This common misconceptions covers Common Misconceptions within Gas Tests for GCSE Chemistry. Revise Gas Tests in Chemical Analysis for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 8 of 13 in this topic. Use this common misconceptions to connect the idea to the wider topic before moving on to questions and flashcards.
⚠️ Common Misconceptions
Misconception 1: "Carbon dioxide turns limewater cloudy permanently"
Not always. When you first bubble CO₂ through limewater, it turns milky as CaCO₃ precipitates. But if you continue passing excess CO₂, the calcium carbonate reacts further with the CO₂ and water to form soluble calcium hydrogencarbonate (Ca(HCO₃)₂), and the solution clears again. The GCSE positive result is the initial clouding — note this if given a data question about extended CO₂ exposure.
Misconception 2: "Use a burning splint to test for oxygen"
Wrong! You use a glowing splint for oxygen. A burning splint is used for the hydrogen test. If you use a burning splint for oxygen, there is no obvious change. The whole point of the glowing splint test is that it is just below the threshold needed to reignite without the extra oxygen.
Misconception 3: "Dry litmus paper can be used to test for chlorine"
The litmus paper must be damp. Water is needed for the reaction: Cl₂ + H₂O → HClO + HCl. Without water present, hypochlorous acid cannot form, and no bleaching occurs. Dry litmus will not turn white in chlorine gas.
Practice questions for Gas Tests
Which observation confirms a gas is hydrogen when tested with a burning splint?
Explain why hydrogen gas produces a squeaky pop when tested with a burning splint.