Holiday Chemistry

I love chemistry! Ever since sixth grade, I’ve been fascinated by the patterns and intricacies of the microscopic world. This year in AP Chemistry, I’ve been able to delve further into the many wonders of the periodic table. Here are two holiday chemistry experiments I have conducted over the past couple of weeks: one at home and one at school.

The Mirrored Christmas Tree Ornament (above) captured our holiday family portrait! My entire chemistry class had fun doing this experiment. Always wearing our protective goggles, we started with plain glass orbs from an art supply shop. We rinsed the interior of the orb with acetone (added through the opening at the top of the orb), which removed any potentially troublesome dust or particles. We then added a little silver nitrate solution, ammonium nitrate solution, dextrose solution, and sodium hydroxide solution. We then swirled the reactants around the orb, so that the reaction took place evenly over the ornament’s interior sides. This coated the inside of the orb with a 1.51 x 10^-6 meter silver layer.

Voila! Mirrored Christmas tree ornament.

Removing the tarnish on the gravy boat using chemistry (in our kitchen):

I had fun explaining to my mom, who says she can’t remember anything about her high school chemistry class, the general principles involved in the polishing of the gravy boat.

To polish our very tarnished gravy boat, I didn’t want to use commercial silver polish, which contains toxins. I decided to try this natural method:

Line your sink or a bucket with aluminum foil and drop in tarnished silver;

Pour in boiling water to cover silver objects;

Pour one cup of baking soda and a dash of salt over objects.

Let sit for a few minutes.

Watch as the tarnish transfers from the silver to the foil.

It’s probably some sort of redox reaction (I’ll have to check with Dr. Phillips, my chemistry teacher), which means electrons are exchanged between atoms or electrons. In this case, there would be aluminum (Al), a sodium ion (Na⁺), a chloride ion (Cl^–), HCO₃^–, and some sulfur and oxygen containing compounds.

The sodium and chloride are the table salt.

The chloride and bicarbonate are the baking soda.

Sulfur and oxygen in the air react with the silver to make the tarnish, and the aluminum is, of course, the foil.

So, when you add them all together with the boiling water, the particles switch around and the tarnish bonds with some of the surrounding ions, thus detaching from the silver item.

Voila! Polished gravy boat.

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Here is Dr. Phillip’s reply to Natalie’s query about the gravy boat:

Yes, Natalie, the tarnish removal is definitely reduction-oxidation (redox). Aluminum is a more active metal than silver, so when put in contact, the sulfur from the silver sulfide is transferred to the more active aluminum. The silver ion is reduced back to silver atom, and the aluminum is oxidized to aluminum ions. This type of tarnish removal conserves the silver. In more traditional approaches, an abrasive (polish) is used which, upon rubbing,  removes the silver sulfide along with some of the silver. In theory, with enough traditional polishing, your silver gravy boat would eventually disappear (or spring leaks!).

Here is the redox reaction:

3Ag₂S(s)   +   2Al   à    6Ag(s)   +     Al₂S₃(s)

The NaCl adds ionic conductivity to the aqueous solution, while the sodium bicarbonate (NaHCO₃) adds both ionic conductivity and a little bit of a basic environment, which helps remove the oxide layer from the Al foil^*. Depending upon how tarnished the silver, you may have noticed some yellow crystals of aluminum sulfide on the aluminum foil or floating in the mix.