come on chem chums (1 Viewer)

[Maddy1012]

I have never EVER understood this. Ive tried so hard lol.
I dont understand why you only have to rinse the conical flasks and volumetric flasks with distilled water... It says it doesnt change the moles of the solution... but how cant it? When you rinse is with water then add the solution its going to change the moles coz that is why you rinse the pippette and burette with the solution... oh god im confusing myself here.

 

[Forbidden.]

Because water has equal amounts of H⁺ and OH^- ions and in the end you are supposed to neutralise whatever is in the flask.

 

[brenton1987]

I dont understand why you only have to rinse the conical flasks and volumetric flasks with distilled water... It says it doesnt change the moles of the solution... but how cant it?

It doesnt change the moles of solution, it changes the molarity.

If you add 100 mL of 0.01 M acid to a flask, there is 0.001 mol of acid in the flask. Even if there is 20 mL of residual water you have still only added 0.001 mol. The water wont react with the analyte or the titrant so it doesnt factor into the calculations.

 

[yoakim]

So basically, you know the numbers in front of a balanced chemical equation right, adding water doesn't affect that, but affects the CONCENTRATION of the solution. ie: adding water into an HCl solution makes it DILUTE, but it does not become a weak acid.

 

[jlnWind]

I have never EVER understood this. Ive tried so hard lol.
I dont understand why you only have to rinse the conical flasks and volumetric flasks with distilled water... It says it doesnt change the moles of the solution... but how cant it? When you rinse is with water then add the solution its going to change the moles coz that is why you rinse the pippette and burette with the solution... oh god im confusing myself here.

Hey Maddy, as the others have mentioned it does not affect amount of moles, but the concentration.

The burette and pipette must be rinsed with a portion of the solution because they are measuring quantities of the solution. A film of water remaining on the inside surface would effectively lower the accuracy of your experiment.

This differs from the volumetric or conical flasks used for titration because (as everyone has said) the water will not affect the amount of moles which will react with the titrant.

Similarly when performing titration, as we nearing the end point, as opposed to letting the titrant (in burette) flow through we only allow portions of a drop to fall in at a time. This is done by letting the drop build up on the tip before washing it in with water since this water has no effect on the moles reacting and entering the titrating flask.