Question

Arrange the following resultant mixtures in increasing order of their pH values}
A. \(10 \text{ mL } 0.2 \text{ M Ca(OH)}_2 + 25 \text{ mL } 0.1 \text{ M HCl}\)
B. \(10 \text{ mL } 0.01 \text{ M H}_2\text{SO}_4 + 10 \text{ mL } 0.01 \text{ M Ca(OH)}_2\)
C. \(10 \text{ mL } 0.1 \text{ M H}_2\text{SO}_4 + 10 \text{ mL } 0.1 \text{ M KOH}\)

• A. B <C <A
• B. C <A <B
• C. C <B <A
• D. A <C <B

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The topic is Ionic Equilibrium, specifically acid-base neutralization.
We need to determine if the final solution in three different neutralization reactions is acidic, basic, or neutral, and then arrange them by increasing pH. A lower pH means more acidic.
Step 2: Key Formula or Approach:
1. Calculate the millimoles (mmol) of \(H^+\) and \(OH^-\) ions for each reaction. Remember to account for the number of ions produced per formula unit (e.g., \(H_2\text{SO}_4\) gives 2 \(H^+\)).
2. Determine the net mmol of \(H^+\) or \(OH^-\) after neutralization.
3. An excess of \(H^+\) means an acidic solution (pH<7). An excess of \(OH^-\) means a basic solution (pH>7). If they are equal, the solution is neutral (pH = 7).
Step 3: Detailed Explanation:
Mixture A:
mmol of \(OH^- = (\text{Volume} \times \text{Molarity} \times \text{n-factor}) = 10 \times 0.2 \times 2 = 4 \text{ mmol}\).
mmol of \(H^+ = (\text{Volume} \times \text{Molarity} \times \text{n-factor}) = 25 \times 0.1 \times 1 = 2.5 \text{ mmol}\).
After neutralization, net mmol of \(OH^- = 4 - 2.5 = 1.5 \text{ mmol}\). The solution is basic (pH>7).
Mixture B:
mmol of \(H^+ = 10 \times 0.01 \times 2 = 0.2 \text{ mmol}\).
mmol of \(OH^- = 10 \times 0.01 \times 2 = 0.2 \text{ mmol}\).
The millimoles are equal, resulting in complete neutralization. The solution is neutral (pH = 7).
Mixture C:
mmol of \(H^+ = 10 \times 0.1 \times 2 = 2 \text{ mmol}\).
mmol of \(OH^- = 10 \times 0.1 \times 1 = 1 \text{ mmol}\).
After neutralization, net mmol of \(H^+ = 2 - 1 = 1 \text{ mmol}\). The solution is acidic (pH<7).
Ordering by pH:
The acidic solution (C) has the lowest pH. The neutral solution (B) is next. The basic solution (A) has the highest pH.
Therefore, the order of increasing pH is C<B<A.
Step 4: Final Answer:
The correct order is C < B < A.