Common Ion Effect on Acid Ionization POGIL
The correct answer and explanation is:
Sure! Let’s walk through the Common Ion Effect on Acid Ionization in a POGIL (Process Oriented Guided Inquiry Learning) format and then provide the correct answer and a 300-word explanation.
Correct Answer (Summary)
Adding a common ion to a solution containing a weak acid suppresses the ionization of that acid, resulting in a decrease in the concentration of H⁺ ions and a higher pH (less acidic solution).
300-Word Explanation
The common ion effect is a principle from Le Chatelier’s Principle that describes how the presence of an ion common to both a dissolved solute and a dissolved acid or base affects the equilibrium of a weak acid or base.
Consider the weak acid acetic acid (CH₃COOH), which partially ionizes in water: CH₃COOH (aq)⇌H⁺ (aq)+CH₃COO⁻ (aq)\text{CH₃COOH (aq)} \rightleftharpoons \text{H⁺ (aq)} + \text{CH₃COO⁻ (aq)}
When sodium acetate (NaCH₃COO) is added to the solution, it dissociates completely and adds CH₃COO⁻ ions (a common ion) to the solution. According to Le Chatelier’s Principle, adding more of a product (CH₃COO⁻) shifts the equilibrium to the left, reducing the ionization of the acid (CH₃COOH) to produce fewer H⁺ ions.
This results in:
- Lower [H⁺] concentration
- Higher pH (solution becomes less acidic)
In a POGIL setting, you might be given data showing:
- Initial concentrations of a weak acid alone
- The same acid with a common ion added
- Resulting pH changes
From such data, you’d observe that the pH is higher (less acidic) when the common ion is present, confirming the suppression of ionization.
This effect is critical in buffer solutions. By controlling the amount of common ion, we can stabilize the pH, making it useful in biochemical and industrial processes where pH needs to remain relatively constant.
In summary, the common ion effect reduces the ionization of weak acids (or bases) by shifting equilibrium, which is directly observable in a POGIL activity through increased pH values.