Lightning in a test tube

Lightning in a test tube: I have a teacher who is planning on performing the 'lightning in a test tube' demonstration in the school lecture theatre. The experiment involves layering ethanol on top of sulfuric acid in a test tube and then dropping some potassium permanganate crystals into the sulfuric acid. I would prefer it to be performed in a fume cupboard.

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Publication Date: 20 August 2015
Asked By: Kellee
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Lightning in a test tube

Science ASSIST strongly advises against this demonstration being performed in a school. The risks are too high and the demonstration is not able to be adequately controlled.


Each of the chemicals involved in this activity has its own particular significant hazards.


  • Ethanol: flammable liquid
  • Sulfuric acid: corrosive acid
  • Potassium permanganate: oxidising agent

Sulfuric acid reacts with potassium permanganate to form manganese (VII) oxide (Mn2O7) [also called manganese heptoxide], which is explosive and reacts violently with the ethanol. Significant risks of explosion or fires or both are foreseeable and cannot be controlled, so the risk assessment would conclude that the risks of the demonstration are significant and cannot be adequately controlled at the moment and therefore should not be conducted.


An alternative method for demonstrating this reaction in a controlled way can be found here: http://www.rsc.org/eic/2013/12/dehydration-permanganic-acid-sulfuric


The Queensland Department of Education and Training has produced a safety alert on the topic of unpredictable experiments, which is worth reading: see http://education.qld.gov.au/health/pdfs/healthsafety/unpredictable-exper...


References:

‘Balls of fire’ 2014. Royal Society of Chemistry Education in Chemistry website. http://www.rsc.org/eic/2013/12/dehydration-permanganic-acid-sulfuric


‘Unpredictable experiments’. (2014). Queensland Department of Education and Training website. http://education.qld.gov.au/health/pdfs/healthsafety/unpredictable-exper...

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