Question

Calculate how to prepare 500 mL of 32.5 part per million KOH from a solution 50% of KOH with a density of 1.58 g/mL

Answer 1

1 ppm is, in terms of percentage is essentially 1g of the substance in 1000000g of the solution. So, 1 g/mL is equal to 1000000 ppm.

Now, given that the stock solution contains 50% KOH or 0.5 g/mL and that its density of the 50% KOH is 1.58 g/mL, it can be said to contain 500000 ppm of KOH. Also, 32.5 ppm, in terms of percentage will then be 32.5x10^-6 g/mL.

Using the law of equivalence for dilution, we get,

This on substitution gives 500*(32.5x10^-6) = X*0.5

The unknown X amounts to 500*(32.5x10^-6)/0.5 = 0.0325 mL.

So, taking 0.0325 mL of the 50% KOH solution and diluting it to 500 mL will produce a solution contain 32.5 ppm of KOH.