userdata-paziras-Chem101-Chap_01B

Measurementoftemperature

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Unformatted text preview: lways think : ­ Which unit is larger ? (m) ­ Which unit is smaller ? (mm) 6 1m = 10 mm 1 mm ¾¾¾¾> IS CORRECT = 1 x 10 6 m ¾¾¾¾> IS Also Correct 18 Chemistry 101 Chapter 1 I. BASE UNITS 1.Measurement of Length Base unit: The meter = m Also commonly used in chemistry: cm, mm, mm, nm, pm (for atomic sizes) 1 m 1 m 1 m 1 m 1 m = = = = = 2 10 cm 3 10 mm 6 10 mm 9 10 nm 12 10 pm 10-2 m 10-3 m 10-6 m 10-9 m 10-12 m OR OR OR OR OR 1 cm 1 mm 1 mm 1 nm 1 pm = = = = = OR 1 A = 10-10 m Also used: the Angstrom, A 1 m = 10 10 A · NOTE : The Angstrom IS NOT AN SI UNIT 2. Measurement of Mass Base Unit: the kilogram, kg (the gram would not be practical since it is too small) 3. Measurement of Time Base Unit: the second, s · Conversion to minutes (60 sec/min) or hours (60 min/hr) is an exception to the decimal­based prefixes of the SI (is due to the calendar) · Recently, nanoseconds (10-9 s) and picoseconds (10-12 s) are increasingly used in computer work 19 Chemistry 101 Chapter 1 4. Measurement of Temperature · Temperature is a measure of how hot or cold a substance is. · It is a quantity that determines the direction of heat flow: warmer ® cooler · Three temperature scales are commonly used: Celsius, Kelvin (absolute) and Fahrenheit · To convert between Fahrenheit and Celsius; REMEMBER: 1.8 unit F = 1 unit C 32 oF = 0 oC o o o F = 32 + (1.8 x C) or o C = F ­ 32 1.8 · To convert between Celsius and Kelvin: REMEMBER: ­The Kelvin temperature is 273 degrees higher than the Celsius K = o C + 273 o C = K ­ 273 20 Chemistry 101 Chapter 1 II. DERIVED UNITS 1. Volume Base Unit : Commonly used: 3 m 3 dm Not practical because it is very large Also called “THE LITER (L)” 1 dm = 10 cm 3 3 1 dm = 1 L 1 cm = 1mL NOTE: 3 1 dm 1 L 3 = (10 cm)3 = 1,000 cm = 1,000 mL IMPORTANT RELATIONSHIPS TO REMEMBER: 3 1 dm = 1 L 3 1 cm = 1 mL 3 3 1 dm = 1000 cm 1 L = 1000 mL 3 3 1 cm = 0.001 dm 1 mL = 0.001 L 2. Density (d): Density is the mass of a unit volume d = m ass m = volu m e V 21 Chemistry 101 Chapter 1 Examples: 1. Calculate the density of a piece of glass with a mass of 6.65 g and a volume of 2.95 mL. m = 6.65 g V = 2.95 mL d =? 2. Calculate the thickness of an Aluminum foil 15.38 cm long and 14.39 cm wide. The mass of 3 the foil is 1.4939 g. The density of aluminum is 2.70 g/cm . (HINT: We consider the Aluminum foil to be a rectangular solid). L = 15.38 cm W = 14.39 cm m = 1.4939 g 3 d = 2.70 g/cm Thickness = Height = ? d = m m = V L x W x Th Solve the equation for the unknown (Th), before using numbers: Th = m 1.4939 g = = 2.50 x 10­3 cm 3 d x L x W (2.70 g/cm )(15.38 cm)(14.39 cm) Notes: · The units cancel out. The units obtained for the answer are cm, which is to be expected. · If the units would not be units of length, that would imply that you made a mistake in your algebra (when you solved for the unknown) 22 Chemistry 101 Chapter 1 DIMENSIONAL ANALYSIS (FACTOR­LABEL METHOD) · It is a method...
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