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

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

Coach KelsoeCoach Kelsoe

ChemistryChemistry

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

SI MeasurementSI Measurement

Scientists all over the world have agreed on Scientists all over the world have agreed on the SI system of measurement. This 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 Some combination units are given their own names, like the Pascal.their 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

nn

AreaArea 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

metermeter

kg/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

VVmmCubic Cubic

meters per meters per molemole

mm33/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 is the amount of space occupied by an object. It is found by occupied by an object. It is found by multiplying length x width x height.multiplying length x width x height.

The standard unit for volumes of solids The standard unit for volumes of solids is mis m33. For liquids and gases it is liters . For liquids and gases it is liters (L).(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:

m

D V

DensityDensity

The standard unit for density is kg/mThe standard unit for density is kg/m33, but in , but in the lab, this unit is typically way too large. We the lab, this unit is typically way too large. We may use units like g/cmmay use units like g/cm33 or g/L. or g/L.

Density is a characteristic physical property. It Density is a characteristic physical property. It is an intensive property because it doesn’t is an intensive property because it doesn’t matter how much we have, the measurement matter how much we have, the measurement will always be the same.will 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 derived from the equality between two different units that can be used two different units that can be used to convert from one unit to the other.to 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