# Scientific Thinking and Problem Solving

```Year 8-Scientific Thinking and Problem Solving
Unit Reference: Transport Highways in Humans
This task consists of two parts.
The tasks will assess you and your partner’s abilities to think critically, solve
problems and to analyse data.
The first part of this task examines your ability and that of your group to come up
with a suitable investigation plan to solve a given problem.
The second part of this task examines your ability to work independently.
Part A-Investigation Plan- Group Work
The air around us that we breathe in contains a small amount of carbon dioxide.
When we breathe out (exhale), the air coming from our lungs contains a larger
amount of carbon dioxide (than the air that we breathe in). If we exercise we
breathe out even more carbon dioxide.
Carbon dioxide is a colourless odourless gas. However, it can be detected using
limewater (calcium hydroxide). Limewater left in a beaker or test tube gradually
turns a “cloudy milky white” colour due to carbon dioxide gas in the air
dissolving in it and then reacting to form a cloudy white precipitate.
If carbon dioxide gas or air containing carbon dioxide gas is bubbled into
limewater this cloudy white precipitate forms much more quickly.
One problem to overcome in this investigation may be how to tell when the
limewater solution has reached the same degree of milkiness in each test. You may
want to use the following idea but feel free to offer your own suggestions if you wish.
Idea- looking through the limewater solution at a cross drawn on a piece of paper
may assist you.
Your group may be able to come up with other methods to solve this problem. You
should include these in your report with a final judgement as to which method
would be the best and why.
Science Unit Curriculum K–12 Directorate
NSW Department of Education and Training
Oxley High School
page 1 of 8
The Problem
You can ask for an extra ANSWER SHEET if it is required.
1. Work out a practical procedure that would allow you to compare the amount of carbon dioxide
breathed out for different rates of exercise.
Note a) In order to consider “rates of exercise”, you must take into account the time taken to do the
exercise.
Note b) Any equipment you list should be available at school.
Note c) Limewater can irritate the skin, eyes, nose and mouth if it makes contact.
2. Explain how you would measure the amount of carbon dioxide gas produced for different rates
of exercise.
3. List any problems that are likely to occur with your procedure and possible solutions to
overcome these.
4. Include any extra ideas to solve this problem as well- (under the heading Extra Ideas) .Compare
methods giving reasons for your choice of the best method.
* On your ANSWER SHEET record the names or initials of the student or
students who came up with that particular idea or suggestion. Write the initials
next to each part.
Science Unit Curriculum K–12 Directorate
NSW Department of Education and Training
Oxley High School
page 2 of 8
Group Names…………………………………………………………….Class………
Experiment: Carbon dioxide and breathing
Aim
To investigate whether the amount of carbon dioxide exhaled increases with the rate of exercise.
1. Procedure
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Science Unit Curriculum K–12 Directorate
NSW Department of Education and Training
Oxley High School
page 3 of 8
2. How to measure the amount of carbon dioxide produced for different rates of exercise.
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3. Some likely problems and their possible solutions
Likely Problems
Possible Solutions
4. Extra ideas to solve this problem- comparison of different methods
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Science Unit Curriculum K–12 Directorate
NSW Department of Education and Training
Oxley High School
page 4 of 8
Marking Criteria-Part A
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Lists all equipment required to complete the task described
Clearly outlines all steps required to successfully complete this investigation
in correct sequence
Clearly explains how to measure and compare amounts of CO2 produced for
different rates of exercise.
Demonstrates creativity in the plan proposed and in proposed solutions to
potential problems
Appraises viable alternative methods of tackling the problem
Lists most equipment required to complete the task described
Outlines most steps required to satisfactorily complete this investigation in
sequence
Correctly explains how to measure OR compare amounts of CO2 produced
for different rates of exercise
Shows some initiative in their plans or solutions to likely problems
Provides an alternative viable method of investigation
A
5 marks
Each
B
4 marks
Each
Lists some equipment needed to complete the task described
Lists some steps required to complete this investigation mostly in sequence
Outlines a possible method for measuring OR comparing amounts of CO2
produced for different rates of exercise
Identifies a viable solution to a possible problem
Suggests a possible alternative method
C
3 marks
Each
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Identifies some equipment relevant to the task
Mentions some steps relevant to this problem
Correctly describes the change to limewater or indicator when CO2 is
bubbled through.
Identifies a possible problem and a possible solution
Provides an alternative to the suggested method
2 marks
Each
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Lists some equipment
Lists some steps in their investigation plan
Mentions doing a limewater or indicator test
Identifies a possible problem in the investigation
1 mark
Each
D
E
A: 22 - 25
B: 17 - 21
C: 10 - 16
D: 6 - 9
E: 1 - 5
Comment
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Science Unit Curriculum K–12 Directorate
NSW Department of Education and Training
Oxley High School
page 5 of 8
Scientific Thinking &amp; Problem Solving- Teacher’s Marking Scheme
This information should assist in making a judgement about the level of performance i.e. A, B, C, D
or E for each of the marking criteria listed in Part A of this task.
Marking Guidelines-Equipment List
Necessary (N)
Suggested (S)
Limewater or indicator solution
Safety goggles
Stopwatch
Paper to mark a cross on
Straw or tube
Pen(s) to draw a cross
Test tube/ beaker / flask/ bottle
Exercise equipment if required
Marking Criteria- Equipment
A 4N, 1-4S
B 3N, 1-4S
C 2N, 1-4S
D 1N, 1-4S
E 1-4S
Procedure
 Choose one person to do the exercise or activity.(N)
 It is best that the same activity/ sort of activity be done prior to each limewater (or equivalent)
test. (S)
 To increase the rate of the activity the same number of repetitions should be done in a shorter
time eg. step up and down on a box or steps a prescribed number of times in a shorter time
interval for each successive test / or for each successive test perform it at a faster rate eg
walk…..run…..jog……sprint. .(N)
 Exercise for the same measured time period. (S)
 Perform each limewater test using freshly poured solution (immediately prior to testing). .(N)
 Use the same quantity (volume) of limewater for each test .(N)
 If using the “cross method ”to compare carbon dioxide levels- bubble out / exhale air containing
carbon dioxide at the same rate into the limewater for each test(N)
 If using the precipitate method count the number of bubbles of air exhaled into the limewater or
measure the volume of air exhaled- make this the same for each test.(N)
 Position a cross below the vessel into which the air is bubbled and time from the onset of
bubbling till the instant when the cross can no longer be seen. Record these times. (N)
 Repeat the process to check on results.(S)
 Observe safety precautions when using limewater- eg use of safety goggles to protect eyes,
gentle bubbling to avoid splashes, avoid sucking on the straw, wash the skin, mouth or eyes
thoroughly if they come into contact with limewater. (S)
2. How to measure the amount of carbon dioxide produced for different rates of exercise.
a) Time how long it takes from the beginning of exhaling bubbles of air (containing carbon
dioxide), till the cross disappears. The shorter the time the more carbon dioxide in the exhaled air
or
b) Count the number of bubbles of exhaled gas required for this to happen remembering to exhale
at a slow constant rate – no faster than 1 bubble per second. The greater the content of carbon
dioxide, the less the bubbles of gas needed for the limewater to change colour.
or
c) Determine the mass of the precipitate produced after bubbling into limewater
Marking Criteria- Procedure
A 6N in sequence, 1-4S; 2 a) or b) or c) B 4-5 N in sequence, 1-4S, 2a) or b) or c)
C 3-4 N mostly in sequence 1-4 S, 2a) or 2b)
D 2-3 N, 1-4 S
E 1-2 N or S
Science Unit Curriculum K–12 Directorate
NSW Department of Education and Training
Oxley High School
page 6 of 8
3. Some likely problems and their possible solutions
Likely Problems
Possible Solutions
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blowing air into the limewater at a
constant rate
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person tested to breathe out at a slow
constant rate - keep the number of
bubbles in a measured period of
time eg. 10 seconds, the same
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exhaling the same quantity of air in
each test
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person tested to breathe out at a slow
constant rate - keeping the total
number of bubbles of gas the same
for each test
or trap the expired air and bubble
equal quantities into limewater for
each test eg. using a syringe
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limewater reacting(responding) to
carbon dioxide in the surrounding air
as well as to expired air after exercise
Limewater spills on skin, eyes or
mouth
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Pour a fresh sample of limewater just
prior to each test
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Wear safety goggles and bubble out
slowly to avoid splashes on to face or
skin. Care in handling.
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Different people have different lung
capacities and fitness levels
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Test the same person each time
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The limewater may turn milky too
quickly to detect differences between
tests
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dilute the limewater
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It may be difficult deciding when the
cross disappears
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Different types of exercise may
produce different amounts of carbon
dioxide
Breathing rate and carbon dioxide
while after exercise
Inaccuracies (lack of reliability) in
expired air tests etc.
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Look through a longer column of
limewater at a dark cross on a white
background
Perform the same type of exercise at
successively greater rates
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Test for carbon dioxide levels 15
seconds after each exercise period
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Repeat the process- compare, average
etc.
4. Extra Ideas
These should include other ideas suggested by members of the group which weren’t referred to in
the procedure but can also include other possible solutions to problems identified in the table
above eg. creative ways to ensure the same quantity of air is tested each time. In either case rate
student answers on the basis of how creative they have been in their proposals and also on their
judgement of the alternatives suggested. Refer to the marking criteria to make your judgement.
Refer back to the marking criteria to make your final judgement.
Marking Criteria- Solutions to Problems and Extra Ideas
Base your judgement on the given criteria.
Science Unit Curriculum K–12 Directorate
NSW Department of Education and Training
Oxley High School
page 7 of 8
Scientific Thinking Problem Solving and Critical Thinking
Part A
Outcome 4.20: A student uses an identified strategy to solve problems.
4/5.20 problem-solving:
a) identify the nature of a presented problem
b) describe different strategies that could be employed to solve an identified problem
c) use identified strategies to develop a range of possible solutions to a particular problem
d) evaluate the appropriateness of different strategies for solving an identified problem
Outcome 4.21: A student uses creativity and imagination to suggest plausible solutions to familiar
problems.
4/5.21 the use of creativity and imagination:
a) produce creative solutions for problems
b) propose ideas that demonstrate coherence and logical progression
c) apply critical thinking in the consideration of proposals
Part B
Outcome 4.19 : A student draws conclusions based on information available.
4/5.19 thinking critically:
a) justify inferences in light of gathered information
b) identify data which supports or discounts an hypothesis, a question being investigated or a proposed
solution to a problem
d) make generalisations in relation to a relevant set of observations or experimental results
e) anticipate and/or respond to problems as they arise in practical situations
f) use models, including mathematical ones, to explain phenomena or make predictions
g) use cause and effect relationships to explain ideas.
Science Unit Curriculum K–12 Directorate
NSW Department of Education and Training
Oxley High School