When 100 ml of M/10 NaOH solution and 50 ml of M/5 HCI solution are mixed, the pH of resulting solution would be

Options

A. 0
B. 7
C. Less than 7
D. More than 7

Answer

To find the pH of the resulting solution when 100 ml of M/10 NaOH solution is mixed with 50 ml of M/5 HCl solution, we can follow these steps:

### Step 1: Calculate the number of millimoles of NaOH
- **Molarity of NaOH** = M/10 = 0.1 M
- **Volume of NaOH** = 100 ml = 0.1 L
- **Millimoles of NaOH** = Molarity × Volume (in L) × 1000
\[ \text{Millimoles of NaOH} = 0.1 \, \text{mol/L} \times 0.1 \, \text{L} \times 1000 = 10 \, \text{mmol} \]

### Step 2: Calculate the number of millimoles of HCl
- **Molarity of HCl** = M/5 = 0.2 M
- **Volume of HCl** = 50 ml = 0.05 L
- **Millimoles of HCl** = Molarity × Volume (in L) × 1000
\[ \text{Millimoles of HCl} = 0.2 \, \text{mol/L} \times 0.05 \, \text{L} \times 1000 = 10 \, \text{mmol} \]

### Step 3: Determine the reaction between NaOH and HCl
- The reaction between NaOH and HCl can be represented as:
\[ \text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} \]
- Since both NaOH and HCl have equal millimoles (10 mmol each), they will completely neutralize each other.

### Step 4: Analyze the resulting solution
- After the reaction, all the NaOH and HCl will be consumed, resulting in a neutral solution.
- For strong acid-strong base reactions, when the number of millimoles of acid equals the number of millimoles of base, the resulting solution is neutral.

### Step 5: Determine the pH of the resulting solution
- The pH of a neutral solution at 25°C is 7.

### Final Answer:
The pH of the resulting solution is **7**.

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