14 What is a chemical reaction? 11-14 Working in groupsSelf assessmentPeer assessmentSharing objectives and criteriaQuestioningUsing feedbackUsing tests

In this activity, a diagnostic probe and a simple practical introduce students to the idea that a chemical reaction produces one or more new substances with no loss of material. Group discussion and feedback help students to develop their thinking.

Learning objectives

Students will be able to explain that:

  • one or more new substances result from a chemical reaction
  • the amount of matter is conserved in a chemical reaction
  • particles are rearranged in a chemical reaction.

Sequence of activities

Ask students how they would recognise if a chemical reaction had occurred.

Prompts that may help include: diluting fruit squash, burning coal, frying an egg, dissolving sugar in water.

Collect ideas to review later.

Give each student the worksheet Phosphorus. Circulate and support as students complete the sheet individually.

Allow 10 minutes maximum to complete the task.

Organise a snowball.

  • Ask students to share their responses with a partner.
  • Join up pairs to form groups of four.
  • Ask groups to discuss their answers and agree if possible.
  • Suggest that groups elect a spokesperson to feedback to the class.

Allow about 15 minutes for students to discuss their answers.

In a short plenary:

  • select students to give responses
  • ensure a range of views are represented
  • comment on and question the responses, but don’t give away the correct answer.

Introduce the next activity called Kallium and plumbate. Give each student a copy of the sheet Kallium and plumbate. Give one set of the equipment to each group.

Supervise and support as groups:

  • work through the practical task
  • answer the question, ‘Where did the yellow stuff come from?
  • devise and agree rules for determining when a chemical reaction has occurred
  • elect spokespersons to give their answers to the class.

In a plenary:

  • collate answers to the yellow stuff question.
  • develop the idea that chemical reactions involve making new substances.
  • invite spokespersons to give their group’s ‘rules’ for identifying when chemical reactions have happened
  • compare these to the lists given at the start of the lesson and the responses to the Phosphorus sheets
  • lead students towards obvious changes, but mention the particle model
  • agree a set of rules for determining when a chemical reaction has happened – these should include ‘visible’ and ‘non-visible’ components
  • encourage the students to write down how their thinking about chemical reactions has changed.

Give feedback based on the quality of students’ ideas and the extent of change. Highlight where further development is needed, for example, in developing particle ideas.

Assessment for learning commentary

This resource looks at the key concept in chemistry. Through the diagnostic probe students are made aware of their own thinking about this idea. Discussion with peers allows them to change their thinking in a ‘safe’ context, especially when linked to shared experiences of a simple practical.

Reviewing how they have moved forward from their ideas given in the diagnostic probe will help students to recognise their own progress. Teacher feedback is used to confirm this and help students with any lingering misconceptions.

Resources

Props

For each student

Download Word Download PDF Phosphorus
Download Word Download PDF Kallium and plumbate

Equipment

For each group

  • Three pestles and mortars, or similar
  • Samples of solid potassium iodide (labelled Kallium) and lead(II) nitrate (labelled Plumbate) – about 50 g each
  • A tray to hold everything
  • Access to a balance weighing to 0.01 g.

Safety note

It is the responsibility of the teacher to carry out appropriate risk assessments.

Answers

Phosphorus

  • Yes. White smoke is a sign that a chemical change has occurred.
  • 400 g. Mass is conserved when a chemical change occurs.
  • Production of a new substance that did not exist before by rearranging atoms, molecules or ions.

Kallium and Plumbate

  • A reaction occurs in the final bowl when the substances were ground together.
  • There was a colour change to bright yellow.
  • By discussion.

Acknowledgements

V. Barker, Beyond Appearances: Student’s misconceptions about basic chemical ideas: A report prepared for The Royal Society of Chemistry, London. London: Royal Society of Chemistry, 2000, available at www.chemsoc.org/networks/learnnet/miscon.htm (accessed October 2005).

V. Barker, Building Success in GCSE Science: Chemistry. Dunstable: Folens, 2002.

W. DeVos and A. Verdonk, J. Chem. Ed. Part 1, 1985, A new road to reactions.