ARTICLES
Snot, Snow, Milk – Chemistry! (continued)
• Determine the effects of using more than one group 2 ion e.g.
try adding Mg 2+ in varying quantities to the calcium chloride
solution.;
of food colouring for dramatic effect and you can then filter off
the white solid, remove the food colouring from the filtrate using
charcoal absorption, and evaporate the water to leave behind a
chloride salt. The plastic bag can be washed and re-used, as the
calcium carbonate does not adhere to the plastic.
• Filter the precipitate and measure % yield for different grade
filter papers.
As an example, one of my Year 9 students investigated the
effect of adding a few drops of phenolphthalein to the potassium
carbonate, and discovered the pink colour remains all the way
through to the formation of the solid. Then as the waters of
hydration are released, the pink colour fades. A research paper
confirms that as the crystals becomes more ordered, the pH falls
below 9. (Wang et al, 2013).
References
Declet, A., Reyes, E., and Suarez, O. (2015). “Calcium carbonate
precipitation: A review of the carbonate crystallization process
and applications in bioinspired composites.” Rev.Adv.Mater.Sci.
44, pp 87-107. Available: https://bit.ly/32gokT8
Finally, the experiment does not need to use expensive laboratory
reagents for some of these projects. Washing soda sells for about
$4 a kilogram and moisture absorbers (e.g. Damp-Rid) cost
about $6 a kilogram in bulk from hardware/supermarkets. These
are cheap sources of sodium carbonate and calcium chloride
respectively. For the reaction in the plastic bags, you can also use
tap water for making up the solutions rather than distilled water.
The calcium chloride solution has a relatively short shelf life (a
few weeks) as it absorbs carbon dioxide from the atmosphere,
so make it up fresh when possible.
General Chemistry: An Atoms First Approach (2019), Howard
University. Available: https://bit.ly/2sRWtbU
Jones, J. (2019), “Year 7 Practical Skills for Inquiry Learning”,
Science Education News 68(1), pp 57-67.
Rodriguez-Blanco, J.D., Shaw, S., and Benning, L.G. (2010).
“The kinetics and mechanisms of amorphous calcium carbonate
(ACC) crystallization to calcite, via vaterite” Nanoscale, 3(6).
Available: https://bit.ly/33wvCCB
Wang,H., Huang, W., and Han, Y. 2013). “Diffusion-reaction
compromise the polymorphs of precipitated calcium carbonate”,
Particuology, 11(3). Available: https://bit.ly/2Mgh3gs
The products of the reaction can also be repurposed. It can be
used in Stage 4 for filtration practice instead of using chalk dust
and water. To add other separation techniques, try adding a bit
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