Cleaning Glasswear

[redxman]

I always get these questions wrong, don't know why. So can someone help me out.

What do you clean the pipette with

What do you clean the burette with

and what do you clean the volumetric glass with.

Thank you.

[t35t]

General rule of thumB: the pipette and the burette are always cleaned with the solution that they are washed in- cleaning say the burette with distilled water would in fact dilute what ever you intend to put in it. That's the same for the burette.
The volumetric fflask tends to be cleaned with water- as the pipette containing the accurate concentration of the aliquot to be delivered is unaffected and remains the same as you know specifically that what your diluting is the correct amount. I'm cautious about cleaning the volumetric flaask with the solution that it will contain, because if that *were* to be done, the concentration would increase- as you're adding the amount of mol from the pipette on top of what's already inside the volumetric flask... Things get much more complicated with reverse order and normal-order titrations- not to mention back titrations too

In a normal order titration, in which the known solution is within the burette, neutralising the unknown solution in the volumetric flask, the addition of water to the burette would firstly result in a more dilute known concentration- so say if HCL was in the burette, the addition of water would dilute the concentration of known HCl, as C=n/V is affected by a greater volume. Therefore, when carrying out the titration, as the acid or the known concentration is now weaker, a greater titre woud be required would be required to neutralise the *more* concentrated unknown solution. Hence, when doing calculations, that is, finding the mole of the unknown, you would do n=CxV- as V is now greater, multiplied with C, it will give the impression that the mole required of the unknown solution is now greater. Hence. rinsing the burette with water would result in a higher concentration of unknown calculated.

In a reverse order titration- it's bascially what I said but now inversed. As now the unknown is in the burette, any addition of water would result in a dilution. Hence, when titrating, the titre of the unknown is now less, as it is readily neutralised by the strong acid/ known concentration in the volumetric flask.

ANd then there's back titrations which complicates things a bit. If say, the titre volume has increased, then therefore the calculated moles would also increase- so thus, when subtracting the moles in excess from the original moles, it appears as if that only a small amount of moles has reacted as the moles in excess is now greater.

[redxman]

thanks man, you don't know how much this helps