ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: liuetenant on June 14, 2011, 03:02:45 pm
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JUst to recap, how do we all do significant figures again???
if it's a multi step question, do we use the round off answer or the asnwer in the calculator?
the thing is, i jsut did VCAA 2009 Q10, and they used the rounded off answer to calculate the final mass....whereas i did not and used the calculator answer...safe to say they got 0.19mg, whilst mine was 0.2mg..so would i be wrong? :O
any help is much appreciated!
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that is the same answer except yours is one sig fig over their's (watch your sig figs)
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so what would i do? used the rounded answer from the prevous question to work out my subsequent question like they did? or use my unrounded answer?
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I didn't make this, but it's good shit.
a + b = c: (or -)
c is rounded to the least number of decimal places of a or b:
Eg: 20.21 + 1.22 = 21.43 and 21.23 + 6.2 = 27.4
a x b = c: (or /)
this is the one most people are familiar with; c is rounded to least number of sig figs of a or b
Eg: 12.0 x 4.00 = 48.0
a^b = c:
If b has x decimal places, c is rounded to x sig figs:
Eg 10^1.24 = 17. (the . is there for a reason, it signifies that both the 1 and the 7 are significant)
NB: If you're wide awake you would wonder what would happen if you get something like 4^3 or 10^5, with no decimal places; I did some experimenting and worked out that it's best to leave it as 10^x: so 4^3 = 10^2 ("no" significant figures) and 10^5 = 10^5. Try it out for yourself if you don't believe me.
log(base a) b = c
If b has y sig figs, then c is rounded to y decimal places:
Eg: [H+] = 0.00100 M => pH = -log(10)0.00100 = 3.000
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Always use the numbers in your calculator.
Example, if you got 4.5463405 in your calculator and the information given is to 3 sig figs then
you write down 4.55 on the paper but leave the 4.5463405 in the calculator to be used for the
next calculation
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alriteo, that helps. thanks!