pH of water
Q. The pH of water is 30* is 6.92, give a reason why it is neutral at this temp.
Ive been hardwired to write [H+]=[OH-]
but if this was the case wouldn't the pH be 7?
TIA
Ive been hardwired to write [H+]=[OH-]
but if this was the case wouldn't the pH be 7?
TIA
Original post by uhhhh6678987654
Q. The pH of water is 30* is 6.92, give a reason why it is neutral at this temp.
Ive been hardwired to write [H+]=[OH-]
but if this was the case wouldn't the pH be 7?
TIA
Ive been hardwired to write [H+]=[OH-]
but if this was the case wouldn't the pH be 7?
TIA
No, because the pH of pure water is only 7 at 25°C, since [H^+] = 10^-7 mol dm^-3.
The dissociation of water is endothermic:
H2O (l) <=> H^+ (aq) + OH^- (aq)
At 30°C, the temperature is greater than 25°C, so it favours the endothermic route and more water dissociates, so [H^+] > 10^-7 mol dm^-3. As such, the pH simply cannot be 7.00
(edited 11 months ago)
Original post by uhhhh6678987654
Q. The pH of water is 30* is 6.92, give a reason why it is neutral at this temp.
Ive been hardwired to write [H+]=[OH-]
but if this was the case wouldn't the pH be 7?
TIA
Ive been hardwired to write [H+]=[OH-]
but if this was the case wouldn't the pH be 7?
TIA
@TypicalNerd said it well
"Neutral" means that [H+] = [OH-]
pH = -log [H+]
When H2O dissociates, the amounts of H+ and OH- formed will be the same.
The extent to which water dissociates depends on the temperature – at higher temperatures a greater proportion will dissociate, meaning that there is more [H+] at 30°C than there is a 25°C. This means that the pH is lower at higher temperatures.
A handy chemguide page: https://chemguide.co.uk/physical/acidbaseeqia/kw.html
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