Question

Why is it ok to wash the sides of a flask with DI water during titration even though you are diluting the acid present?

Answer 1

Because the mols of acid don't change with the amount of solvent present.

---

Titration relies on merely knowing the number of mols of acid. If you know the initial volume you pipetted into the Erlenmeyer flask you do the titration in, and you know the concentration WITHIN that volume, you know the mols that were transferred.

Since the mols are independent of what volume of solvent you have (the mols being of the SOLUTE), adding more water makes no difference as to what number of mols of acid you involve in the titration.

And furthermore, since mols are an extensive quantity, you can scale the system to account for the fact you used a certain aliquot.

If you started with a `"200.00 mL"` volumetric flask to prepare your acid solution, but used a `"10.00 mL"` aliquot of it for the titration, you can scale the number of mols from the `"10.00 mL"` you titrated to the `"200.00 mL"` you had of the original solution.