pH of a 100 cc solution is 2. It will not change if

Options

A. 100 cc of `0.1` M HCI is added to it
B. 100 cc of water is added to it
C. 100 cc of`0.01` N HCI is added to it
D. 1 cc of `0.1` M HCI is added to it

Explanation

To solve the question regarding the pH of a 100 cc solution that is currently at pH 2, we need to determine what can be added to this solution without changing its pH. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the pH of the solution
The pH of a solution is a measure of the concentration of hydrogen ions (H⁺) in the solution. A pH of 2 indicates a hydrogen ion concentration of 0.01 M (since pH = -log[H⁺]).

### Step 2: Identify the options provided
We need to analyze the options given to see which one will not change the pH of the solution. The options typically include different concentrations of acids or bases.

### Step 3: Analyze the first option (0.1 M HCl)
- When we add 0.1 M HCl to the solution, it will dissociate completely, increasing the concentration of H⁺ ions.
- The new concentration of H⁺ ions will be higher than 0.01 M, resulting in a pH lower than 2.
- Therefore, this option will change the pH and is incorrect.

### Step 4: Analyze the second option (adding water)
- Adding water will dilute the solution, which will decrease the concentration of H⁺ ions.
- As a result, the pH will increase (become less acidic).
- Thus, this option will also change the pH and is incorrect.

### Step 5: Analyze the third option (0.01 N HCl)
- 0.01 N HCl has a molarity of 0.01 M because HCl provides one H⁺ ion per molecule.
- The pH of a 0.01 M solution is calculated as:
\[ \text{pH} = -\log(0.01) = 2 \]
- Since the pH of this solution is the same as the original solution, adding this will not change the pH. This option is correct.

### Step 6: Analyze the fourth option (0.1 N HCl)
- Similar to the first option, 0.1 N HCl will also dissociate completely, leading to an increase in H⁺ concentration.
- This will result in a pH lower than 2, thus changing the pH. This option is incorrect.

### Conclusion
The only option that does not change the pH of the original solution is the third option, which is the addition of 0.01 N HCl.

### Final Answer
The pH of the 100 cc solution will not change if we add 0.01 N HCl.

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