|MadSci Network: Chemistry|
Mr. Nelson, Without reciting the rules for determining significant numbers which can be read from the text book, I will attempt to answer your question. If you look at the number carefully you will note that there is a unit of measurement at the end of the number, which I noticed is absent from your question. This then becomes the fundamental error. In science and in the particular case at hand, numbers are not theoretical abstractions that indicate mearly the magnitude away from the theoretical point on the number line of (0,0); but rather have a dual dimension which indicate magnitude and (and this is of utmost importance) the quantity being measured. In the case at hand, the quantity is the mass of something in grams. This number then comes from the concrete fact that something was measured to be 24.090grams. Since this is true, the number given as the test question demonstrates or indicates that the instrument used to measure whatever was measured was precise to 1/1000 of 1 gram and the last digit is understood to be estimated. This you have experienced in the lab yourself. If the instrument used is precise to that degree, then the zeros that comes between non zero digits could very well have been any magnitude from 0, in this case meaning "zero tenths of a gram" to a magnitude of nine tenths of a gram. The fact that that particular place in the decimal scheme is a zero is of no consequence since it could have been any digit as I've noted above. The zero at the end of the number and to the right of the decimal shows the precision of the instrument being used and is understood to be estimated. Again, this zero is not acting as a place holder but could have very well been any digit. Hope this satisfies your curiosity
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