Question

sir,
A bottle of commercial sulphuric acid (density = 1.787 gm/ml) is labeled 86% by weight. What is the
molarity of the solution? What volume of the acid is required to make it 1 liter of 0.2 M H2SO4?

Answer 1

In chemistry, the molar concentration, $c_{i}$ is defined as the amount of a constituent $n_{i}$ (usually measured in moles – hence the name) divided by the volume of the mixture $V$:

$$c_{i} = \frac{n_{i}}{V}$$

It is also called molarity, amount-of-substance concentration, amount concentration, substance concentration, or simply concentration. The volume $V$ in the definition $c_{i} = n_{i} / V$ refers to the volume of the solution, not the volume of the solvent. One liter of a solution usually contains either slightly more or slightly less than 1 liter of solvent because the process of dissolution causes volume of liquid to increase or decrease. So, if you have one liter of commercial acid the weight of it is:

$$\mathrm{m} = 1000 \mathrm{ml} \times 1.787 \mathrm{g/ml} = 1767 \mathrm{g}$$

The mass of acid in this case is:

$$\mathrm{m}_{\mathrm{a}} = 1767 \times 86\% / 100\% = 1519,62 \mathrm{g}$$

Amount of acid is:

1519,62 / 98 = 15,5 mol the same is molarity ( it was calculated for one liter )

Second part:

If you need 0,2 M solution, it means that it is 0,2 mol in one liter.

So you need dissolve some volume X of 15,5 M solution that includes 0,2 mol of acid.

If 1000 ml includes 15.5 mol

X ml includes 0,2 moles

$$\mathrm{x} = 12.9 \mathrm{ml}$$

So you need mix $12.9\mathrm{ml}$ of commercial acid with 987,1 ml of water. (Together it's one liter.)