CHEMISTRY Question: Genius needed

[bleuiko]

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?

 

[Phil21]

3.2

 

[GoldenBear]

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

 

[bleuiko]

let's pretend i have to answer this question or eath will blow up

^^BUMP for the sake of humanity ^^

 

[eakers]

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]

ps also remember that you have a strong base and week acid.

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

 

[Splork]

Hmm...I think the weak acid and strong base plays a major roll.

-sp

 

[bleuiko]

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]

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.

 

[Phil21]

3.2!!!

 

[bleuiko]

<< 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

 

[Splork]

water is slightly acidic, but for all practical purposes it's ph is 7.

-sp

 

[Passions]

3.2

 

[bleuiko]

hummm... thanks guys, back to studying and hitting the refresh button

 

[datalink7]

I concur with the 3.2











(This is basically a bump for ya. DOn't remember much chem)

 

[loogie]

3.2!!!

 

[bleuiko]

/me looks for a shotgun...

 

[FrontlineWarrior]

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]

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

 

[Hamburgerpimp]

3.2

 

[goodoptics]

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.