Chemistry for the gifted and talented: rusting

This resource accompanies the article Raising expectations. The activity originally appeared in the book Chemistry for the gifted and talented.

Learning objectives

1. Develop higher order thinking skills including lateral thinking and creative thinking.
2. Design a valid investigation which models one of the factors that might affect the rate of rusting at different depths below sea level.

Introduction

This activity looks at rusting in the context of shipwrecks. It aims to develop higher order thinking skills including some lateral thinking and creative thinking. It has different demands to the traditional experiment to show the factors needed for rusting to occur.

Prior knowledge

Learners will need to be familiar with the topic of rusting in order to be able to ask probing questions and design an appropriate experiment. Learners will need to be confident with the following scientific ideas:

• Rusting of iron requires oxygen and water.
• Salt speeds up rusting.
• The sacrificial protection of iron by more reactive metals, such as zinc or magnesium.

The questions on slide 8 help to assess and activate this prior knowledge and free up working memory so that learners can use the higher order thinking skills.

Teacher notes

This resource is best used as a teacher-led class discussion using the accompanying Powerpoint presentation. The discussion will lead on to group and practical work. The lateral thinking section could be used as a lesson to follow on from an introduction to rusting of iron. The experiment design section is optional and the activity can be used without it.

Part 1: Lateral thinking exercise

The learners may not have met these before and you might want to go through an example with them – ‘Anthony and Cleopatra lie dead on the floor (in a pool of water)’. The learners ask questions which require a yes or no answer. Answer the questions to help your learners discover that Anthony and Cleopatra are goldfish whose bowl has fallen on the floor when the shelf, on which it was sitting, broke.

In the lateral thinking exercise in this activity the shipwreck in deeper water was carrying a cargo of zinc and magnesium. Learners in need of more challenge could devise their own lateral thinking problems, perhaps for homework.

Ask your learners to design a concept cartoon on the predictions about the shipwrecks. They can do this all together or in groups. The cartoon should have a drawing in the middle showing the shipwrecks at different depths and four speech bubbles around it expressing opinions about why one will be rustier than another. The support sheet contains templates for learners who do not want to draw the central image. The best cartoons will be those with the greatest number of plausible explanations. An example of a good concept cartoon is given on slide 11. It might be a good idea to do a group effort on a different topic on the board before the students produce their own. One example could be four opinions on: whether mayonnaise is a liquid or a solid; whether magnesium would dissolve in acid on a space station; what climate change will mean for the UK; who is doing the greater good for humanity, the doctor or the research scientist working on a cure for cancer.

Part 2: Planning an investigation

Learners will plan an investigation to investigate one of the factors that affect the rate of rusting. The planning itself is the aim of the exercise, but if you also want your learners to carry out their planned investigations it will need some advance preparation. A suggested list of some apparatus required is included for technicians.

Learners may find it difficult to get reliable results and should be encouraged to run their experiment more than once so that they get an idea of the reliability. A couple of methods they could try for measuring the amount of rusting are: weighing the dried rust after filtering or weighing the nails and recording the mass lost as rust.

Practical notes

The actual requirements will depend on the plans written by the learners.

If the class are going to carry out their plans it is a good idea to ask your science technician, if you have one, which pieces of glassware they are happy to leave nails in to rust. There is advice about rust stain removal in CLEAPPS Bulletins 103 and 108.

The practical may need to be left for some time (a week or more) so you will need to check with the technician or other teachers in your department which equipment will need to be returned if it needs to be used again during that time. Agree a suitable place where the experiment can be stored between lessons to prevent it being cleared away prematurely or tampered with in a way that might affect the results.

Apparatus

• Test tubes
• Thermometers
• An electronic balance
• Water pumps
• Apparatus to draw air through the mixture in a boiling tube
• A kettle

Materials

• Nails
• Salt
• Distilled water
• Cooking oil
• Emery paper
• Filter paper