CHEMISTRY 161
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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


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