Question

A sodium hydroxide solution containing 40% by weight of pure NaOH has a specific gravity of 1.5. What volume if this solution will be required in the preparation of 500ml of a 0.45 M NaOH solution.

Answer 1

Given:

• % purity of the NaOH solution by mass is 40%
• The density of the solution (d) = 1.5g/mL
• The volume of the solution required (v) = 500 mL
• Molarity of the solution (M) = 0.45M
• Molar mass of NaOH (Mm) = 40g/mol

To find:

The volume of the impure NaOH solution required.

Solution:

• Let the volume of the impure solution required be x mL
• Mass of the impure solution required equals to (x*d) = 1.5x g
• Mass of pure NaOH is 40% of 1.5x = 0.6x g
• Mass of NaOH in the prepared solution equals ( M*v*Mm/1000) = 9 g
• Hence, 0.6x = 9 ⇒ x = 15 mL

Answer:

The volume of the impure NaOH solution required is equal to 15 mL