Hydrogen sulfide sensor
In a laboratory, hydrogen sulphide is prepared by the action of dilute sulphuric acid on iron sulphide.
- FeS(s)+H2SO4(aq) = FeSO4(aq) + H2S(g)
Concentrated sulphuric acid and nitric acid cannot be used for this process as they oxidise hydrogen sulphide to sulphur. 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 sulphide placed at bottom of the bottle. When iron sulphide reacts with diluted sulphuric acid, hydrogen sulphide is formed which is collected in the gas jar by upward displacement of air.
Purification of hydrogen sulphide 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 bisulphide. The bisulphide on heating above 60°C gives a steady stream of pure H2S gas.
- MgO + 2H2S --> Mg(HS)2 + H2O (magnesium bisulphide)
- 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 sulphide:
- a H2S sensor is used to detect hydrogen sulphide in the hydrogen feed stream of fuel cells to prevent catalyst poisoning and to measure the quality of guard beds used to remove sulphur from hydrocarbon fuels.
- a hydrogen sulphide sensor is used in personal protective equipment to warn for the presence of hydrogen sulphide gas, e.g. on acid gas production sites.