Organic chemicals may react with plastic containers when stored in them for an extended period of time. It appears that the paraffin oil in your situation may have reacted with the plastic container and/or the sodium has reacted with the oxygen in the headspace of the container, thereby creating a vacuum. Therefore, your original container has been compromised and you will need to repackage your sodium metal.
Sodium metal is highly reactive with water generating flammable hydrogen gas and sufficient heat to cause ignition. It is essential that sodium is stored so that it cannot come into contact with water, including moisture in the atmosphere. Sodium is usually supplied under paraffin oil or under kerosene. It is usually good practice to keep chemicals in the containers in which they are supplied.
Science ASSISTS recommends the following:
- Purchase sodium that is under paraffin oil, rather than kerosene. The use of kerosene introduces additional hazards due to it being an aspiration hazard as well as being a flammable liquid. Kerosene also has a much lower boiling point than paraffin oil and is more prone to loss of liquid by evaporation.
- Keep stocks of sodium to a minimum and only purchase as required.
- Transfer sodium to a suitable stock jar for storage if the structural integrity of the original container is compromised, or if directed by your jurisdiction.
- Sodium metal in schools is best stored under paraffin in a suitably labelled, screw capped, clear glass, wide mouthed jar.
- The clear glass helps you see that the level of paraffin oil is covering the sodium.
- The glass does not react with the paraffin oil
- The wide mouth enables you to easily remove the sodium metal from the jar.
- Consideration could be given to PVC coated glass and/or the glass jar could be stored in a secondary containment such as a chemically resistant plastic container. E.g. a polypropylene beaker
- Minimum quantities only should be taken into the classroom for demonstrations, therefore a small jar with one small lump of sodium should be established for use in the classroom.
- DO NOT pre-cut the sodium for use in the classroom as this needs to be conducted as part of the demonstration. For more information regarding handling sodium metal see SOP: Demonstrating the reaction of alkali metals lithium and sodium with water
- Regularly check that the jars are in good condition and that the sodium is covered with paraffin oil. (This is most easily done at stocktake)
- Ensure that sodium is stored in a secure locked location as it has been listed as a chemical known to be used in the illicit manufacture of drugs.
Transfer Procedure for establishing a new stock and classroom container of sodium:
- It is essential that all jars and implements used (scalpels, forceps etc.) are clean and dry. In addition, use a clean dry surface to cut it on.
- Establish 2 jars for storing the sodium: a smaller one to be used in the classroom and a larger one as a stock jar.
- The two jars should be screw capped, clear glass, wide mouthed jars, clean and dry (air dried is sufficient) and labelled appropriately.
- Place some clean paraffin oil in the jars.
- Using dry forceps, transfer one small lump of sodium into the demonstration jar and the rest of the pieces into the stock jar.
- Cover the sodium in both jars with clean paraffin oil.
- If the sodium is in kerosene, using dry forceps, remove the sodium, blot off excess kerosene by rolling the pieces on paper towel and place under paraffin oil so that it is stored in a non-flammable liquid.
- Dispose of old paraffin oil/kerosene and container appropriately labelled via a chemical waste disposal contractor.
References and further reading:
Chem-Supply. 2015. Sodium metal, Safety Data Sheet, Chem-Supply website, https://www.chemsupply.com.au/documents/SL0741CH6J.pdf
‘Chemical Resistance Reference Guide’, Thermofisher website, https://tools.thermofisher.com/content/sfs/posters/LCD-Chemical-Resistan...
Chemistry Australia and Science Industry Australia. 2008. Code of Practice for Supply Diversion into Illicit Drug Manufacture, Chemistry Australia website, https://chemistryaustralia.org.au/Library/PageContentVersionAttachment/9...
Science ASSIST. 2018. Chemical Management Handbook for Australian Schools Edition 3, Science ASSIST website, https://assist.asta.edu.au/resource/4193/chemical-management-handbook-australian-schools-edition-3
Science ASSIST. 2016. SOP: Demonstrating the reaction of alkali metals lithium and sodium with water, Science ASSIST website, https://assist.asta.edu.au/resource/3591/sop-demonstrating-reaction-alkali-metals-lithium-and-sodium-water
‘Storage of Sodium & Phosphorus’, Science ASSIST Q&A, Science ASSIST website, https://assist.asta.edu.au/question/3835/storage-sodium-phosphorus (25 May 2016)
‘Use of Sodium in Schools’, Science ASSIST Q&A, Science ASSIST website, /question/2498/use-sodium-schools (9 October 2014)