PURPOSE: To show the direction of convection of hot air.
A tall and a short candle, a glass cylinder.
DESCRIPTION: Take a short and tall candle and light them on. Cover the candles with a glass cylinder. You will see the tall candle goes out first. The flames are consuming oxygen and produce carbon dioxide. The product is hot so it is less dense than the cold air. Hence the carbon dioxide rises to the top and suffocate the tall candle. The convection make the cold air sink. The remaining oxygen in the cold air keeps the shorter flame on. When the oxygen in the cylinder is used up the short candle dies too.
When you try to extinguish a candle by putting a glass above it, does all the oxygen get consumed? Or there is any other reason why the candle goes off? What will happen if you had three candles of different heights? Which one will go off first? Or all of them will go off simultaneously? All this questions can be answered by a really simple experiment. Three candles of different heights are lit. Put an inverted glass over them to extinguish them. You’ll notice that he tallest candle extinguishes first followed by the middle one and the shortest one is the last to go off. Why did this happen? Burning produces carbon dioxide which is heavier than other gases in air. This suggests that the lowest one should get extinguished first. But as the carbon dioxide is being produced, it is also heated up due to the flame. This hot gas expands and has lower density this accumulates at the top of the glass. Thus the top candle experiences deficit of oxygen first followed by the middle one and finally the last one. This happens due to the combination of expansion of hot gases and oxygen deprivation which results in extinguished candles. This experiment allows students to think about multiple factors that may play a role in certain experiment and how to account for them while interpreting results.
Disclaimer and Safety Precautions
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state’s handbook of Science Safety.
- Put on protective eyewear. Conduct the experiment on the plastic tray and in a well-ventilated area.
- Keep a bowl of water nearby during the experiment.
- Keep flammable materials and hair away from flame.
- Avoid looking directly at burning magnesium to prevent eye discomfort.
- Do not attempt to extinguish the solid fuel and magnesium — let them burn down completely. Do not touch the stove after the experiment — wait until it cools down.
- Do not allow chemicals to come into contact with the eyes or mouth.
- Keep young children, animals and those not wearing eye protection away from the experimental area.
- Store this experimental set out of reach of children under 12 years of age.
- Clean all equipment after use.
- Make sure that all containers are fully closed and properly stored after use.
- Ensure that all empty containers are disposed of properly.
- Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
- Do not replace foodstuffs in original container. Dispose of immediately.
- In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
- If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
- In case of inhalation: Remove person to fresh air.
- In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
- In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
- In case of injury always seek medical advice.
- The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
- This experimental set is for use only by children over 12 years.
- Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
- The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
- The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
- Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.
Dispose of the reagents and solid waste together with household garbage.