Question

10. A solution is prepared by dissolving 75.0 g

KNO3 to make 725 mL of solution.


a. Find the molar mass of potassium nitrate.


b. Find moles of potassium nitrate.


c. Find the molarity (M)

Answer 1

a. The molar mass of potassium nitrate (KNO3) can be calculated by adding the atomic masses of potassium (K), nitrogen (N), and three oxygen atoms (O).

Molar mass of KNO3 = atomic mass of K + atomic mass of N + (3 x atomic mass of O)

= 39.10 g/mol + 14.01 g/mol + (3 x 16.00 g/mol)

= 101.10 g/mol

Therefore, the molar mass of potassium nitrate is 101.10 g/mol.

b. The number of moles of potassium nitrate can be calculated using the formula:

moles = mass / molar mass

mass of KNO3 = 75.0 g

molar mass of KNO3 = 101.10 g/mol

moles of KNO3 = 75.0 g / 101.10 g/mol

= 0.741 mol

Therefore, there are 0.741 moles of potassium nitrate in the solution.

c. Molarity (M) is defined as the number of moles of solute per liter of solution.

Volume of solution = 725 mL = 0.725 L

Molarity (M) = moles of solute / volume of solution in liters

Molarity (M) = 0.741 mol / 0.725 L

= 1.02 M

Therefore, the molarity of the potassium nitrate solution is 1.02 M.