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Unformatted text preview: Chemical Measurements C125 Prelab C125 – Exp er im en tal Che m i st ry 1 Purpose • Investigate what is meant by: – Precision – Accuracy • Determine the density of water: – Differences in various pieces of glassware – Analyzing error of glassware Important Terms for This Experiment • Aliquot • Significant digits/figures • Density • Accuracy • % error • Uncertainty • Precision • Standard deviation Definition of Aliquot • The portion of the measurement added • The amount of the substance that is to be measured that is added to the collection vessel • In this experiment, we will be using an aliquot of 10ml of water for each trial Definition of Significant Figures • The number of meaningful digits in a measured or calculated quantity • Digits beyond the significant figures are due to systematic and random error of the glassware that you are using and your technique when using that glassware • The last digit is understood to be the digit of uncertainty in the measurement Rules for Significant Figures • Any nonzero digit in a measurement is significant • Zeros between nonzero digits are significant • Zeros to the left of the 1 st nonzero digit are insignificant • Zeros to the right of the last nonzero digit are significant Rules for Rounding • Wait until the end of the calculation to round to the appropriate amount of significant figures • If the digit removed is more than 5 increase the preceding number • If the digit removed is less than 5 do not change the preceding number • If the digit removed is 5: – Increase preceeding number if it is odd – Do not change the preceeding number if it is even Calculation Rules for Significant Digits/Figures • Adding/Subtracting – Answer cannot have more digits to the right of the decimal point than either of the original numbers – 2.097 – 0.12 = 1.977 • Because the 2 nd number only goes to the hundreths place, the answer is 1.98 Calculation Rules for Significant Digits/Figures • Multiplying/Dividing –...
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This note was uploaded on 11/02/2009 for the course CHEM C125 taught by Professor Staff during the Fall '08 term at IUPUI.
 Fall '08
 STAFF
 Chemistry

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