# Calculate the ion concentrations of Fe3+ and Cl- when 0.100 M FeCl3 dissolves in water

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1. Calculate the ion concentrations of Fe3+ and Cl- when 0.100 M FeCl3 dissolves in water.

Solution

· Write out the balanced chemical equation showing the substance dissolving in water.

FeCl3 (s) → Fe3+ (aq) + 3Cl- (aq)

· Look at the balanced equation. You can see that for each mole of FeCl3 that is dissolved, 1 mole of Fe3+ ions and 3 moles of Cl- ions are produced. Thus a solution that is 0.100 M FeCl3 contains 0.100 M Fe3+ and (3 × 0.100 M) Cl- ions or 0.300 M Cl-

2. Give the concentration of each type of ion in 0.50 M Co(NO3)2.

Solution

· Using the same method as above, we first write out the balanced chemical equation

Co(NO3)2 (s) → Co2+(aq) + 2NO3- (aq)

· When Co(NO3)2 dissolves, 1 mole of Co2+ ions and 2 moles of NO3- ions are produced. So our ion concentrations are 0.50 M Co2+ and (2 × 0.50 M) NO3- ions which is 1.0 M NO3-