The Effects of Temperature on the pH of Water
A substance's pH is a measure of its acidity. A pH value below 7 implies an acidic substance, while a pH above 7 means the material is alkaline. Water is often thought of as "neutral," which means it has a pH of 7 and is neither acid nor alkaline. However, this is only true for pure water and only at a specific temperature. As temperatures move away from the neutral range, pH will inevitably change.
Other People Are Reading
-
Definition
-
PH is a scale that is used to measure a substance's acidity. When working with a liquid, chemists use the concentration of hydrogen (H) to calculate pH levels. The higher the concentration of hydrogen, the lower the pH, which indicates high acidity. Conversely, low concentrations of hydrogen ions mean that the substance has low acidity (or is more basic, or alkaline, rather than acidic) and has a high pH.
Measurement
-
While an absolutely accurate measurement of pH levels requires advanced equipment, a rough measurement can be made with pH test strips. A staple of chemistry labs all around the world, these inexpensive strips are simply dipped into the liquid whose pH level is being gauged. After a short while, the color of the strip will change, and the final color is then compared to the rainbowlike color palette on the package, where each shade is assigned a pH number. Darker colors usually mean a high pH value, while lighter colors indicate low pH levels.
-
Water
-
The pH scale varies between 0 and 14, with the midvalue 7 indicating a substance that is neither an acid nor a base; in other words, neutral. Water is the typical example of a pH-neutral substance. Pure water, however, is surprisingly hard to find. The water that comes out of the faucet or flows in a clean river will have many impurities and its pH will rarely be 7.
Effect of Temperature
-
Temperature will have a measurable yet very slight effect on the pH of water. In fact, pure water has a pH of exactly 7 only at 25 degrees Celsius, or 77 degrees Fahrenheit. As the water temperature goes up, pH goes down. The converse is also true, in that colder water has a higher pH value. At 60 degrees Celsius (140 degrees Fahrenheit), pure water will register a pH value of 6.96. In other words, the change is very slight and cannot be registered with crude measurement techniques such as pH test strips.
Reason
-
The reason temperature affects water's pH is that water molecules tend to break down into their constituents, hydrogen and oxygen, as the temperature increases. As temperatures increase, a larger proportion of water molecules break up, producing more hydrogen, which then increases the pH of the water.
-
References
- Photo Credit water drop and water rings image by glgec from Fotolia.com
