Bell-ringerBell-ringer You are driving in your car You are driving in your car

down the interstate (70 down the interstate (70 mph) to Tuscaloosa to watch mph) to Tuscaloosa to watch the University of Alabama the University of Alabama crush the Tennessee crush the Tennessee Volunteers. It appears as Volunteers. It appears as though you are going to be though you are going to be late for the kickoff if you late for the kickoff if you don’t speed up. If you are don’t speed up. If you are traveling at a speed of 90 traveling at a speed of 90 km/h, are you breaking the km/h, are you breaking the speed limit?speed limit?

Chapter 2, Section 2:Chapter 2, Section 2:Units of MeasurementUnits of Measurement

Coach KelsoeCoach KelsoeChemistryChemistryp. 33–42p. 33–42

Units of MeasurementUnits of Measurement Measurements are quantitative.Measurements are quantitative. We must use units to make any kind We must use units to make any kind

of measure.of measure.– Imagine getting a treasure map saying, Imagine getting a treasure map saying,

go 5 right, 10 forward, and left 7 to find go 5 right, 10 forward, and left 7 to find Captain Jack Sparrow’s treasure. How Captain Jack Sparrow’s treasure. How far would you have to go?far would you have to go?

Measurements represent quantities. Measurements represent quantities. A A quantityquantity is something that has is something that has magnitude, size, or amount.magnitude, size, or amount.

Units of MeasurementUnits of Measurement Nearly every Nearly every

measurement we measurement we make involves a make involves a number and a unit.number and a unit.

Many measurements Many measurements we use have we use have different units, like different units, like feet or meters for feet or meters for distance, or gallons distance, or gallons or liters for volume.or liters for volume.

SI MeasurementSI Measurement Scientists all over the world have agreed Scientists all over the world have agreed

on the SI system of measurement. This on the SI system of measurement. This system was adopted in 1960.system was adopted in 1960.– SI stands for Le Système International d’UnitésSI stands for Le Système International d’Unités

SI has seven base units, and most other SI has seven base units, and most other units are derived from these seven.units are derived from these seven.

Some non-SI units are still commonly used.Some non-SI units are still commonly used. SI units are defined according to standards SI units are defined according to standards

of measurement.of measurement.

SI Base UnitsSI Base Units There are 7 base units in the SI There are 7 base units in the SI

system:system:– Meter (m)- length Meter (m)- length (l)(l)– Kilogram (kg)- mass Kilogram (kg)- mass (m)(m)– Second (s)- time Second (s)- time (t)(t)– Kelvin (K)- temperature Kelvin (K)- temperature (T)(T)– Mole (mol)- amount of substance Mole (mol)- amount of substance (n)(n)– Ampere (A)- electric current Ampere (A)- electric current (I)(I)– Candela (cd)- luminous intensity Candela (cd)- luminous intensity (I(Ivv))

SI PrefixesSI Prefixes Prefixes can be added to a base unit to Prefixes can be added to a base unit to

represent quantities larger or smaller than represent quantities larger or smaller than the base unit. Some examples of prefixes:the base unit. Some examples of prefixes:

Giga- (G)Giga- (G)101099

Mega- (M)Mega- (M) 101066

Kilo- (k)Kilo- (k) 101033

Hecto- (h)Hecto- (h) 101022

Deka- (da)Deka- (da) 101011

Deci- (d)Deci- (d) 1010-1-1

Centi- (c)Centi- (c)1010-2-2

Milli- (m)Milli- (m) 1010-3-3

Micro- (µ)Micro- (µ)1010-6-6

Nano- (n)Nano- (n)1010-9-9

Bell-ringerBell-ringer Convert the following quantities:Convert the following quantities:

– 525 mL to liters525 mL to liters– 7 km to centimeters7 km to centimeters– 0.003 Gs to seconds0.003 Gs to seconds– 48 g to micrograms48 g to micrograms

MassMass The SI unit for mass is the kilogram (kg).The SI unit for mass is the kilogram (kg). When we measure smaller objects, When we measure smaller objects,

especially in the lab, we will use grams especially in the lab, we will use grams rather than kilograms.rather than kilograms.

Mass and weight are different!Mass and weight are different!– MassMass is the amount of matter in an object. is the amount of matter in an object.– WeightWeight is the gravitational pull on matter. is the gravitational pull on matter.

Which measure can change without Which measure can change without affecting the substance measured?affecting the substance measured?

LengthLength The SI unit for length The SI unit for length

is the meter.is the meter. To express longer To express longer

distances, we use the distances, we use the kilometer.kilometer.

Most countries use the Most countries use the kilometer when kilometer when measuring distances, measuring distances, but we use miles.but we use miles.

The centimeter is used The centimeter is used for shorter distances.for shorter distances.

Derived SI UnitsDerived SI Units Many SI units are combinations of the Many SI units are combinations of the

standard SI units.standard SI units. Derived units usually come from Derived units usually come from

multiplying or dividing two standard SI multiplying or dividing two standard SI units.units.

Some combination units are given their Some combination units are given their own names, like the Pascal.own names, like the Pascal.

We can also add prefixes to derived We can also add prefixes to derived units.units.

Derived UnitsDerived UnitsQuantityQuantity SymbolSymbol UnitUnit Abbrev.Abbrev. DerivatioDerivatio

nnAreaArea AA Square Square

metermeter mm22 Length x Length x widthwidth

VolumeVolume VV Cubic meterCubic meter mm33 Length x Length x width x width x heightheight

DensityDensity DD Kilograms Kilograms per cubic per cubic

metermeterkg/mkg/m33 Mass/Mass/

VolumeVolume

Molar Molar MassMass

MM Kilograms Kilograms per moleper mole kg/molkg/mol Mass/ Mass/

amount of amount of substancesubstance

ConcentratiConcentrationon cc Moles per Moles per

literliter MM Amount of Amount of substance/ substance/

vol.vol.Molar Molar volumevolume VVmm

Cubic Cubic meters per meters per

molemolemm33/mol/mol Vol./amount Vol./amount

of substanceof substance

EnergyEnergy EE JouleJoule JJ Force x Force x lengthlength

VolumeVolume VolumeVolume is the amount of space occupied is the amount of space occupied

by an object. It is found by multiplying by an object. It is found by multiplying length x width x height.length x width x height.

The standard unit for volumes of solids is The standard unit for volumes of solids is mm33. For liquids and gases it is liters (L).. For liquids and gases it is liters (L).

What if we’re comparing volumes of What if we’re comparing volumes of solids to liquids or gases?solids to liquids or gases?– One liter (1 L) is equal to 1000 cmOne liter (1 L) is equal to 1000 cm33..– One milliliter (1 mL) is equal to 1 cmOne milliliter (1 mL) is equal to 1 cm33..– Also keep in mind that cmAlso keep in mind that cm33 = cc. = cc.

Converting VolumesConverting Volumes If 1 meter is equal to 100 centimeters, If 1 meter is equal to 100 centimeters,

then wouldn’t 1 mthen wouldn’t 1 m33 be equal to 100 cm be equal to 100 cm33?? NO!!!!!!!! Here’s why:NO!!!!!!!! Here’s why:

– 1 meter x 1 meter x 1 meter = 1 m1 meter x 1 meter x 1 meter = 1 m33..– If we measured the same object in cm then:If we measured the same object in cm then:– 100 cm x 100 cm x 100 cm = 1 000 000 cm100 cm x 100 cm x 100 cm = 1 000 000 cm33

– So we see that 1 mSo we see that 1 m3 3 does NOT equal 100 cmdoes NOT equal 100 cm33!! Remember that mL and cmRemember that mL and cm33 are are

interchangeable!interchangeable!

DensityDensity Density is the ratio of mass to volume.Density is the ratio of mass to volume. Mathematically, we see it like this:Mathematically, we see it like this:

– Density = mass/volumeDensity = mass/volume or or D = m/VD = m/V It may be easier to see it like this:It may be easier to see it like this:

mD V

DensityDensity The standard unit for density is kg/mThe standard unit for density is kg/m33, but in the , but in the

lab, this unit is typically way too large. We may lab, this unit is typically way too large. We may use units like g/cmuse units like g/cm33 or g/L. or g/L.

Density is a characteristic physical property. It is Density is a characteristic physical property. It is an intensive property because it doesn’t matter an intensive property because it doesn’t matter how much we have, the measurement will how much we have, the measurement will always be the same.always be the same.

Different densities is what allows things to float Different densities is what allows things to float or sink in water. PURE water has a density of or sink in water. PURE water has a density of 1 1 g/mLg/mL..– If a substance is less dense than water, it floats.If a substance is less dense than water, it floats.– If it is more dense than water, it sinks.If it is more dense than water, it sinks.

Conversion FactorsConversion Factors A A conversion factorconversion factor is a ratio is a ratio

derived from the equality between two derived from the equality between two different units that can be used to different units that can be used to convert from one unit to the other.convert from one unit to the other.

Conversion factors are arranged to Conversion factors are arranged to cancel out the original unit.cancel out the original unit.

For example, converting 78 feet to For example, converting 78 feet to yards:yards:– 78 feet x 78 feet x 1 yard1 yard = =

– 26 yards26 yards

3 feet3 feet

What if…What if… What if I had chosen the wrong What if I had chosen the wrong

conversion factor? Then…conversion factor? Then…– 78 feet x 78 feet x 3 feet3 feet = 234 ft = 234 ft22/yard/yard

Even though 3 feet/1 yard is a Even though 3 feet/1 yard is a correct conversion factor, it does not correct conversion factor, it does not give us the units we need!give us the units we need!

1 1 yardyard

Using Multiple Conversion Using Multiple Conversion FactorsFactors

What if I asked you to convert 110 710 What if I asked you to convert 110 710 inches to miles?inches to miles?

You would have to do the following:You would have to do the following:– 110710 inches x 110710 inches x 1 foot1 foot x x 1 mile1 mile = 1.75 = 1.75

milesmiles 12 12 inchesinches

5280 5280 feetfeet