Measurements and Calculations. Chapter 2

Transcription

1 Measurements and Calculations Chapter 2

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3 Scientific Method Observing/Collecting Data Hypothesis Testing Theorizing Publishing

4 Units of Measurement All measurements require two parts 1. Quantity 2. Unit SI Measurement Base Units Mass kilogram - kg Length meter - m Time seconds s Temperature Kelvin K Amount of substance mole mol Electric current ampere A Luminous intensity candela - cd

5 Units of Measurement SI Measurement derived units Area m 2 Volume m 3 Density kg/m 3 Molar mass kg/mol Concentration mol/l Energy joule - J

6 Units of Measurement SI Prefixes Kilo k Centi c Milli m Micro Nano n Pico p

7 Conversion Factors Ratio derived from the equality between two different units that is used to convert between units How many slices are in 3 pizza pies?

8 Conversions How many seconds are in one day? How many centigrams are in one kilogram?

9 Measurements A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty. Record the certain digits and the first uncertain digit (the estimated number).

10 Measurements

11 Measurements The volume is read at the bottom of the liquid curve (meniscus). Meniscus of the liquid occurs at about??? Certain digits: 20.1 Uncertain digit: 20.15

12 Significant Figures Rules for Counting Significant Figures Nonzero integers always count as significant figures has 4 sig figs (significant figures).

13 Significant Figures Rules for Counting Significant Figures There are three classes of zeros. a. Leading zeros are zeros that precede all the nonzero digits. These do not count as significant figures has 2 sig figs.

14 Significant Figures Rules for Counting Significant Figures There are three classes of zeros. b. Captive zeros are zeros between nonzero digits. These always count as significant figures has 4 sig figs.

15 Significant Figures Rules for Counting Significant Figures There are three classes of zeros. c. Trailing zeros are zeros at the right end of the number. They are significant only if the number contains a decimal point has 4 sig figs. 150 has 2 sig figs.

16 Significant Figures Rules for Counting Significant Figures Determine the number of significant figures in each of the following. a b c d. 400 e f

17 Significant Figures Rules for Counting Significant Figures Suppose the value seven thousand centimeters is reported to you. How should the number be expressed if it is intended to contain the following? a. 1 significant figure b. 4 significant figures c. 6 significant figures

18 Significant Figures Rules for Counting Significant Figures Round the following number to the indicated amount of significant figures a. 8 significant figures b. 6 significant figures c. 3 significant figures d. 1 significant figure

19 Significant Figures Significant Figures in Mathematical Operations 1. For multiplication or division, the number of significant figures in the result is the same as the number in the least precise measurement used in the calculation =

20 Significant Figures Significant Figures in Mathematical Operations 2. For addition or subtraction, the result has the same number of decimal places as the least precise measurement used in the calculation Corrected 31.28

21 Significant Figures Significant Figures in Mathematical Operations Carry out the following calculations. Express each answer to the correct number of significant figures. a b. 2.4 x c / 8.47 d

22 Homework #s 13, 14, 28, 29, 30, 33, 36, 38, 40, 41, and 43