Chem Lecture Notes Sept 3 Units

Chem Lecture Notes Sept 3 Units - Units and Conversion...

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Units and Conversion Factors Units are tags attached to numbers. They obey the algebraic rules of multiplication and division. Conversion factors allow one to change units. Example: How many meters tall is a 4.0 foot Emperor Penguin? Answer: 4.0 ft X 12in/ftX2.54cm/inX1m/100cm = 1.2 m
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How do Conversion Factors Work? Note that the formula 12 in = 1 ft can be arranged to read 12 in/1 ft = 1 or 1 ft/12 in = 1. Multiplying anything by 1 does not change it. Thus, for example a 39.0 in stick is, 39.0 in X 1 ft/ 12 in = 3.25 ft A series of such multiplications by 1 converts from one set of units to another
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The Standard Units Scientists have agreed on a set of international standard units for comparing all our measurements called the SI units Système International = International System Quantity Unit Symbol length meter m mass kilogram kg time second s temperature kelvin K
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Some Standard Units in the Metric System Quantity Measured Name of Unit Abbreviation Mass gram g Length meter m Volume liter L Time seconds s Temperature Kelvin K
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Metric to English Units and Conversions
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Length Measure of the two-dimensional distance an object covers SI unit = meter About 3½ inches longer than a yard 1 meter = one ten-millionth the distance from the North Pole to the Equator = distance between marks on standard metal rod in a Paris vault = distance covered by a certain number of wavelengths of a special color of light Commonly use centimeters (cm) 1 m = 100 cm 1 cm = 0.01 m = 10 mm 1 inch = 2.54 cm (exactly)
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Mass Measure of the amount of matter present in an object SI unit = kilogram (kg) about 2 lbs. 3 oz. Commonly measure mass in grams (g) or milligrams (mg) 1 kg = 2.2046 pounds, 1 lbs. = 453.59 g 1 kg = 1000 g = 10 3 g, 1 g = 1000 mg = 10 3 mg 1 g = 0.001 kg = 10 -3 kg, 1 mg = 0.001 g = 10 -3 g
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Related Units in the SI System All units in the SI system are related to the standard unit by a power of 10 The power of 10 is indicated by a prefix The prefixes are always the same, regardless of the standard unit
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Prefixes Used to Modify Standard Unit kilo = 1000 times base unit = 10 3 1 kg = 1000 g = 10 3 g deci = 0.1 times the base unit = 10 -1 1 dL = 0.1 L = 10 -1 L; 1 L = 10 dL centi = 0.01 times the base unit = 10 -2 1 cm = 0.01 m = 10 -2 m; 1 m = 100 cm milli = 0.001 times the base unit = 10 -3 1 mg = 0.001 g = 10 -3 g; 1 g = 1000 mg micro = 10 -6 times the base unit 1 μ m = 10 -6 m; 10 6 μ m = 1 m nano = 10 -9 times the base unit 1 nL = 10 -9 L; 10 9 nL = 1 L
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Prefixes
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Volume
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Volume Measure of the amount of three-dimensional space occupied SI unit = cubic meter (m 3 ) a Derived Unit Commonly measure solid volume in cubic centimeters (cm 3 ) 1 m 3 = 10 6 cm 3 1 cm 3 = 10 -6 m 3 = 0.000001 m 3 Commonly measure liquid or gas volume in milliliters (mL) 1 L is slightly larger than 1 quart 1 L = 1 dL 3 = 1000 mL = 10 3 mL 1 mL = 0.001 L = 10 -3 L 1 mL = 1cm 3
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Which is Larger? 1 yard or 1 meter?
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Chem Lecture Notes Sept 3 Units - Units and Conversion...

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