A chemist prepares a solution of iron chloride by measuring out 0.10 g of FeCl2 into a 50. mL volumetric flask and filling to the mark with distilled water.

Question

Calculate the molarity of anions in the chemist's solution.

Answer 1

Molarity = moles of the species of interest/liters of solution.

We know the liters of solution are 50. ml x 1 L/1000 ml = 0.050 liters.

So now we need to find moles of FeCl₂ and then moles of Cl^- ions (the anions)

Molar mass of FeCl_{2 =} 126.8 g/mole

moles FeCl₂ present = 0.10 g x 1 mol/126.8 g = 7.89x10^-4 moles

moles Cl^- = 7.89x10^-4 moles FeCl₂ x 2 moles Cl^- / mole FeCl₂ = 1.58x10^-3 moles

Molarity of Cl^- = 1.58x10^-3 moles Cl^- / 0.050 L = 0.0316 M Cl^- = 0.32 M Cl^- (to 2 significant figures)