DILUTION

We often must prepare dilute solutions from more concentrated stock solutions. The millimole of stock solutions taken for dilution will be identical to the millimoles in the final diluted solution.

Example 1

You have a stock solution 0.200 M of KMnO4 and a series of 100 mL of volumetric flask. What volumes of the stock solution will you have to pipet into the flask to prepare standard solution of 0.005 M KMnO4?

Solution

Moles of 0.005 M KMnO4
= 0.005 x 100
= 0.5 mmol

We must pipet this amount from the stock solution
0.5 = 0.200 X x
    X= 0.5 / 0.200
       = 2.5 mL

Example 2

How much water should be added in 6.0 M 40 mL of H2SO4 solution to produce a 5.0 M H2SO4 solution ?

Solution

6.0 x 40 mL = 5.0 x Volume
Volume = 48 mL

The amount of water that should be added = 48 – 40 = 8 mL