Density

Question 1

What does density tell you about a substance?

Answer 1

How compact the substance is, or how much mass there is per unit of volume

Question 2

What’s the equation used for calculating density?

Answer 2

Density = mass / volume or ρ = m / V

Question 3

True or false? The volume of a liquid in cm3 is equal to its volume in ml.

Answer 3

TRUE

1ml = 1cm3

Question 4

A marshmallow has a mass of 7g and a volume of 14cm3. What is its density?

Answer 4

ANSWER: 0.5g/cm3

METHOD: density = mass / volume = 7 / 14 = 0.5g/cm3

Question 5

The dimensions of a cuboid are 4cm by 5cm by 3cm. The cuboid has a density of 2g/cm3. What is the mass of the cuboid?

Answer 5

ANSWER: 120g

METHOD: volume of cuboid =length x width x height, so the volume is 4 x 5 x 3 = 60cm3
mass = density x volume This means the cuboid has a mass of 2 x 60 = 120g

TIP: Remember to take notice of the units that are used in questions like this. Density is sometimes given in kg/m3 and sometimes in g/cm3

Question 6

Briefly describe how you could find the density of a small metal unicorn.

Answer 6

Use a balance to measure the mass of the unicorn, m1. Fill a density bottle with water, stopper it and dry the outside, then measure its mass, m2.
Empty the bottle, put the unicorn inside, then repeat the previous step to find the mass of the bottle and unicorn, m3.
The mass of water displaced by the unicorn = m2 - (m3 - m1).
Rearrange the density formula to find the volume of the displaced water, and therefore the unicorn, from the mass of the displaced water and the density of water.
Put the unicorn’s mass and volume into the formula to work out the density. (You could also use a eureka can to find the volume of displaced water)