Calculate The Ph of Pure Water at The Following Temperatures
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Reviewed by Calculator Editorial Team
Pure water's pH changes slightly with temperature due to the temperature dependence of the dissociation constant of water. This calculator helps you determine the pH of pure water at any given temperature between 0°C and 100°C.
Introduction
The pH of pure water is not exactly 7 at all temperatures. At 25°C (298.15 K), the pH of pure water is defined as exactly 7. However, as temperature changes, the pH of pure water shifts slightly due to the temperature dependence of the dissociation constant of water.
This phenomenon is important in various scientific and industrial applications where precise pH measurements are required at different temperatures.
How to Use This Calculator
To calculate the pH of pure water at a specific temperature:
- Enter the temperature in Celsius in the input field
- Click the "Calculate" button
- View the calculated pH value and interpretation
- Use the chart to visualize how pH changes with temperature
The calculator uses the standard formula for the temperature dependence of the pH of pure water.
The Formula
The pH of pure water at any temperature can be calculated using the following formula:
pH = 7 + (ΔpKw/ΔT) × (T - 25)
Where:
- ΔpKw/ΔT = -0.0014 (temperature coefficient for the dissociation constant of water)
- T = temperature in °C
This formula accounts for the slight change in the dissociation constant of water with temperature.
Worked Example
Let's calculate the pH of pure water at 30°C:
pH = 7 + (-0.0014) × (30 - 25)
pH = 7 + (-0.0014) × 5
pH = 7 - 0.007
pH = 6.993
At 30°C, the pH of pure water is approximately 6.993, which is slightly acidic compared to the standard pH of 7 at 25°C.
How Temperature Affects pH
The pH of pure water decreases slightly as temperature increases. This is because the dissociation constant of water (Kw) increases with temperature, making water slightly more acidic.
At 0°C, the pH of pure water is approximately 7.48. At 100°C, it's approximately 6.14. This temperature dependence is important in various scientific and industrial applications.
Comparison Table
Here's a comparison of the pH of pure water at different temperatures:
| Temperature (°C) | pH of Pure Water | Interpretation |
|---|---|---|
| 0 | 7.48 | Slightly basic |
| 25 | 7.00 | Neutral (by definition) |
| 30 | 6.993 | Slightly acidic |
| 50 | 6.97 | Slightly acidic |
| 100 | 6.14 | Acidic |
FAQ
Why does the pH of pure water change with temperature?
The pH of pure water changes with temperature because the dissociation constant of water (Kw) increases with temperature, making water slightly more acidic at higher temperatures.
What is the standard pH of pure water?
The standard pH of pure water is defined as exactly 7 at 25°C (298.15 K).
How accurate is this calculator?
This calculator provides accurate results based on the standard formula for the temperature dependence of the pH of pure water. The formula accounts for the temperature coefficient of the dissociation constant of water.
Can I use this calculator for temperatures outside the 0-100°C range?
The calculator is designed for temperatures between 0°C and 100°C. For temperatures outside this range, the results may not be accurate.