Home Chemistry

We're doing some home chemistry this summer because both our kids like doing experiments on school break. There are many chemistry resources on the web. Our son's in middle school and daughter's in 6th, I combined a little teaching about chemical compounds and the "logic" of balancing chemical equations with look-and-see learning from home experiments.

The theory of oxidation grew out of theories regarding combustion. The Flemish physician Johann Baptista van Helmont was the first to hypothesize that a spiritus sylvestre (wild spirit) was responsible for combustion. This wild spirit theory evolved in to the concept of a substance phlogiston that could be driven out by the burning process.

French chemist Antoine Laurent Lavoisier (1743–1794)theorized instead that combustion was the mechanism by which a substance combined with oxygen. He advanced his theory by meticulous experiments involving the weighing of material. The oxidation theory was born.

I found the Home Chemistry Blog and the pennies and vinegar experiment seemed like a great start to our discussion of oxidation. Vinegar comes from French, vin-algre, or wine-sour.

I. Dull to Shiny Penny

1. Mix 1/4 c vinegar with 1 teaspoon salt. Collect a dozen or so dull / black pennies. Dip one into the mixture so that it is half shiny.

A dark penny has been oxidized by oxygen in the air. Instead of copper (Cu), it is CuO, or copper oxide.

II. Verdigris and Copper Plating Iron Nails

1. Put the remaining pennies in the vinegar-salt mixture. Wait for about an hour.
2. Rinse half of the pennies in water, and the other half let dry on a paper towel.
3. Now add some nails to the vinegar-salt solution that had the pennies. You can use galvanized or non-galvanized nails if you have them. We added a paper clip and aluminum nails that we found.
4. Check back in 10-15 minutes. Do you see small bubbles forming on some of the nails? It's hydrogen gas being released from a reaction between the vinegar (acetic acid) and metal oxides.
5. Check back in an hour. The control (non-washed pennies) should have a nice verdigris finish (like the Statue of Liberty!) and the iron nails will be copper-coated, and so light brown. Our paper clip also became brown, and our aluminum nails were unchanged.

The reactions: CuO + CH3COOH (vinegar) + Salt (increases ionic strength) --> Copper acetate (CuOCH3CO2-) + H2 (hydrogen gas).

When the iron nails are put in the copper solution (made from the pennies), the reaction is: Cu2+ (aq) + Fe (s) --> Cu(s)+ Fe2+ (aq), where aq = aqueous and s = solid. Copper is more avid for electrons than iron so it steals electrons in the solution to become solid plating.

The history of copper dates back 1000's of years. At left is a copper-headed axe found in Europe with the body of a 5200 year old corpse(called Otzi).

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