To prepare 250mL of 2.0M HNO3 from 70% concentrated nitric acid:
Molarity of HNO3 =
2.0 =
Moles of HNO3 = 0.5 mol
Mass of 0.5 mol of HNO3 = Molar mass of HNO3 Moles of HNO3 = 630.5 = 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 31.5)/70 = 45g
Hence, 45g of HNO3 is required.