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Unformatted text preview: y of only ±0.1; however, 101.20 implies and
accuracy of ±0.01, ten times the accuracy of the previous number. The “0” will not
figure into any of the calculations, but it is telling the reader that you were very careful in
your measurements (only 10 times more careful than if you write 101.2).
So, what are the rules for significant figures? What is significant, and
what is not? Let’s separate this into two different categories:
Numbers Less than One:
(1) Any non zero number is significant;
(2) Any zero between non zero numbers is significant;
(3) Any zero after the last nonzero number is significant;
(4) Any zero before or after the decimal point, but proceeding the first non zero
number, is NOT significant.
I know, that last one has you confused. We say “it is not significant because it
merely places the decimal point,” to which students typically scream “knowing where the
decimal point is pretty %*$(@ significant!!!” No, actually, it’s pretty %*$(@ important,
but it is not significant. Let me explain a bit further; the number of zeros before the first
nonzero number can change by simply changing the units. For example, there are 4
significant figures in the number 0.2330 mm, but if we convert from millimeters to
meters, this number becomes 0.0002330 m. We should not be able to change the number
of significant figures simply by changing the units, so “0.000” are not significant zeros,
although they are very important.
Numbers Greater than One:
(1) Any non zero number is significant
(2) Any zero between non zero numbers is significant;
(4) Any zero after a decimal point is significant;
(5) if there is no decimal point shown, then any zeros after the last non zero
number is NOT significant, however; Dakota State University page 229 of 232 Significant Figures General Chemistry I and II Lab Manual (6) if there is a decimal point shown, then any zeros after the last non zero
number IS significant
I know your head hurts; have you tried aspirin? This seems like an odd thing, so
why should it matter if I wrote down a simple little “.” or not? I think of it this way, the
author did not HAVE to write down that decimal point, since the zeros place it; thus, if
(s)he does go through the effort of writing it, then the author is trying to tell us
something. Thus, for example, if you ask how much money I have, I might write $100 as
my answer. This means it’s somewhere around $100, but I’m not giving you an exact
number. Maybe it’s as low as $90, or as high as $110; all you have is a ballpark figure.
However, if I write $100. as my answer, notice that I did not have to write that decimal
point. I am telling you that, ±$1, I have 100. Maybe it’s only $99, or as high as $101,
but you know much more precisely how much I have, and the say I tell you that I am
giving you a more exact figure is with the decimal point. Notice that I can get even more
precise by telling you I have $99.32; now you know, to the penny, exactly how m...
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 Fall '11
 Kumar
 Chemistry, pH, The Crucible

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