# How do you calculate the PH of pure water at 50 degrees?

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#1
Can someone help me with this, the answer says 13.3 but some people say its 6.6 You sumhow use Kw to find the answer but i dont know how. Could someone show me the working to get the answer plz ?
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#2
Anyone ?
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11 years ago
#3
It will be around 7. 13.3 is very alkaline, on par with a strong alkaline such as NaOH.

First, you need your Kw value. Just looked in my notes, and for 60 degrees it is 5.60 x 10-14 mol2 dm-6. Check the question and use the value from there. I'll use the 60 degrees value for this example.

Kw = [H+][OH-]

so [H+][OH-]

[H+](squared) = 5.60 x 10-14

[H+] = square root of 5.60 x 10-14

[H+] = 2.366 x 10-7 mol dm-3

-----
pH = -log10 [H+]

so log 2.366 x 10-7 = 6.62

pH = 6.62

Thats for 60 degrees, I think the Kw value for 50 degrees will be different. Hope that helps!
2
9 years ago
#4
Hi, if you calculate pOH and then calculate the pH from there it will be different><

Kw = [H+][OH-]

so [H+][OH-]

[OH-](squared) = 5.60 x 10-14

[OH-] = square root of 5.60 x 10-14

[OH-] = 2.366 x 10-7 mol dm-3

-----
pOH = -log10 [OH-]

so -log 2.366 x 10-7 = 6.62

pH = 14-6.62=7.38

Could you explain the difference. Thanks a lot!
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9 years ago
#5
(Original post by Da_hopeful_1)
Can someone help me with this, the answer says 13.3 but some people say its 6.6 You sumhow use Kw to find the answer but i dont know how. Could someone show me the working to get the answer plz ?
First off, the answer 13.3 is way wrong. Water gets more acidic as it warms up. This is logical because the equilibrium:

H2O <=> H+ + OH- is endothermic, so increased temperature pushes the equilibrium to the RHS

Secondly, you cannot work out the pH without more information. Just the temperature is not enough.

kw = [H+][OH-] = 1 x 10-14 @ 25ºC

hence

[H+] = [OH-] = 1 x 10-7

Therefore pH = 7
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1 year ago
#6
(Original post by charco)
First off, the answer 13.3 is way wrong. Water gets more acidic as it warms up. This is logical because the equilibrium:

H2O <=> H+ + OH- is endothermic, so increased temperature pushes the equilibrium to the RHS

Secondly, you cannot work out the pH without more information. Just the temperature is not enough.

kw = [H+][OH-] = 1 x 10-14 @ 25ºC

hence

[H+] = [OH-] = 1 x 10-7

Therefore pH = 7
Water is always neutral no matter the temperature as the concentrations of h+and oh- are exactly the same
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