What is the pH of an aqueous solution of Ca1OH22 at 25.0 °C with a concentration of 6.3 * 10-5 M? (LO 16.7) (a) 4.20 (b) 10.10 (c) 11.36 (d) 9.80

Verified step by step guidance

1. Identify the chemical formula: The given compound is Ca(OH)_2, which is calcium hydroxide, a strong base.
2. Determine the dissociation: Ca(OH)_2 dissociates in water to form Ca^{2+} and 2 OH^- ions. The balanced equation is: Ca(OH)_2 \rightarrow Ca^{2+} + 2 OH^-.
3. Calculate the concentration of OH^- ions: Since each formula unit of Ca(OH)_2 produces 2 OH^- ions, the concentration of OH^- ions is 2 times the concentration of Ca(OH)_2. Therefore, [OH^-] = 2 \times 6.3 \times 10^{-5} M.
4. Calculate the pOH: Use the formula pOH = -\log[OH^-] to find the pOH of the solution.
5. Determine the pH: Use the relationship pH + pOH = 14 to find the pH of the solution.

Key Concepts

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is neutral, below 7 indicates acidity, and above 7 indicates basicity. The pH is calculated as the negative logarithm of the hydrogen ion concentration, pH = -log[H+]. Understanding the pH scale is essential for determining the nature of the solution in the given question.

Hydroxide Ion Concentration

In a basic solution, the concentration of hydroxide ions (OH-) is crucial for calculating pH. For calcium hydroxide, Ca(OH)2, it dissociates in water to produce calcium ions and hydroxide ions. The concentration of hydroxide ions can be determined from the concentration of the calcium hydroxide solution, which directly influences the pH calculation.

Ion Product of Water

The ion product of water (Kw) at 25 °C is 1.0 x 10^-14, which relates the concentrations of hydrogen ions and hydroxide ions in water. This relationship is expressed as Kw = [H+][OH-]. Knowing Kw allows us to find the hydrogen ion concentration from the hydroxide ion concentration, which is necessary for calculating the pH of the solution in the question.