The Properties And Composition Of Candles

The main raw material for candles is paraffin (C ₂ Å H Å ₂), which is made from waxy fractions of petroleum by cold pressing or solvent dewaxing. It is a mixture of several higher alkanes, mainly n-docosane (C22H46) and n-octadecane (C28H58), with a carbon content of about 85% and a hydrogen content of about 14%. The auxiliary materials added include white oil, stearic acid, polyethylene, essence, etc. The stearic acid (C17H35COOH) is mainly used to improve the softness. The specific addition depends on the type of candle produced.
Easy to melt, with a density lower than that of water and difficult to dissolve in water. When heated, it melts into a liquid state, colorless and transparent, and is easily volatile when slightly heated. The unique odor of paraffin can be heard. When cold, it solidifies into a white solid with a slight special odor.
The candle combustion we see is not the combustion of paraffin solid, but rather the ignition device that ignites the cotton core, releasing heat to melt the paraffin solid and vaporize it, generating paraffin vapor, which is flammable.
When a candle is lit, the initial flame that burns is smaller and gradually increases. The flame is divided into three layers (outer flame, inner flame, and flame core). The core of the flame is mainly candle vapor, with the lowest temperature; The combustion of paraffin in the inner flame is not sufficient, with a higher temperature than the flame core and containing carbon particles; The external flame is in full contact with the air, making the flame the brightest, fully burning, and at the highest temperature. Therefore, when a match stem is quickly placed flat into the flame and removed after about 1 second, the part of the match stem that comes into contact with the outer flame first turns black.
At the moment of blowing out the candle, a wisp of white smoke can be seen. Using a burning match to light this wisp of white smoke can cause the candle to reignite, so it can be proven that the emitted white smoke is a solid small particle produced by the condensation of paraffin vapor.
When candles burn, the products of combustion are carbon dioxide and water. Chemical expression: C25H52+O2 → (ignition) CO2+H2O. The combustion phenomenon in an oxygen bottle is a bright flame emitting white light, releasing heat, and water mist appearing on the bottle wall.
Simple proof experiment:
Light the candle and cover it with a cold and dry beaker. After 5 minutes, quickly invert the beaker and notice that the inner wall of the beaker has become blurry and water droplets have formed, indicating that the candle is burning and generating water.
Add a small amount of clarified lime water to the beaker and shake it. It is observed that the clarified lime water becomes turbid, indicating that carbon dioxide is generated during candle combustion.