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CHEMISTRY 161 Chapter 3 Measurements. Measurements. measurements are numerical (quantitative) observations. how much?. weight; volume; speed; energy; density; distance . qualitative observations. what?. color, small. Measurements. error*. unit. number. *uncertainty. SI base unit.
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CHEMISTRY 161 Chapter 3 Measurements
Measurements measurements are numerical (quantitative) observations how much? weight; volume; speed; energy; density; distance qualitative observations what? color, small
Measurements error* unit number *uncertainty
SI base unit measurement unit symbol length meter m mass gram g time second s electrical current ampere A temperature Kelvin K amount of substance mole mol luminous intensity candela cd all units are derived from 7 SI base units
derived units area length width length width height volume distance / time velocity velocity / time acceleration Force [N] acceleration mass force / area Pressure [Pa; mbar, torr]
Measurements unit number 50 m s-1 m s-1 300,000,000
Decimal Multipliers prefix symbol factor power of 10 mega M 1000000 106 kilo k 1000 103 deci d 0.1 10-1 centi c 0.01 10-2 milli m 0.001 10-3 1000 g 0.001 g 0.01 g
Conversion Measurement English to Metric Metric to English Length 1 ‘’ = 2.54 cm 1 m = 39.37 in. 1 yd = 0.9144 m 1 km = 0.6215 mile 1 mile = 1.609 km Mass 1 lb = 453.6 g 1 kg = 2.205 lb 1 oz = 28.35 g Volume 1 gal = 3.785 L 1 L = 1.057 qt 1 pt = 946.4 mL 1 oz (fluid) = 29.6 mL 1 L = 1000 mL = 1000 cm3
Temperature 0 K -273 OC
Measurements unit number error measuring device inaccurate reading multiple measurements average (statistics)
Significant Digits T = 24.3 ºC (3 significant digits) T = 24.32 ºC (4 significant digits) 3.4 10-2 0.034 K 3.40 10-2 0.0340 K combining significant digits
Summary • SI units and conversion of units • 2. error • 3. number of significant digits