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766 Chapter 14 | Acid-Base Equilibria
Figure 14.16 When an aluminum ion reacts with water, the hydrated aluminum ion becomes a weak acid. Additional examples of the first stage in the ionization of hydrated metal ions are:
Example 14.18
Hydrolysis of [Al(H2O)6]3+
Calculate the pH of a 0.10-M solution of aluminum chloride, which dissolves completely to give the hydrated aluminum ion in solution.
Solution
In spite of the unusual appearance of the acid, this is a typical acid ionization problem.
Step 1. Determine the direction of change. The equation for the reaction and Ka are:
The reaction shifts to the right to reach equilibrium.
Step 2. Determine x and equilibrium concentrations. Use the table:
Step 3. Solve for x and the equilibrium concentrations. Substituting the expressions for the equilibrium concentrations into the equation for the ionization constant yields:
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