Question

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

• A. $ SrCl_2$
• B. $BACl_2$
• C. $MgCl_2$
• D. $CaCl_2$

Answer 1

The Correct Option is B

To determine which equimolar solution will record the highest pH, we need to consider the behavior of the respective cations from their chlorides when dissolved in water. The solutions provided are:

1. SrCl_2
2. BACl_2
3. MgCl_2
4. CaCl_2

These compounds dissociate in water as follows:

• SrCl_2 \rightarrow Sr^{2+} + 2Cl^{-}
• BaCl_2 \rightarrow Ba^{2+} + 2Cl^{-}
• MgCl_2 \rightarrow Mg^{2+} + 2Cl^{-}
• CaCl_2 \rightarrow Ca^{2+} + 2Cl^{-}

In aqueous solutions, the cations of these chlorides can undergo hydrolysis, which can affect the pH:

• Alkaline Earth Metals cations like Mg^{2+} are slightly acidic due to their small size and high charge density, causing more hydrolysis, resulting in lower pH.
• The hydrolysis tends to increase the concentration of H^+ ions, thus decreasing the pH.

However, upon hydrolysis, BaCl_2 is expected to have minimal hydrolysis because Ba^{2+} has a larger ionic radius and lower charge density compared to others like Mg^{2+}, Ca^{2+}, and Sr^{2+}. Less hydrolysis means fewer H^+ ions released, resulting in a higher pH.

Therefore, among the given options, the solution that records the highest pH is BaCl_2.