can anyone tell how to find the range of ph values of a mixture when its acting like a buffer from the titration curve?
or how to kind Ka using the curve? plzzz
x
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kriztinae
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- 24-06-2004 09:07
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- 24-06-2004 09:14
(Original post by kriztinae)
can anyone tell how to find the range of ph values of a mixture when its acting like a buffer from the titration curve?
or how to kind Ka using the curve? plzzz
because when alkali is added, the pH value is almost constant -
kriztinae
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- 24-06-2004 09:15
(Original post by keisiuho)
the horizontal region
because when alkali is added, the pH value is almost constant
but i believe you coz it makes more sence
how abt ka? -
tammypotato
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- 24-06-2004 09:16
how do u calculate the pH of the buffer?
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kriztinae
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- 24-06-2004 09:17
(Original post by tammypotato)
how do u calculate the pH of the buffer?
dont worry just go study! -
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- 24-06-2004 09:17
(Original post by kriztinae)
no hehe
dont worry just go study! -
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- 24-06-2004 09:19
(Original post by kriztinae)
thats what i thought! but on the mark scheme its wrong! argg
but i believe you coz it makes more sence
how abt ka?
From the titration curve, find the pH when half of the volume of the base at the end point is added.
at that point, half of the acid is neutralised.
so [HA] = [A-]
Ka = [H+]
pKa = pH at that point -
kriztinae
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- 24-06-2004 09:20
(Original post by tammypotato)
lol no im asking how do u calcul8 the ph of a buffer coz im stuck.
well
ka = [H+][A-]/ [HA]
you will be given Ka, maybe the conns of A- and HA if not you will be given enough information to calculate them!
then you find [H+] using that equation
then use ph = -long [H+]
got it? -
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- 24-06-2004 09:22
(Original post by kriztinae)
oh lol im good at this!
well
ka = [H+][A-]/ [HA]
you will be given Ka, maybe the conns of A- and HA if not you will be given enough information to calculate them!
then you find [H+] using that equation
then use ph = -long [H+]
got it?
ph= pka- log(acid/salt)... -
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- 24-06-2004 09:33
(Original post by kriztinae)
oh lol im good at this!
well
ka = [H+][A-]/ [HA]
you will be given Ka, maybe the conns of A- and HA if not you will be given enough information to calculate them!
then you find [H+] using that equation
then use ph = -long [H+]
got it? -
tammypotato
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- 24-06-2004 09:34
(Original post by Tanaz)
there is also an easier way of learning this: u could just use this equation:
ph= pka- log(acid/salt)... -
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- 24-06-2004 09:41
(Original post by tammypotato)
lol no im asking how do u calcul8 the ph of a buffer coz im stuck.
PH=-log concentration of H+ ions -
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- 24-06-2004 09:45
(Original post by kriztinae)
oh lol im good at this!
well
ka = [H+][A-]/ [HA]
you will be given Ka, maybe the conns of A- and HA if not you will be given enough information to calculate them!
then you find [H+] using that equation
then use ph = -long [H+]
got it?
2) moles alkali
3) moles acid left = moles acid - moles alkali
4) concentration acid left
5) concentration of alkali added
Then substitute the values into the Ka=[H+][A-]/[HA] and rearrange for [H+]
With A- being the concentration of alkali added and HA being the concentraion of acid left.
Then work out the pH through logging.
If the alkali is found to be in excess just work out the conctration of the excess and from that work out pOH, with pH = 14 - pOH. -
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- 24-06-2004 09:45
(Original post by zazy)
ok , basically without the graph the hydrogen concentration is equal to ka multiplied by the concentration of the acid/concentration of the salt
PH=-log concentration of H+ ions -
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- 24-06-2004 09:51
hey everyone, I have to go now
good luck! -
madmazda86
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- 24-06-2004 09:56
(Original post by kingpong)
If the alkali is found to be in excess just work out the conctration of the excess and from that work out pOH, with pH = 14 - pOH. -
kriztinae
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- 24-06-2004 09:58
(Original post by keisiuho)
hey everyone, I have to go now
good luck!
ok well good luck!! you be fine!! -
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- 24-06-2004 10:05
(Original post by madmazda86)
Arrrrgh, are they gonna give questions where the damn thing's in excess? *sob*
Remember we can only get questions on calculating the pH of acid buffers, not alkaline buffers.
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Updated: June 24, 2004
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