CHEMISTRY Question: Genius needed

bleuiko

Golden Member
Feb 22, 2001
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Chem final is tomorrow, and I can't figure out this problem on the practice test, help?

What is the pH at the stoichiometric point for the titration of 0.100 M CH3COOH(aq) with 0.100 M KOH(aq)? The value of Ka for acetic acid is 1.8E-5.

A) 8.72
B) 5.28
C) 9.26
D) 8.89
E) 7.00


*Cross fingers* com'on there's got to be a chemist, bioengineer or a professor among us... com'on com'on

EDIT: I don't think AOL has anything for this... or do they? they have homework help for college students too?
 

GoldenBear

Banned
Mar 2, 2000
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Try to find someone with AOL (seriously). There's bound to be someone in the homework section that'll help.
 

bleuiko

Golden Member
Feb 22, 2001
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let's pretend i have to answer this question or eath will blow up

^^BUMP for the sake of humanity ^^
 

eakers

Lifer
Aug 14, 2000
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hederson hasselback
ph= pka + log(acid/base)

those are the concentrations (remember that at the s. point the number of moles of base = number moles of acid)

recall that the pka = -logka

hope that helps.

*kat. <-- chem wiz.
 

eakers

Lifer
Aug 14, 2000
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ps also remember that you have a strong base and week acid.

*kat. <-- thinking that might be a factor
 

bleuiko

Golden Member
Feb 22, 2001
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i tried that.

ph = pka + log(acid/base)
ph = -log(1.8E-5) + log(.1/.1)
ph = 4.74

None of the above?? that's not an answer... :(
 

rich1er

Senior member
Jan 3, 2000
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eaker's is right:) anyways you have a strong acid and weak base. Just plug it into the equation. Also not that water has ph 7 or 8, i forgot already. So make sure your answer is reasonable.
 

bleuiko

Golden Member
Feb 22, 2001
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<< The answer is C. >>



14-4.74?

but wouldn't that give me the pOH?

phil: that's not one of the choices... i dunno what to say
 

FrontlineWarrior

Diamond Member
Apr 19, 2000
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silly goose it's pH 7. strong base will neutralize all of the acid. the weak acid part only comes into play when there isn't enough base to neutralize it, but it's not the case here, as you have a 1:1 ratio.
 

FrontlineWarrior

Diamond Member
Apr 19, 2000
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One thing I'm not sure about is whether the conjugate base CH3COO- will attack the water after the initial reaction. IF that happens, the solution will be *slightly* basic. 3.2 is no where near the correct answer because you can't have an acidic solution by adding strong base in a 1:1 ratio. If I had to guess I would pick 7.00
 

goodoptics

Platinum Member
Aug 18, 2000
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8.89


don't think henderson-hasslebach is suitable for this problem since it wants the pH value at equilibrium, not within the buffer region. Since this is a strong base-weak acid titration, at equilibrium, you may use Kb=x^2/ini. concentration = Kwater/Ka
or x = sqrt(.1*(1*10^14)/(1.8*10^-5)) = 5.12764.. = pOH
pH = 14 - pOH = 14 - 5.12764 = 8.87236..
The closet answer is D) 8.89

more chem stuff here.