How many moles of potassium nitrate are required to make 550 mL of a 2.1M solution?

1.155 moles

Explanation:

Given;

volume of solution, V = 550 mL

solution molality, M = 2.1M

Molality = number of moles of solute / litre of solvent

number of moles of solute (potassium nitrate) = molality x litre of solvent

number of moles of solute (potassium nitrate) = 2.1 x 550 x 10⁻³

number of moles of solute (potassium nitrate) = 1.155 moles

Therefore, there are 1.155 moles of potassium nitrate in the solution.