Density
The amount of matter (mass) in a given space (volume)
Solving for Density

Density = mass divided by volume
D = m/V

If you have a glass of water with a mass of 500g (minus the
glass), and the volume amounts to 500mL, what is the
density of water?
500g/500mL = 1g/mL

Density is a useful physical property for identifying
substances, because each substance has a unique
density.

The density of a substance is always the same at a given
temperature and pressure. Except…. ???
Density of Liquid

Liquid density units are g/ml or kg/L

When different liquids combine, the densest liquids form layers on
the bottom, less dense layers form at the top.

Water is the only non-metallic substance on Earth whose density
in solid form (ice) is less than its density in liquid form. Why?

Liquid water is most dense (1.00 g/mL) as a liquid and becomes less
dense as the water molecules form crystals of ice as the temperature
drops to 0 °C. This is due to hydrogen bonds forming between the water
molecules, which line up molecules less efficiently (in terms of volume)
when water is frozen.
Hydrogen bonds are weak,
constantly forming and breaking
to create partially ordered
structures in liquid water; in ice,
each water molecule bonds
rigidly to four others.
Density of Solids

Solid density units are g/cm3 or kg/m3

If you have a 1 kilogram of iron and a 1 kilogram of cotton, which
would be less awkward to carry around?
 Since cotton is much less dense than iron, it would take up a lot more
space, or volume. So it would be very awkward to carry a 1
kilogram of cotton (about 2.2 pounds).
D = m/V

Greater mass means greater density. Greater volume means
less density.

A solid floats when it is less dense than the liquid that
its in, and sinks when it is more dense.

So wood is less dense than water and a rock is more dense.
Ice will suspend in water, most of
its mass will be below water, and
about 8%) will be above the
water. This is because its density
(.92 g/cm3) is very close the
density of liquid water (1.0 g/mL)
Buoyancy

The upward force
that a fluid exerts on
an object less dense
than itself.
~ Drews 2008
Measuring mass

The amount of matter in an object.

Use an electric balance to determine
mass

For solids use g, or kg

For liquids, use the same method and units but remember to
subtract the mass of the container from the total mass to find the
mass of the liquid only.
 Example: 200g total mass – 40g beaker = 160g of liquid
Measuring Volume

The amount of space occupied by a 3
dimensional object.

Volume of regular shaped solids can be
determined using simple equations like
=LxWxH

For volume of a liquid, use graduated
cylander.

For irregular shaped solids, use the
water displacement method.

For solids, use cm3 or m3

For liquids, use mL or L

Conversion: 1 cm3 solid = 1 mL liquid
Density Calculation Practice

What is the density of an object whose mass is
23.5 g and whose volume is 10 cm3?
 D = m/V
 D = 23.5g/10cm3
 D = 2.35 g/cm3
 Does the object float?