Calculate molality of a 20.0% w/w hydrogen peroxide solution. the reported density of a 20.0% aqueous solution of hydrogen peroxide is 1.085 g/mL g

molality = 7.35 m

Explanation:

To get this, let's write the expression of molality:

mo = n / kg water   (1)

n is the moles of solute.

But we don't have the moles of solute, we have the %w/w of 20%. This means the following:

20 g solute > 100 g solution

We also has the density of 1.085 g/mL This means:

1.085 g solution > 1 mL of solution.

To solve this, we need to know the volume of solution. As we don't have the volume of solution, we can assume a volume of 1 L.

With this volume we can calculate the mass of solution:

d = m/V  > m = d*V

Solving for the mass of solution:

m = 1.085 * 1000 = 1085 g solution

Now that we have the mass of solution, we can know the mass of solute using the %w/w:

m solute = 1085 * (20/100) = 217 g of solute

We have solute, solution, let's get the solvent which is water:

mass of water = 1085 - 217 = 868 g of water or 0.868 kg of water

All we have to do now, is to get the moles. The hydrogen peroxide has the formula H₂O₂ and it's molecular weight is 34 g/mol, so the moles are:

n = 217 / 34 = 6.38 moles

Finally, the molality is:

mo = 6.38 / 0.868

mo = 7.35 m