[BaO]

Which of the following equations describes the predominant reaction that occurs at the equivalence point of a titration between
CH₃COOH(aq) and NaOH (aq)?
A. H⁺(aq) + OH ^- (aq) <-> H₂O (l)
B. CH₃COO^- (aq) +H₂O (l) <-> CH₃COOH(aq) +OH^- (aq)
C CH₃COOH (aq) + NaOH (aq) <-> NaCH₃COO (aq) +H₂O (l)
D. H⁺ (aq) +CH3COO^- (aq) +Na⁺(aq) +OH^- (aq) <-> Na⁺ (aq) +CH₃COO^- (aq) +H₂O(l)

could you please explain what "the predominant reaction that occurs at the equivalence point of a titration " means?  i dont understand it 

thanks very much

[sdekivit]

at the equivalence point you added such an amount of base that just all the acid has reacted, thus all the HAc has been converted to Ac^-.

Thus reaction 2 is the equilibrium at the equivalence point.

[BaO]

and we ignore the base NaOH here because Na+ is a spectator , right?

[Borek]

There is no NaON in the solution at the equivalence point - only sodium acetate. That's by the definition of the equivalence point.

[Yggdrasil]

I think the answer is A.  At the equivalence point, all of the acetic acid has been converted to acetate ion.  If equilibrium B is occuring at the equivalence point, that implies that there is some acetic acid present at the equivalence point, which is not true.

[BaO]

I think the answer is A.

now i'm really confused

[BaO]

oh , i just thought of something : CH3COOH is a weak acid, NaOH is a strong base ,so at equivalence point , the pH > 7 , therefore B is correct , right? i'm not sure if that is the right explanation, please check it for me!!!

[Borek]

I think the answer is A.  At the equivalence point, all of the acetic acid has been converted to acetate ion.  If equilibrium B is occuring at the equivalence point, that implies that there is some acetic acid present at the equivalence point, which is not true.

Every solution containing acetate ions contains some acetic acid, as defined by the dissociation equilibrium.

Think in terms of acetate hydrolyzis.

[Borek]

oh , i just thought of something : CH3COOH is a weak acid, NaOH is a strong base ,so at equivalence point , the pH > 7 , therefore B is correct , right? i'm not sure if that is the right explanation, please check it for me!!!

Just because NaOH is a strong base doesn't mean pH at equivalence point is higher then 7.

Equivalence point is when there is stoichiometric amount of base added to the titrated acid. Thus you have solution of sodium acetate only. CH₃COO^-, being conjugate base of weak acid, is a base - it reacts with water in hydrolyzis reaction. That's B. No other reaction (apart from A) is taking place at the equivalence point. Thing is, equiilbrium concentration of H⁺ and OH^- are 10^-7M. Concentration of OH^- produced in hydrolyzis is much larger and these ions are responsible for the solution pH.