girlworld_club
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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
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
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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...