Ammonium sulfide, (NH4)2S, is a soluble ionic compound. When it dissolves, how does it exist in solution (e.g., how would you write it in an ionic equation)?
(NH4)2S (s)
NH4+2 (aq) + S-2 (aq)
2 NH4+1 (aq) + S-2 (aq)
NH4+1 (aq) + 2 S-2 (aq)
NH4+1 (aq) + S-2 (s)
N-3 (aq) + H+1 (aq) + S-2 (aq)
2 N-3 (aq) + 8 H+1 (aq) + S-2 (aq)
The Correct Answer and Explanation is :
The correct answer is:
2 NH₄⁺ (aq) + S²⁻ (aq)
Explanation:
Ammonium sulfide, (NH₄)₂S, is an ionic compound that dissociates when dissolved in water. In its solid form, ammonium sulfide consists of ammonium cations (NH₄⁺) and sulfide anions (S²⁻) held together by electrostatic forces. When this compound dissolves in water, these ions separate due to the interaction with water molecules, which stabilize the ions in solution.
The process can be described in the following steps:
- Dissociation of Ammonium Sulfide in Water:
- The solid ammonium sulfide breaks apart into its ions: two ammonium ions (NH₄⁺) and one sulfide ion (S²⁻). This happens because the ionic bonds between NH₄⁺ and S²⁻ are disrupted by the polar water molecules, which surround and solvate the ions.
- Ionic Equation:
- The dissociation is represented by the ionic equation:
[
(NH₄)₂S (s) \rightarrow 2 \, NH₄⁺ (aq) + S²⁻ (aq)
] - This equation shows that two ammonium ions (NH₄⁺) dissociate for every one sulfide ion (S²⁻) produced in solution.
- Solubility and Ion Pairing:
- Ammonium sulfide is highly soluble in water, meaning that the ions exist as free ions in solution rather than forming new compounds. The ions are fully dissociated in the solution, and there is no indication of any ion pairing or insoluble salts.
Why Other Options Are Incorrect:
- NH₄⁺₂ (aq) + S²⁻ (aq): This notation implies that the ammonium ion exists as a diatomic ion (NH₄⁺₂), which is not the case. Ammonium exists as NH₄⁺ in water.
- NH₄⁺ (aq) + 2 S²⁻ (aq): This implies that only one ammonium ion dissociates per sulfide ion, but this is incorrect. Two ammonium ions dissociate for each sulfide ion.
- NH₄⁺ (aq) + S²⁻ (s): This would suggest that the sulfide ion remains in the solid phase, which is incorrect. The sulfide ion dissociates into the solution.
- N³⁻ (aq) + H⁺ (aq) + S²⁻ (aq) and 2 N³⁻ (aq) + 8 H⁺ (aq) + S²⁻ (aq): These equations suggest the formation of nitride ions (N³⁻) and are not related to ammonium sulfide, which contains only ammonium (NH₄⁺) and sulfide (S²⁻) ions.
Thus, the correct dissociation equation for ammonium sulfide is: 2 NH₄⁺ (aq) + S²⁻ (aq).