At 20°C, an aqueous solution that is 24.0% by mass in ammonium chloride has a density of 1.0674 g/mL. What is the molarity of ammonium chloride in the solution? The formula weight of NH4Cl is 53.50 g/mol.

Molarity = 4.79 M

Explanation:

Mass percentage -

Mass percentage of A is given as, the mass of the substance A by mass of the total solution multiplied by 100.

i. e.

mass % A = mass of A / mass of solution * 100

Given,

24% by mass of ammonium chloride,

so,

100 g solution contains, 24 g of ammonium chloride,

mass of solution = 100g

and mass of the solute, i. e., ammonium chloride = 24 g.

Hence,

Moles -

Moles are calculated as the given mass divided by the molecular mass.

i. e.,

moles = (mass / molecular mass)

Given,

The molecular mass of ammonium chloride is 53.50 g / mol

moles of ammonium chloride = 24 g / 53.50 g / mol

moles of ammonium chloride = 0.449 mol

Density -

Density of a substance is given as the mass divided by the volume,

Density = mass / volume,

Volume = mass / density

Given,

Density of ammonium chloride = 1.0764 g / mL

Calculated above, mass of solution = 100 g

volume of solution = 100 g / 1.0764 g / mL

volume of solution = 93.69 mL

Since, 1 ml = 1/1000 L

volume of solution = 93.69 / 1000 L

volume of solution = 0.09369 L

Molarity -

Molarity of a solution is given by the moles of solute per liter of the solution

Hence,

M = moles of solute / volume of solution (in L)

As calculated above,

moles of ammonium chloride = 0.449 mol

volume of solution = 0.09368 L

Putting in the above formula

Molarity = 0.449 mol / 0/09368 L

Molarity = 4.79 M