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: Anonymous
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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 on the Royal Society of Chemistry Education in Chemistry website: https://edu.rsc.org/eic and search for 'Balls of fire' 

The Queensland Department of Education and Training has produced a safety alert on the topic of unpredictable experiments, which is worth reading: see https://education.qld.gov.au/ and search for 'Unpredictable science experiments' and ‘Science experiments, investigations and activities’  

Note: a risk assessment should be conducted for each practical activity, taking into consideration aspects including staff training, student skills and behaviour, staff/student allergies, school facilities and whether it is permitted in your jurisdiction. 

References:
‘Balls of fire’ 2014. Royal Society of Chemistry Education in Chemistry website. https://edu.rsc.org/eic and search for 'Balls of fire' 

‘Unpredictable experiments’. (2014). Queensland Department of Education and Training website. Note: This information was updated in August 2018 See https://education.qld.gov.au/ and search for 'Unpredictable science experiments' and ‘Science experiments, investigations and activities’  

9/12/2019 Answer edited to provide additional notes (in red) and instructions for accessing links

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