Question

Calculate the concentration of nitric acid in moles per litre in a sample which has a density of $1.41g/ml$ and the mass percentage of nitric acid is $69\%$.

Answer 1

We have to find a number of moles in a litre of solution. We assume the volume of solution is one litre and find the mass of one litre of solution by density. Now we have mass of one litre solution and we have given mass percentage of nitric acid, and using this we find mass of nitric acid. And after dividing mass of nitric acid with mass of solution we get moles per litre of nitric acid.

Complete step by step answer:
Given, density of solution is $1.41g/ml$ and the mass percentage of nitric acid is $69\%$.
We need a number of moles of nitric acid in one litre of solution. Then assume that the volume of solution is one litre.
We know that the mass of a liquid is a product of its volume and its density.
Here, density $d = 1.41g/ml$ and volume $V = 1000ml$.
Then mass of solution is given by
${M_{Sol}} = d \times V = 1.41 \times 1000 = 1410g$.
Mass percentage of nitric acid is given and we have mass of solution also.
Then mass of nitric acid is given by
${M_{Nitric}} = \dfrac{{69}}{{100}} \times 1410 = 972.9g$.
Molar mass of nitric acid $(HN{O_3})$ is 63.
Then number of moles of nitric acid is given by
${\text{no}}{\text{. of moles = }}\dfrac{{{\text{mass}}}}{{{\text{molar mass}}}} = \dfrac{{972.9}}{{63}} = 15.44$

Hence, concentration of nitric acid in moles per litre is $15.44.$

Note: Concentration of nitric acid may change with change in temperature of solution. When the temperature of solution changes, the density of solution also changes with it. And concentration depends on density and why concentration also changes.