Melissa Rooney Blogging

Melissa Rooney Blogging

"There is more to life than increasing its speed." – Mahatma Gandhi

Fun Science: Easy Hands-on Chemistry Lesson

 

This is a picture of my 6YO son’s back-to-school Magic Crystals, obtained after immersing dolostones in vinegar (with a little orange food coloring) for 5 days . I’ve never made mushroom crystals before, so we were both truly enthralled. Click HERE to get my six-year-old’s take on the experience.

Dolostones (which can be purchased from Educational Innovations) are dolomite rocks, which are primarily composed of calcium magnesium carbonate or CaMg(CO3)2. When the calcium magnesium carbonate reacts with acetic acid (aka vinegar, CH3COOH), mushroom-shaped aragonite crystals made of calcium carbonate (CaCO3), easily form. In chemistry terms, dolomite *decomposes* to aragonite, producing carbon-dioxide in the process (which may be visible as a very small ‘fizz’ under a simple microscope). Here’s the proposed overall chemical equation for the reaction: CaMg(CO3)2 = MgO + CaCO3 + CO2.

For simple instructions regarding how to make aragonite crystals using dolomite rocks and vinegar (including a bit of history and chemistry), see https://s3.amazonaws.com/cdn.teachersource.com/downloads/lesson_pdf/RM-375.pdf.

Another (though less easy) way to make crystals using sugar and water is detailed here: http://www.ehow.com/how_4603964_crystals-as-science-project.html.

And here’s a 6th-grade slide show on minerals like dolomite: http://slideplayer.com/slide/5914901/.

Want even more detail? See the following in google books: Dolomite and Acetic Acid

and

http://www.rigaku.com/downloads/journal/Vol5.2.1988/engler.pdf

Note the following:

1) The reaction of dolomite with acetic acid (Dolomite and Acetic Acid) produces carbon dioxide:
4HCH3CO2 + CaMg(CO3)2 => Ca(CH3CO2)2 + Mg(CH3CO2)2 + 2CO2 + H2O
[acetic acid (x4) + dolomite = calcium acetate + magnesium acetate + carbon-dioxide (x2) + water]

2) Based on the Rigaku link above (conclusions section on the last page), when dolomite is in the presence of excess gaseous carbon-dioxide, it can decompose to form calcium carbonate. The manner in which the resulting calcium carbonate solidifies produces aragonite (or ‘mushroom’) crystals:
CaMg(CO3)2 → CaCO3 + MgO+ CO2 under CO2.

3) Note also the overall reaction of calcium carbonate with acetic acid below. This reaction can be reversed or “pushed to the left”, meaning that calcium carbonate (CaCO3) is formed by calcium acetate (Ca(CH3COO)2) rather than the other way around. This happens because, during the course of the first reaction of dolomite with vinegar (1 above), calcium acetate, water and carbon dioxide all increase, while over the course of several days the acetic acid evaporates (as does some water). As a result, the reaction below reverses, so that the excess calcium acetate can be reduced and the disappearing acetic acid can be replenished. Thus, calcium carbonate is produced in the form of aragonite crystals.

2 CH3COOH + CaCO3 = H2O + CO2 + Ca(CH3COO)2.

For more info regarding the ‘Acid Test’ for identifying carbonate minerals and rocks, see:
http://geology.com/minerals/acid-test.shtml

For more detailed info on dolomite and other carbonate minerals:
http://www.galleries.com/dolomite

For info on balancing the first equation for producing calcium carbonate from dolomite:
http://www.webqc.org/balance.php?reaction=CaMg(CO3)2+%3D+MgO+%2B+CaCO3+%2B+CO2

One Response to Fun Science: Easy Hands-on Chemistry Lesson

  1. If you have any questions, don’t hesitate to email me: melissarooneywriting@gmail.com

    Your kids (and YOU) will love this easy educational and truly magical activity.

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