GCSE ChemistryUnit 4 Controlled Assessment

This unit is assessed by Controlled Assessment. It is worth 25% of the total marks and consists of a minimum of one practical investigation based on topics in the specification.

Access arrangements (see sections 4.5 and 5.4) can enable candidates with special needs to undertake this assessment.

Teachers are encouraged to undertake a wide range of practical and investigative work, including fieldwork, with their candidates. We take the view that it is not good practice to do practical work only for the Controlled Assessment. As teachers know well, candidates enjoy and are motivated by practical work. Throughout this specification we have given many examples of practical work supporting the science content. Full details of this practical work are included in our resources package.

In this unit, candidates use a range of practical skills and knowledge in one investigation chosen from those supplied by AQA. The investigations are based on topics in the specification. Guidance for teachers will be given with each investigation. Every year, three Controlled Assessments will be available; one for Unit 2 and two for Unit 3. Each task assesses How Science Works skills, not candidates' knowledge and understanding of the science context.

The Assessment Focus thread from National Strategies APP (Assessing Pupils' Progress) is shown next to each task. This will enable teachers to ensure progression from KS3 to KS4.

AF/thread 1/4a) being able to develop a hypothesis

Candidates should be able to:

• suggest the outcome of an investigation.

AF/thread 1/4b) being able to test hypotheses

Candidates should be able to:

• plan a fair test to hypotheses.

AF/thread 4/1c) using appropriate technology.

Candidates should be able to:

• appreciate that technology such as data logging may provide a better means of obtaining data. They should be able to suggest appropriate technology for collecting data and explain why a particular technological method is the most appropriate.

AF/thread 4/4a) identifying some possible hazards in practical situations

Candidates:

• will be expected to independently recognise a range of familiar hazards and consult appropriate resources and expert advice.

AF/thread 4/4b) suggesting ways of managing risks.

Candidates should be able to:

• assess risks to themselves and others and take action to reduce these risks by adapting their approaches to practical work in order to control risk.

AF/thread 4/3a) carrying out practical work and research, and using the data collected to develop hypotheses.

AF/thread 4/3a) appreciating that, unless certain variables are controlled, the results may not be valid

Candidates should be able to:

• explain whether results can be considered valid and recognise when an instrument or technique might not be measuring the variable intended

AF/thread 4/3b) identifying when repeats are needed in order to improve reproducibility

Candidates should be able to:

• recognise that a second set of readings with another instrument or by a different observer could be used to cross check results

AF/thread 4/3c) recognising the value of further readings to establish repeatability and accuracy

Candidates should be able to:

• understand that accuracy is a measure of how close the measured value is to the true value

AF/thread 4/3d) considering the resolution of the measuring device

Candidates should be able to:

• explain that resolution is the smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the indication (output)

AF/thread 4/3e) considering the precision of the measured data where precision is indicated by the degree of scatter from the mean

Candidates should be able to:

• distinguish between accuracy and precision when applied to an instrument's readings

AF/thread 4/3f) identifying the range of the measured data.

Candidates should be able to:

• identify the upper and lower limits of the range and be able to identify which extra results, within or outside the range, would be appropriate.

AF/thread 5/1a) appreciating when it is appropriate to calculate a mean

AF/thread 5/1b) calculating the mean of a set of at least three results.

Candidates should be able to:

• recognise the need to exclude anomalies before calculating means to an appropriate number of decimal places.

AF/thread 3/2a) drawing tables

Candidates should be able to:

• draw up a table of two or more columns, with correct headings and units, adequately representing the data obtained

AF/thread 3/2b) drawing charts and graphs

Candidates should be able to:

• construct an appropriate graphical representation of the data such as a bar chart or line graph and draw a line of best fit when appropriate. Candidates may use ICT to produce their graphs or charts.

AF/thread 3/1c) choosing the most appropriate form of presentation.

Candidates should be able to:

• identify the most appropriate method of display for any given set of data.

AF/thread 2/1a) recognising that an opinion might be influenced by factors other than scientific fact

Candidates should be able to:

• recognise that the opinion may be influenced by economic, ethical, moral, social or cultural considerations.

AF/thread 1/2b) identifying scientific evidence that supports an opinion.

AF/thread 5/2a) identifying causes of variation in data

Candidates should be able to:

• identify from data whether there is any variation other than obvious anomalies, and identify a potential cause for variation

AF/thread 5/2b) identify from data whether there is any variation other than obvious anomalies, and identify a potential cause for variation or uncertainty

Candidates should be able to:

• appreciate that human error might be the cause of inaccurate measurements and explain how human error might have influenced the accuracy of a measurement or might have introduced bias into a set of readings

AF/thread 5/2c) recognising and identifying the cause of anomalous result

Candidates should be able to:

• identify anomalous results and suggest what should be done about them

AF/thread 5/2d) recognising and identifying the cause of systematic errors.

Candidates should be able to:

• identify when a data set contains a systematic error and appreciate that repeat readings cannot reduce the effect of systematic errors
• realise that a zero error is a type of systematic error. Candidates should be able to identify if a scale has been incorrectly used and suggest how to compensate for a zero error.

AF/thread 5/3a) describing the relationship between two variables and deciding whether the relationship is causal or by association.

• use terms such as linear or directly proportional, or describe a complex relationship.

AF/thread 5/3a) writing a conclusion, based on evidence that relates correctly to known facts

Candidates should be able to:

• state simply what the evidence shows to justify a conclusion, and recognise the limitations of the evidence

AF/thread 5/3b) using secondary sources

Candidates should be able to:

• appreciate that secondary sources or alternative methods can confirm reproducibility

AF/thread 5/4c) identifying extra evidence that is required for a conclusion to be made

Candidates should be able to:

• suggest that extra evidence might be required for a conclusion to be made, and be able to describe the extra evidence required

AF/thread 5/4d) evaluating methods of data collection.

Candidates should be able to:

• appreciate that the evidence obtained may not allow the conclusion to be made with confidence. Candidates should be able to explain why the evidence obtained does not allow the conclusion to be made with confidence.

AF/thread 1/2a) considering whether or not any hypothesis made is supported by the evidence

Candidates should be able to:

• assess the extent to which the hypothesis is supported by the outcome

AF/thread 1/2b) developing scientific ideas as a result of observations and measurements.

• suggest ways in which the hypothesis may need to be amended, or whether it needs to be discarded in light of the achieved outcome of an investigation.