Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: patkaand on February 20, 2017, 02:57:41 PM
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Hi guys,
could you please help me out
I made 1000 ppm standard solution of caffeine by dissolving 198,2mg caffeine in 200 ml of purified water.
Than mixture was pipetted to different 50 ml volumetric flask as follows 25 ml, 12.5 ml, 10 ml, 7.5 ml, 5 ml and 2.5 ml and than diluted to volume with purified water.
QUESTIONS IS How to calculate these samples caffeine concentration (ppm)?
It shows on my lab protocol that 25 ml is 100 ppm, 12.5 ml is 50ppm, 10 ml is 40 ppm.
Can not get my head right to answer and tried everything. I really need your help people PRETTY PLEASE!
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I made 1000 ppm standard solution of caffeine by dissolving 198,2mg caffeine in 200 ml of purified water.
This concentration is 10005103 ppm
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??? I am really lost right now... please see attachment.. It is a fragment from Bibby Scientific protocols. :'(
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And that is what I have in results. ??? :-[ :'(
Please help me. This is my 'be or not to be' now.
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My fault. But you did not check. Assuming that this is 1000 at 20 C then
50 ml volumetric flask as follows 25 ml
this gives you twofold dilution ie 500 ppm, and eg 5 ml gives you tenfold dilution ie 100ppm.
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What formula did you use to calculate it?
I need to show my work quite clear with evaluation of my results.
I am on biomedical sciences doing my Graded unit based on Chemistry, Physiology and Pharmacology. Please so keep in mind that I am not a great chemist and need simpler explanation. ;)
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(25/50)x1000=
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I've tried to calculate the concentration for my own. for 25 ml and 12.5 ml it works fine. But for 10, 7.5, 5 and 2.5 it shows some rubbish results.
I also tried the easiest way to calculate C = n/v :rarrow: NOT WORKING!
Tried to do 1000ppm x (total sample vol) / (measured sample vol x 100) :rarrow: NOT WORKING!
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So referring to calculations in protocol (on picture) are they wrong?
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But for 10, 7.5, 5 and 2.5 it shows some rubbish results.
(7.5/50)x1000=150
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OMG GOT IT AT LAST
is 25/50 X 200 not 1000 :D :D :D My grade A saved lmao.
Thank you for help and tips. ;D