Density

There are 2 things that make something matter.

• It has volumeThis means that

it takes up space.

• It has massThis means that it

is made of particles.

Today we will be focus on how mass and volume can be related.

Mass is measured using either a __________ or a __________.

In the lab, mass is measured in ______.or __________.grams

scale balance

kilograms

Volume is measured using a __________________.

In the lab, volume is measured in _________ or __________.milliliters

graduated cylinder

liters

Remember: In science, we always use the International System of Units (SI units), also known as the metric system.

Milliliters are defined as the amount of space in a cube whose

sides are all 1 cm in length. 1 cm

1 cm

1 cm

This means that a milliliter is equal to a cubic centimeter 1 mL = 1 cm3

We will often use mL to describe the volumes of liquids and cm3 to describe the volumes of solids, but they are

just 2 ways of saying the SAME THING!

Density is the relationship between mass and volume. It is the measurement of how tightly the

particles of a substance are packed together.

Sample 1:Solid Iron

Sample 2: Liquid Iron

Sample 3: Iron Vapor

Which sample is the most densely packed?

Solid Iron Liquid Iron Iron Vapor

Notice that solids are the most dense phase of matter and gases are the least dense phase of matter.

Density and the Phases of Matter

m

D v

Density shows the relationship between mass and volume. The formula on your formula chart represent this relationship mathematically.

Use the formula to derive all three ways of expressing this relationship.

D = mv v =

mDm = D × v

cm3

gv

mgv

Since density is the relationship between mass and volume, we must show this relationship in the units of density.

D = mv

Units of D =

What are the units of mass?grams

What are the units of volume?milliliters or cubic centimeters

mLor

Complete the densityword problems on

your notes.

m18.4 gv

68.4 86.8

Before After

The picture shows a graduated cylinder on a scale before and after a solid sample was placed into it. Use the information in the picture to determine the density of the solid.

Volume = 36 mL - 23 mL = 13 mLMass = 86.8 g - 68.4 g = 18.4 g D = = 1.4 g/mL

13 mL

18.4 g

68.4 86.8

Before After

When shown the mass and volume before and after a sample has been added, you find the difference in the masses and the difference in volumes first. Then you have the information you need to calculate the density.Diffence means subtract!

Volume = 36 mL - 23 mL = 13 mLMass = 86.8 g - 68.4 g = 18.4 g D = = 1.4 g/mL

13 mL

Visualizing Density:Which of the samples below is the most tightly packed

together and therefore, the most dense?

A B CThey are all equally packed together:

they all have the same density!

Remember:Density is the relationship between mass and volume. It is a physical property of matter. At a given temperature, different samples of the same substance will have the same densities regardless of the amount of the substance in each sample.

Mass = 17.50 g

Volume = 13.0 cm3

Mass = 8.75 g

Volume = 6.50 cm3

Mass = 35.0 g

Volume = 26.0 cm3

Density = 1.35 g/cm3 Density = 1.35 g/cm3 Density = 1.35 g/cm3

3 samples of the same substance are shown below along with their individual masses and volumes. Calculate the density of each.

3 samples of the water are shown below along with their individual masses and volumes. Calculate the density of each.

Mass = 85.0 g

Volume = 85 cm3

Mass = 60.0 g

Volume = 60 cm3

Mass = 40.0 g

Volume = 40 cm3

Density = 1.0 g/cm3 Density = 1.0 g/cm3 Density = 1.0 g/cm3

Remember:Density is an intrinsic physical property of a substance. It does not matter how much of the substance is in a sample. If they are all the same temperature, then they will all have the same density!

So why does temperature matter?

As the temperature of matter increases, its particles expand!

This makes the matter LESS dense!

We will discuss temperature more next class. Now we will learn how matter with different densities interact.

Based on your observations, how do liquids with different densities stack?

The liquid with the GREATEST DENSITY will be on the BOTTOM!

Density of liquid 1.21 g/mL

Density of liquid 5.82 g/mL

Density of liquid 3.07 g/mL

A B C

If these 3 liquids are placed into the same beaker, how will they stack?

(Assume that they will not mix when stacked in the correct order.)

Sample ASample CSample B

Q: What is the density of water? A: 1.00 g/mL

Density of water 1.00 g/mL

Density of water 1.00 g/mL

Density of water 1.00 g/mL

Density of water 1.00 g/mL

D = 1.25 g/cm3 c D = 0.50 g/cm3 D = 2.85 g/cm3 D = 0.95 g/cm3

Watch what happens when each solid is placed into water.

Explain what determines if a solid floats or sinks:If the solid is more dense than the liquid, it sinks. If the solid is less dense than the liquid, it floats.

The density of the cube is 0.85 g/cm3. Based on what you have just learned, when will this cube stop sinking if it is placed into the cylinder shown?

It sinks through the ether because it is more dense than ether, but it floats on the water because it is less dense than water.

Important Vocabulary:What force causes things to float?

The Buoyant ForceFluids exert a buoyant force on objects that are placed inside of them. Fluids with greater

densities exert a greater amount of buoyant force.

This is why objects might sink through one layer, but float on

the next.

Buoyancy makes things float!

When solutes dissolve in water, they also affect the density of the water. Do dissolved solutes make an

aqueous solution more dense or less dense?

Dissolved solutes make aqueous solutions more

dense!

This is why the salt water in the ocean is more dense and easier to float on than freshwater.

Important VocabularyWhat force affects how fluids pour?

ViscosityViscosity is like the friction in a fluid. It affects

how fast a fluid is able to flow or pour.

Viscosity affects how things pour!

High Viscosity

Low Viscosity