Tell them apart: one test for two substances sim
Ten look-alike pairs. Drag one test from the shelf onto both tubes, write both results, and get marked as an exam would: a clear, different result for each, both stated. See why the tempting tests fail.
Qualitative analysis: choosing one test that distinguishes two substances, and stating both results · covers the GCSE, IGCSE, O-Level topic
What the sim shows
"Describe a test to tell X from Y" needs three things: one test, a clear result for X and a different clear result for Y, both stated. A test that changes neither tube, changes both the same way, or makes a change too faint to see, earns nothing. The pairs here are the usual ones. Two halides: silver nitrate after nitric acid (chloride white, iodide yellow). Carbonate and sulfate: acid (only carbonate fizzes, and the gas turns limewater milky) or acid then barium nitrate (only sulfate gives a white precipitate). Zinc and aluminium: both white hydroxides dissolve in excess sodium hydroxide, but only zinc hydroxide dissolves in excess ammonia. Iron(II) and iron(III): green and red-brown hydroxides. Ammonium: warm with alkali, and ammonia turns damp red litmus blue. Hydrochloric and sulfuric acid: the anion test, not the acid tests. Hexane and hexene: aqueous bromine. Ethanol and ethanoic acid: indicator or carbonate. Iodide and chloride: an oxidising agent (acidified manganate(VII), or bromine water) turns iodide brown as iodine forms; or silver nitrate (yellow and white). Carbon dioxide and sulfur dioxide: both turn limewater milky, so use acidified manganate(VII), which only sulfur dioxide turns colourless (IGCSE and AQA; not in the SG practical). The observations match the library's own test figures. Model limits: one textbook result for each test; the metal-ion sulfates are all shown as slightly acidic on indicator paper.
- Tubes A and B: two look-alike substances
- Shelf: eight reagents, two papers, carbonate, magnesium
- One test, both results stated: 2 marks
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