5 mL of 0.4 N NaOH is mixed with 20 mL of 0.1 N HCl. The pH of the resulting solution will be

Options

A. 6
B. 7
C. 8
D. 5

Answer

To find the pH of the resulting solution when 5 mL of 0.4 N NaOH is mixed with 20 mL of 0.1 N HCl, we can follow these steps:

### Step 1: Calculate the number of equivalents of NaOH
To find the number of equivalents of NaOH, we use the formula:

\[ \text{Equivalents} = \text{Volume (L)} \times \text{Normality (N)} \]

For NaOH:
- Volume = 5 mL = 0.005 L
- Normality = 0.4 N

\[ \text{Equivalents of NaOH} = 0.005 \, \text{L} \times 0.4 \, \text{N} = 0.002 \, \text{equivalents} \]

### Step 2: Calculate the number of equivalents of HCl
Now, we calculate the number of equivalents of HCl using the same formula:

For HCl:
- Volume = 20 mL = 0.020 L
- Normality = 0.1 N

\[ \text{Equivalents of HCl} = 0.020 \, \text{L} \times 0.1 \, \text{N} = 0.002 \, \text{equivalents} \]

### Step 3: Determine the reaction between NaOH and HCl
The reaction between NaOH and HCl is a neutralization reaction:

\[ \text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} \]

From the calculations, we see that both NaOH and HCl have the same number of equivalents (0.002 equivalents). This means that they will completely neutralize each other.

### Step 4: Calculate the pH of the resulting solution
Since the reaction goes to completion and both reactants are in equal amounts, the resulting solution will be neutral. The pH of a neutral solution at 25°C is 7.

### Final Answer
Thus, the pH of the resulting solution will be **7**.

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