Ch 2 Student Notes

# Ch 2 Student Notes - 1 Chapter 2 Measurements in Chemistry...

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1 Chapter 2 Measurements in Chemistry Standard measuring device Standard scale gram (g)

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2 Reliability of Measurements Accuracy closeness to true value Precision reproducibility Example: 98.6 o F 98.5 o F 98.7 o F average: o F + 0.1 o F precision: 0.1 o F
3 Ch. 2.1 Measurement Systems “English” metric

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4 Ch. 2.2 Metric System Units base unit =
5 base unit = mass vs weight

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6 base unit =
7 10cm x 10cm x 10cm 1 L = 1000 mL

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8 Table 2.1 Common Metric System Prefixes You must know all of these for exams and quizzes.
9 Ch. 2.3 Exact and Inexact Numbers E x a c t no uncertainty direct count defined equivalency Inexact any measurement has a degree of uncertainty

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10 Ch. 2.4 Uncertainty in Measurement and Significant Figures # of significant figures = all certain digits + one estimated digit 2 sig. fig. 3 sig. fig.
11 Guidelines for Determining Significant Figures 1. All nonzero digits are significant. 2. Zeros may or may not be significant. a. Leading zeros – not significant 0.00729 0.0000052 __ sig fig __ sig fig b. Confined zeros always significant 5 0.00 3 0.006 0 1 __ sig fig __ sig fig c. Trailing zeros are significant if a decimal point is present in the number 63. 0 5 0 0.09 0 1 0 __ sig fig __ sig fig

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12 Trailing zeros in numbers that do not contain a decimal point: 30600 g ambiguous To remove ambiguity, use prefixes or scientific notations (Ch 2.6) 30.600 kg 5 sig fig 30.6 kg 3 sig fig Stoker text pg 43 100 o F = 3 sig fig 30 o C = 2 sig fig
13 Ch. 2.5 Significant Figures and Mathematical Operations Rounding off Numbers These rules are listed on page 36 of your lab manual: 1. If the first nonsignificant figure is less than 5, drop it and all other nonsignificant figures. 2.

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## This note was uploaded on 06/03/2011 for the course CHM 123 taught by Professor Woodward during the Fall '08 term at Ohio State.

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Ch 2 Student Notes - 1 Chapter 2 Measurements in Chemistry...

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