Ph And Temperature

The question addresses the effect of temperature on the pH of water. To understand the answer, we need to discuss the relationship between temperature and the dissociation of water.

1. Understanding pH and Water Ionization:
   Water dissociates into hydrogen ions ( ) and hydroxide ions ( ) as follows:

1. 
   At 25°C, the concentration of both ions is mol/L, giving water a neutral pH of 7.
2. Effect of Temperature on Dissociation:
   Increasing temperature causes the dissociation of water to increase. As temperature rises, more and ions are produced. This is due to the fact that the process is endothermic.
3. Change in pH with Temperature:
   Because higher temperature leads to more ions, the pH of water will decrease. This does not indicate the water becomes acidic; neutral pH simply shifts to lower numerical values at higher temperatures.
4. Conclusion:
   Hence, when water is heated to 80°C from 25°C, the pH will decrease due to increased dissociation of water molecules.

Answer: Decrease