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Scorching silicon demo

 
 

Overview

Materials list

  • 100 ml of hydrochloric acid (0.1M)
  • 500 ml of water
  • Boiling tube containing 5mm sand and 5mm magnesium powder
  • 1 litre heatproof beaker
  • Stirrer
  • Tongs
  • Tweezers
  • Spatula
  • Bunsen burner
  • Heatproof gloves
  • Goggles or full-face shield
  • Safety screen

Practicalities

This experiment is an impressive way to capture students’ attention and encourage discussion. However, it is not suitable for students to do themselves and should only be conducted by an experienced 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.

When heating the magnesium powder and sand in the boiling tube be ready to tip it into the water and acid solution as soon as it glows orange. This will take approximately one minute. If you heat it beyond this point the contents will fuse to the tube and you will not be able to tip it out.

Stand well back and add the contents of the tube at arm’s length. The resulting explosion will give of a bright white flash and a cloud of silicon gas.

During the explosion and occasionally while heating, small particles of the magnesium powder catch fire and give off a bright white flash. Take care not to look directly at this light and warn students to look around the reaction rather than directly at it. The explosion itself only lasts for a split second and should not present a significant risk.

The heatproof beaker will get very hot, particularly at the top, and will remain hot long after the demonstration. The boiling tube and beaker may not be usable after the demonstration.

The explosion will produced a plume of smoke so present this demo in a well ventilated lab well away from a smoke detector or use a fume cupboard.

Technicians’ notes

Ensure that you use only 0.1 Molar hydrochloric acid for this demonstration.

To dispose of the products of this demonstration, carefully place the used boiling tube in a beaker of 1Molar hydrochloric acid. Place the beaker in a bucket of water and stand it in a fume cupboard for a number of hours or overnight to ensure that all the magnesium powder has completely reacted (i.e. until it stops bubbling).

Carefully dispose of the boiling tube (which may be cracked) in the glass bin and dilute the remaining liquid thoroughly before disposing of it down the drain.

For more detailed information on storage, transportation and disposal please contact CLEAPPS .

Discussion

  • What is fuelling the fire?
  • What is the white smoke?
  • What is formed at the bottom of the bowl?
  • What is the gas produced?
  • Is the process reversible or irreversible?

Transition to KS4

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

Extension

  • Find out more about silicon and its uses. Silicon is a metalloid ceramic material that can be extracted from sand. Sand is also the raw material out of which glass is made. There are many different properties of silicon which are all dependent on its internal structure. Silicon is the second most abundant element on Earth, making up over 27% of the crust.
  • Discuss the differences between silicone, a plastic material, and silicon, a ceramic material. Although silicones contain silicon atoms, they are not made up exclusively of silicon, and have completely different physical characteristics from elemental silicon.

Links to everyday life

Microchips
The main uses of silicon are in the industries that manufacture silicon chips and microprocessors. These consist of a miniaturised electronic circuit that has been integrated into the surface of a semiconductor material. 
 
Super-chips
Very large integrated circuits that use an entire silicon wafer to produce a single ‘superchip’ are known as wafer-scale integration (WSI) chips. It is hoped that this manufacturing process could lead to dramatically reduced costs for systems such as supercomputers.