Extracting iron from breakfast cereal

Read our standard health & safety guidance

Lesson organisation

This can be a class experiment or a demonstration as preferred. The experiment is easy to set up, and can be completed in 10 minutes.

Apparatus and chemicals

For the demonstration, the teacher will require:

Mortar and pestle, size sufficient to contain 50 g of the cereal
Beaker (1 dm³)
Magnetic stirrer and follower (stirrer bar) coated in white plastic (Teflon or nylon)
Forceps or clean tongs

Breakfast cereal containing added iron, about 50 g (see note 1)

For the class experiment, each working group will require:

Mortar and pestle, small size
Beaker (250 cm³)
Strong magnet (e.g. neodymium magnet) (see note 2)

Breakfast cereal containing added iron, a few g (see note 1)

Technical notes

1 Kellogg’s ‘Special K’ contains a higher proportion of iron than many other breakfast cereals; see the ingredient lists on packets if a different cereal is preferred.

2 Neodymium magnets are available from science education equipment suppliers as electronics parts and are also recoverable from old computer disk drives.

Procedure

Demonstration

1 Crush about 50 g of the cereal to create a powder and place in the beaker with about 500 cm³ of water.

2 Drop in a white magnetic follower (stirrer bar) and place on a magnetic stirrer for a few minutes.

3 Retrieve the stirrer bar with forceps or tongs and study the grey coating it will have acquired, which consists of fine iron powder.

Class experiment

This can be done using the same procedure as for the demonstration. However, it is unlikely that many schools will have sufficient magnetic stirrers, so this alternative may be useful:

1 Place a few flakes of cereal on a table or bench surface. Hold the magnet close to the flakes and see if they stick to the magnet or are moved by it.

2 Reduce the friction on the flakes by floating four to six flakes on a beaker of water. Hold the magnet close to the flakes and see if they stick to the magnet or are moved by it.

3 Reduce the size of some dry flakes by crushing them to a fine powder using a pestle and mortar. Spread the resulting powder on a piece of paper.

4 Place a magnet under the paper and move the paper over the magnet. Observe any effect the magnet may be having on the movement of the powder. Do NOT put the magnet in direct contact with or close to the powder without the paper in between. With careful manoeuvring, it should be possible to separate out fine grey specks of iron from the rest of the powder.

Teaching notes

In the class experiment, students test whether iron is present in the cereal. In their first test, the cereal is very unlikely to stick to the magnet, and friction is too great to allow the flakes to move on the table or bench surface. Floating the cereal flakes on water reduces friction, however visible movement is still unlikely. Crushing the cereal to a fine powder reduces the size and mass of the particles, and therefore also the friction with the paper. Students should be able to separate out fine grey specks of iron in this final step.

Manufacturers add iron to many cereals – and other food products such as flour – as a finely divided powder of food-grade material. This is believed to react with stomach acid before passing to the small intestine. The body contains enough iron for two small nails, and it is essential for the production of haemoglobin.

It is added in this form (before cooking) because it does not produce any taste or interact chemically with other components of the product. ‘Special K’ packets quote 20 mg of iron per 100 g of cereal. Products such as cornflakes, which are fortified at a lower level, have about 6 - 7 mg of iron per 100 g, while un-fortified breakfast cereals have 1 – 2 mg of iron per 100 g.

An able class may wish to test the grey deposit to confirm that it is indeed iron. The iron powder will have to be reacted in a test-tube with dilute hydrochloric acid (Low hazard below 2 mol dm^-3, refer to CLEAPSS Hazcard 47A and Recipe Card 31) to form iron(II) chloride and hydrogen. The presence of iron(II) ions can be confirmed by adding a few drops of potassium hexacyanoferrate(III) solution (Low hazard, refer to CLEAPSS Hazcard 79 and Recipe Card 38) to give the intense colour of Prussian Blue. Eye protection must be worn if this test is carried out.

Health & Safety checked May 2008

Web Links

Alternative approaches to this experiment are described on a number of websites, mainly from the USA; for example:
www.mcrel.org/whelmers/whelm07.asp
www.stevespanglerscience.com/experiment/00000034

For a detailed review of the processes involved in iron-absorption by the body, see:
http://sickle.bwh.harvard.edu/iron_absorption.html