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 number error* unit *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 number unit 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 0.01 g 0.001 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

NASA-Mars Polar Lander

number unit error Measurements measuring device inaccurate reading multiple measurements average (statistics)

Significant Digits T = 24.3 ºC (3 significant digits) 0.034 K 3.4  10-2 0.0340 K 3.40  10-2 combining significant digits

Summary SI units and conversion of units 2. error 3. number of significant digits