Which compound is soluble in water? PbS AgI Fe(OH): CuBr2
The Correct Answer and Explanation is:
The correct answer is: CuBr₂ (Copper(II) bromide) is soluble in water.
Explanation:
To determine the solubility of ionic compounds in water, chemists rely on solubility rules—guidelines based on experimental evidence about how different combinations of ions behave in aqueous solutions.
Let’s examine each compound using the solubility rules:
- PbS (Lead(II) sulfide)
- Rule: Most sulfides (S²⁻) are insoluble, except those of alkali metals (e.g., Na⁺, K⁺), ammonium (NH₄⁺), and some alkaline earth metals.
- Pb²⁺ is not an exception.
- ✅ Insoluble
- AgI (Silver iodide)
- Rule: Most halides (Cl⁻, Br⁻, I⁻) are soluble, except those of silver (Ag⁺), lead (Pb²⁺), and mercury (Hg₂²⁺).
- Ag⁺ is an exception.
- ✅ Insoluble
- Fe(OH)₃ (Iron(III) hydroxide)
- Rule: Most hydroxides (OH⁻) are insoluble, except those of alkali metals and some alkaline earth metals (like Ba²⁺).
- Iron is not an exception.
- ✅ Insoluble
- CuBr₂ (Copper(II) bromide)
- Rule: Most halides (like Br⁻) are soluble, except those of Ag⁺, Pb²⁺, and Hg₂²⁺.
- Cu²⁺ is not an exception.
- ✅ Soluble
Why CuBr₂ is Soluble:
When CuBr₂ is placed in water, it dissociates into Cu²⁺ and 2Br⁻ ions:CuBr2(s)→Cu2+(aq)+2Br−(aq)\text{CuBr}_2 (s) \rightarrow \text{Cu}^{2+} (aq) + 2\text{Br}^- (aq)CuBr2(s)→Cu2+(aq)+2Br−(aq)
Water’s polarity allows it to surround and stabilize these ions, leading to the compound dissolving readily. Because bromide salts are generally soluble (except when combined with Ag⁺, Pb²⁺, or Hg₂²⁺), CuBr₂ follows the rule and is soluble in water.
Final Answer: CuBr₂ is soluble in water.
