POGIL Common Ion Effect on Solubility Extension Questions:
- Would the four beakers in Model 1 have the same reading on a pH meter? Explain your reasoning.
- Consider any of the beakers in Model 1. Predict what might happen to the solubility of the insoluble salt if a 1.0 M acid solution was added drop wise to the beaker. Hint: Which ion species in the beaker will react with the acid? How will this reaction alter the concentration of the common ion?
Thank you!
Certainly! Here are the correct answers followed by a detailed explanation of each:
16. Would the four beakers in Model 1 have the same reading on a pH meter? Explain your reasoning.
Answer:
No, the four beakers in Model 1 would not have the same pH readings.
17. Consider any of the beakers in Model 1. Predict what might happen to the solubility of the insoluble salt if a 1.0 M acid solution was added dropwise to the beaker. Hint: Which ion species in the beaker will react with the acid? How will this reaction alter the concentration of the common ion?
Answer:
The solubility of the insoluble salt will increase because the acid will react with the common ion (typically a basic anion like CO₃²⁻ or OH⁻), reducing its concentration and shifting the equilibrium to dissolve more salt.
✨ Detailed Explanation (300+ words):
The Common Ion Effect is a concept rooted in Le Châtelier’s Principle, which states that a system at equilibrium will adjust to counteract any changes. In Model 1, you likely observed several beakers containing an insoluble salt (e.g., calcium carbonate or silver chloride) in water, and in some cases, with a solution containing a common ion already dissolved.
Question 16:
Beakers with different solutes or added substances will have different pH values. For example, a beaker containing only pure water and an insoluble salt will have a neutral or near-neutral pH. However, if the salt dissociates into an ion like CO₃²⁻ (carbonate), which can accept hydrogen ions (H⁺), the solution becomes basic. On the other hand, adding a solution that already contains an acid or acidic salt (e.g., NH₄⁺ from NH₄Cl) will lower the pH. Therefore, the pH readings differ due to the varying presence and nature of dissolved ions.
Question 17:
Adding a 1.0 M acid solution dropwise introduces H⁺ ions into the beaker. If the common ion in solution is a basic anion like CO₃²⁻ or OH⁻, it will react with H⁺:
- CO₃²⁻ + H⁺ → HCO₃⁻
- OH⁻ + H⁺ → H₂O
This neutralization reduces the concentration of the common ion that was suppressing the salt’s solubility. According to Le Châtelier’s Principle, the equilibrium will shift to dissolve more of the salt to restore the concentration of the removed ion. As a result, the solubility of the originally insoluble salt increases.
This effect is commonly exploited in chemical processes to enhance the solubility of salts, particularly when dealing with sparingly soluble compounds in acidic environments.