02 Acids and alkalis 2 11-14 Working in groupsSelf assessmentPeer assessmentSharing objectives and criteriaQuestioningUsing feedbackUsing tests

A concept cartoon, in which different strategies for dealing with an acid spill are explored, helps students to focus their thinking and discussion about acids and alkalis.

The cartoon is designed to check on the following concepts and misconceptions.

  • The difference between neutralising and diluting when water is added to an acid.
  • The idea that alkalis such as antacids somehow ‘break down’ acids.
  • The idea that an indicator reacts with and therefore uses up an acid.
  • The idea that an alkali such as sodium hydroxide will react with an acid to make it neutral.
  • The addition of excess alkali to an acid produces a solution that is also hazardous.

Learning objectives

Students will understand:

  1. how to deal with acids or alkalis if they are spilt or splashed on the skin
  2. that adding water to an acid or alkali solution dilutes it and makes it less hazardous
  3. that a neutral solution can be obtained by adding an acid to an alkali.

Sequence of activities

Show a newspaper report of an acid spillage from a road tanker. Simulate an acid spill using, for example, 1 mol dm-3 hydrochloric acid. Describe the lesson objectives.

Give each student a copy of the Concept cartoon and a Response sheet.

Circulate and support with prompts while students:

  • work individually
  • read the four suggestions about how to deal with an acid spill
  • comment on the ideas on the Response sheet (including challenging the points made and adding anything they think necessary to the suggestions).

Arrange students in groups of three. Ask them to:

  • compare what they have written with the other two in the group and agree a group response (allowing minority views)
  • select a spokesperson.

In a plenary, ask:

  • each spokesperson to comment on the four suggestions
  • other groups to add to the comments made.

 Circulate and support with prompts while students:

  • work individually
  • annotate their response in the light of the whole-class discussion

and then

  • work in their group
  • identify those ideas about which they were uncertain.
Use ‘thumbs up’ to gain a whole-class view about what they found difficult.

Circulate and support with prompts while students:

  • work individually
  • identify which ideas they found most difficult
  • write, on the back of the Response sheet, how they are going to work on these points
  • hand in the sheet.
Give individual written feedback on the responses and reflections. As well as acknowledging achievement, provide comments that lead the students to recognise their next steps and how to take them.

Assessment for Learning commentary

By working from their own understanding and thinking about other students’ ideas on dilution and neutralisation, a student is more likely to grasp the key messages. Students themselves identify their weaknesses. The teacher gains a clear picture of the level of individual understanding and that of the class as a whole.

Either of the suggested stimuli leads naturally to the objectives.

Specific feedback on the comments the students write on their sheets, is another useful feature of this approach.

Resources

Download Word Download PDF ‘What should we do with the acid spill?’ concept cartoon for each student
Download Word Download PDF Response sheet for each student

Answers

Download Word Download PDF Response sheet answers

Acknowledgement

V. Barker, Beyond Appearances: Student’s misconceptions about basic chemical ideas: A report prepared for The Royal Society of Chemistry, London, Section 7 Acids, bases and neutralisation. London: Royal Society of Chemistry, 2000, available at www.chemsoc.org/networks/learnnet/miscon.htm (accessed October 2005).