[Discosucks]

Hi guys .

so we'v done a back tit ration of aspirin using an acid base titration , the aim is to work out the purity of the aspirin

50ml of NaOH + 10ml ethanol + aprox 1g of asprin  .

First of all a standardization was completed and the NaOH was worked out to be 0.05225M

Then the titration blank of 10ml ethanol and 50 ml NaOH was carried out .
the result was it took 47ml of HCL to reach the end point of the titration .

what i don't understand is how do i use the information gained via the blank to
incorporate it into my calculation .

[Borek]

Blank tells you how much base is needed to reach the end point when there is no aspirin.

[Discosucks]

Ahhhhhh , ok , so 47ml is starting amount of NaOH in the system . and i use this , not 50ml as the amoung in ml of NaOH in the system ??

[AWK]

In back titration you have:
moles of NaOH = sum of moles (aspirin +HCl) - in your case

Note: NaOH slowly hydrolyzes aspirin, hence the titration with HCl should be done relatively fast.