Question

You are asked to prepare 250.0 mL of 1.25 M KNO₃ solution. What mass of solid KNO₃ should you use?

Answer 1

Solution

250.0 ml * 1 L / 1000 ml = 0.250 L

Formula to calculate the molarity is

molarity = moles / volume in liter

therefore moles = molarity * volume in liter

                      = 1.25 mol per L * 0.250 L

                     = 0.3125 mol KNO3

now lets convert moles of KNO3 to its mass

mass = moles * molar mass

molar mass of KNO3 = 101.1032 g per mol

mass of KNO3 = 0.3125 mol * 101.1032 g per mol

                      = 31.6 g KNO3

Therefore we need 31.6 g KNO3