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Flammable ice demo

 
 

Overview

Materials list

  • Shallow heatproof dish
  • Ice
  • 8 pieces of calcium carbide (approximately 2cm long)
  • Heatproof tile
  • Tweezers
  • Splint
  • Sand bucket
  • Safety screen
  • Lab coat
  • Goggles

Practicalities

This experiment is very impressive and a great way to capture students’ attention and encourage discussion. However, this is not suitable for students to do themselves and should only be conducted by an experienced member of staff e.g. a science teacher or lab technician.

All necessary safety equipment should be used; ensure you are wearing full safety equipment including lab coat and goggles and tie back long hair. Make sure your students and other members of staff are at the standard safe distance behind the safety screen and are also wearing goggles and lab coats.

Water is the catalyst for this reaction so before you add the ice ensure you have tipped away any melt water. This will ensure that the gas is produced at a more controlled rate, allowing you to light it safely.

Do not allow the gas to build up before lighting it. As soon as you add the ice to the calcium carbide the gas will start being released (as it reacts with the water melting from the ice) so you should light it immediately. If it blows itself out then you should relight it or cover it completely with sand.

The heatproof dish will get very hot, particularly at the top, and will remain hot long after the demonstration. The container may not be usable after the demonstration. The flames will produce a sooty smoke so ensure that you demonstrate this in a well ventilated lab well away from a smoke detector. Alternatively use a fume cupboard.

When choosing your calcium carbide it is worth noting that the size of the pieces will affect the speed of the reaction. Powder or small pieces of calcium carbide have a larger surface area so the gas will be produced more quickly. The bigger the pieces the easier it is to control and the longer it will burn. More pieces will produce more gas and therefore more flames (and more smoke).

Warning: Do NOT attempt to extinguish this flame with water as this is what is catalysing the reaction. Have a sand bucket to hand and use this to completely cover the flames, and then stand the dish in a fume cupboard until the reaction is finished. Take care, it will still be very hot.

Technicians’ notes

To dispose of the products of this demonstration, first allow the hot dish to stand in the fume cupboard for a number of hours or overnight to ensure that all the calcium carbide has completely reacted with the melted ice. Once the reaction has finished, dispose of the contents of the container in the normal lab refuse. For more detailed information on storage, transportation and disposal please contact CLEAPSS (www.cleapss.org.uk).

Discussion

  • How is the ice on fire?
  • What stops the water putting the fire out?
  • What can put the fire out?
  • Why should you not use water to put out the fire?
  • What are the changes of state?
  • What use could this reaction have?
  • If you can hear a popping sound, what is causing that?

Transition to KS4:

  • What are the products of the reaction?
  • Can you think what the chemical equation would be?

Extensions

  • How do fire extinguishers work? Why are there different types of fire extinguishers for different types of fires?
  • What would happen if you used water instead of ice for this demonstration?
  • What if you used steam? Would it affect the outcome of this experiment?
  • Are there any other chemicals that react with water?

Links to everyday life

Miners’ lamps

Calcium carbide was commonly used in miner’s lamps. The lamps were designed to drip water on the calcium carbide to produce acetylene gas. This gas was then ignited to produce a light. These lamps were phased out as they were very unsafe in mines where flammable methane gas made them a serious hazard.