Hydrogen sulfide sensor
In a laboratory, hydrogen sulfide is prepared by the action of dilute sulfuric acid on iron sulfide.
- FeS(s)+H2SO4(aq) → FeSO4(aq) + H2S(g)
Concentrated sulfuric acid and nitric acid cannot be used for this process as they oxidize hydrogen sulfide to sulfur. A Woulf's bottle is fitted with a thistle funnel and a delivery tube. Diluted H2SO4 is run down the funnel so as to cover the iron sulfide placed at bottom of the bottle. When iron sulfide reacts with diluted sulfuric acid, hydrogen sulfide is formed which is collected in the gas jar by upward displacement of air.
Purification of hydrogen sulfide gas
H2S gas obtained from above may contain hydrogen gas and acid impurities. So it is passed through a suspension of MgO in water which gives magnesium bisulfide. The bisulfide on heating above 60 °C gives a steady stream of pure H2S gas.
- MgO + 2H2S → Mg(HS)2 + H2O (magnesium bisulfide)
- Mg(HS)2 → MgS + H2S
Drying of gas
H2S gas is dried over phosphorus pentoxide (P2O5).
This type of sensor has been under constant development because of the toxic and corrosive nature of hydrogen sulfide:
- a H2S sensor is used to detect hydrogen sulfide in the hydrogen feed stream of fuel cells to prevent catalyst poisoning and to measure the quality of guard beds used to remove sulfur from hydrocarbon fuels.
- a hydrogen sulfide sensor is used in personal protective equipment to warn for the presence of hydrogen sulfide gas, e.g. on acid gas production sites.