GRADE: 8
SUBJECT: NATURAL SCIENCES
TERM TWO
ASSESSMENT TASK EXEMPLAR
PRACTICAL TASK / INVESTIGATION
PRACTICAL TASK / INVESTIGATION
TOTAL MARKS
20
Grade: 8
Practical TASK / INVESTIGATION
Term 2
Topic: Investigating how fast liquids mix
Aim: To investigate how fast liquids mix
Materials and Apparatus used
•
•
•
•
Food colouring
3 droppers
3 beakers labelled A, B and C
o beaker A - filled with 50 ml ice water,
o beaker B - filled with 50 ml tap water at room temperature
and
o beaker C - filled with 50 ml hot water.
Stop watch
ACTIVITY 1
Method:
•
•
Work in pairs.
Place one drop of food colouring simultaneously in each of the
three beakers, filled with:
A
B
C
•
filled with 50 ml ice water,
filled with 50 ml tap water
filled with 50 ml hot water
Place one drop of food colouring simultaneously in each of the
three beakers, A, B and C.
Investigating how fast liquids mix
A
Ice water
C
B
Tap water at
room
temperature
Hot water
Note: Do not stir or mix the liquids
•
Measure the time it takes for the food colouring to completely
mix with the water
•
Draw a table to record your results.
Sarah and Lerato completed this investigation and obtained the results
below:
Liquid
Time it took to mix completely (s)
Beaker A: Ice water
73
Beaker B: Tap water at
room temperature
58
Beaker C: Hot water
45
Question 1
1.1
Describe what happens when the drop of food
colouring enters the water.
(2)
1.2
What property of liquids does the observation above
illustrate?
(1)
1.3
What conclusion can be drawn from Sarah and
Lerato’s results?
(2)
1.4
Why is it important to use the same amount of liquid
in each of the three beakers?
(2)
Use your knowledge of the particle model of matter
and try to give an explanation for this observation.
(2)
1.5
ACTIVITY 2
Instructions
• Complete this activity outside the classroom, preferably on an
open field and on a windless day
Method:
•
Use three containers with vanilla essence as follows;
First container
Second
container
Third container
Vanilla essence in a beaker filled with ice
Vanilla essence in a beaker filled with hot water
Vanilla essence in a beaker filled with tap water at
room temperature
Note: Place the three containers at least 10 m apart.
Ice
Container
with
vanilla
essence
Hot
water
Container
with
vanilla
essence
Tap water
at room
temperature
Container
with
vanilla
essence
•
Let a group of learners (three to four) stand exactly 3m away from
the container with the vanilla essence.
•
Open the containers and measure the time it takes before most
of the learners smell the vanilla essence.
•
Record your findings
Rosemoor and Lungi completed this investigation and obtained the
results below:
Vapour
Time (s)
Vanilla essence kept in ice
31
Vanilla essence at room
temperature
20
Vanilla essence kept in boiling
water
14
Question 2
2.1
What conclusion can be drawn from these results?
(2)
2.2
Identify the independent variable in this investigation
(1)
2.3
Identify the dependent variable in this investigation
(1)
2.4
Why is it important that the three containers are far apart from
each other?
(1)
Is it better to use a group of learners to detect the smell or a
single learner? Give a reason for your answer.
(3)
2.5
(8)
2.6
Draw a graph to illustrate the results of this investigation. Make
sure your graph has:
•
An appropriate heading,
•
Both the axes have appropriate headings and
•
All the data are plotted correctly.
•
Also ensure that the correct variable is placed on the
correct axis for this investigation.
(4)
TOTAL MARKS:
(20)
Draw a graph in the template below.
(4)
Practical TASK / INVESTIGATION
MARKING GUIDELINES
Topic: Investigating how fast liquids mix
Question 1
1.1
The food colouring slowly starts to spread through the liquid.
Strands of colour can be observed in the entire liquid that
spreads out and eventually forms an even colour.✓
(1)
1.2
Liquids consist of particles✓ that continuously moves around ✓
(2)
1.3
The colder the water✓, the longer it takes for the mixture to
mix.✓
(2)
If more water is used, the water will take longer to mix with all
the water, but this will not tell us anything about the influence of
the temperature on the experiment (the amount of water is a
control variable) ✓
(1)
When the temperature is higher the particles move faster ✓ and
will therefore take less time to move through the entire liquid.✓
(2)
1.4
1.5
(8)
Question 2
2.1
2.2
The hotter the vanilla essence✓, the faster you will be able to
smell it.✓
Temperature of the vanilla essence✓
(2)
(1)
2.3
Time it takes for learners to smell the vanilla essence✓
(1)
2.4
If they are too close, learners that are investigating one
container, might smell the vapour coming from another
container.✓
(1)
It is better to use a group of learners. ✓ All learners do not have
the same sense of smell - it is not a very accurate measuring
instrument. ✓ The average of a number of measurements will
therefore give a more accurate reading.✓
(3)
2.5
2.6
Graph Drawing
(4)
TOTAL MARKS: (20)
Time it takes for vanilla gas to spread through the room
vs. temperature of vanilla
35
31
30
Time (s)
25
20
20
14
15
10
5
0
Vanilla essence kept in ice
Vanilla essence at room
temperature
Criteria for Marking the Graph
Heading
✓
Headings of Axis
✓
Correct Data on Correct Axis
✓
Plotting of Points
✓
(4)
Vanilla essence kept in boiling
water