Question

Calculate the concentration of nitric acid in moles per litre in a sample which has a density of 1.42 g/ mL and the mass percent of nitric acid is 69%.

Answer 1

Density, mass of a unit volume of a material substance. Density is the ratio of the mass of the substance to its volume. Density is usually expressed in units of grams per cubic centimetre.Mass percent is a method of expressing a concentration or describing the component in a particular mixture.For a solution, the mass percent is described as the grams of solute per grams of solution, multiplied by 100 to get the percentage.Molarity can be defined as the moles of a solute per litres of a solution. Molarity is also known as the molar concentration of a solution. The formula for molarity is given below:
$\dfrac{\text{Mass}\,\text{of}\,\text{nitric}\,\text{acid}}{\text{Molar}\,\text{mass}\,\text{of}\,\text{nitric}\,\text{acid}\,\text{ }\\!\\!\times\\!\\!\text{ }\,\text{Volume}\,\text{of}\,\text{solution}}$

Complete step by step answer:
The density of the given solution is 1.41 g/mL.
1000 g of the solution will have a volume =$\dfrac{Mass}{Density}=\dfrac{1000}{1.41}=709\,ml$
It is given that the mass percent of nitric acid is 69% which means that 1000 g of the solution will have $1000\times \dfrac{69}{100}=690\,gm$ of nitric acid.
Hence, the molarity of solution is $\dfrac{\text{Mass}\,\text{of}\,\text{nitric}\,\text{acid}}{\text{Molar}\,\text{mass}\,\text{of}\,\text{nitric}\,\text{acid}\,\text{ }\\!\\!\times\\!\\!\text{ }\,\text{Volume}\,\text{of}\,\text{solution}}$​
= $\dfrac{690}{63\times 709}=0.0155\,M$

Note: The quantitative units of concentration include molarity, molality, mass percentage, parts per thousand, parts per million, and parts per billion. Concentrations are usually expressed in terms of relative units. The concentration is defined as the abundance of a constituent divided by the total volume of a mixture.