Tests for gases sim
Test the gas at the mouth of the tube as soon as it is made, because gases escape.
Tests for gases · covers the GCSE, IGCSE, O-Level topic
What the sim shows
Test the gas at the mouth of the tube as soon as it is made, because gases escape. Hydrogen needs a lighted splint: the gas burns with a squeaky pop. Oxygen needs a glowing splint: it relights. Carbon dioxide turns limewater milky, Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. Here the limewater is 5 cm³ of 0.02 mol/dm³ calcium hydroxide, so 2.4 cm³ of carbon dioxide makes it the most milky; keep bubbling and it clears again, as soluble calcium hydrogencarbonate forms, so stop as soon as it goes milky. Ammonia turns damp red litmus blue. Chlorine turns damp blue litmus red, then bleaches it white. Sulfur dioxide turns acidified potassium manganate(VII) from purple to colourless. Carbon dioxide and sulfur dioxide both turn damp blue litmus red, so litmus alone cannot tell them apart. Limewater cannot either: sulfur dioxide also turns it milky (white calcium sulfite), so use acidified manganate(VII), which only sulfur dioxide turns colourless. Litmus must be damp: dry paper gives the gas nothing to dissolve in.
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