6. How much water must be added to 600 mL of a 0.15 mol/L Ca (OH); solution

to make a solution with a concentration of 0.10 mol/L? (4 marks)

300mL

Explanation:

To obtain the volume of water added, let us calculate the volume of the diluted solution.

Data obtained from the question include:

Molarity of stock solution (M1) = 0.15mol/L

Volume of stock solution (V1) = 600mL

Molarity of diluted solution (M2) = 0.1mol/L

Volume of diluted solution (V2) = ... ?

The volume of the diluted solution can be obtained as follow:

M1V1 = M2V2

0.15 x 600 = 0.1 x V2

Divide both side by 0.1

V2 = 0.15 x 600 / 0.1

V2 = 900mL.

Therefore the volume of the diluted solution is 900mL.

Finally, we can obtain the volume of the water added by calculating the difference in the volume of the diluted solution and that of the stock solution. This is illustrated below:

Volume of stock solution (V1) = 600mL

Volume of diluted solution (V2) = 900mL

Volume of water added = ... ?

Volume of water added = V2 - V1

Volume of water added = 900 - 600

Volume of water added = 300mL

Therefore, the volume of water added is 300mL