Embed Size (px)
Citation preview
Honors ChemistrySection 2.2 – Units of Measurement
ObjectivesStudents will be able to:
Use the SI system of measurement Identify and use the prefixes Identify and use the base units Determine and use derived units
Use mass and volume to calculate densitySolve problems using dimensional analysis
Solve dimensional analysis problems with square and cubic units.
SI MeasurementScientists all over the world have agreed
on a single measurement system called Le Système International d’Unités, abbreviated SI.
SI has seven base units
All other units are derived from the seven base units
SI Base Units
Note – the
quantity is the
parameter being
measured.
The unit is the standard being used
to determine the measurement
SI Measurement
Derived SI UnitsThe beauty of this system is all other units are “derived”
by combining the seven SI Base Units in different ways.This simplifies the SI System tremendously compared to
the British System
Note this uses the
Base Units – we will more commonly use g/cm3
VolumeVolume is the amount of space occupied by an object. This is an example of a quantity.
The derived SI unit is cubic meters, m3
The cubic centimeter, cm3, is more commonly used
The liter, L, is a non-SI unit 1 L = 1000 cm3
1 mL = 1 cm3
DensityDensity is the ratio of mass to volume, or mass divided by volume.
Density is a character• The derived SI unit is kilograms per cubic meter, kg/m3
• g/cm3 or g/mL are also used • Density is a characteristic physical property (intrinsic property) of a substance.
mass mDensity = or D=
volume v
Density Triangle
Density
Mass
Volume
DensityDensity can be used as one property to
help identify a substance
Conversion FactorsA Conversion factor is a ratio derived from the
equality between two different units that can be used to convert from one unit to the other.
example: How quarters and dollars are
related
Conversion FactorsDimensional analysis is a mathematical
technique that allows you to use units to solve problems involving measurements.
example: the number of quarters in 12 dollars
quantity given conversion factor = quantity sought
1
Conversion Factors
Deriving Conversion FactorsYou can derive conversion factors if you
know the relationship between the unit you have and the unit you want.
example: conversion factors for meters and decimeters
Si ConversionsPrefix Symbol
Example Conversion (numbers)
Example Conversion (powers of 10)
tera T 1,000,000,000,000 m = 1 Tm 1 x 1012 m = 1 Tm
giga G 1,000,000,000 m = 1 Gm 1 x 109 m = 1 Gm
mega M 1,000,000 m = 1 Mm 1 x 106 m = 1 Mm
kilo k 1,000 m = 1 km 1 x 103 m = 1 km
hecto h 100 m = 1 hm 1 x 102 m = 1 hm
deka da 10 m = 1 dam 1 x 101 m = 1 dam
deci d 1 m = 10 dm 1 x 10-1 m = 1 dm
centi c 1 m = 100 cm 1 x 10-2 m = 1 cm
milli m 1 m = 1000 mm 1 x 10-3 m = 1 mm
micro µ 1 m = 1,000,000 µm 1 x 10-6 m = 1 µm
nano n 1 m = 1,000,000,000 nm 1 x 10-9 m = 1 nm
pico p 1 m = 1,000,000,000,000 pm 1 x 10-12 m = 1 pm
femto f 1 m = 1,000,000,000,000,000
fm 1 x 10-15 m = 1 fm
atto a1 m =
1,000,000,000,000,000,000 am 1 x 10-18 m = 1 am
Prefix Tera Giga
Mega Kilo
Hecto
Deka
Standard Deci
Centi Milli
Micro
Nano Pico
Places 3 3 3 1 1 1 1 1 1 3 3 3
Move Decimal to the Right
Move Decimal to the Left
PracticeUsing conversion factors, express a mass of
5.712 grams in milligrams and in kilograms.
Converting from large to small or vice versaWhen you are doing a complex conversion, it
is always better to do it in steps that you know.
If you are changing 5.86 Gm to mm, use the following logic:Gm m (the base unit) mm
9125.86 1 10 1000
5.86 101 1 1
Gm x m mmx mm
Gm m
PracticeHow many km are there in 7.88 Tm?
Conversions with Squares and CubesUse the cube
Conversions with Squares and CubesUse the same conversion factor. Square of
cube the conversion factor as appropriate.
33 3256 1
( )( ) 0.0002561 100
cm mm
cm
PracticeIf you have a plot of land that is 57,000 m2, how
many km2 does it cover?
Practice (cont.)If you decided to use this plot of land to give
each of your friends a 10 dm2 area to garden. How many friends could you invite?
