At `100^(@)C,` the `P^(H)` of pure water is

Options

A. 7
B. Greater than 7
C. less than 7
D. zero

Answer

To find the pH of pure water at 100°C, we can follow these steps:

### Step 1: Understand the Ionic Product of Water (Kw)
At any temperature, the ionic product of water (Kw) is defined as:
\[ K_w = [H^+][OH^-] \]
For pure water, the concentration of hydrogen ions \([H^+]\) is equal to the concentration of hydroxide ions \([OH^-]\). Therefore, we can express this as:
\[ K_w = [H^+]^2 \]

### Step 2: Recognize the Effect of Temperature on Kw
As temperature increases, the ionic product of water (Kw) also increases. At 25°C, \( K_w \) is \( 1.0 \times 10^{-14} \), which corresponds to \([H^+] = 10^{-7} \, \text{mol/L}\) and a pH of 7. However, at 100°C, \( K_w \) is higher than \( 1.0 \times 10^{-14} \).

### Step 3: Determine the Concentration of H⁺ at 100°C
At 100°C, the concentration of \([H^+]\) will be greater than \( 10^{-7} \, \text{mol/L} \) due to the increased dissociation of water. Let’s denote this concentration as:
\[ [H^+] > 10^{-7} \, \text{mol/L} \]

### Step 4: Calculate the pH
The pH is calculated using the formula:
\[ \text{pH} = -\log[H^+] \]
Since \([H^+]\) is greater than \( 10^{-7} \, \text{mol/L} \), the pH will be:
\[ \text{pH} < 7 \]

### Conclusion
Thus, at 100°C, the pH of pure water is less than 7.

### Final Answer
The pH of pure water at 100°C is less than 7.

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