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Gases are identified using their properties. Properties such as colour, odour, combustibility, action on litmus paper, and so on are the common properties used to identify gases. The table below summarizes the common gases and key properties used to identify them.
Common Gases and the Important Properties used in Identifying them
Gas | Physical Properties | Test | Result |
Hydrogen, H2(g) | Colourless, odourless gas; neutral to litmus paper | Ignite | Burns with ‘pop’ sound |
Oxygen, O2(g) | Colourless, odourless gas; neutral to litmus paper | Insert a glowing splint | The splint rekindles |
Carbon (IV) oxide, CO2(g) | Colourless, odourless gas; acidic | Bubble the gas through lime water | Limewater turns milky |
Chlorine, Cl2(g) | Greenish-yellow;choking smell | (i) Insert moist blue litmus paper (ii) Insert a moist starch-iodide paper | Litmus paper turns red then becomes bleached to white Moist starch-iodide paper turns blue |
Ammonia, NH3(g) | Colourless;Pungent smell; alkaline | (i) Insert moist red litmus paper.(ii) Contact with fumes of concentrated hydrochloric acid. | (i) Litmus paper turns blue. (ii) Gives white dense fume of NH4Cl with HCl. |
Hydrogen Chloride, HCl(g) | Colourless, odourless;gives acidic solution in water | (i) Insert damp blue litmus. (ii) Apply a drop of silver nitrate on the end of a glass rod and hold it over gas | (i) Litmus paper turns red (ii) A white precipitate |
Hydrogen sulphide, H2S(g) | Colorless gas;rotten egg smell | Test with damp lead (II) ethanoate (lead acetate) paper | Lead(II) ethanoate paper turns black |
Sulphur (IV) oxide, SO2(g) | Colourless, odourless; acidic | Test with freshly made potassium dichromate (VI) paper | Paper turns from orange to green |
Nitrogen (IV) oxide, NO2(g) | Reddish brown; pungent smell;Acidic | (i). Insert moist blue litmus paper (ii). Pass into silver trioxonitrate (V) solution | (i). Litmus paper turns red (ii). Cream precipitate is formed. |
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