Elias Kalogirou and Eleni Nicas introduce a selection of very small-scale chemistry experiments for school.
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By industrial standards, all school chemistry is small-scale – 50 ml here, 1 g there. For the past three years, however, we have been doing microscale chemistry experiments at our school – using one or two drops of each reagent.
Working at this scale has many advantages. Using smaller amounts of reagent reduces the time, cost and waste involved, and encourages students to think about environmental protection. Although safety precautions are still necessary, the risk involved is lower with smaller volumes – and the students had no difficulties manipulating such small quantities. At this scale, the experiments do not need normal laboratory glassware but can be performed using simple household materials such as chewing-gum packets; these are cheap, can be reused several times and require little storage space.
Below are instructions for some microscale experiments that we perform with 14- to 15-year-old students. Our students carried out the experiments in groups of four. Alternatively, the teacher could demonstrate the experiments by placing the apparatus on an overhead projector.
chewing-gum packet
Image courtesy of Elias
Kalogirou and Eleni Nicas
The reactions are part of the usual Greek education curriculum for this age of students, but would normally be studied on a larger scale.
Rather than using normal, full-scale laboratory equipment, these experiments are carried out in a chewing-gum blister packet, from which the foil and the gum have been removed (see image). Tablet packets would be fine too, if the tablets were large enough. Each experiment takes place in a separate well of the packet.
The tables (experimental procedures and results) for all the experiments can be downloaded as a Word® document from the Science in School websitew1.
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Kulikova / iStockphoto
To prepare the red cabbage indicator, cover 10 g fresh, chopped red cabbage leaves with 200 ml distilled water and bring to the boil. Boil until the liquid turns light purple. Leave it to cool and strain off the liquid, which is the indicator solution.
To prepare the sodium hydroxide (NaOH) solution, dissolve 0.4 g sodium hydroxide in 100 ml water.
To prepare the limewater (saturated calcium hydroxide solution), fill a 500 ml beaker one-third full with calcium hydroxide [Ca(OH)2] and add distilled water up to the 400 ml mark. Stir the mixture well and leave the resulting suspension to settle for several hours. The colourless, saturated solution (limewater) should be poured into a dropping bottle, taking care not to disturb the sediment.
Hydrochloric acid solution (15% w/w) can be bought in the supermarket in some countries. Alternatively, make a 1 M solution (approximately) in the laboratory.
(Note that the hydrochloric acid solution used is more concentrated than the sodium hydroxide solution, to ensure that the acid reactions can be observed with the naked eye, while the base reactions do not waste reagents.)
For the experiments, each of the solutions should be placed in a dropping bottle.
The purpose of Experiment 1 is for the students to realise both that acids and bases change the colour of pH indicators, and that the colour change is different between acids and bases.
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alexeynovikov / iStockphoto
In Experiment 2, the students observe how acids react with metals. They should observe the production of bubbles (effervescence) and also that magnesium reacts more strongly (producing more heat and more bubbles) with acid than iron does – although less acid is used. We explain to our students that the gas produced is hydrogen.
In Experiment 3, the students observe how acids react with carbonates. They should observe the production of bubbles (effervescence). We explain that the gas in the bubbles is carbon dioxide.
Experiment 4 gives the students the opportunity to practise using pH indicator paper. They should learn that the pH of a solution can be determined with indicator paper and the solutions classified as either acid or base.
In Experiment 5, the students investigate the conductivity of distilled water, hydrochloric acid and sodium hydroxide solution. They should learn that whereas distilled water does not conduct electricity, both acid and base solutions do.
diagonally, so that it can be
used to measure out small
quantities of powder
Image courtesy of Elias
Kalogirou and Eleni Nicas
Well 1
|
Well 2
|
Well 3
Stir the mixture |
Well 4
|
Well 5
|
Well 6
|
Indicator | Original colour of indicator | Colour after acid is added | Colour after base is added |
---|---|---|---|
Red cabbage | Well 1: | Well 2: | |
Litmus indicator solution | Well 3: | Well 4: | |
Phenolphthalein | Well 5: | Well 6: |
iron powder
Image courtesy of Elias
Kalogirou and Eleni Nicas
Well 1
|
Well 2
|
/ iStockphoto
Well 1
|
Well 2
|
/ iStockphoto
Solution | Vinegar | Hydrochloric acid | Ammonia | Limewater | Distilled water |
---|---|---|---|---|---|
pH | |||||
Acid or base |
The next step is to construct the electric circuit (left).
circuit
Images courtesy of Elias
Kalogirou and Eleni Nicas
Does the LED light up?
What can you conclude? Does distilled water conduct electricity?
Does the LED light up now?
What can you conclude? Does hydrochloric acid solution conduct electricity?
Does the LED light up?
What can you conclude? Does sodium hydroxide solution conduct electricity?
The authors would like to thank Penelope Galanopoulou, who teaches English at the 3rd Pyrgos Lyceum Pierre de Coubertin, for translating this article from Greek into English.
Κ. Γιούρη – Τσοχατζή (2003) Σχολικά Πειράματα Χημείας, Από τη Μακρο- στη Μικροκλίμακα. Θεσσαλονίκη , Ελλάδα : Εκδόσεις Ζήτη . ΙSBN: 9604318608
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More microscale chemistry
The reactions of chlorine can also be investigated at the microscale. In this experiment, chlorine gas is generated on a microscale from bleach solution and used directly to investigate its reaction with water and halide ions in solution. See:
http://www.practicalchemistry.org/experiments/intermediate/periodic-tabl...