How to How to Calculate Calculate DensityDensity

How do we know the How do we know the density of a substance?density of a substance?

• We can’t see the molecules inside a substance to know how dense it is.

• Instead we can calculate how dense something is.

• Remember, density is how much mass is in a certain space.

• Therefore…

Remembering MassRemembering Mass• To get the density of an object you need to

know its mass and its volume.• Mass- the amount of matter in an object. • To measure mass, we use a triple beam

balance.

Units for mass= grams

Remembering VolumeRemembering Volume• Volume- the amount of

space an object takes up.

• To measure the volume of a liquid, we use a graduated cylinder.

• To measure the volume of a solid, we calculate : L x W X H

• To measure the volume of an irregular solid we use volume displacement.

Unit with graduated

cylinder-= mL

Unit with a ruler= cm3

Unit with displaceme

nt-= mL

Calculating DensityCalculating Density• Imagine you had a metal cube that has a

mass of 20.0 grams and a volume 5.0 cm3. What is its density?

D = M__ V

D= 20.0 grams 5.0 cm3

D= 4.0 D= 4.0 _g_ cm3

SHOW ALL WORK!

You try…You try…• The mass of an object is 10.0 grams and its

volume is 4.0mL. What is its density?

D = M__ V

D= 10.0 grams 4.0 mL

D= 2.5

D= 2.5 _g_ mL

SHOW ALL WORK!

The Density of WaterThe Density of Water• The mass of water is 10.0 grams and its volume

is 10.0mL. What is its density?

D = M__ V

D= 10.0 grams 10.0 mLD= 1.0

D= 1.0 _g_ mL

THE DENSITY OF WATER IS 1.0!

SHOW ALL WORK!

Will it sink or float?Will it sink or float?• If an object has a density greater than

water (1.0), it will sink.• If an object has a density less than water

(1.0), it will float.

Less than 1.0

More than 1.0

Liquid LayersLiquid Layers• If you pour together

liquids that don’t mix and have different densities, they will form liquid layers.

• The liquid with the highest density will be on the bottom.

• The liquid with the lowest density will be on the top.

Check out this picture Check out this picture • Which layer has the highest

density?• Which layer has the lowest

density?• Imagine that the liquids

have the following densities: 10.0 g/cm3

3.0 g/cm3

6.0 g/cm3

5.0 g/cm3

• Which number would go with which layer? 1

0

6

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