While methane (CH4) is the gas most commonly associated with flatulence and swamp gas, it is hydrogen sulphide (H2S) that provides the stench. The human olfactory system (i.e. the nose) is extremely sensitive to hydrogen sulphide, being able to detect its presence at air concentrations as low as 2.3 parts per billion (ppb). Therefore, when preparing hydrogen sulphide in the laboratory, it's important to take proper measures to ensure that the gas doesn't accidentally leak out into the room.
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Things you need
- 2 plastic syringes, 60mL
- Silicone oil
- 2 pieces of latex tubing, 20cm
- 6M solution of hydrochloric acid (HCl)
- 1 rubber stopper, 2 holed
- Digital laboratory scale
- Plastic weighing dish
- Measuring spatula
- Zinc sulphide (ZnS) powder
- 1 test tube, 18-by-150mm
- Tubing clamp
Remove the plungers from both 60mL plastic syringes.
Apply a layer of silicone oil to the entire rounded surface on the rubber head of each plunger to create lubrication between the plastic walls of the syringe and the rubber edges of the plunger heads.
Push each lubricated plunger back into its respective syringe, leaving no air space inside.
Twist one end of a piece of latex tubing onto the opening of the first syringe. The walls of the tubing should fit between the inside threading and the outer wall of the opening, forming an airtight seal.
Twist the end of another piece of latex tubing onto the opening of the second syringe. Once again, make sure that the fit is airtight.
Submerge the free end of the latex tubing attached to the first syringe in the hydrochloric acid.
Draw the first syringe's plunger back until you have drawn 15mL of acid into that syringe via the latex tubing.
Fit the free end of each syringe's tubing into one of the holes on the top (i.e. the wider end) of the rubber stopper. The goal is to eventually fit the stopper into the test tube and have the tubing from each syringe opening into the test tube's interior.
Place the weighing dish on the digital scale and press the "Tare" button. This will recalibrate the scale so that you weigh only the powder you add.
Move 0.20g of zinc sulphide power onto the weighing dish using the measuring spatula.
Pour the 0.20g of zinc sulphide into the test tube.
Press the rubber stopper into the opening of the test tube, forming an airtight seal.
Press down slowly on the plunger of the hydrochloric -acid-filled syringe, causing all of the acid to gradually enter the test tube and react with the zinc sulphide. The entire reaction will take about 15 seconds. During this time, allow the second syringe's plunger to move backward as the syringe fills with the hydrogen sulphide gas from the test tube.
Place a clamp on the latex tubing between the test tube and the hydrogen-sulphide-filled syringe.
Release the hydrogen sulphide gas safely by either taking the syringe-test-tube assembly outdoors placing it inside a laboratory fume hood and turning on the hood's exhaust fan.
Tips and warnings
- In sufficient quantities, hydrogen sulphide can be deadly. According to New World Encyclopedia, hydrogen sulphide starts to burn the eyes at concentrations between 10 and 20 parts per million (ppm). At 320 ppm, life-threatening pulmonary oedema can occur and levels of 1,000 ppm or more cause immediate unconsciousness upon exposure.
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