- Many household substances can be analysed with an indicator in this way. Students can analyse various cleaners based on lemon or vinegar, lemon concentrate, essence of vinegar and decalcifying substances in either solid form (sometimes they consist of pure citric acid) or in liquid form (look for products containing a 50 % citric acid solution).
- The substances colour the dyed filter in different shades of pink. Based on the differences, students can deduce that there are different substances with acidic properties. From the differences in intensities, they can also see that there are variations regarding the intensity of acidic behaviour.
- Providing an opportunity for incorporating ICT: students could use a pH-meter when dealing with household acids (quantify how acidic solutions are; and for further activities how acidic it has to be to affect inorganic & organic substances, for example).
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Freienberg, J. & Flint, A. "Chemie fürs Leben - am Beispiel von Zitronensaft und 'Rohrfrei'; eine alltags- und schülerorientierte Unterrichtseinheit zum Thema Säuren, Laugen und Salze im Chemieunterricht der Sekundarstufe I." University of Rostock, pdf (in German) accessible at:
http://sinus-transfer.uni-bayreuth.de/fileadmin/MaterialienBT/Skript_Flint.pdf |