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Law of conservation of mass – ABOVE

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Science

Year 9

Above satisfactory

Law of conservation of mass

Summary of task

Prior to the sample task, students learnt the basic concepts and history of atomic theory, the difference between elements and compounds, the law of conservation of mass, and different types of chemical reactions.

In this task, students were asked to perform three different chemical reactions to investigate the validity of the law of conservation of mass and to prepare a scientific report on their findings. Following a given procedure, students were asked to mix a solution of copper sulphate with solutions of sodium carbonate, sodium hydroxide, and ammonia. They were to record the mass of reactants before and after mixing and observe and record any changes that occurred. Students were provided with detailed guidelines on how to structure their report, what style of language to use and what content to cover in each section. In the introduction, students were asked to include:

an explanation of chemical reactions
three examples of chemical reactions (one helpful, one unhelpful and one used in industry) with explanations and balanced equations including state symbols
a statement about the importance of the law of conservation of mass
the reasoning behind carrying out the experiment
the intended process and execution of the experiment.

In the discussion, students were asked to:

list evidence that chemical reactions took place in all three reactions
compare the total masses before and after mixing
state the law of conservation of mass and assess whether the results support it
explain whether they would have been able to demonstrate the law of conservation of mass to the same extent, if they had done a similar experiment using acetic acid and baking soda.

Students had two lessons for the practical work and four lessons to analyse their results and complete the report.

Achievement standard

By the end of Year 9, students explain chemical processes and natural radioactivity in terms of atoms and energy transfers and describe examples of important chemical reactions. They describe models of energy transfer and apply these to explain phenomena. They explain global features and events in terms of geological processes and timescales. They analyse how biological systems function and respond to external changes with reference to interdependencies, energy transfers and flows of matter. They describe social and technological factors that have influenced scientific developments and predict how future applications of science and technology may affect people’s lives.

Students design questions that can be investigated using a range of inquiry skills. They design methods that include the control and accurate measurement of variables and systematic collection of data and describe how they considered ethics and safety. They analyse trends in data, identify relationships between variables and reveal inconsistencies in results. They analyse their methods and the quality of their data, and explain specific actions to improve the quality of their evidence. They evaluate others’ methods and explanations from a scientific perspective and use appropriate language and representations when communicating their findings and ideas to specific audiences.

Show all annotations

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Annotations
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Annotation 1
Explains chemical reactions in terms of electron rearrangements
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Annotation 2
Describes occurrence, use and importance of selected chemical reactions, including balanced molecular equations
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Annotation 3
Explains and demonstrates how chemical equations are balanced using colour coding to aid readers’ comprehension
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Annotation 4
States law of conservation of mass including type of system it applies to
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Annotation 5
Explains why law of conservation of mass is important
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Annotation 6
States reason for experiment
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Annotation 7
Outlines how experiment will be conducted

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Annotation 1
Formulates hypothesis
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Annotation 2
Describes safety precautions undertaken
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Annotation 3
Describes experimental procedure

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Annotation 1
Presents measured data and detailed observations in table
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Annotation 2
Provides photographic evidence of reactions

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1
Annotation 1
Identifies colour change as evidence for chemical reaction
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Annotation 2
Summarises experimental results
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Annotation 3
Reflects critically on experimental setup and correctly concludes that law of conservation of mass cannot be demonstrated conclusively by this experiment
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Annotation 4
Explains how a reaction involving production of a gas would not support law of conservation of mass when conducted in an open system
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Annotation 5
Concludes that experiment was not suitable to confirm law of conservation of mass
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Annotation 6
Reflects on understanding gained through conducting this experiment