Acidity and Basicity of titrate and titrant in Acid-Base titration

I want to know that do we always use monoprotic acid and bases in the Acid-Base Titration. And, if the answer is No. Then, I am confused in the definition of Equivalence Point, because I had seen on internet (on Khan academy site) that at Equivalence point moles of acid and bases are equal. (You can also see it below in the image):
  

  

  



[![enter image description here](https://i.stack.imgur.com/P68uT.png)](https://i.stack.imgur.com/P68uT.png)


  

  

  

So, in the lase line they had written that line for which I'm talking about. This line can we wrong, ***if we will use Diprotic acid with Monoprotic base or vice-a-versa***. Because then equal number of moles of acid and bases, will have different number of H+ and OH- ions.
  

Please correct me if I'm going conceptually wrong.




It makes sense to always use a monoprotic strong acid or base as the titrant. The analyte might be monoprotic or polyprotic (you don't have a choice if that is your sample).


In general (any titration, not only acid/base), the equivalence point is reached when the compound of interest in the analyte is used up. You would want a reaction that goes to completion, and be aware of all other reaction apart from the one you are using to quantitate the analyte. For a polyprotic acid or base, you have to know the protonation state before you start. Then, you can titrate either to the first or the second equivalence point, or (let's say you are monitoring with a pH meter) jot down both points and use them in your quantitation.



> 
> I am confused in the definition of Equivalence Point, because I had seen on internet (on Khan academy site) that at Equivalence point moles of acid and bases are equal.
> 
> 
> 


In general, you have to check the stoichiometry of the reaction. In acid/base titrations, the relevant stoichiometry is usually 1:1 because most acids give of protons one at a time, and most bases pick up protons one at a time. However, if you use barium hydroxide, you would have to consider that it contains two hydroxide ions per formula unit, so there would be a factor 2 in your calculations. I know of no reason to use barium hydroxide, though, given that sodium hydroxide is much more soluble.


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There are polyprotic acids that will generate multiple equivalence points during titration. One example is $\ce{H3PO4}$ being titrated by $\ce{NaOH}$.


Initially, you would react $\ce{H3PO4}$ with $\ce{NaOH}$ to form essentially $\ce{H2O}$ and $\ce{NaH2PO4}$ at the first equivalence point. Now, technically, $\ce{NaH2PO4}$ is a salt, and the moles of $\ce{NaOH}$ added should be the same as the moles of the acid $\ce{H3PO4}$. So the last statement of that definition is not necessarily wrong. However, the difference is that $\ce{H2PO4-}$ will serve as the acid to react further upon adding more $\ce{NaOH}$.


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