Question

In the laboratory you are asked to make a 0.721 m potassium chloride solution using 255 grams of water.

How many grams of potassium chloride should you add?
_____ grams.

Answer 1

Mass = 13.42 g

Step-by-step explanation:

Given data:

Molality of potassium chloride solution = 0.721 m

Mass of water = 255 g (255 g /1000 = 0.255 Kg)

Potassium chloride added = ?

Solution:

Molality:

Molality = number of moles of solute/ Kg of solvent

0.721 m = moles / 0.255 Kg

m = mol/Kg

Moles = 0.721mol/Kg×0.255 Kg

Moles = 0.18 mol

Mass of potassium chloride:

Number of moles = mass/molar mass

0.18 mol = Mass /74.55 g/mol

Mass = 0.18 mol × 74.55 g/mol

Mass = 13.42 g