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how does the ph of pure water decreases on increasing temperature even when same amount of H+ and OH- ion formed???

how does the ph of pure water decreases on increasing temperature even when same amount of H+ and OH- ion formed???

Grade:12th pass

2 Answers

VENKATA RAJA
32 Points
4 years ago

Temperature plays a significant role on pH measurements. As the temperature rises, molecular vibrations increase which results in the ability of water to ionise and form more  hydrogen ions. As a result, the pH will drop. The dissociation of water into hydrogen and hydroxide ion can be represented as:

H2O (l) ⇌ H+ (aq) + OH− (aq)

 pH of water at 0degree is 7.47, but the same water at 100 degree will have a pH of 6.14

Vikas TU
14149 Points
4 years ago
Dear student 
If the pH falls as temperature increases, this does not mean that water becomes more acidic at higher temperatures. A solution is acidic if there is an excess of hydrogen ions over hydroxide ions (i.e., pH
The problem is that we are all familiar with 7 being the pH of pure water, that anything else feels really strange. Remember that to calculate the neutral value of pH from  Kw . If that changes, then the neutral value for pH changes as well. At 100°C, the pH of pure water is 6.14, which is "neutral" on the pH scale at this higher temperature. A solution with a pH of 7 at this temperature is slightly alkaline because its pH is a bit higher than the neutral value of 6.14.
Similarly, you can argue that a solution with a pH of 7 at 0°C is slightly acidic, because its pH is a bit lower than the neutral value of 7.47 at this temperature. Hence, there is an excess of  H+  ions vs.  OH−  ions.

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