Are [OH] and [H30] always equal at equivalence point?

[GomerPyle]

So at equivalence point, the added base concentration equals the anylate acid concentration. Does that also mean that [OH] equals [H30+] at equivalence point?

[OH] = [H30+] at PH 7 obviously...

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[FeinMS]

I don't have a logical reasoning behind my answer, but I've seen many equivalence points at pH other than 7. So equivalence point doesn't necessarily mean [H+]=[-OH]. Correct me if I'm wrong.

 

[deh2ase]

This is true if you are neutralizing a strong base with a strong acid, pH = 7 thus OH- = H+. If you are neutralizing a weak acid or a weak base the eq. point will not be at pH = 7 because it forms a conjugate acid or conjugate base.

 

[HesitantManatee]

So at equivalence point, the added base concentration equals the anylate acid concentration. Does that also mean that [OH] equals [H30+] at equivalence point?

[OH] = [H30+] at PH 7 obviously...

In titration their are only two situations . Strong by Weak and Strong by Strong. In each case one reagent must be strong. In Strong by Strong titration the equivalence point is always at pH 7. In Strong by weak the equivalence point can either be basic( pH>7) or acidic (pH<7). If the weak reagent is an acid the equivalence point will be basic. If the weak reagent is a base the equivalence point will be acidic. At the equivalence point in both cases the moles of acid will equal the moles of base. But remember neutralizing a weak base will produce its weak conj acid so the pH wont be 7.

 

[GomerPyle]

In titration their are only two situations . Strong by Weak and Strong by Strong. In each case one reagent must be strong. In Strong by Strong titration the equivalence point is always at pH 7. In Strong by weak the equivalence point can either be basic( pH>7) or acidic (pH<7). If the weak reagent is an acid the equivalence point will be basic. If the weak reagent is a base the equivalence point will be acidic. At the equivalence point in both cases the moles of acid will equal the moles of base. But remember neutralizing a weak base will produce its weak conj acid so the pH wont be 7.

Okay. But my question is - is [OH] = [H+] ALWAYS at equivalence point?

Is [OH] = [H+] the same thing as saying concentration of base = concentration of acid? Because [OH] and [H+] are the dissociated forms of the base and acid?

 

[Jepstein30]

Okay. But my question is - is [OH] = [H+] ALWAYS at equivalence point?

Is [OH] = [H+] the same thing as saying concentration of base = concentration of acid? Because [OH] and [H+] are the dissociated forms of the base and acid?

No, they are not always equal at equivalence points.

[OH] is not the same thing as [base]. It is if the base is a strong base and completely hydrolyzes.. but if the base is weak than [base] >> [OH-]. Not all of it is able to hydrolyze, i.e. not all of it 'acts' as a base. Same with acids.

So if its a strong acid by strong base titration, then [OH-] = [H+] which means pH = 7. But if it involves a weak base or acid, than [OH-] >> [H+] leading to a pH > 7 or vice versa.

 

[GomerPyle]

Okay...great, thanks for the clarification. But anytime [OH] = [H] then PH = 7, right?

That is what it says in the answer of one of the questions in AAMC FL 10.

 

[Jepstein30]

Okay...great, thanks for the clarification. But anytime [OH] = [H] then PH = 7, right?

That is what it says in the answer of one of the questions in AAMC FL 10.

Yep. You have one 'acid' for every 'base' .. hence an overall neutral pH.

Just not the case with every titration.

 

[deh2ase]

Okay...great, thanks for the clarification. But anytime [OH] = [H] then PH = 7, right?

That is what it says in the answer of one of the questions in AAMC FL 10.

Yes, since pH + pOH = 14. But just remember that pH of 7 does not always equate to the equivalence point.

 

[GomerPyle]

thx guys..appreciate it.