Question

What volume of water must be added to 85.0mL of a 0.400 mol/L solution of sodium carbonate to make a 0.250 mol/L solution?

Answer 1

First, we need to make difference between the 2 solutions here.

Solution 1)

Volume 1 = V1 = 85.0 mL = 0.0850 L (volume of solution)

Concentration 1 = C1 = 0.400 mol/L

Solution 2)

V2 = Need to be found

C2 = 0.250 mol/L

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We want to get from Solution 1 to Solution 2 by adding water, so we dilute solution 1. To this we use this formula:

C1 x V1 = C2 x V2, we clear V2, so we get to

`V2\text{ = }\frac{C1\text{ x V1}}{C2}=\text{ }\frac{0.400\text{ mol/L x 0.0850 L}}{0.250\text{ mol/L}}=\text{ 0.136 L }`

V2 = volume of solution 2 = 0.136 L

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The volume of water we need to add solution 1 is:

V2 - V1 = V of water added = 0.136 L - 0.085 L = 0.0510 L of water

Answer: 0.0510 L of water