pH of a 0.001 M NaOH solution will be

Options

A. 9
B. 3
C. 11
D. 12

Answer

To find the pH of a 0.001 M NaOH solution, we can follow these steps:

### Step 1: Understand the dissociation of NaOH
NaOH is a strong base and completely dissociates in water. The dissociation can be represented as:
\[ \text{NaOH} \rightarrow \text{Na}^+ + \text{OH}^- \]

### Step 2: Determine the concentration of OH⁻ ions
Since NaOH completely dissociates, the concentration of OH⁻ ions in the solution will be equal to the concentration of NaOH. Therefore:
\[ [\text{OH}^-] = 0.001 \, \text{M} \]

### Step 3: Calculate pOH
The pOH of a solution can be calculated using the formula:
\[ \text{pOH} = -\log[\text{OH}^-] \]
Substituting the concentration of OH⁻:
\[ \text{pOH} = -\log(0.001) \]

### Step 4: Calculate the logarithm
Calculating the logarithm:
\[ \text{pOH} = -(-3) = 3 \]

### Step 5: Use the relationship between pH and pOH
We know that:
\[ \text{pH} + \text{pOH} = 14 \]
Now, substituting the value of pOH:
\[ \text{pH} = 14 - \text{pOH} = 14 - 3 \]

### Step 6: Final calculation of pH
\[ \text{pH} = 11 \]

Thus, the pH of a 0.001 M NaOH solution is **11**.

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