To make 500ml of a 28% solution, how many ml of a 20% stock solution will be needed?

To determine how many milliliters of a 20% stock solution are required to make 500 ml of a 28% solution, it’s essential to use the concept of mixing solutions with different concentrations.

First, you can set up the equation based on the final volume and concentration desired. You want a total of 500 ml of a 28% solution, which means you will have 28% of 500 ml as the solute.

Calculating the amount of solute needed:

• 28% of 500 ml = 0.28 x 500 ml = 140 ml of solute.

Next, let’s denote the volume of the 20% stock solution needed as ‘x’ ml. Since the stock solution is 20% concentration, it contains:

• 20% of x = 0.20x ml of solute.

In addition, the remaining volume to complete 500 ml will have to be made up with a 0% solution, which means you need to find out how much volume you will mix to reach 500 ml:

• 500 ml total solution = x ml of 20% solution + (500 - x) ml of 0% solution.

You can establish the