A hydrocarbon candle is burned, and the gases produced are drawn through cobalt chloride paper and limewater using a pump. The cobalt chloride paper detects water, while limewater detects carbon dioxide, revealing the main products of hydrocarbon combustion.

1. Assemble the apparatus with a funnel, tubing, and two boiling tubes—one containing cobalt chloride paper and the other half-filled with limewater.
2. Connect the tubes so that air drawn by the pump passes first over the cobalt chloride paper, then through the limewater.
3. Light the candle beneath the funnel so combustion gases are directed into the system.
4. Turn on the pump to gently draw the gases through.
5. Observe as the cobalt chloride paper changes from blue to pink (indicating water) and the limewater turns milky (indicating carbon dioxide).
6. Optionally, repeat the setup without the candle to show that normal air does not produce the same rapid changes.

Combustion Demo - CRRChem:

Year 10 Products of combustion - susanna wilkinson:

📄 Identifying the products of combustion - Practical Chemistry: https://assets.ctfassets.net/pc40tpn1u6ef/file-14239/06ccf8c2ec55efed84c6ae5f2cfb095f/8492-Motr_vehicle_maintenance_teachers_notes.pdf

• Burn alcohols such as ethanol using a spirit burner instead of a candle.
• Use a camera and projector to display the color changes to the whole class.
• Try comparing different hydrocarbon fuels to see if results vary.

• Wear eye protection.
• Handle cobalt chloride paper carefully, as it is toxic, a sensitizer, and a category 2 carcinogen. Minimize handling and wash hands after use.
• Limewater (calcium hydroxide solution) is an irritant; avoid skin or eye contact.
• Ensure tubing near the flame is made of heat-resistant glass or properly joined to prevent melting.
• Use a stable candle such as a tealight to reduce fire hazards.
• Work in a well-ventilated area to avoid inhaling combustion fumes.

• What elements are present in hydrocarbons such as candle wax? (Carbon and hydrogen)
• What products are formed when these elements burn in oxygen? (Carbon dioxide and water)
• Why is it important to compare the results with and without the candle? (To show the observed changes are due to combustion, not normal air content)
• How does the production of carbon dioxide relate to environmental issues such as the greenhouse effect? (Carbon dioxide is a greenhouse gas contributing to global warming)