[eric343]

Quote:

Originally Posted by dffman2001 ok, its relatively simple CH3COOH + NaOH -> H20 +NaCH3COO 0.014175 L x 0.1mol/L x 1/1 x 1/0.01 L volume of NaOH x concentration of NaOH x molar ratio x volume of vinegar so the concentration of the vinegar is 0.147175 mol/L if i did this correctly. hope this helps!

Equation isn't right... it's a weak acid, and therefore the reaction is reversible and doesn't proceed to completion. This is what I wrote down...
CH3COOH + H2O <--> CH3COO- + H3O+
shifts in reverse:
CH3COOH + OH- --> CH3COO- + H20

I don't think you can calculate it that easily... I may be wrong though.

Oh, by the way, the 14.175mL was for the HCl, not the CH3COOH -- the correct value is 8.45mL.

 

[MuZI]

Yeah, i doubt it can be done that easily.
That is BASIC stoich...

 

[MuZI]

Quote:

Originally Posted by dffman2001 therefore Le Chatalier's principle will state that the equilibrium will drive towards the H3O+ until all the CH3COOH is consumed - which is at the equivalence point

Are you sure that is when neautralization is met?

 

[MuZI]

CH3COOH + H2O <--> CH3COO- + H3O+
shifts in reverse:
CH3COOH + OH- --> CH3COO- + H20
QUOTE]

Yeah, the proton transfer of H+ right?

From Acid -> Base, that is what i thought at first...but what would you do with that in the mole bridge!?

 

[dffman2001]

alright, there are several steps to follow in an acid bbase reaction.

1. species list

create your species list and determine which will ionize and which will not

2. Pick strongest acid and strongest base

3. transfer 1 proton

4. draw your arrows

follow these rules for drawing the equilibriumn arrows:

a) the reaction is quantitative (not equilibrium) if OH and a fairly strong acid is present
or H30+ and fairly strong base

b) the reaction is equilibrium if the above is not the case. In the equilibrium, the third arrow denoting the favored side will point from the stronger acid to the weaker acid

 

[dffman2001]

Quote:

Originally Posted by eric343 Equation isn't right... it's a weak acid, and therefore the reaction is reversible and doesn't proceed to completion. This is what I wrote down... CH3COOH + H2O <--> CH3COO- + H3O+ shifts in reverse: CH3COOH + OH- --> CH3COO- + H20

well, when your CH3COOH ionizes to CH3COO- + H3O+ and then you add the OH- from the NaOH, the H3O+ will react first, because it is the stronger acid as compared to the CH3COOH.

 

[MuZI]

CH3COOH- is amphiprotic...how fun...that makes the equation even better.

 

[dffman2001]

although the acid is weak, it essentiall reacts to completion with the hydroxide ion, a very strong base.

so its an equilibrium, but the products are favored so incredibly greatly that we can treat it as a quantitative (simple stoich) reaction

 

[MuZI]

Hmmm, that is true that they still equal teh same once they join, but that isn`t the point, the answer of concentration isn`t simple because of the fact it is weak...it is not lopsided which must be taken into affect in the equation.

 

[dffman2001]

take a look at this webpage, it is just some random one i pulled off of google.
it leads you through the steps with calculating concentration of vinegar through titration

http://www.geocities.com/CapeCanaver.../lab-C-15.html

 

[DanT]

It been so long since I'v done this I don't remember anything. From this page they are searching something else but here goes In method 2nd paragraph. Only the bold part relate to your question. It basicly tell that at equilibrium all the acid has been neutralise and gone to completion.

http://www2.volstate.edu/CHEM/1120/Labs/WeakAcid.htm

Quote:

However, we still need to determine the equilibrium concentration of HA. Unfortunately, this is difficult to determine since most methods of analysis will change the concentration of the HA and cause the equilibrium to shift. Since we can not directly determine the [HA] , we need to find the initial concentration of HA. To do this we need to neutralize all of the HA present by titrating it with a strong base of known concentration. As the H+ from the weak acid is neutralized by the strong base, the equilibrium will shift to the right generating more H+. This process will continue as the strong base is added until all of the HA has been converted to H + and A- (equivalence point). This is no longer an equilibrium solution, it only contains A-(aq), Na +(aq), and H2O(l). For example, if 23.6 mL of 0.321 M NaOH were required to neutralize 50.0 mL of the HA solution, then the initial concentration of HA would have been: MHAVHA = MNaOHVNaOH MHA = MNaOH VNaOH / VHA MHA = 0.321 x 23.6 / 50.0 MHA = 0.152 M

 

[hongda]

Figure out the pH of a solution containing only NaCH3COO. That should be pH where the condition for stoichometry is met. It will be slightly basic solution.

 

[MuZI]

Well he is suppsoed to do it 2 ways, using stoich and using the pH method i think..

 

[Textual Intercou]

you're thinking too hard. it's true that there are some pretty nasty calculations (for high school, at any rate) that involve Ka values, but this isn't one of them.

vinegar is a weak acid so it'll only partially dissociate in water. However, sodium hydroxide is a strong base, so it'll always react with any available H+ ions, making only the salt and water. thanks to the le chatlier principle, even a weak acid will dissociate if there's no H+ ions, and once you put in an excess of strong base (or just enough to reach equivalence point, rather) the fact that vinegar is weak doesn't matter. after all, Ka is just a way of relating the concentration of undissociated to dissociated ions...if NaOH is sucking up all the hydronium, the Ka of the acid isn't important.

so it is just as simple as comparing the molarity/volume at the equivalence point. I could be wrong, as it's been a year since I've taken this kind of chemistry, but I'm pretty sure about this.

hey, if I'm right you can repay me by letting The Terabyte and me listen to your setup

(we're in Edmonds)



EDIT: bah, dffman2001 aleady said it hours ago. oh well, you can still invite terabyte and I over anyway

 

[eric343]

Quote:

Originally Posted by Textual Intercou hey, if I'm right you can repay me by letting The Terabyte and me listen to your setup (we're in Edmonds)

Who's Terabyte?

But hey, you guys are welcome to come over and have a listen. Unfortunately, I've got finals this week and next, but perhaps the evening of Friday, June 4th?