Equimolar solutions of the following were prepared in water separately. Which one of the solutions will record the highest pH ?

Options

A. `CaCI_2`
B. `SrCI_2`
C. `BaCI_2`
D. `MgCI_2`

Answer

To determine which equimolar solution will record the highest pH, we need to analyze the nature of the salts provided and their corresponding hydroxides. The salts in question are derived from strong acids and bases, and we will focus on their cationic components to assess their basicity.

### Step-by-Step Solution:

1. **Identify the Salts and Their Hydroxides**:
- The salts mentioned are derived from strong acids (like HCl) and bases. The cations from the bases will dictate the pH of the solution.
- The cations and their corresponding hydroxides are:
- **MgCl2** → Mg(OH)2
- **CaCl2** → Ca(OH)2
- **SrCl2** → Sr(OH)2
- **BaCl2** → Ba(OH)2

2. **Determine the Basicity of Hydroxides**:
- The strength of the hydroxides increases down the group in the periodic table. Therefore, we can rank them based on their basicity:
- Mg(OH)2 (least soluble and weak base)
- Ca(OH)2 (stronger base than Mg(OH)2)
- Sr(OH)2 (stronger base than Ca(OH)2)
- Ba(OH)2 (strongest base)

3. **Analyze the Solubility**:
- The solubility of hydroxides increases down the group. Thus, Ba(OH)2 is more soluble than Sr(OH)2, which is more soluble than Ca(OH)2, and Mg(OH)2 is the least soluble.
- Since Ba(OH)2 is the most soluble, it will dissociate more completely in solution, leading to a higher concentration of OH⁻ ions.

4. **Predict the pH**:
- The pH of a solution is determined by the concentration of hydroxide ions (OH⁻). The more OH⁻ ions present, the higher the pH.
- Since Ba(OH)2 produces the highest concentration of OH⁻ ions, it will yield the highest pH.

5. **Conclusion**:
- Among the equimolar solutions of MgCl2, CaCl2, SrCl2, and BaCl2, the solution of **BaCl2** will record the highest pH due to the presence of Ba(OH)2, which is the strongest base among the hydroxides derived from these salts.

### Final Answer:
The solution that will record the highest pH is **BaCl2**.

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