Determine the concentrations of OH-, pH, and pOH of a solution that is 0.125 M in CO32-.

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Identify the relevant equilibrium reactions for carbonate ion (\( \text{CO}_3^{2-} \)) in water: \( \text{CO}_3^{2-} + \text{H}_2\text{O} \rightleftharpoons \text{HCO}_3^{-} + \text{OH}^- \).

Use the equilibrium constant expression for the reaction: \( K_b = \frac{[\text{HCO}_3^-][\text{OH}^-]}{[\text{CO}_3^{2-}]} \).

Assume initial concentration of \( \text{CO}_3^{2-} \) is 0.125 M and set up an ICE table to find changes in concentration at equilibrium.

Solve for \([\text{OH}^-]\) using the equilibrium expression and the known \( K_b \) value for carbonate ion.

Calculate pOH from \([\text{OH}^-]\) using the formula \( \text{pOH} = -\log[\text{OH}^-] \) and then find pH using \( \text{pH} = 14 - \text{pOH} \).

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Carbonate Ion Chemistry

The carbonate ion (CO32-) is a polyatomic ion that can act as a base in aqueous solutions. It can accept protons (H+) to form bicarbonate (HCO3-), which is crucial for understanding its role in acid-base equilibria. The presence of CO32- in a solution will influence the concentrations of hydroxide ions (OH-) and the overall pH of the solution.

pH and pOH Calculations

pH is a measure of the hydrogen ion concentration in a solution, while pOH measures the hydroxide ion concentration. They are related through the equation pH + pOH = 14 at 25°C. Understanding how to calculate pH and pOH from ion concentrations is essential for determining the acidity or basicity of a solution.

Equilibrium Constants and Ionization

The ionization of carbonate ions involves equilibrium constants such as Kb for the reaction with water to form hydroxide ions. The concentration of OH- can be derived from the equilibrium expression, which relates the concentrations of the reactants and products at equilibrium. This concept is vital for calculating the resulting pH and pOH of the solution.