Question

In the lab, a 2.00 x 10-4 M FeSCN2+ stock solution will be provided. Calculate the volume of stock solution (in mL) required to prepare a 10.00 mL 1.50 x 10-4 M solution. Report your answer to two decimal places. Example: If the calculated volume is 1.2 mL, input 1.20. Exclude units in your answer.

Answer 1

The required answer is 7.50.

EXPLANATION -

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 solvent, the final volume of the solution increases. As molarity(M) is given by the number of moles 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 = 2.00 * 10^-4 M

M₂ = 1.50 * 10^-4 M

V₂ = 10.00 mL

We have to calculate V₁.

V₁ = 7.50 mL

The required answer is 7.50.