Density

Comparing Feathers and Rocks

1 kg of feathers 1 kg of rock

Which do you think would have the greater mass?Which do you think would have the greater volume?

Density

Density is defined as mass per unit volume. Density is a measure of how tightly packed

molecules are in an object. Basically, it is the amount of matter within a

certain volume.

The Math…

The Units: Mass = Grams (g)

Volume (2 ways) Ruler = cm3

Displacement = ml

Density (2 ways) Ruler = g/cm3

Displacement = g/ml

What is Density?

IRON! It has the most mass for that volume.

If you take the same volume of different substances, thenthey will weigh different amounts.

Water IronWood

1 cm3

1 cm3

1 cm3

0.50 g 1.00 g 8.00 g

Q) Which of these is most dense? Why?

Density for different things…

Each substance has it’s own density.It does not matter how much of a substance you have, it will have the samedensity.

1 gram of water will have the same density as 100 grams of water Distilled Water has a density of 1 g/cm3

(This is the only density you need to memorize!)

Substance Density (g/cm3)

Hydrogen 0.00009Helium 0.000178Air (atmospheric air) 0.001293Carbon Monoxide 0.00125Carbon Dioxide 0.001977Gasoline 0.70Ice 0.922Water (@ 20deg C) 0.998Water (@ 4deg C) 1.000Milk 1.03Magnesium 1.07Water in the Dead Sea (31.5% salt in the water)

1.24

Aluminum 2.7Iron 7.8Lead 11.3Mercury 13.6Gold 19.3Lead 21.4

Density for different things…

Objects with different densitiesinteract in a very predictable way

The more dense object will sink, theless dense will rise to the top…

Substance Density (g/cm3)

Hydrogen 0.00009Helium 0.000178Air (atmospheric air) 0.001293Carbon Monoxide 0.00125Carbon Dioxide 0.001977Gasoline 0.70Ice 0.922Water (@ 20deg C) 0.998Water (@ 4deg C) 1.000Milk 1.03Magnesium 1.07Water in the Dead Sea (31.5% salt in the water)

1.24

Aluminum 2.7Iron 7.8Lead 11.3Mercury 13.6Gold 19.3Lead 21.4

Different objects have different densities

Is the ice or the water more dense?The water is more dense

than the ice because the ice floats!

Objects with less than 1 g/cm3 density will float in tap water (ex: ice at 0.93)

Objects with more than 1 g/cm3

density will sink in tap water (ex: gold at 19.3)

Sidenote…

Sulfur hexaflouride. Density? Explain this.

The Math…

The Units: Mass = Grams (g)

Volume (2 ways) Ruler = cm3

Displacement = ml

Density (2 ways) Ruler = g/cm3

Displacement = g/ml

Determining Density

Step 1:Find the mass of the object

Determining Density

STEP 2: Determine Volume

We have 2 ways to determine VOLUME. Measure

Cube = L * W * H Cylinder = Πr2H Sphere = (4Πr3)/3

Calculate Displacement Displacement is how much liquid is moved out of the way

to make room for the object placed in water

Determining Volume: Displacement

Calculate Displacement Displacement is how much liquid is moved out of the way

to make room for the object placed in water

Determining Density

Step 3:Calculate

Density = Mass Volume

Units:For ruler: g/cm3

For displacement: g/ml

1) Find the mass of the object

2) Find the volume of the object

3) Divide : Density = Mass / Volume

To find density:

Ex. If the mass of an object is 35 grams and it takes up 7 cm3 of space, calculate the density.

1) Find the mass of the object

2) Find the volume of the object

3) Divide : Density = Mass / Volume

To find density:

Set up your density problems like this:

Known: Mass = 35 grams Unknown: Density (g/cm3) Volume = 7 cm3

Formula: D = M / V Solution: D = 35g / 7cm3

D = 5g/cm3

Ex. If the mass of an object is 35 grams and it takes up 7 cm3 of space, calculate the density.

Osmium is a very dense metal. What is its density in g/cm3 if 50.00 g of the metal occupiesa volume of 2.22cm3?

1) 2.25 g/cm3

2) 22.5 g/cm3

3) 111 g/cm3

Practice Problem 1

lecturePLUS Timberlake

18

What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL? A) 0.2 g/ cm3 B) 6 g/cm3 C) 252 g/cm3

25 ml 33 mL

Practice Problem #3