Analytical Chem Experiment #5

Toledo Mettler print out.
For those of us who didn't get a print out, what was the meaning of the % KHP given by the Titrator?
I think we are finding the purity of the unknown. Was the F.W. entered as 204.23?
Since I never saw a print out, it would be really nice if someone could share what is supposed to be on it.
What I do have is the volume of base used & % KHP.
Are we supposed to have concentration? Original pH? Graph? Slope represents what?

Standard deviation? RSD?
Thanks -
For now, I'm plugging this into the titration spreadsheet, hoping to come up with something ...

The print out only gives you % KHP, mean % KHP from the 3 trials and calculates standard deviation and RSD. The only thing you should calculate if you don't have the print out is the mean % KHP, standard deviation and RSD. The point of this is to determine how much KHP was in your unknown. The RSD will tell you how precise your trials were. The only things that could have caused a high RSD in this experiment were mass errors and errors with the titrator itself.
The conclusion for this lab is really simple because all you have to do is talk about your % KHP and RSD and reasons for it.

Thanks, Stacy. SD & RSD. It's never pretty. (I moved on to Experiment 8 & it just gets uglier.)

I just find it weird that the % correlates with the grams. As the grams increased, so did the %.
RSD looks like 32 ppt. Great.

What were your 3 percentages?

I think I will be turning in a spreadsheet like we did in Exp 3 &4. I just can't figure for what to take the SD & RSD.
My samples didn't weigh the same, so I don't expect percentage to be the same for each sample. It seems wrong to take the mean of the percentages, unless I figure the percentages also based on the weight of the actual sample.
So, it's back to calculating moles, grams/mole.

My percentages vs Titrator percentages
38.29% 38.25%
36.39% 36.35%
36.15% 36.09%

You shouldn't be calculating your own percentages. You just use the ones the titrator gave you. The SD and RSD are calculated using those. You should just plug in the % the titrator gave you to get mean, SD and RSD. So take average of 38.25, 36.35, and 36.09. Then once you have that get SD and then RSD. That is all you have to do.

OK, so % KHP was supposed to be the same for all samples. Now I get it. It didn't matter what the concentration of the solution was - we measured percent of Hydrogen & that should be the same.
Was percentage high for everybody's first sample?
Are we allowed to throw out an outlier, if we have one, & only ran 3 samples?

I got an RSD of 4.3, so mine were ok. Not sure about throwing one out. You would probably have to do Grubb's to see if you can.

I asked the instructor about throwing one out. I had 3 samples. He said that he told us in class we could throw one out if it "appeared out of whack." Also, he's working on answers to the take-home & hopes to have it on Blackboard tomorrow.