Question

How many grams of concentrated nitric acid solution should be used to prepare 250mL of 2.0M HNO3 ?The concentrated acid is 70% HNO3.

Answer 1

To prepare 250mL of 2.0M HNO3 from 70% concentrated nitric acid:

Molarity of HNO₃ = $\frac{\mathrm{Moles}\mathrm{of}{\mathrm{HNO}}_3}{\mathrm{Volume}\mathrm{of}\mathrm{solution}}\times 1000$

2.0 = $\frac{\mathrm{Moles}\mathrm{of}{\mathrm{HNO}}_3}{250}\times 1000$

Moles of HNO₃ = 0.5 mol

​Mass of 0.5 mol of HNO₃ = Molar mass of HNO₃ $\times$ Moles of HNO₃ = 63$\times$0.5 = 31.5 g​

70% concentrated nitric acid means, 70g of HNO₃ is present in 100g of HNO₃ solution
Therefore, 31.5g of HNO₃ is present in (100 $\times$31.5)/70 = 45g

​Hence, 45g of HNO₃ is required.