Identification of Common GasesAQA GCSE Chemistry: Flashcards

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What is the test for hydrogen gas?

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What is the test for hydrogen gas?: Hold a burning splint at the mouth of the test tube containing the gas. Hydrogen produces a squeaky pop sound as it burns.
Why does hydrogen produce a squeaky pop when tested with a burning splint?: Hydrogen burns rapidly in oxygen with a loud explosion sound. The gas ignites immediately when it comes into contact with the flame, producing the characteristic squeaky pop.
What is the test for oxygen gas?: Insert a glowing splint (a splint that is no longer alight but still glowing) into the test tube. Oxygen will relight the glowing splint, causing it to burn brightly again.
Why does a glowing splint relight in the presence of oxygen?: Oxygen is a supporter of combustion. It allows fuel to burn rapidly, so the glowing splint (containing burning carbon) will burst back into flame when exposed to oxygen.
What is the test for carbon dioxide gas?: Bubble the gas through limewater (calcium hydroxide solution). The limewater turns milky or cloudy white due to the formation of calcium carbonate precipitate.
Write the equation for the reaction between carbon dioxide and limewater.: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O Calcium hydroxide + carbon dioxide → calcium carbonate + water
What causes limewater to turn milky when carbon dioxide is passed through it?: Carbon dioxide reacts with calcium hydroxide to form calcium carbonate, which is an insoluble white precipitate. This precipitate makes the solution appear milky or cloudy.
What is the test for chlorine gas?: Hold damp litmus paper at the mouth of the test tube containing chlorine gas. The litmus paper will be bleached and turn white (or it will turn red first, then bleach white).
Why does chlorine bleach damp litmus paper?: Chlorine is a strong bleaching agent. In the presence of moisture, it forms hypochlorous acid which removes the colour from the litmus dye, leaving the paper white.
What is the colour change observed when damp litmus paper is exposed to chlorine?: The litmus paper is bleached white. It may briefly turn red first (due to the acidic nature of chlorine in water) before being bleached colourless.
Name the four common gases tested in chemical analysis and their test methods.: Hydrogen — burning splint produces squeaky pop Oxygen — glowing splint relights Carbon dioxide — limewater turns milky Chlorine — damp litmus paper bleaches/turns white
What type of splint is used to test for oxygen?: A glowing splint is used. This is a splint that is no longer actively burning but still has a glow from the hot carbon.
What type of splint is used to test for hydrogen?: A burning splint (lit splint) is used. The flame of the splint must be brought to the mouth of the test tube.
What solution is used in the test for carbon dioxide?: Limewater, which is a solution of calcium hydroxide, Ca(OH)₂.
Explain why the litmus paper must be damp for the chlorine test to work effectively.: Moisture is required for chlorine to form hypochlorous acid, which is the bleaching agent. Without water, the bleaching effect is much weaker or does not occur.