Question

An aqueous solution contains 1.2 mM of total ions. (a) If thesolution is NaCl(aq), what is the concentration of chlorideion? (b) If the solution is FeCl₃(aq), what is the concentrationof chloride ion?

Answer 1

The concentration of chloride ion in a 1.2 mM NaCl(aq) solution is 1.2 mM. In a FeCl₃(aq) solution, the concentration of chloride ion is 3.6 mM, as FeCl₃ produces three Cl- ions per formula unit.

Step-by-step explanation:

To determine the concentration of chloride ion in an aqueous solution of NaCl and FeCl₃, one must remember that the total ion concentration represents the sum of all individual ions present in the solution. For NaCl, which dissociates into an equal number of Na+ and Cl- ions, the concentration of chloride ions will be equal to the total ion concentration.

(a) If the solution is NaCl(aq), for every mole of NaCl dissolved, one mole of Cl- ions is produced. Therefore, the concentration of chloride ions will be 1.2 mM.

(b) If the solution is FeCl₃(aq), FeCl₃ dissociates to produce one Fe3+ ion and three Cl- ions per formula unit. This means for every mole of FeCl₃ dissolved, three moles of Cl- ions are produced. Given the total ion concentration of 1.2 mM, the concentration of chloride ions would be 3.6 mM (3 times the concentration of FeCl₃).