DENSITYDENSITY

How dense is dense?

What’s the matter?What’s the matter?

Matter exists in 3 main forms: solid liquid and gas.

Density is the concentration of matter (atoms) in a substance.

Silicon atoms

Density is a ratioDensity is a ratio

The density of an object is the ratio of its mass (g) to its volume (cm3 or ml).

A B C

Density calculations Density calculations convert to metricconvert to metric

7 X 3.625 X 1.75in.

2.54cm = 1 inch

Length = ?

Width = ?

Height = ?

Volume = ?

454g = 1lb

Mass = 30.98lb

Mass = ?

Density equationDensity equation

Density = Mass Volume

D = M V

D

M

V

Density calculationsDensity calculations

7 X 3.625 X 1.75in.

2.54cm = 1 inch

Length = 17.78cm

Width = 9.21cm

Height = 4.45cm

Volume = ?

454g = 1lb

Mass = 30.98lb

Mass = 14,064.9g

WorkWork

Volume

17.78cm X 9.21cm X 4.45cm = 728.7 cm3

Volume = 728.7 cm3

Mass

30.98lb X 454g = 14,064.9g

1lb

Mass = 14,064.9g

More workMore work

D = M

V

D = 14,064.9g

728.7 cm3

D = ?

More workMore work

D = M

V

D = 14,063.9 g

728.7 cm3

D = 19.3 g/cm3

Are we correct?Are we correct?

 Densities of Common Elements and Compounds

Substance Density(g/cm3 )

 Water 1.00

 Aluminum, Al  2.70

 Iron, Fe  7.80

 Gold, Au  19.30

 Mercury, Hg  13.50

Effect of phase of matter on densityEffect of phase of matter on density

Most substances increase in density as they change from gas to liquid to solid.

Quite simply, the atoms are closest together in the solid phase.

gas liquid solidincreasing density

decreasing density

Water is an exceptionWater is an exception

ice liquid water water vapor

Water is densest as a liquid at 3.98oC. That’s why ice floats.

Size or shape does not affect the Size or shape does not affect the density of a substancedensity of a substance

= same density

= same density

Even when Even when cut, the cut, the density of a density of a substance substance remains the remains the same.same.

Factors that affect densityFactors that affect density

Temperature– Heat - pushes molecules apart– Cold - pushes molecules together

Pressure– Low - allows molecules to spread apart– High - pushes molecules together

It’s the volume that changes and density is dependent on the ratio d=m

v

Float?Float?

If the density of an object is less than the liquid it will float.

The lower the density of an object the higher it will float in the liquid.

Sink?Sink?

If the density of an object is greater than that of the liquid, it will sink.

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If an object and a liquid have the same density, the object can remain stationary anywhere in the liquid.

LayeringLayering

Liquids of different densities will form layers.

http://www.youtube.com/watch?v=-CDkJuo_LYs