Question

A student needs to prepare 50.0 mL of a 1.20 M aqueous H2O2 solution. Calculate the volume of 4.7 M H2O2 stock solution that should be used to prepare the solution.

volume: mL

Answer 1

During preparation of a diluted solution from a stock solution, the number of moles remains constant.

As we are diluting the stock solution by adding more of the solvent, the final volume of the solution increases. As molarity (M) is given by the number of moles of solute per liter of solvent, it will decrease on dilution.

Molarity of the solution multiplied by its volume gives the number of moles of the compound in the solution, which is a constant.

So we can write

or,

where M₁ = molarity of the stock solution

V₁ = volume of the stock solution

M₂ = molarity of the final solution

V₂ = volume of the final solution

If any three are known, the 4^th value can be calculated.

Given:

M₁ = 4.7 M

M₂ = 1.20 M

V₂ = 50.0 mL

We have to calculate V₁.

V₁ = 12.8 mL

This is the required answer.

Hope this helps, thanks!