(i) Carbon Dioxide (CO₂)
– Limewater Test: When CO₂ is bubbled through limewater (a solution of calcium hydroxide), it turns milky due to the formation of calcium carbonate, which is a white precipitate.
(ii) Sulfur Dioxide (SO₂)
– Bleaching Test: SO₂ has the ability to decolorize an acidified potassium permanganate solution (which is purple) and turns it colorless.
– Lead Acetate Test: SO₂ reacts with moist lead(II) acetate paper, turning it brown due to the formation of lead sulfide.
(iii) Oxygen (O₂)
– Glowing Splint Test: A glowing splint (a wooden stick that is not fully burnt) will reignite when placed in a jar of oxygen, indicating the presence of this gas.
(iv) Hydrogen (H₂)
– Pop Test: When a lit splint is brought near hydrogen gas, it produces a characteristic ‘pop’ sound due to a small explosion as hydrogen burns in oxygen.
