Is the ionic compound AgBr soluble or insoluble, and does each of its ions tend to be soluble?
a. Both ions soluble
b. Both ions insoluble
c. Ions differ; soluble
d. Ions differ; insoluble
The correct answer and explanation is :
Correct Answer: d. Ions differ; insoluble
Explanation:
The compound AgBr (silver bromide) is classified as insoluble in water. To understand this, we must explore both the solubility rules and the behavior of the individual ions: Ag⁺ (silver ion) and Br⁻ (bromide ion).
Solubility Rules Review:
- Bromides (Br⁻) are generally soluble with most cations, except when combined with certain transition metals such as silver (Ag⁺), lead (Pb²⁺), and mercury (Hg₂²⁺).
- Silver compounds (Ag⁺) are often insoluble, with a few exceptions like AgNO₃ (silver nitrate) and Ag(C₂H₃O₂) (silver acetate).
Breakdown of AgBr’s Solubility:
- Br⁻ ion (bromide):
Bromide ions are typically soluble, which means that when paired with common cations like Na⁺ or K⁺, the resulting compound dissolves easily in water. - Ag⁺ ion (silver):
Silver ions tend to form insoluble compounds with halides (Cl⁻, Br⁻, I⁻). Therefore, AgBr is insoluble in water due to the low solubility of silver halides.
Why AgBr Is Insoluble:
When AgBr is placed in water, it does not dissociate significantly into its ions. This is because the lattice energy (the energy that holds the ionic solid together) is greater than the hydration energy (the energy released when ions interact with water). As a result, very little Ag⁺ and Br⁻ enter the solution.
The Ksp (solubility product constant) for AgBr is extremely low (around 5.0 × 10⁻¹³ at 25°C), indicating poor solubility. This means it precipitates out of solution rather than dissolving.
Conclusion:
- AgBr is insoluble.
- The ions differ in solubility: Br⁻ is usually soluble, but Ag⁺ tends to form insoluble salts.
- Hence, the correct answer is d. Ions differ; insoluble.