Determining Density. Mass We can measure mass by using a balance or a digital scale.

Determining Density

Mass

We can measure mass by using a balance or a digital scale.

Volume

Volume is a measurement of the amount of space occupied by the substance.

How can we measure volume?1. Liquids can be measured using a

measuring cup or a graduated cylinder.

Volume

2. Gases can be determined by measuring the volume of the container it is in.

3. Irregular solids can be determined by immersing them into a beaker of water and measuring the volume of the displaced fluid. Displacement is the amount of space that an object takes up when placed in a fluid.

Volume

4. Regular solids can be determined by measuring the length, width, and height:

V = l × w × h.

How to Calculate Density

Density (D) = Mass (m) or simply, D= _m Volume V

Or V= m and m = V x D D

Sample Problem

Find the density of a 10 g mass of a substance that has a volume of 2.0 cm3.

D = D = m m D= D= 10g 10g = 5 g/ cm= 5 g/ cm33

V V 2.0 cm 2.0 cm33

Sample Problem

You want to put 10.0 g of salt into a container. If the density of salt is 2.16 g /cm3 , what is the volume of the container if the salt completely fills it?

V= V= mm V= V= 10.0 g10.0 g V= V= 4.6 4.6 g/cmg/cm33

D 2.16 g/cmD 2.16 g/cm33

Sample Problem

What is the mass of 1500 mL of helium, if the density of helium is 0.0002 g/mL?

m= D x V m= 0.0002 g/mL x 1500 m= D x V m= 0.0002 g/mL x 1500 mL mL m= 0.3 g m= 0.3 g

Changes in Density

As Temperature Increases

↓Particles Gain Energy

↓Particles spread out

↓Decrease in Density

As Temperature As Temperature DecreasesDecreases

↓↓Particles Lose EnergyParticles Lose Energy

↓↓Particles closer togetherParticles closer together

↓↓Increase in DensityIncrease in Density

Examples of Changes in Density

Hot Air Balloons(intentional change) a gas burner that heats

the air inside the balloon particles gain energy and

spread further apart the density of air inside

the balloon decreases (less dense than air surrounding the balloon)

so it rises pilot controls the altitude

of the balloon by controlling the amount of heat


Warm vs. Cool Tire Pressure (natural change)

Tires on an automobile need more air during the winter than they do during the summer.

Winter as the temperatures decrease

particles lose energy and take up less space.

the density of the air decreases, and the tire deflates a little

Summer increasing temperatures increases

particle energy (spread further apart)

air in the tire expands tire inflates


water in its three states – natural change

Most substances are denser in their solid state than in their liquid state; water is an exception

when water freezes, it expands and its density decreases (this is why ice floats)

otherwise, water follows the normal trend


drying of wood (seasoning of wood) – natural change

freshly cut wood from a living tree is much heavier than wood that has been cut and dried in the air

water evaporates and is replaced with air

air is much less dense than water, so dry wood is less dense than moist wood (and easier to burn)


salt water being easier to float in – natural change

much easier to float in salt water than in fresh water

the density of salt water is greater than that of fresh water

Determining Density. Mass We can measure mass by using a balance or a digital scale.

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