Identification of Gases.2009

I dentification dentification of  Gases You have a sample of gas. You suspect it is carbon dioxide, but you are not sure. So you need to do a test. Below are some tests for common gases. Each is based on particular properties of the gas, including its appearance and some times its smell . Ammonia, NH3 Properties Test Result Carbon dioxide,CO2 Properties

Test Result

Gas is lighter than air. Collect downward displacement of air. Ammonia is a colourless alkaline gas with a pungent smell. Carefully smell gas, and hold damp indicator paper in it. Recognizable odour, and damp red litmus paper turns blue. Gas is heavier than air. Collect the upward displacement of air or over water. Carbon dioxide is colourless, weakly acidic gas. It reacts with lime water(a solution calcium hydroxide in water) to give a white precipitate of calcium carbonate). Turns damp blue litmus paper to r ed. CO2(g) + Ca(OH)2(aq) CaCO3(s) + H2O(l) Bubble the gas through lime water. Lime water turns cloudy or milky.

Chlorine, Cl2 Properties Test Result

Gas is heavier heavier than air. Collect the upward displacement of air. Chlorine is a green poisonous gas which bleaches dyes. Hold damp indicator paper in the gas, in a fume cupboard. Indicator paper turns white. (bleach)

Hydrogen,H2 Properties Test Result

Gas is lighter than air. Collect downward displacement of air or over water. Hydrogen is colourless.It combines violently with oxygen when ignite.tak care Collect the gas in a tube and hold a lighted splint to it. The gas burns with a squeaky pop.

Hydrogen chloride,HCl Properties

Test Result Oxygen,O 2 Properties Test Result Sulphur dioxide,SO 2 Properties

Test Result Hydrogen sulfide,H2S Properties

Test Result

Gas is heavier than air. Collect the upward displacement of air. Hydrogen is a colourless, acidic gas with a choking choking smell. Turns damp blue litmus paper to red. It reacts with the alkali ammonia to form the salt ammonium chloride: HCl(g) + NH3(g) NH4Cl(s) Hold a rod dipped in concentrated ammonia solution in the the gas,in gas,in a fume fume cupboard.  A white ‘smoke’ of ammonium ammonium chloride chloride form. form.

Gas is sparingly soluble in water. Density is equal to the air. over water method water method is used to collect. Oxygen is colourless gas. Fuels burn much more readily in it than air. Collect the gas in a test tube and hold a glowing splint to it. The splint immediately bursts into flame. Gas is heavier heavier than air. Collect the upward displacement of air. Sulphur dioxide is a colourless colourless gas. With a choking smell. Turns damp blue litmus litmus paper tored. tored. It reacts with acidified potassium dichromate solution, reducing the orange -2 +3 dichromate, Cr 2O7 to the green chromium ion Cr  + -2 -2 +3 3SO2 (g) + 2H (aq) + Cr 2O7 (aq) 3SO4 (aq) + H2O(l) + 2Cr  (aq) acid orange solution green solution Hold a piece of filter paper soaked in acidified potassium dichromate solution in the gas, In a fume cupboard. The paper turns from orange to green. Hydrogen sulfide is a colourless colourless gas. With a choking smell. It reacts with acidified potassium chromate solution, reducing the yellow -2 +3 chromate, CrO4 to the green chromium ion Cr  -2 + +3 3H2S(g) + 2CrO4 (aq) + 10H (aq) S(s) + 2Cr  (aq) + 8H2O(l) Hold a piece of filter paper soaked in acidified potassium chromate solution in the gas, In a fume cupboard. The paper turns from yellow to green.