Density

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

1 kg of feathers 1 kg of rock

Same mass! Larger volume

Same mass! Smaller volume

Volume vs. Mass

Volume is the amount of space something takes up

Mass is the amount of matter in an object (how “heavy” something is)

Finding Mass

Place the object on a scale or

balance

Units should be grams (g) or

kilograms (kg)

Finding Volume of a Regular Shape

An object with a “regular” shape is measurable and symmetric

1.Measure length (L), width (W) and height (H)

2.Multiply L x W x H3.Make sure units make sense (cm3, m3)

4 cm x 6 cm x 5 cm = 120 cm3

Conversion Factor: 1 cm3 = 1mL

Finding Volume of an Irregular Shape

An object that can not easily be measured

1.Use displacement Fill a graduated

cylinder or overflow can with water

Measure how much water goes up/spills out when object is placed in water

Remember: 1 cm3 = 1mL

• Density is defined as mass per unit volume. It is a measure of how tightly packed and how heavy the molecules are in an object.

• Density is the amount of matter within a certain volume (how much “stuff” is crammed into something)Units of Density:

g/cm3 or g/mLDepends on the units used

for mass and volume

Density of Phases of MatterWhich phase of matter is the densest?

Which phase of matter is the least dense?

*Usually the solid phase of a substance will sink in it’s liquid phase because it is more dense• Water is an

exception!• Because water

expands when it freezes, solid water (ice) is actually less dense than liquid water

SOLID

GAS

SolidsBone 2

Brick 1.8

Cork 0.2

Ice 0.92

Marble 2.7

Paraffin 0.9

Rubber 1.2

Bamboo 0.3

Oak Wood 0.7

Pine Wood 0.6

Densities of Common Substances (g/mL)

Metals

Aluminum 2.7

Copper 8.9

Gold 19.3

Iron 7.8

Lead 11.3

Silver 10.5

Liquids

Pure Water 1.0

Sea Water 1.03

Alcohol 0.8

Gylcerine 1.3

Milk 1.03

Turpentine 0.9

Mercury 13.6

Gasoline 0.7

Note: The density of a substance will always be the same, regardless of it’s shape or sizei.e. the density of pure water is always 1 g/mL

Finding Density

Formula:

M = mass

V= volume

D = density

D = M / V

M = D x V

V = M / D

Density (D) is mass (m) per unit volume (v)per = divided byD = m/v (m ÷ v)

Divided by Multiplied by

Practice Problem #1

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

Given:

Mass = 35 grams

Volume = 7 cm3

Density = ? (g/ cm3)

Formula: D = M / V

Solution:

D = 35 g / 7 cm3

D = 5 g/cm3

Practice Problem #2

A rectangular block of copper metal has a mass of 1896 g. The dimensions of the block are 8.4 cm by 5.5 cm by 4.6 cm. From this data, what is the density of copper? Given:

M = 1896 grams

V = 8.4 cm x 5.5 cm x 4.6 cm

= 212.52 cm3

D = ? (g/ cm3)

Formula: D = M / V

Solution:

D = 1896 g / 212.52 cm3

D = 8.92 g/cm3

Practice Problem #3

Find the mass of 250.0 mL of benzene. The density of benzene is 0.8765 g/mL.

Given:

V = 250.0 mL

D = 0.8765 g/mL

M = ? g

Formula: M = D x V

Solution:

M = 0.8765 g/ mL x 250.0 mL

M = 219.13 g

Practice Problem #4

What volume of silver metal will has a mass of exactly 2500.0 g. The density of silver is 10.5 g/cm3.

Given:

M = 2500.0 g

D = 10.5 g/cm3

V = ? cm3

Formula: V = M / D

Solution:

V = 2500.0 g / 10.5 g/cm3

V = 238.10 cm3