Tests for ions and gases; identifying a compound
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 worked examples, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- A chemical detective
- Flame tests
- Tests for gases
Read the transcript of the teaching part
Last time
Before we start: last time, in Reactions of alkanes and alkenes, and addition polymers, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
A chemical detective
A white powder is found at a crime scene. What is it? A chemist does not guess. She runs a few quick tests, each with a clear colour change, and builds up the answer one clue at a time. You can do the same: flame colours, gas tests, and precipitates.
Flame tests
Dip a clean wire in concentrated hydrochloric acid, then in the solid, and hold it in a blue Bunsen flame. Lithium gives red, sodium yellow, potassium lilac. Calcium gives orange-red, barium light green, and copper(II) blue-green.
Tests for gases
Hydrogen: a lighted splint gives a squeaky pop. Oxygen: a glowing splint relights. Carbon dioxide turns limewater milky. Ammonia turns damp red litmus paper blue. Chlorine bleaches damp litmus paper. Sulfur dioxide turns acidified potassium manganate(VII) from purple to colourless.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Identifying a compound from test results · Tests for aqueous cations · Tests for anions · Tests for cations · Tests for gases and water.
The whole chapter: Experimental Techniques and Chemical Analysis, Experimental Techniques and Chemical Analysis.
Chapter 12: Experimental techniques
- Separation methods and chromatography 6 min
- Tests for ions and gases; identifying a compound 6 min
Also for IGCSE Chemistry 0620
Which topics come up most in IGCSE Chemistry 0620 past papers, counted from every paper since 2004.