Density

Vocabulary

Proportional

Inversely proportional

Ratio

TEKS and TAKS

The density concept will be tested on your TAKS Test in the Spring.

Goals and Expectations

What is density?

What is the density formula?

How is density relevant to chemistry?

What are the relationships between density & mass and density & volume and density & temperature?

What is specific gravity?

Which box weighs more?

These boxes are the same size and have the same volume.

If each red ball weighs the same, which box weighs more?

Density is…

The ratio of the mass of an object to its volume

A physical property that depends on the composition of a substance, NOT the sample size

Density Equation

Density (D) = Mass (m) Volume (v)

The Density Equation

The density equation contains only three variables: density, mass and volume.

quantity variable common unit(s)

density D g/mL, g/L, g/cm3

volume V mL, L, cm3

mass m g

Understanding Density

Mass = the amount of matter

Volume = the amount of space

Density is the relationship between the amount of matter and how much space that matter occupies.

Solve these problems

Wood has a density of 5.53g/cm3. What must the volume be of 33.3 g of wood?

Sodium has a density of 1.95 g/cm3. What is the volume of 56.2g of sodium?

Density of Liquids

If several liquids of different densities are placed in a container, the liquids will be layered in order from smallest to largest going top to bottom.

Application Question

Using the chart.

If the liquids is the chart were placed in a test tube. How would they be layered from top to bottom? Let’s assume that all of the examples are liquids.

Which weighs more?

One gram of gold

One gram of water

One gram of lead

Trick Question! They all weigh the same!!

Density and Mass

Density is proportional to the mass of the substance

As one increases the other will also increase

If two substances have the same volume, the substance with the greater mass will have the greater density.

Which substance will be denser?

Fe Auvolume = 10.00 cm3 volume = 10.00 cm3

mass = 78.74 g mass = 193.1g density = 7.874 g/cm3 density = 19.31 g/cm3

Fe

Au

Which has a larger mass?

One cm³ of gold (density = 19.3 g/cm³)

One cm³ of water (density = 1.00 g/cm³)

One cm³ of lead (density = 11.3 g/cm³)

Think of the relationship between mass and density.

Let’s calculate to see if your predictions were accurate.

One cm³ of gold (density = 19.3 g/cm³)

One cm³ of water (density = 1.00 g/cm³)

One cm³ of lead (density = 11.3 g/cm³)

m = D x Vm= 19.3 x 1m = 19.3 g

m = D x Vm = 1.00 x 1m = 1.00 g

m = D x Vm = 11.3 x 1m = 11.3 g

Density and Volume

Are inversely proportional

As one increases the other will decrease.

Therefore, if two substances have the same mass, the substance with the greater volume will have the smaller density.

A large density means a small volume.

A small density means a large volume.

Which has a larger volume?

One gram of gold (density = 19.3 g/cm³)

One gram of water (density = 1.00 g/cm³)

One gram of lead (density = 11.3 g/cm³)

Think of the relationship of density and volume.

Let’s see if your predictions were correct.

One gram of gold (density = 19.3 g/cm³)

One gram of water (density = 1.00 g/cm³)

One gram of lead (density = 11.3 g/cm³)

V = m/D = 1 / 19.3 = 0.052 cm³

V = m/D = 1 / 1 = 1.00 cm³

V = m/D = 1 / 11.3 = 0.0884 cm³

Density vs. Temperature

As the temperature rises, substances expand

Expansion = an increase in volume

Because of this, density is temperature dependent.

Look at the particles in each phase.

Ask yourself, what happens to the volume as the temperature is increased?

Which phase has the most volume?

What is the relationship between volume and temperature

Which phase is the most dense?

Water is an exception to the rule.

Water is most dense at 4°C.

Think about what temperature water freezes (0°C). So it is still a liquid at 4°C.

In the solid phase of water the molecules are spread further apart than in the liquid phase.

Remember: the closer the particles the more dense the phase.

THIS IS WHY ICE FLOATS ON WATER

Determining the density of different objects.

Geometric solid1. weigh the object and record its mass

2. Measure its length, width, and height and use these measurements to determine the volume.

3. Calculate the density

Irregularly shaped object 1. weigh the object and record its mass

2. Use the volume displacement method to determine its volume.

3. Calculate the density

Determining the density of different object.

Liquid 1. Weigh a 10 mL graduated cylinder and

record its mass. 2. Pour approximately 7mL(this is the volume)

of the liquid into the graduated cylinder and weigh it. Record its mass.

3. Subtract the weight of the graduated cylinder from the weight of the graduated cylinder and the liquid (this is your mass).

4. Then calculate your density.