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Science at key stage 3    (Year 9)

Unit 9M: Investigating scientific questions
Section 6: Using secondary sources to develop and test hypotheses about factors that might affect the pH of rainwater

QCA

Objectives
Children should learn:
  • to decide which factors may be relevant to an enquiry
  • when it is appropriate to use data from secondary sources
  • how to search for information
  • how to decide which sources of information are appropriate
  • to select appropriate data from secondary sources
  • to identify and describe patterns in data
  • to present information appropriately
  • to look critically at sources of secondary data
  • to look critically at results to decide how strongly they show a trend
  • to interpret results using scientific knowledge and understanding

Activities

Outcomes
Children:
  • Ask pupils to consider what might affect the pH of rainwater, eg location, wind direction, volume fallen, time of year, weather pattern, and put forward a hypothesis.
  • Ask pupils to consider why it is appropriate to use secondary sources to get information, eg it might not rain for several days, it would be difficult to collect enough data to identify trends using rainwater collected over a short period of time.
  • Help pupils search for an environmental database on the pH of rainwater, eg on websites, on CD-ROMs or in reference books.
  • Ask pupils to search for patterns in data, eg by considering whether pH is generally more acidic when wind is from the east, or whether pH is less acidic following stormy weather, to describe any patterns found and present the data they have used as evidence of these patterns.
  • Ask pupils to look critically at the source of secondary data, eg
    • Is the data collection carried out by volunteers?
    • Is there data from some areas but not others?
  • Ask pupils to identify the limitations of their own selection of evidence, eg
    • I only looked at the link between wind direction and pH over 30 days. If I had considered evidence over a longer period I would have more confidence in my results
    • Factors such as location and weather patterns may have affected the pH and I have not had time to investigate these
    • All areas I had data about were in towns and cities; pH in rural areas might be different
  • Help pupils to interpret results in the light of their scientific knowledge and understanding, eg oxides of non-metals such as sulphur and nitrogen are acidic, so when the wind blows towards us from countries with high emissions of these oxides, the rainwater is likely to be more acidic.
  • suggest factors that might affect the pH of rainwater
  • explain why it is appropriate to use secondary sources
  • select appropriate data from appropriate sources
  • search for patterns in data
  • describe any patterns found
  • present the evidence they used to identify patterns
  • evaluate their data in terms of the quality of the source of information and the limitations of their own selection of evidence
  • use their scientific knowledge to explain results

Points to note
  • A database such as the National Environmental Database Project carries relevant information on the pH of rainwater.
  • A similar strategy is used in investigating whether we are fitter than our grandparents, in unit 9B 'Fit and healthy', and to investigate changes in pollution, in unit 9G 'Environmental chemistry'.

Sections in this unit

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This unit is divided into sections. Each section contains a sequence of activities with related objectives and outcomes. You can view this unit by moving through the sections or print/download the whole unit.
1. What sort of questions can be investigated scientifically?
2. Using and evaluating a way of finding out how much of an apple is water
3. Using a model and data from a fair test to find out why elephants throw water over themselves
4. Carrying out a survey, using a suitable sample size, to find out how the moisture level in the soil affects the variety and abundance of plants on the school field
5. Developing a classification system for a variety of plants that grow in and around water
6. Using secondary sources to develop and test hypotheses about factors that might affect the pH of rainwater
7. Concluding the unit on investigating scientific questions