What is sum of `pH + pOH " at " 25^(@) C` ?

Answer

To find the sum of pH and pOH at 25°C, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding pH and pOH**:
- pH is a measure of the hydrogen ion concentration \([H^+]\) in a solution.
- pOH is a measure of the hydroxide ion concentration \([OH^-]\) in a solution.

2. **Relationship between pH, pOH, and pKw**:
- At any temperature, the relationship between pH, pOH, and the ion product of water (\(K_w\)) is given by:
\[ pH + pOH = pK_w \]

3. **Finding \(K_w\) at 25°C**:
- At 25°C, the value of \(K_w\) (the ionic product of water) is:
\[ K_w = 1.0 \times 10^{-14} \]

4. **Calculating \(pK_w\)**:
- To find \(pK_w\), we use the formula:
\[ pK_w = -\log(K_w) \]
- Substituting the value of \(K_w\):
\[ pK_w = -\log(1.0 \times 10^{-14}) \]

5. **Evaluating the logarithm**:
- The logarithm can be calculated as:
\[ -\log(1.0 \times 10^{-14}) = -(-14) = 14 \]
- Therefore, \(pK_w = 14\).

6. **Final Calculation**:
- Now substituting back into the relationship:
\[ pH + pOH = pK_w = 14 \]

### Conclusion:
The sum of pH and pOH at 25°C is:
\[ \boxed{14} \]