DENSITYDENSITY

KHS 2014KHS 2014

Q) Which weighs more:-

A kilogram of feathers or a kilogram of iron?

What is Density?What is Density?

Density is the Mass per unit Volume

Wood Water Iron

1 cm3 1 cm3 1 cm3

If you take the same volume of different substances, then they will weigh different

amounts.

0.50 g 1.00 g 8.00 g

Q) Which has the greatest mass and therefore the most dense?

IRON

Density = MassVolume

g or kg

cm3 or kg3

g/cm3 or kg/m3

= m

V

Example:

Q) Liquid water has a density of 1000kgm-3, while ice has density of 920kgm-3.

Calculate the volume occupied by 0.25kg of each.

Density Equation:

m

V

V = m = 0.25 = 0.000250m3

1000V = m = 0.25 = 0.000272m3

920

DENSITY OF A REGULAR SOLIDDENSITY OF A REGULAR SOLID

Find the Mass Find the Mass of the solid on of the solid on a balance.a balance.

Measure the Measure the three lengths three lengths and calculate and calculate the Volume.the Volume.

(ie V = l x w x h )(ie V = l x w x h ) Calculate the Calculate the

Density.Density.4.0 cm

2.0 cm

3.0 cm

= m = 240 =10.0 g/cm3

V 24

m = 240 g

DENSITYDENSITY g/cmg/cm33

AluminiumAluminium 2.702.70

BrassBrass 8.508.50

IronIron 7.867.86

WoodWood 0.500.50

SlateSlate 2.802.80

GlassGlass 2.502.50

LeadLead 11.311.3

MarbleMarble 2.702.70

WaxWax 0.890.89

DENSITY OF AN IRREGULAR DENSITY OF AN IRREGULAR SOLIDSOLID

Find the Mass of the Find the Mass of the solid on a balance.solid on a balance.Fill the Measuring Fill the Measuring Cylinder with Water to a Cylinder with Water to a known Volume.known Volume. Add the Object.Add the Object. Work out the Volume Work out the Volume of Water that is of Water that is displaced.displaced. Calculate the Density.Calculate the Density.

50 cm3

80 cm3

m = 360 g = m = 360 =12.0 g/cm3

V 30

DENSITY OF AN IRREGULAR DENSITY OF AN IRREGULAR SOLIDSOLID

OR use a Eureka Can to find the Volume.OR use a Eureka Can to find the Volume.

Find the mass of the solid Find the mass of the solid on a balance.on a balance.Add water until just Add water until just overflowing.overflowing. Place a Measuring Cylinder Place a Measuring Cylinder under the spout.under the spout. Add the Object.Add the Object. Collect the Water and read Collect the Water and read off the Volume.off the Volume.Calculate DensityCalculate Density

m = 440 g

40.0 cm3

= m = 440 =11.0 g/cm3 V 40

DENSITYDENSITY g/cmg/cm33

AluminiumAluminium 2.702.70

IronIron 7.867.86

BrassBrass 8.508.50

WoodWood 0.500.50

SlateSlate 2.902.90

GlassGlass 2.502.50

DENSITY OF A LIQUIDDENSITY OF A LIQUID

Find the Mass of an empty Find the Mass of an empty Measuring Cylinder.Measuring Cylinder.

Add a certain Volume of Add a certain Volume of Liquid.Liquid.

Find the Mass of the Find the Mass of the Measuring Cylinder and Measuring Cylinder and LiquidLiquid

Calculate the Mass of Liquid.Calculate the Mass of Liquid. How?How? Calculate Density of Liquid.Calculate Density of Liquid.

Mass of Liquid = Mass of Measuring Cylinder and Liquid – Mass of

empty Measuring Cylinder

25.0 g

20.0 cm3

45.0 g

45 – 25 = 20 g

= m = 20 =1.00 g/cm3 V 20

DENSITY OF A GASDENSITY OF A GAS

Remove the air Remove the air from a flask of a from a flask of a known Volume, known Volume, using a vacuum using a vacuum pump.pump.

Find its Mass.Find its Mass. Add the gas to be Add the gas to be

tested.tested. Reweigh.Reweigh. The difference is The difference is

the Mass of gas.the Mass of gas. Calculate Density.Calculate Density.

To vacuum flask

1000 cm3

150.0 g170.0 g

= m = 20 =0.0200 g/cm3 V 1000

170 -150 = 20.0g

Warm-UpWarm-Up

Estimate how long it would take for the Estimate how long it would take for the entire world’s population to count up to entire world’s population to count up to one mole.one mole.

If you stacked a mole of marshmallows If you stacked a mole of marshmallows on top of each other and covered the on top of each other and covered the United States how deep would the United States how deep would the marshmallows be?marshmallows be?

Working 48 hours a week it would take approximately 8 million years

600 miles

The MoleThe Mole

The Mole

What is the mole?What is the mole?

The Mole: The amount of a substance The Mole: The amount of a substance that contains 6.02 x 10that contains 6.02 x 102323 representative particles of that representative particles of that substance.substance.

The value of 6.02 x 10The value of 6.02 x 102323 is known as is known as Avagadro’s numberAvagadro’s number

In other words, the mole is a In other words, the mole is a HUGE HUGE number! number!

Question?Question? If you had a mole of dollars and spent 1 If you had a mole of dollars and spent 1

billion dollars a second how long would it billion dollars a second how long would it take for you to spend all of your money?take for you to spend all of your money? $6.02 x 10^23 / $1,000,000,000 = 6.02 x 10 ^14 seconds$6.02 x 10^23 / $1,000,000,000 = 6.02 x 10 ^14 seconds 6.02 x 10 ^14 seconds / 60 seconds = 1.003 x 10^13 minutes6.02 x 10 ^14 seconds / 60 seconds = 1.003 x 10^13 minutes 1.003 x 10^13 minutes / 60 minutes = 1.672 x 10^11 hours1.003 x 10^13 minutes / 60 minutes = 1.672 x 10^11 hours 1.672 x 10^11 hours / 24 hours = 6.968 x 10^9 days1.672 x 10^11 hours / 24 hours = 6.968 x 10^9 days 6.968 x 10^9 days / 365 days = 1.908 x 10^7 years6.968 x 10^9 days / 365 days = 1.908 x 10^7 years

It would take over 19 million years!!It would take over 19 million years!!

Why is a mole so big?Why is a mole so big?

Mass of atoms is so small you need many of them Mass of atoms is so small you need many of them to have mass significant enough for people to to have mass significant enough for people to weigh. weigh.

The mass of an atom is measured in atomic mass The mass of an atom is measured in atomic mass units (AMUs)units (AMUs)

Chemists picked a number equal to a certain mass Chemists picked a number equal to a certain mass of a certain element. of a certain element.

The mass is 12.000 grams and the element is The mass is 12.000 grams and the element is carbon-12.carbon-12.

Carbon-12 has 6 protons and 6 neutrons.Carbon-12 has 6 protons and 6 neutrons. The masses of all other elements are standardized The masses of all other elements are standardized

against the carbon-12 atom.against the carbon-12 atom.

How is the mole useful?How is the mole useful?

One atom of an element in AMUs = One atom of an element in AMUs = the mass of one mole of that element the mass of one mole of that element in gramsin grams

For example look at helium:For example look at helium: Number below helium is 4.00260.Number below helium is 4.00260.

This indicates that the mass of one helium This indicates that the mass of one helium atom is 4.00260 AMUatom is 4.00260 AMU

In addition, this indicates that if you have In addition, this indicates that if you have one mole of helium atoms those helium one mole of helium atoms those helium atoms would weigh 4.00260 gramsatoms would weigh 4.00260 grams

PracticePractice

1 mole = g Fe1 mole = g Fe

1 mole = g H1 mole = g H2200

3.011 x 10^23 atoms of Carbon = mol 3.011 x 10^23 atoms of Carbon = mol CC

1.0037 x 10^23 atoms of Neon = mol 1.0037 x 10^23 atoms of Neon = mol Ne Ne

55.85

18.0

1/2

1/6