Homework Help: Chemistry

Posted by Mary on Wednesday, April 23, 2008 at 10:08pm.

I'm practicing for my lab final and I came across a question I do not understand...

If a 0.092 g sample of a 1:1 mixture of acetylferrocene and ferrocene was separated by column chromatography, and the recovered fractions weighed 0.019 g (acetylferrocene) and 0.020 g (ferrocene), what was the percent recovery of acetylferrocene ?

a. 20.6%
b. 41.3%
c. 21.7%
d. 43.5%

I thought the answer was (a) because .019/.092 x 100 = 20.7, but it is saying the answer is (b). Can anyone please explain this? Thank you.

Chemistry - DrBob222, Wednesday, April 23, 2008 at 10:29pm
Here is how it was done.
0.092 was the total mass of both materials. It was a 1:1 mixture; therefore, each had a mass of 0.092/2 = 0.046 g.
percent recovery then for the one compound is [0.019/0.046]*100 = 41.3%,

I think the secret word is "recovery." If we wanted the percent in the original mixture, then a would be correct; however, when we say recovery, that means, "how much did we get out of what we put in" and this approach usually means we want some quantitative number for the effectiveness of the procedure.
Chemistry - Mary, Wednesday, April 23, 2008 at 10:47pm
Thanks so much for the help, I didn't even consider what you mentioned!

Again, I really appreciate it!

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