Concentration and Molarity Worked Example Problem

Concentration and Molarity Worked Example Problem - Finding Concentration of Ions in a Aqueous Solution

Question

a. State the concentration, in moles per liter, of each ion in 1.0 mol Al(NO₃)₃.
b. State the concentration, in moles per liter, of each ion in 0.20 mol K₂CrO₄.

Solution

Part a.) Dissolving 1 mol of Al(NO₃)₃ in water dissociates into 1 mol Al³⁺ and 3 mol NO^3- by the reaction:

Al(NO₃)₃(s) → Al³⁺(aq) + 3 NO^3-(aq)

Therefore:

concentration of Al³⁺ = 1.0 M
concentration of NO^3- = 3.0 M

Part b.) K₂CrO₄ dissociates in water by the reaction:

K₂CrO₄ → 2 K⁺(aq) + CrO₄^2-

One mol of K₂CrO₄ produces 2 mol of K⁺ and 1 mol of CrO₄^2-. Therefore, for a 0.20 M solution:

concentration of CrO₄^2- = 0.20 M
concentration of K⁺ = 2×(0.20 M) = 0.40 M

Answer

Part a).
Concentration of Al³⁺ = 1.0 M
Concentration of NO^3- = 3.0 M

Part b.)
Concentration of CrO₄^2- = 0.20 M
Concentration of K⁺ = 0.40 M