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Materials: Density

Q1.

(a) Barry wanted to determine the density of a small piece of rock.

Describe how Barry could measure the volume of the piece of rock.

This type of question allows the examiner to give you marks within a range according to how clearly you express your ideas.

It is worth taking the time to plan this type of answer...

In pencil - list what would need to be done... you can then change the order when you think it through. Then carefully write an account.

To get 3 - 4 marks you needed to give a method that would lead to the production of a valid outcome - key steps identified and logically sequenced.

To get 1 - 2 marks the method would not necessarily lead to a valid outcome but some relevant steps are identified.

There are two possible methods - depending on the size and shape of the rock. Either will get you the marks. For a small object this would be the best method...

If it will fit into the neck of a measuring cylinder you can:

part fill a measuring cylinder with water

read the initial volume at eyelevel (bottom of the meniscus)

place object in water

measure final volume

volume of object = final volume – initial volume

 

Otherwise you will need to:

fill a displacement/eureka can with water and stand it on a support in a sink

the water level must be just at the lip of the spout, so fill beyond that and allow the excess to run out down the drain

place a measuring cylinder beneath the spout

gently place the object in the water

collect the displaced water in the measuring cylinder

determine the volume of displaced water

[4 marks]

(b) The volume of the piece of rock was 18.0 cm3.

Barry measured the mass of the piece of rock as 48.6 g.

Calculate the density of the rock.

density = mass/volume

ρ = m/V

ρ = 48.6/18.0

ρ = 2.70 g/cm3

You should give the answer to three significant figures asthe question has all 3sf data

[3 marks]

(c) The bar chart shows the densities of different types of rock.

What type is the rock Barry investigate most likely to be?

Limestone

[1 mark]

(d)

(i) Suggest one source of error that may have occurred when the student measured the volume of the rock.

eye position when using measuring cylinder (parallax error)

water level in can (at start) not at level of spout

not all water displaced by stone is collected in container (any one)

[1 mark]

(ii) How would the error you described affect the measured volume of the rock?

parallax error could result in a lower or higher result - depending on whether you looked above or below the level.

lower value from water not at spout

lower value from water not collected correctly (any one)

[1 mark]

[Total: 10 marks]