Calculate the mass in grams of Iron (III) Chloride in a solution of 500 cm^3 which has a concentration of 0.200 mol/dm^3
First work out the moles of Iron (III) Chloride using the equation concentration = moles/volume, rearranging the eqaution in order to calculate moles gives moles = concentration x volume. Check the units!! Before calculating all the units must match, in this question the volume is given in cm3 so it must be converted into dm3 by dividing by 1000. moles = 0.2 x 500/1000 = 0.1 moles of Iron (III) Chloride Now we have to find the Mr of Iron (III) Chloride so we can use the equation Mass = Mr x moles The (III) denotes that the Iron has an oxidation state of +3 and so must be cancelled out by a negative charge of -3. Chloride ions have a charge of -1 as they are in group 7. So 3 Chloride ions are needed to cancel out the charges so the formula is FeCl3 Ar of Iron = 55.8; Ar of Chlorine = 35.5 Therefore the Mr of FeCl3 = 55.8 + 3 x 35.5 = 162.3 Finally substitute into the equation to find the mass. Mass = 162.3 x 0.1 = 16.2 g to 3 s.f.
