Tilia Posted February 21, 2009 Report Share Posted February 21, 2009 (edited) We did a lab about how much ethanoic acid vinegar contained. Since the value stated on the vinegar bottle was in percent, I gave my answer in percent, but now I don't know how to state the uncertainty. According to our measurements, 6.2 % of the vinegar was ethanoic acid and the percentage uncertainty was 7.203 %. If I write 6.2 % plusminus 7.203 %, does that mean that 7.203 is "the percentage uncertainty of the percentage value"? Or should I write 6.2 % plusminus 0.4 %, like the percentage as the unit? I'm quite confused and the report is due Monday, can someone help me out, please? By the way, titration can only be used for acid/bases, right? Edited February 21, 2009 by Tilia Reply Link to post Share on other sites More sharing options...
KLSmash Posted February 21, 2009 Report Share Posted February 21, 2009 Whatever volume of vinegar you used, take 6.2% of that and that's your volume of ethanoic acid. Now, calculate 7.203% of the volume of the ethanoic acid, and that would be your uncertainty for it. So if you used 100mL of vinegar, you'd have 6.2 +- 0.5 mL Reply Link to post Share on other sites More sharing options...
Parami143_Kella Posted February 21, 2009 Report Share Posted February 21, 2009 Yes titration can be used for acid/ base. Reply Link to post Share on other sites More sharing options...
Tilia Posted February 21, 2009 Author Report Share Posted February 21, 2009 [quote name='KLSmash' post='37600' date='Feb 21 2009, 02:38 PM']Whatever volume of vinegar you used, take 6.2% of that and that's your volume of ethanoic acid. Now, calculate 7.203% of the volume of the ethanoic acid, and that would be your uncertainty for it. So if you used 100mL of vinegar, you'd have 6.2 +- 0.5 mL[/quote] Yeah, I know. But since literature value was in percent, I presented my answer as percentage too. Or is there some rule saying that I shouldn't do that? Reply Link to post Share on other sites More sharing options...
KLSmash Posted February 22, 2009 Report Share Posted February 22, 2009 From my knowledge-there's no rule that says you have to write it as a percent. Reply Link to post Share on other sites More sharing options...
slavenweb Posted February 22, 2009 Report Share Posted February 22, 2009 [quote name='Tilia' post='37591' date='Feb 21 2009, 01:20 PM']By the way, titration can only be used for acid/bases, right?[/quote] it can be used for acid and base neutralization reactions but other reactions can also be applied to titrimetry. there are several techniques. A familiar one may be redox reaction titrations. So it is not ONLy for acid/bases Reply Link to post Share on other sites More sharing options...
GNRS Posted February 22, 2009 Report Share Posted February 22, 2009 [quote name='Tilia' post='37591' date='Feb 21 2009, 01:20 PM']Or should I write 6.2 % plusminus 0.4 %, like the percentage as the unit?[/quote] I think that this is the correct answer. If the initial data is given in % you have to present your results in % (if they don't give other instructions). If you take this 0.4% of absolute uncertainty, it will be a correct value for all volumes [e.g. if you have 2L, it will be (0.124+-0.008)L]. Reply Link to post Share on other sites More sharing options...
Tilia Posted February 22, 2009 Author Report Share Posted February 22, 2009 Thanks! I really want to do well on this report and all this uncertainty confused me. Reply Link to post Share on other sites More sharing options...
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