Spot a mixture on a strip of silica, stand it in a little solvent, and within minutes the components have spread out into a ladder of spots. The greasy, nonpolar ones nearly keep pace with the solvent, while the polar ones lag near the start. The reason why nonpolar compounds travel farther in TLC (thin layer chromatography) comes down to a tug-of-war between a polar surface and a much less polar liquid. Once that’s clear, most of the practical rules […]
Hand a chemistry student a white powder and ask what’s in it, and half the job is finding the anion: the negatively charged part of the salt. Is it a carbonate, a chloride, a sulfate? Classic anion analysis answers that with a handful of reagents and a careful eye for fizzing, cloudiness and colour. The order of the tests matters almost as much as the tests. The three signals: gas, precipitate, colour Most anion tests rely on one of three […]
Add a drop of pale yellow iron(III) chloride solution to a little salicylic acid in water and the tube turns violet almost at once. Do the same with clean aspirin and the colour barely changes. That contrast is the whole basis of the salicylic acid iron III chloride test, one of the most familiar quick checks in an undergraduate lab. It’s simple to run, but the chemistry behind the colour is worth a closer look, and so are the limits […]
Take one carbon atom, bolt three benzene rings onto it, and add a single OH group. The result, triphenylmethanol, is an unremarkable-looking white powder. Drop it into concentrated sulfuric acid, though, and it dissolves to give a bright yellow solution. That colour change helped chemists realise, more than a century ago, that a positively charged carbon could be stable enough to sit in a flask. The same crowded molecule also sits at the root of the first organic free radical […]
A brass doorknob, a trumpet and a plumbing valve can look like the same golden metal, but they aren’t the same recipe. Brass is copper with zinc mixed in, and the amount of copper in brass decides a surprising amount: whether it glows reddish or pale yellow, whether it bends cold or cracks, and how cleanly it cuts on a lathe. Chemists have reliable ways to measure that copper share, and the methods are a tidy tour of analytical chemistry. […]
Stir a white powder into a colourless liquid, add a few drops of strong acid, warm it for ten minutes, and you have aspirin, plus a lab that smells faintly of vinegar. The salicylic acid and acetic anhydride reaction is one of the most familiar syntheses in chemistry teaching. It’s also a compact lesson in how esters form, why chemists choose some reagents over others, and where the leftover smells and gunk come from. A safety note before the chemistry: […]