test: covered earlier. There are no simple reagents that will
precipitate sodium compounds. test: covered earlier. There are
no simple reagents that will precipitate potassium compounds.
Dilute sulphuric acid gives a white precipitate of calcium
sulphate if the original solution is fairly concentrated:
Ca2+(aq) + SO42-(aq) " CaSO4(s) Calcium sulphate solution is
permanently hard water; its solubility is about 0.05 mol dm-3 at
25oC. Ca2+(aq) + CO32-(aq) Ammonium ethanedioate solution
precipitates white calcium ethanedioate from neutral or alkaline
solutions. The precipitate dissolves readily in dilute acid:
Ca2+(aq) + C2O42-(aq) " CaC2O4(s) ethanedioate (calcium oxalate)
is found in rhubarb leaves - it is what makes them Sodium
hydroxide solution precipitates grey-green chromium(III)
hydroxide, which reacts with excess NaOH to give a deep green
solution of the chromite ion: [Cr(H2O)6]3+(aq) + 3OH-(aq) "
Cr(OH)3(s) + 6H2O(l) Cr(OH)3(s) + 3OH-(aq) " [Cr(OH)6]3-(aq)
solution precipitates grey-green chromium(III)