Chemistry of Candles Trivia Quiz

Answer: Alkane

As a chemical term, a paraffin is an alkane or saturated hydrocarbon. All alkanes have the formula CnH(2n+2) and consist of a straight chain of carbon atoms connected by single bonds. The carbons' valence electrons not needed to form the chain (two for an atom in the middle, three for each atom at the end) each bond with the single electron of a hydrogen atom.

Paraffin wax is, to a large percentage, composed of actual paraffins with 20 to 40 carbon atoms.

Answer: Triglyceride

Stearin is a triglyceride or, as you may want to call it, an organic fat. Like every such molecule, it is an ester composed of glycerol (propanetriol) and three fatty acids. In the case of stearin, all three fatty acid molecules are stearic acid, the linear and saturated fatty acid with 18 carbon atoms.
Stearin is still very similar to a hydrocarbon in composition with just the three ester groups breaking the pattern, thus it will burn essentially in the same way as an alkane.

Answer: Capillary action

Capillary action is actually not a chemical process but a purely physical one. Molecules of a liquid are drawn to the surface of a solid because the adhesion between the liquid and the solid is greater than the cohesion between the liquid molecules and thus they tend to spread along the surface which, in a capillary medium, is highly porous.

The molecules evaporating in the flame cause surface spots to become vacant to which molecules from further down the wick then move and so on.

Answer: Gas

Hydrocarbons are relatively stable molecules in spite of the fact that they can release a lot of energy when being burnt. In order for a reaction to occur between the hydrocarbon and the oxygen of the air, the molecules will need to mix freely and have enough energy for the existing bonds to split and re-form in new ways.

This requires the gaseous state. In the hottest area of the flame, a small fraction of the molecules exist as a plasma - molecules partially stripped of their electrons and free electrons.

These molecular fragments are extremely reactive and contribute to the speed of combustion, but they are not absolutely necessary for the reaction to occur.

Answer: Toluene

When an alkane burns, the most common place for oxidation to occur is the end of each chain, adding one oxygen atom at a time. The first is added into one of the C-H bonds, resulting in an alcohol (R-CH2OH). The second one would do the same, but any compound with two -OH groups on the same carbon is unstable and will dissociate, splitting off a water molecule. This results in an aldehyde (R-CH=O). In the third step, another oxygen forms a new -OH group resulting in a carboxylic acid (R-COOH) and the fourth results in splitting off the end group, resulting in a CO2 molecule and an alkane one atom shorter than the original, whereupon the process repeats.

Toluene is an aromatic alcohol, which would be very unlikely to be generated in the burning of a paraffin as this would require the previously open chain to reconnect into a ring.

Answer: Two: Carbon dioxide and water

Our ideal candle is composed only of carbon, hydrogen and a little oxygen (in the cellulose and, if we used stearin, in its ester groups). Thus its complete combustion will result in the same compounds as the complete combustion of any hydrocarbon. These are carbon dioxide and water, almost in an identical number of molecules. (Paraffin will result in a slightly higher percentage of water while stearin has a similarly slight excess of carbon dioxide.)

Answer: 350 grams

We have already seen that most of the paraffin and stearin is composed of repeating -CH2- elements making up the chain, so for a rough estimate, we can just look at these. You need two oxygen atoms to oxidize the carbon to CO2 and one more to turn the two hydrogens into a molecule of water (H2O). So for 14 atomic mass units of hydrocarbon, you need 48 mass units of oxygen - a ratio of 3.43 to 1.

With air being only approximately 20% oxygen and a cubic meter of air weighing about one kilogram, this means that our 100 gram candle will consume the entire oxygen in about 1.75 cubic meters of air. If you were to hermetically seal your living room (20 square meters / 220 square feet and 2.40 m / 8 ft high), it would not even take thirty such candles to consume all oxygen!

Answer: Carbon nanoparticles

Soot is a result of an incomplete combustion process. If the flame has a mild oxygen deficit, not all carbon can completely be oxidized (the hydrogen will be oxidized first). This can result in carbon monoxide (which escapes as a gas) or elementary carbon (which forms amorphous agglomerates) escaping from the flame. The latter is the main component of soot - essentially a nanoparticular form of coal. Soot also contains a small amount of various hydrocarbons and partially oxidized fuel molecules.

The soot-hing (here's an accidental pun) yellow light of a candle is actually emitted by glowing carbon - soot - particles. The light emitted by the actual combustion reaction is the blue glow of the flame's hot core.

Answer: They will combust, yielding the same products as the wax

Almost all of the scents used in candle making are esters and ethers - substances composed, again, of carbon, hydrogen and oxygen. Not only do these cover a large variety of pleasant odors but they also have the great advantage of burning to the same harmless end products as the candle's wax if ignited, thus eliminating the possible health hazards that could result if compounds including other elements were used.

A responsible chandler will thus always stick to this class of aromas.

Answer: Metal oxides

Candles leave very little ash due to two facts - for one, the paraffin and/or stearin used is very pure and has a very low mineral content and, additionally, the little that is still there (most of it from the wick) will drop into the molten wax of the stump.

As it is almost impossible for a candle to burn away completely (without support, the wick will fall over and go out first), you will hardly notice the traces of ash. Still they are there, and, like any other ash, they consist of the solid oxidation products of the metallic compounds present in any organic matter which could not escape due to their weight and high boiling point.