Calcium Carbide

Calcium Carbide: My teachers are wondering whether there are any restrictions on us storing and using Calcium carbide for pracs here at school? They apparently used to do some wonderful pracs with it in the past, which they have not done for many years, however I am concerned about the safety of these pracs.

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Publication Date: 14 August 2017
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Calcium Carbide

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Storage and properties


Calcium carbide can be safely stored with Dangerous Goods Class 4.3, segregated from incompatible chemicals, and MUST be kept dry.


When calcium carbide reacts with water it forms acetylene gas (ethyne) and calcium hydroxide, and generates heat. 


CaC2 (s) + 2H2O (l)   C2H2 (g) + Ca(OH)2 (s) 


Calcium carbide may contain impurities of phosphorus, nitrogen and sulfur compounds. While pure acetylene gas is odourless and non-toxic, these impurities in the calcium carbide, when reacted with water, produce trace amounts of phosphine, ammonia and hydrogen sulfide, which are toxic and can impart an unpleasant odour to the gas. Acetylene can form explosive mixtures with air.


Safe Handling


Calcium carbide is not banned from use; however, the following safe practices should be observed:


  • Be familiar with the information contained in the Safety Data Sheet
  • Conduct a risk assessment of the proposed activity
  • Only use under controlled conditions
    • Wear suitable PPE Safety glasses, nitrile gloves, enclosed shoes, laboratory coat
    • Use in an operating fume cupboard, or a well-ventilated area
    • Control the scale of the activity by using only a very small lump (2-3g)
    • A small lump of calcium carbide reacts more slowly and is more controllable than fine powder, which reacts faster due to the larger surface area.
  • Trial the proposed activity prior to classroom demonstrations
  • Have dry sand available in the event of a fire

DO NOT:


  • handle calcium carbide with bare hands
  • inhale the gas produced
  • use large quantities or fine powder of calcium carbide
  • take the stock container of calcium carbide into the classroom
  • perform any reactions in a closed vessel
  • react acetylene with aqueous silver or copper(I) salts, because explosive acetylides are formed
  • assume that reactions shown on YouTube are suitable for use in the classroom

A suitable activity:


  • place about 50mL of water in a 250mL beaker
  • place a small lump (2-3g) calcium carbide into the water
  • bubbles of acetylene will form and these can be ignited using a long taper

Alternatively, the following suitable videos could be viewed:


1. ‘Calcium Carbide & Acetylene - Periodic Table of Videos’, YouTube (6:20 min), https://youtu.be/KQSLpuVZK9Y (7 May 2012)


2. ‘Combustion of Acetylene’, YouTube (11:14 min), https://youtu.be/i-shpoG6jeM (17 December 2012)


3. ‘Carbide lamp.wmv’, YouTube (3:37 min) https://youtu.be/UqXnBXmPQ3U  (21 February 2010)


4. ‘Acetylene Production from Calcium Carbide’, YouTube (2:44 min) https://youtu.be/5hExAXfqI4w  (5 August 2012)


References:


‘Calcium Carbide & Acetylene - Periodic Table of Videos’, YouTube (6:20 min), https://youtu.be/KQSLpuVZK9Y (7 May 2012)


Chem-Supply. 2016. Calcium carbide, Safety Data Sheet, Chem-Supply website, https://www.chemsupply.com.au/documents/CT1661CHA0.pdf (January 2016)


NSW Department of Education and Training. 1999. Chemical Safety in Schools Appendix D. Calcium carbide, NSW Department of Education and Training; Sydney. p68


Queensland Department of Education, Training and Employment. 2014. Unpredictable science experiments. Health & Safety Alert, DET website, https://education.qld.gov.au/health/pdfs/healthsafety/unpredictable-experiments.pdf (October 2014)

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