girlworld_club
Member
i was just thinking this in term of water, say i had 100ml then added another 1000ml then the ph would still be neutral. However, according to the formula ph should change. can someone clear this up. thanks
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does increasing the concentration of HCl increase ph? (1 Viewer)
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Riproot
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HCl is not neutral...
So adding more (moles of) HCl into the same volume of water would decrease the pH, because HCl has a low pH.
So adding more (moles of) HCl into the same volume of water would decrease the pH, because HCl has a low pH.
Riproot
Addiction Psychiatrist
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E.g. If you have a HCl/H2O solution with 0.010 moles of HCl and 1.0L of water the concentration would be:
c = n/v
c = 0.010 moles/1.0L
c = 0.010 moles/L
since, doing HSC Chem, we can assume HCl dissociates completely, we can say
[H+] = 0.010 M
so,
pH = -log[H+]
pH = -log[0.01]
pH = 10
Therefore, adding more HCl to this, let's say 0.10 moles, would increase the concentration.
n = 0.010 moles + 0.10 moles
n = 0.11 moles
Therefore,
c = n/v
c = 0.11 moles/1.0L
c = 0.11 moles/L
since, doing HSC Chem, we can assume HCl dissociates completely, we can say
[H+] = 0.11 M
so,
pH = -log[H+]
pH = -log[0.11]
pH = 0.95860731484...
pH = 0.96 (2 significant figures)
c = n/v
c = 0.010 moles/1.0L
c = 0.010 moles/L
since, doing HSC Chem, we can assume HCl dissociates completely, we can say
[H+] = 0.010 M
so,
pH = -log[H+]
pH = -log[0.01]
pH = 10
Therefore, adding more HCl to this, let's say 0.10 moles, would increase the concentration.
n = 0.010 moles + 0.10 moles
n = 0.11 moles
Therefore,
c = n/v
c = 0.11 moles/1.0L
c = 0.11 moles/L
since, doing HSC Chem, we can assume HCl dissociates completely, we can say
[H+] = 0.11 M
so,
pH = -log[H+]
pH = -log[0.11]
pH = 0.95860731484...
pH = 0.96 (2 significant figures)
someth1ng
Retired Nov '14
Doesn't even make sense. pH of HCl solution won't be neutral.
girlworld_club
Member
^ i meant *say i had 100ml of water (oops)
someth1ng
Retired Nov '14
The formula says the pH would change...
pH=-log[H+]
[X] means concentration of X.
pH=-log[H+]
[X] means concentration of X.
bedpotato
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When you add water to water (I'm assuming this is what you're trying to say), it self ionises.
H2O + H2O --> H3O+ + OH-
In water, pH = pOH
If water is neutral i.e. a pH of 7, then [H+] = 10^-7
Now pOH.
pOH = 14 - pH = 7
so [OH-] = 10^-7
[H+] = [OH-]
Even if you add more water, [H+] will always equal [OH-], so the pH will remain the same.
Idk how to explain...
H2O + H2O --> H3O+ + OH-
In water, pH = pOH
If water is neutral i.e. a pH of 7, then [H+] = 10^-7
Now pOH.
pOH = 14 - pH = 7
so [OH-] = 10^-7
[H+] = [OH-]
Even if you add more water, [H+] will always equal [OH-], so the pH will remain the same.
Idk how to explain...