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.
- Understanding pH and Water Ionization:
Water dissociates into hydrogen ions ( ) and hydroxide ions ( ) as follows:
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At 25°C, the concentration of both ions is mol/L, giving water a neutral pH of 7. - 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. - 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. - 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