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Quiz about Chemistry of Candles
Quiz about Chemistry of Candles

Chemistry of Candles Trivia Quiz


One of the joys of Christmas is the flicker of candlelight. To provide us with such a simple but heart-warming joy, quite a few chemical processes need to take place. Do you know them?

A multiple-choice quiz by WesleyCrusher. Estimated time: 6 mins.
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Time
6 mins
Type
Multiple Choice
Quiz #
334,885
Updated
Dec 03 21
# Qns
10
Difficulty
Tough
Avg Score
6 / 10
Plays
1686
Awards
Top 35% Quiz
- -
Question 1 of 10
1. Today, most candles are made of paraffin wax. The word "paraffin" however also has a clearly defined chemical meaning, being a synonym for which other term? (Pick the most exact solution) Hint


Question 2 of 10
2. Stearin, the second most common material from which candles are made, is a specific organic component with the summary formula C57H110O6. This alone should allow you to easily identify the class of substance it represents - which of these is it? Hint


Question 3 of 10
3. Besides the wax, our candle also needs a wick to enable it to burn. The wick is the flame's fuel supply, feeding it molten wax by which mechanism? Hint


Question 4 of 10
4. When the wax reaches the flame, it can take part in the combustion reaction. However, organic substances will burn in normal air only after reaching a specific state - which one? Hint


Question 5 of 10
5. Let's assume a pure paraffin candle for this question. The combustion of paraffins is a reaction that takes many steps. Which of the following would be a very unlikely intermediate product on the way to complete combustion of a paraffin? Hint


Question 6 of 10
6. If we were to put a candle into a sealed chamber filled with just enough pure oxygen to fully burn it, light it and achieve a perfect textbook reaction consuming every last bit of the candle, the chamber would afterwards be filled with just a few compounds. How many and which ones? (Assume the wick is made of pure cellulose, a carbohydrate) Hint


Question 7 of 10
7. A burning candle actually needs quite a lot of oxygen. Assuming a candle made of paraffin and/or stearin weighing 100 grams, how much oxygen would (very roughly) be required to completely burn it?

You can estimate this by visualizing the reaction and remembering that the atomic weight of hydrogen is roughly 1, that of carbon is 12, and that of oxygen is 16.
Hint


Question 8 of 10
8. The burning of a real candle is hardly an ideal reaction and the combustion will never be absolutely complete, also demonstrated by the deposition of black soot. While soot is a complex mixture, what is it mostly composed of? Hint


Question 9 of 10
9. Many candles today are scented, providing an extra-pleasant odor while burning. This odor is caused by perfumes embedded in the wax and evaporating while the candle burns. The pleasant scents are caused by molecules escaping the reactions, but what happens to those caught in the flame? Hint


Question 10 of 10
10. Sadly, every candle will burn down at some point. While you may not realize it due to the minuscule amounts produced, even a very well made candle will leave a little bit of ash due to inevitable impurities. What is the primary composition of ash? Hint



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Quiz Answer Key and Fun Facts
1. Today, most candles are made of paraffin wax. The word "paraffin" however also has a clearly defined chemical meaning, being a synonym for which other term? (Pick the most exact solution)

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.
2. Stearin, the second most common material from which candles are made, is a specific organic component with the summary formula C57H110O6. This alone should allow you to easily identify the class of substance it represents - which of these is it?

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.
3. Besides the wax, our candle also needs a wick to enable it to burn. The wick is the flame's fuel supply, feeding it molten wax by which mechanism?

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.
4. When the wax reaches the flame, it can take part in the combustion reaction. However, organic substances will burn in normal air only after reaching a specific state - which one?

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.
5. Let's assume a pure paraffin candle for this question. The combustion of paraffins is a reaction that takes many steps. Which of the following would be a very unlikely intermediate product on the way to complete combustion of a paraffin?

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.
6. If we were to put a candle into a sealed chamber filled with just enough pure oxygen to fully burn it, light it and achieve a perfect textbook reaction consuming every last bit of the candle, the chamber would afterwards be filled with just a few compounds. How many and which ones? (Assume the wick is made of pure cellulose, a carbohydrate)

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.)
7. A burning candle actually needs quite a lot of oxygen. Assuming a candle made of paraffin and/or stearin weighing 100 grams, how much oxygen would (very roughly) be required to completely burn it? You can estimate this by visualizing the reaction and remembering that the atomic weight of hydrogen is roughly 1, that of carbon is 12, and that of oxygen is 16.

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!
8. The burning of a real candle is hardly an ideal reaction and the combustion will never be absolutely complete, also demonstrated by the deposition of black soot. While soot is a complex mixture, what is it mostly composed of?

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.
9. Many candles today are scented, providing an extra-pleasant odor while burning. This odor is caused by perfumes embedded in the wax and evaporating while the candle burns. The pleasant scents are caused by molecules escaping the reactions, but what happens to those caught in the flame?

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.
10. Sadly, every candle will burn down at some point. While you may not realize it due to the minuscule amounts produced, even a very well made candle will leave a little bit of ash due to inevitable impurities. What is the primary composition of ash?

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.
Source: Author WesleyCrusher

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