CHEM 1&2 Lab Manual & worksheets pg 231

CHEM 1&2 Lab Manual & worksheets pg 231 -...

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Significant Figures General Chemistry I and II Lab Manual Dakota State University page 231 of 232 gives you the number of significant figures. However, analog devices are a little more tricky. Analogue devices have some form of scale, with an indicator. In an old-fashioned thermometer, the scale is on the side, with the indicator being the level of the liquid. Other instruments, like voltmeters, for example, had a scale (usually with a portion mirrored so you always look at it from the same angle by lining up the pointer so you cannot see the image) with a pointer. Whenever you have an instrument like this, you can always estimate one significant figure more than the scale on the instrument. Take the following example; suppose you
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Unformatted text preview: are measuring the liquid in a graduated cylinder, with markings every 0.1 mL, as shown in the figure to the left. We know that the liquid level is above 8.7, but less than 8.8; so what is it? (Forgive the squiggly line; it was drawn by hand.) Well, how far up does it look to you? Maybe 70% of the way? OK, so you record 8.77 in your records. Don’t worry that the last number is a guess, this is what a significant figure means! The reader knows that last 7 is not significant, but if you don’t record it, then the reader will assume that the first 7 was a guess. This is also why you need to record zeros; if the line were exactly on the 8.7 line, record it as 8.70, so the reader knows that your estimate is to 0.01, not just 0.1....
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This note was uploaded on 01/27/2012 for the course CHM 2045 taught by Professor Josephwalter during the Fall '11 term at Dakota State.

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