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Materials: Density

Q5. The photo shows a rock found by Andrew on a beach. To help identify the type of rock, he took measurements to determine its density.

(a) Describe a method Andrew could use to determine the density of the rock.

[6 marks]

 

This type of question is marked in two ways:

- the examiner looks for relevant points

- but also for a logical sequence...

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 3:

The method would lead to the production of a valid outcome. All key steps are identified and logically sequenced.
5 - 6 marks
Level 2:

The method would not necessarily lead to a valid outcome. Most steps are identified, but the method is not fully logically sequenced.

3 - 4 marks
Level 1:

The method would not lead to a valid outcome. Some relevant steps are identified, but links are not made clear.
1 - 2 marks
Level 0:

No relevant content
0 marks

 

Indicative content:

measure mass using a balance or scales

part fill a measuring cylinder with water and measure initial volume

place rock in water and measure final volume

volume of rock = final volume − initial volume

or fill a displacement / eureka can with water level with spout

place rock in water and collect displaced water

measuring cylinder used to determine volume of displaced water

volume of rock = volume of displaced water

use mass and volume to calculate density

use ofthe equation: density = mass/volume

(b) Andrew determined the density of the rock to be 2.55 ± 0.10 g/cm3.

What are the maximum and minimum values for the density of the rock?

maximum density = 2.65 g/cm3

minimum density = 2.45 g/cm3

(both needed for the mark - no 'half marks')

[1 mark]

(c) The table below gives the density of five different types of rock.

Type of rock
Density in g/cm3
Basalt
2.90 ± 0.10
Chalk
2.35 ± 0.15
Flint
2.60 ± 0.10
Sandstone
2.20 ± 0.20
Slate
2.90 ± 0.20

 

Which of the following two types of rock could be the type of rock the student had?

(Tick one box).

Basalt or chalk  
Chalk or flint
Flint or sandstone  
Sandstone or slate  

[1 mark]

(d) Andrew only took one set of measurements to determine the density of the rock.

Explain why taking the measurements more than once may improve the accuracy of the density value.

If more than one value is found a mean valuecan be calculated reducing the effect of random errors, and also allows anomolies to be spotted and eliminated.

[2 marks maximum]

[Total: 10 marks]