[ves]

rightioooooooo just when u thought u got rid of my annoying questions:

0.05 moles of acetic acid, 0.05 moles of NaHCO3... (all together in 500mL solution)

Now i hear that NaHCO3 is actually capable of making a buffer on its own???
then doesnt acetic acid interfere and make carb dioxide somehow?
im a bit confused...

[Alberto_Kravina]

Start with the reaction equation

[ves]

ye thats the thing. im not quite sure wat really happens....

[Mitch]

Its not that hard you are mixing an acid with a base.

[constant thinker]

The ions...
Acetic Acid    H⁺   CH₃COO^-
Sodium Bicarbonate    Na⁺   HCO₃^-

I'll give you a simpler example with a mineral acid instead. Then you can figure out the product that you want.

NaHCO₃ + HCl ? NaCl + H₂O + CO₂

Notice what happens with the the carbonate. Then look at what happened with acid.

Borek once told me something about organic acids that I always remember, "They are acids first, organic later."

[ves]

so u reckon:

CH3COOH + HCO3- <--> CH3COO-   +   H2CO3

where the H2CO3 <---> H20 + C02 ??

dodgy? i dunno
but initialy when i have 0.05 moles of acetic and 0.05 moles of NaHCO3 why is the pH around 5.5ish (experimentally)?

[Alberto_Kravina]

so u reckon:

CH3COOH + HCO3- <--> CH3COO-   +   H2CO3

where the H2CO3 <---> H20 + C02 ??

Seems correct

[constant thinker]

I'll second that.

[ves]

um... i appreciate all your help guys but if u want to help out, i'd be so much greater if i didnt get half-ass answers or "its not that hard" or any of that kinda thing. looking thru the forums i think the amount of posts would decrease by 70% if ppl just answered to questions properly.

My question (dismissing the others which no one has tried to answer anyway):

1. why is the pH around 5.5 wen i have 0.05 moles of acetic acid and 0.05 of sodium bicarb in solution?

your meaningful input would be greatly appreciated

[stoneburner]

You want a seat-of-the-pants understanding?

Mixing equimolar amounts of acetic Acid and sodium bicarb gives you sodium acetate and CO2 (after the H2CO2 comes apart). Sodium acetate is rather basic - strong base, weak acid - but the system is flooded with CO2, which is slightly acidic. (water saturated with C02 has a pH of about 3.. So you've got a somewhat basic solution of sodium acetate that is flooded with C02, bringing the pH back towards 3.8. You can do all the math to figure out exactly what it should be, but that's what's happening. The pH will slowly rise as the CO2 slowly diffuses out of the solution, by the way.