Question

A 60 ppm solution of hydrogen peroxide is 60 mg of H2O2 per 1000 g of solution. Assuming that the density of this solution is 1.00 g/ml, convert this concetration from ppm to molarity.

Answer 1

ppm = parts per million

= 1 mg / 1 L or 1 mg / 1 Kg

So a 60 ppm solution of H2O2 means  60 mg of H2O2 / per 1 Kg of solution

   Or 60 mg of H2O2 / per 1000 g of solution

Now if we take the mass of the solution = 1000 g

given density of solution = 1.00 g/ml

Then volume of solution = mass / density

= 1000 g / 1.00 g/ml

= 1000 mL

= 1 L

Now molarity = moles of solute / volume of solution in L

Here given mass of solute (H2O2) present = 60 mg

= 60 / 1000 g

= 0.060 g

So mols of solute (H2O2) present = mass / molar mass of H2O2

= 0.060 g / 34 g/mol

= 0.0017 mols

So we can say, we have 0.0017 mols of H2O2 present in 1L volume of solution

So molarity = moles of solute / volume of solution in L

= 0.0017 mols / 1 L

= 0.0017 mols/L

= 0.0017 M