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# Ch. 1 lecture b

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Part B of Ch. 1 lecture

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### Ch. 1 lecture b

1. 1. 1/11/13CHM 101 Chapter 1: Matter & Measurement Part B
2. 2. Scientific Notation Scientific notation is used to write very large or very small numbers. A number in scientific notation contains a coefficient and a power of 10. coefficient power of ten coefficient power of ten 1.5 x 102 7.35 x 10-4 To write a number in scientific notation, the decimal point is moved so it will lie after the first digit. All significant figures are written. 52 000. = 5.2000 x 10 4 0.00378 = 3.78 x 10-3 4 spaces left 3 spaces right (use negative exponent) (use positive exponent)See Section 1.6 in your text for a detailed treatment of scientific notation (ASK FOR HELP!)
3. 3. Units of Measurement You MUST know the prefixes below and be able to use them as conversion factors. Used torepresent largequantities Used torepresent smallquantities
4. 4. EqualitiesAn equality states the same measurement in two different units, or in the same unitwith two different prefixes. 1 km = 1 x 103 m 1 cm = 1 x 10-2 1 mg = 1 x 10-3 g 1 m = 1 x 10-3 km m 1 x 103 mg = 1 g 1 m = 100 cm 1000 m = 1 km 1000 mg = 1 g Equalities are also written for relationships between units of the metric system, U.S. units, or between metric and U.S. units. 1 in. = 2.54 cm 454 g = 1 lb
5. 5. Conversion FactorsA conversion factor is a fraction obtained from an equality. Equality: 1 in. = 2.54 cmThe conversion factor is written as a ratio with a numerator and denominator.It can be inverted to give two conversion factors for every equality. 1 in. 2.54 cm or 2.54 cm 1 in. Equality: 1 m = 1 x 106 mm 1m 1×10 6 μm or 1×10 6 μm 1m
6. 6. Factor-Label Method for ConversionsHow many minutes are 2.5 hours?Given unit = 2.5 hrNeeded unit = minUnit Plan = hr minSetup problem to cancel hours (hr).Given Conversion Neededunit factor unit2.5 hr x 60 min = 150 min (2 SF) 1 hr **Always write out the conversion factor with units. Cross through the units that cancel and make sure you end with the desired unit.
7. 7. Factor-Label Method for ConversionsHow many minutes are 2.5 hours?Given unit = 2.5 hrNeeded unit = minUnit Plan = hr minSetup problem to cancel hours (hr).Given Conversion Neededunit factor unit2.5 hr x 60 min = 150 min (2 SF) 1 hr **Always write out the conversion factor with units. Cross through the units that cancel and make sure you end with the desired unit.
8. 8. Units & Conversion FactorsThe diameter of an average sodium atom is 186 nm. What is the diameter in cm?In inches?A man weighs 83.95 kg. What is his weight in pounds? Do you know how to enter scientific notation on your calculator?
9. 9. Record the temperatures on the thermometers below as accurately as possible. 28°C 28°C 27°C 27°C 26°C 26°C 25°C 25°C °C °C Always estimate one digit beyond the last marking.
10. 10. Now Let’s Practice Measuring and Converting Units using the Factor-Label Method