Thank you for the question.
Chemical/salt solids which undergo endothermic solution formation with water are suitable to use in a “cold pack making” investigation. The overall process becomes endothermic when heat is absorbed from surroundings to break up the lattice structures of these salts into individual ions when dissolving in water.
The four inorganic salts mentioned, namely: ammonium chloride, ammonium nitrate, magnesium sulfate and sodium thiosulfate do produce endothermic reactions with water and are listed in Science ASSIST’s list of recommended chemicals for use in science in Australian schools.
Availability: Ammonium chloride, magnesium sulfate and sodium thiosulfate are available for purchase from any laboratory chemicals supplier.
Purchase (and supply) of ammonium nitrate is subject to state government regulations since this product is identified as a security sensitive commodity. Quantities only up to 3kg are permitted in schools. In some jurisdictions, supply of ammonium nitrate is subject to certain paper work requirements, such as ordering with an End User Declaration (EUD) and/or applying for an exemption. Therefore, this product may only be available through selected suppliers.
Safety Issues: Before handling any chemical, the Safety Data Sheets (SDSs) must be consulted.
Science ASSIST recommends conducting a site-specific risk assessment before undertaking this activity. We have published an ASSIST information sheet AIS: Risk management and risk assessment, which offers an instructional guide on how to carry out and document a risk assessment using the Science ASSIST risk assessment template.
Science ASSIST also recommends that you store and dispose of these chemicals in accordance with the information in the Safety Data Sheet (SDS) from the manufacturer.
Work with minimum possible quantities of chemicals to keep risks and exposure at low levels. Practice good hygiene; always wash hands before eating, using the toilet or/and if smoking. Wash contaminated clothing and other protective equipment before storing or re-using. Following is some brief hazard and safety information on the chemicals discussed. Please refer to individual SDSs for detailed information on each chemical.
- Ammonium chloride: Toxic substance. This product is hygroscopic. Keep container tightly closed. Incompatible with oxidising agents such as ammonium nitrate, and must be stored away from them.
- Ammonium nitrate: Oxidising solid. Causes serious eye irritation. Harmful to aquatic environment. May intensify fires. Store with other oxidising agents away and separate from other groups of chemicals. This product is hygroscopic. Keep container tightly closed.
- Magnesium sulfate: Non-hazardous substance according to GHS. Not classified as a dangerous good. Dust may cause minor skin irritation.
- Sodium thiosulfate: Non-hazardous substance according to GHS. Not classified as a dangerous good. Can cause mild irritations (skin/eyes/respiratory). Should handle with caution.
It is recommended that the following PPE is worn for all of the above chemicals: wear safety glasses, laboratory coat and nitrile gloves and ensure that work is always conducted in a well-ventilated area.
Recommended Substitution: Science ASSIST suggests substitution of ammonium nitrate with the less hazardous chemical Urea. This product can be purchased from any laboratory chemical supplier. Please refer to the links below for an example investigation and a current SDS.
Vernier software and technology. ‘An Investigation of Urea-Containing Cold Packs, Investigating Chemistry through Inquiry lab manual’ http://www2.vernier.com/sample_labs/CHEM-I-03-cold_packs_open.pdf (Accessed October 2015)
‘Safety Data Sheet: Urea’. November 2014, ChemSupply website https://www.chemsupply.com.au/documents/UL0011CH7B.pdf
‘Safety Data Sheet: Ammonium chloride’. February 2012. ChemSupply website https://www.chemsupply.com.au/documents/AL0491CH0X.pdf
‘Safety Data Sheet: Ammonium nitrate’. 30 April 2014. Merck Millipore website. http://www.merckmillipore.com/INTERSHOP/web/WFS/Merck-AU-Site/en_US/-/US...
‘Safety Data Sheet: Magnesium sulfate’. June 2014, ChemSupply website https://www.chemsupply.com.au/documents/ML0481CH44.pdf
'Safety Data Sheet: Sodium thiosulfate'. August 2014, ChemSupply website https://www.chemsupply.com.au/documents/SA0181CH6W.pdf