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# Conc H+ from pH water Watch

1. I have this question I'm stuck on:

The pH of a sample of pure water is 6.63 at 50 degrees C.
Calculate the concentration in mol dm-3 of H+ions in this sample of pure water.

What's the relevance of the 50 degrees C and how do I do this?

Thanks.
2. (Original post by wrnicholls)
I have this question I'm stuck on:

The pH of a sample of pure water is 6.63 at 50 degrees C.
Calculate the concentration in mol dm-3 of H+ions in this sample of pure water.

What's the relevance of the 50 degrees C and how do I do this?

Thanks.
You work using the definition of pH = -log[H+]

Hence [H+] = 10-pH
3. (Original post by charco)
You work using the definition of pH = -log[H+]

Hence [H+] = 10-pH
Yeah I know that much, but what's the point of them saying 50 degrees?
How would you adjust if it said 25 degrees for example?

Does it effect working? If not, why not ?
4. (Original post by wrnicholls)
Yeah I know that much, but what's the point of them saying 50 degrees?
How would you adjust if it said 25 degrees for example?

Does it effect working? If not, why not ?
No, it doesn't affect the working out. They use 50º to explain why the pH is not 7.00.

The dissociation of water:

H2O <==> H+ + OH-

at 25ºC [H+] = 1 x 10-7 and hence pH = 7

As the temperature increases the dissociation moves more to the RHS and the value of [H+] also increases.

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