Question

An aqueous KNO3 solution is made using 73.1 g of KNO3 diluted to a total solution volume of 1.87 L .

Part A

Calculate the molarity of the solution. (Assume a density of 1.05 g/mL for the solution.) M=

Part B

Calculate the molarity of the solution. (Assume a density of 1.05 g/mL for the solution.) m=

Part C

Calculate the mass percent of the solution. (Assume a density of 1.05 g/mL for the solution.)

Answer 1

Mass of KNO₃ solution = 73.1 grams

Volume of the solution = 1.87 Litres

Density of the solution = 1.05 gm/ml

1.05 grams present in 1 ml of solution

If 1 litre (1000 ml) of solution is present then 1.05 x 1000 grams of solution is present

If 1.87 Litre is present then 1.05 x 1.87 x1000 grams of solution is present = 1963.5 grams

Mass of solution present in 1.87 Litres of solution is 1963.5 grams

But, mass of solution = mass of solute + mass of solvent

Here KNO₃ is taken as the mass of solute as it is present in smaller quantity

mass of solute = 73.1 grams

mass of solvent = mass of solution - mass of solute = 1963.5 - 73.1 = 1890.4 grams

Number of moles of KNO₃ solution = mass of KNO₃ / Molar mass of KNO₃

Molar mass of KNO₃ = 39 + 14 + 3(16) = 39.1 + 14 + 48 = 39 + 62 = 101.1 grams

Number of moles of KNO₃ = 73.1 / 101.1 =  0.723046 moles

Part A :

Molarity of a solution can be found using the formula

Molarity = Number of moles of solute/ Volume of the solution in litres

Molarity = 0.723046 / 1.87 = 0.386655 M

Molarity = 0.3867 M (Rounding off the answer to 4 decimal places)

Part B :

Molality of a solution can be found using the formula

Molality = Number of moles of solute/ Mass of the solvent in Kgs

Mass of the solvent = 1890.4 grams

Converting grams to kilo grams

1000 grams = 1 Kg

1 grams = 1/1000 Kg

Mass of solvent = 1890.4 grams = 1890.4 / 1000 = 1.8904 Kgs

Molality of the solution = Number of moles of solute/ mass of solvent in Kgs = 0.723046 / 1.8904 = 0.38248 molal

Molality = 0.3825 m

Part C :

Mass percent of solution = (mass of solute/ mass of solution ) x 100

Mass percent = (73.1 / 1963.5 ) x 100 = 7310 / 1963.5 = 3.7229 %