P3 Density of Materials (page 192)

Question 1

9The Density of an object tells you what?

Answer 1

how many of its particles have been squished into a given space.

Question 2

What is Density a measure of?

Answer 2

compactness of a substance.

It relates the mass of a substance to how much space it takes up (i.e. it’s a substance’s mass per unit volume).

Question 3

What are the units of density?

Answer 3

kg/m³ (the mass is in kg and the volume is in m³

Question 4

apart from density units in kg/m³, what might you also see density given in?

Answer 4

g/cm³ (1 g/cm³ = 1000 kg/m³).

Question 5

What is the Density calculation?

Answer 5

mass
Density _______
Volume

(the symbol for density is a Greek letter rho (ρ) - it looks like a p, but it isnt)

              m
           \_\_\_\_\_\_\_
            ρ x V   (see diagram 1 on page 192 for triangle calculation)

Question 6

A gold bar has a mass of 12 kg and a volume of 6.3 x 10-⁴ m³. Calculate the density of the gold bar. Give your answer to two signigicant figures?

Answer 6

1) First, plug the numbers you’ve been given into the equation for density.

2) Then round your answer to two signifcant figures

3) Check your units match what’s given in the question.

Density = mass ÷ volume
= 12 ÷ (6.3 x 10-⁴) = 18047.6…

Density = 19 000 kg/m³ (to 2 s.f.)

Question 7

How do you know the Density of an object?

Answer 7

it depends on what it’s made of and how its particles are arranged.

Question 8

A dense material has its particles packed tightly together, explain what this means?

Answer 8

The particles in a less dense material are more spread out - if you compressed the material, its particles would move closer together, and it would become more dense. (you wouldn’t be changing its mass, but you would be decreasing its volume).

Question 9

Density varies between different states of matter (see page 191), give example?

Answer 9

Solids are generally denser than liquids, and gases are usually less dense than liquids.

Question 10

You need to be able to measure Density in Different Ways, explain how to find the density of a solid object?

Answer 10

1) Use a balance to measure its mass (see p.232).
2) If it’s a regular solid, start by measuring its length, width and height with an appropriate piece of equipment (e.g. ruler). Then calculate its volume using the relevan formula for that shape.
3) For an irregular solid, you can find its volume by submerging it in a eureka can filled with water. The water displaced by the object will be transferred to the measuring cylinder (see diagram on page 192).
4) Record the volume of water in the measuring cylinder. This is the volume of the object.
5) Plug the object’s mass and volume into the formula above to find its density.

Question 11

What is the formula of the volume of a cube?

Answer 11

length x width x height.

make sure you know the formulas for basic shapes.

Question 12

explain how you find the dinsity of a liquid?

Answer 12

1) Place a measuring cylinder on a balance and zero the balance.
2) Pour 10ml of the liquid into the measuring cylinder (see p.232) and record the liquids mass.
3) Pour another 10 mll into the measuring cylinder, repeating the process until the cylinder is full and recording the total volume and mass each time.
4) For each measurement, use the formula to find the density. (remember that 1 ml = 1 cm³)
5) Finally, take an average of your calculate densities. This will give you a value for the density of the liquid.

Question 13

A 0.019 kg gemstone is placed into a full eureka can, causing 7.0 cm³ of water to be pushed out the spout into a measuring cylinder. Calculate the density of the gemstone in g/cm³? (3 marks)

(remember density is all about how tightly packed the particles in a substance are)

Answer 13

Gemstones mass x 0.019 kg = 0.019 x 1000 = 19 g (1 mark)

Gemstones volume = volume of water pushed out of a eureka can = 7.0 cm³
ρ = m ÷ V
= 19 ÷ 7.0 (1mark)
= 2.714…
= 2.7 g/cm³ (to 2 s.f) (1mark)