol of sodium carbonate.

Given:
ω (HNO3) = 7%
n (Na2CO3) = 5 mol

To find:
m solution (HNO3) -?

Decision:
1) Write the reaction equation:
2HNO3 + Na2CO3 => 2NaNO3 + H2O + CO2 ↑;
2) Calculate the molar mass of HNO3:
M (HNO3) = Mr (HNO3) = Ar (H) + Ar (N) + Ar (O) * 3 = 1 + 14 + 16 * 3 = 63 g / mol;
3) Determine the amount of substance HNO3:
n (HNO3) = n (Na2CO3) * 2 = 5 * 2 = 10 mol;
4) Calculate the mass of HNO3:
m (HNO3) = n (HNO3) * M (HNO3) = 10 * 63 = 630 g;
5) Calculate the mass of the HNO3 solution:
m solution (HNO3) = m (HNO3) * 100% / ω (HNO3) = 630 * 100% / 7% = 9000 g.

Answer: The mass of the HNO3 solution is 9000 g.