Solving Yield Gone Wrong in Chemistry Lab

[FaNgS]

Yield gone wrong!

Hi, I just have a question about some practical things in a chemistry lab and errors.

We carried out a recrystallization experiment of benzoic acid and napthalene :zzz: last week and during one of the steps where i was supposed to transfer my pure sample of benzoic acid from a 5mm calibrated test tube onto a filter paper and dry in an electric oven to weigh the mass obtained and calculate the %yield (all of the apparatus used is for macroscale organic chemistry experiments...oh i forgot to mention that this is an organic chemistry experiment, unless its obvious ) i forgot to measure the mass of the filter paper itself and it seems that the filter papers have quite big differences in mass...my friend recorded a filter paper mass of 0.766g
so now all i have is the weight of the pure benzoic acid and filter paper which is 0.879g...so i can't find the mass of pure benzoic acid now since i don't know the weight of the filter paper and hence can't calculate the yeild.
my question is if there is any method to obtain the mass of my filter paper? is it a good idea to measure the mass of a few filter papers and take the average of them and use that value?

fyi i started with 0.103g of impure benzoic acid :shy:

thanks :)

 

[dmoravec]

If the weights vary quite a bit you could use some simple statistics (st. dev or something) to give a good idea to the reader what range of error you might have. It should still be mentioned in your report/write-up that the filter mass wasn't taken originally and that an average mass of a few filters was substituted.

 

[chemisttree]

remove the benzoic acid from the dry filter paper and rinse with solvent to completely remove it. Use acetone. dry filter paper and weigh.

Next time write out your lab leaving spaces (underlined) for data you need to collect. I know it is a pain, but it works. No need to do this once you become familiar with routine tasks.

 

[FaNgS]

thanks for the advice guys :) i'll keep it in mind

chemisttree: remove the benzoic acid from the dry filter paper and rinse with solvent to completely remove it. Use acetone. dry filter paper and weigh.

i'll definitely keep that in mind

(sorry i don't know how to use all the exact functions in here yet)

 

[dmoravec]

If you are going to be washing the filter paper with solvent to remove the benzoic acid it would be a good idea to do the same procedure to a unused filter. This would let you know if the solvent is extracting anything out of the filter (which shouldn't happen, but its still a good thing to check)

 

[FaNgS]

really good point dmoravec thanks :)