Reaction between iron and sulfur

Reaction between iron and sulfur: When we conduct the reaction between Fe and S, it seems to create SO2, which is toxic, and sometimes I smell H2S. Are we allowed to carry out this reaction in the lab? Also, could you please clarify the reaction between FeS and acid? My understanding is that it produces H2S. Is it okay to do this reaction outside?

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Publication Date: 28 April 2016
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Answer by Poonam hosany on question Reaction between iron and sulfur

Fe and S: The reaction between iron fillings and sulfur powder demonstrates the exothermic reaction of two elements to form the compound iron (II) sulfide (FeS). This reaction is usually used to illustrate elements, mixtures and compounds. This reaction generates sulfur dioxide gas, which is toxic and corrosive and small quantities can trigger asthma attacks. Therefore, Science ASSIST recommends that this reaction be conducted as a teacher demonstration only and be carried out in an operating fume cupboard.

The equation for this reaction is Fe(s) + S(s) → FeS(s) and requires Fe and S in a 7:4 ratio by mass. The homogeneous mixture of iron fillings and sulfur powder is heated in a crucible with the lid on using a Bunsen burner. The lid prevents the sulfur vapour from escaping and possibly catching fire. If the sulfur catches fire, then sulfur dioxide gas will be evolved. At the end of the reaction, a hard black residue of iron (II) sulfide is formed at the bottom of the crucible. Iron (II) sulfide can be discarded into the general wastes container, as it is not considered hazardous.

Science ASSIST recommends the following for this reaction.

  • A site-specific risk assessment should be conducted, see the Science ASSIST Risk Assessment Template.
  • Conduct as a teacher demonstration in an operating fume cupboard.
  • Sulfur is an irritant and people handling it should avoid contact with skin, eyes and clothing.
  • Suitable PPE, such as laboratory coat, closed-in shoes and safety glasses, should be worn. Latex or nitrile gloves are suitable for handling sulfur.
  • Sulfur is a flammable solid and the crucible lid should be properly placed so as to prevent combustion.
  • Inspect and discard any chipped or cracked crucible, as it may break during heating, resulting in spillage of hot material.

FeS and acid: This reaction generates hydrogen sulfide gas, which is flammable and toxic and small quantities can trigger asthma attacks. Therefore, Science ASSIST recommends that this reaction be conducted as a teacher demonstration only and be carried out in an operating fume cupboard. This is preferable to conducting the activity outdoors because the fume cupboard is a controlled environment, whereas weather conditions can be unpredictable outside.

The equation for this reaction is FeS(s) + 2 HCl(aq) →  H2S(g) + FeCl2(aq)

Science ASSIST recommends the following for this reaction.

  • A site-specific risk assessment should be conducted, see the Science ASSIST Risk Assessment Template.
  • Conduct as a teacher demonstration in an operating fume cupboard.
  • Suitable PPE, such as laboratory coat, latex or nitrile gloves, closed-in shoes and safety glasses, should be worn.
  • React a small amount of iron (II) sulfide (0.1 g) with 5 mL of 0.5 M hydrochloric acid. The hydrogen sulfide gas generated during the reaction will be extracted by the fume cupboard fan.
  • The reaction mixture should be left in the fume cupboard until the reaction is complete, and then added to water and the resulting liquid disposed of down the sink with dilution. Any unreacted iron (II) sulfide residue can be disposed of in the general waste.

References

‘Iron and Sulfur Reaction’ Royal Society of Chemistry website, http://www.rsc.org/learn-chemistry/resource/res00000713/iron-and-sulfur-reaction?cmpid=CMP00005161  (Accessed April 2016)

‘Hydrogen sulfide hazards’. Safety and health topics. OSHA website https://www.osha.gov/SLTC/hydrogensulfide/hazards.html (Accessed April 2016)

'Iron filings' Safety Data Sheet, Chem Supply website, https://www.chemsupply.com.au/documents/IT0141CH38.pdf (February 2016)

‘Iron (II) Sulfide' Safety Data Sheet, Chem Supply website, https://www.chemsupply.com.au/documents/IT0161CH3A.pdf (September 2012)

OSHA. 2005. Hydrogen sulfide fact sheet. OSHA. https://www.osha.gov/OshDoc/data_Hurricane_Facts/hydrogen_sulfide_fact.pdf

‘Sulfur” Safety Data Sheet, Chem Supply website, https://www.chemsupply.com.au/documents/SL0061CH71.pdf (Aug 2014)

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