ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: Triazic on June 13, 2011, 11:57:09 am
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Hi there, just wondering as to the VCAA definition of concordant results. My chemistry teacher taught us that to be concordant, all 3 titres had to be within 0.05ml of each other (ie ALL 3 within the same 0.05).
On one of the VCAA exams (2010) I think concordant results were all within 0.1ml of each other, and on Insight 2011 concordant titres were within 0.2ml of each other (ie middle titre +.1ml, and middle titre -.1ml were acceptable.)
On insight, the following titres were considered concordant: 16.87, 17.03 and 16.93 (all within a range of 0.2ml from lowest titre to highest)
Just wondering is there was a steadfast definition that anybody knows of, because losing marks for something as dumb as this would be pretty shattering.
Also, what's the rule for Gravimetric results? +- whatever grams? Never been to sure of this stuff, just want to clear it up before the exam.
Thanks in advance.
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On one of the VCAA exams (2010) I think concordant results were all within 0.1ml of each other, and on Insight 2011 concordant titres were within 0.2ml of each other (ie middle titre +.1ml, and middle titre -.1ml were acceptable.)
On insight, the following titres were considered concordant: 16.87, 17.03 and 16.93 (all within a range of 0.2ml from lowest titre to highest)
Concordant titres are titres that differ by 0.1mL from the highest to the lowest. (Basically what VCAA has) In the case of the Insight 2011, I think it was a mistake - a few students pointed that out when we di the practice exam in class. However, my teacher pointed out that as there was obviously one titre that was much less?(or more?) that the others, that was the value to omit. I don't see VCAA ever asking what "concordant titres" mean, but I'm sure if given a table for titres, you'd be able to choose the 3 concordant titres in order to find the average titre.
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OK, so .1ml from lowest to highest is correct, but say, like in Insight... now this is unlikely but I want to be sure, if we get a table of four titres, with one titre being obviously out by a far way, but the others all concordant by .2ml, yes .2ml... do we pick the three that are .2ml or just use two that are .1ml concordant.
ie: do we always use the THREE most concordant titres? or is it better to use only TWO that are completely concordant (ie within .1ml of each other)
that being said... I doubt VCAA will do that to us.
And what's the rule for gravimetric? :buck2:
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And what's the rule for gravimetric? :buck2:
You mean when weighing to a constant mass?
I'm sure once you see the values stay constant (Maybe +- 0.01g or something like that ) it has been dried to a constant mass. I remember seeing in a trial exam question a table with around ~7 weighings. I can't remember exactly what you need to do, but I think you just need to know that at that point, as the mass isnt getting significantly lower, all the water has been removed from the precipitate.
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What if you had:
14.30 ml, 14.40 ml, 14.50 ml, 14.60 ml, 14.70 ml, 14.80 ml?
Average the total?
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What if you had:
14.30 ml, 14.40 ml, 14.50 ml, 14.60 ml, 14.70 ml, 14.80 ml?
no idea... but a) that is not going to happen and b) if it did, I would average the total, which is a reasonable enough thing to do.
So in gravimetric, you just take the final value when weighing?
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What if you had:
14.30 ml, 14.40 ml, 14.50 ml, 14.60 ml, 14.70 ml, 14.80 ml?
Average the total?
Pretty much, but that would have to be some shoddy titration you did to get that much of a spread. :P
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So it's pretty much just +/- 0.05 mL between each individual titre, and the diff b/w the lowest titre and the highest titre must theoretically not exceed 0.10 mL?
E.g. 19.00, 19.05, 19.10
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yeah, seems to be the consensus.