Homework Help: chemistry

Posted by hannah on Tuesday, March 19, 2013 at 4:50pm.

Acetic acid, CH3CO2H, is the active ingredient in vinegar. It's often abbreviated "HOAc". Vinegar is acidic because acetic acid makes H3O+ when it partially ionizes in water:
HOAc(aq) + H2O H3O+(aq) + OAc–(aq)
Suppose that you have a solution of acetic acid in water that is in equilibrium. How will the acidity of this solution change if you do each of these things to it?

(a) Add more acetic acid (HOAc)
The solution will become less acidic (i.e. [H+] will decrease).
The solution will become more acidic (i.e. [H+] will increase).
The acidity of the solution will not change.

(b) Add sodium acetate (NaOAc)

The solution will become less acidic.
The acidity of the solution will not change.
The solution will become more acidic.

(c) Add NaCl
The solution will become less acidic.
The solution will become more acidic.
The acidity of the solution will not change.

(d) Add Ag+(aq), which reacts with acetate ions to make a precipitate: Ag+(aq) + OAc–(aq) AgOAc(s)
The solution will become more acidic.
The acidity of the solution will not change.
The solution will become less acidic.

a)more acidic?
b)less acidic?
c)will noit chnage
d)less

chemistry - DrBob222, Tuesday, March 19, 2013 at 6:25pm
All of these are problems that you solve with Le Chatelier's Principle. In not so eloquent terms this principle says that a system in equilibrium will shift so as to try to undo what we do to it.

I'll help you get started with one or two.
b. Also can be HAc.
HOAc + H2O ==> H^+ + OAc^-
If you add NaOAc, which ionizes as Na^+ + OAc^-, you have added OAc ions to the HOAc equilibrium. The system will shift to try to use the added OAc^-. It wil shift to the left, which reduces OAc^- and it reduces H^+ at the same time. It also increases HOAc.

d. HOAc ==> H^+ + OAc^-
Add Ag^+ + OAc^- to form AgOAc ppt. That means you have removed OAc^- from solution, the reaction will shift to form more OAc^-; therefore, (HOAc) is smaller, (H^+) is larger.
chemistry - hannah, Tuesday, March 19, 2013 at 7:54pm
thanks! were my c and a correct?
chemistry - DrBob222, Tuesday, March 19, 2013 at 8:15pm
I didn't see an answer for a and c. (or any of the others)
chemistry - hannah, Wednesday, March 20, 2013 at 5:56am
at the bottom i put a)more acidic?
b)less acidic?
c)will noit chnage
d)less

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