Chemical tests
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21 Terms
Carbonate test (CO32-)
Add dilute nitric acid, bubble through lime water, colourless to cloudy
Sulphate test (SO42-)
Add barium nitrate, white precipitate forms
Halide test (X-)
Aqueous silver nitrate, precipitates form, chloride white, bromide cream, iodide yellow
Further checking halides
Add dilute aqueous ammonia, chloride is soluble, add conc. aqueous ammonia, bromide is soluble. Iodide insoluble in both.
Anion tests order
carbonate, sulphate, halides
Carbonates first because…
Neither sulphates nor halides produce bubbles with dilute acid, so there is no possibility of an incorrect conclusion and it rules out carbonates
Sulphates second because…
BaCO3 is also a white precipitate, so can’t go first. Halides do not form this
Halides third because…
Silver carbonate and silver sulphate are both precipitates, so you must rule out these two first before carrying out the test
ammonium ion test (NH4+)
Aqueous sodium hydroxide, warm, test gas with moist red litmus paper turns blue
Test fir unsaturation (alkenes)
Bromine water, orange to colourless
Primary and secondary alcohol test
K2Cr2O2/H+, heat, orange to green
Haloalkanes test
Dissolve in ethanol, add water, halide test
[Fe(H2O)6]2+ pale green
Dark green ppt in a few drops of NaOH or NH3 (Fe(OH)2), no reaction with excess NaOH or NH3
[Cr(H2O)6]3+ green/purple
Green ppt in a few drops of NaOH or NH3 (Cr(OH)3), dark green solution in excess NaOH ([Cr(OH)6]3-), purple solution in excess NH3 ([Cr(NH3)6]3+)
[Fe(H2O)6]3+ yellow
Orange-brown ppt in a few drops of NaOH or NH3 (Fe(OH)3), no reaction with excess NaOH or NH3
[Cu(H2O)6]2+ pale blue
Pale blue ppt in a few drops of NaOH or NH3 (Cu(OH)2), no reaction with excess NaOH, deep blue solution in excess NH3 ([Cu(NH3)4(H2O)2]2+)
[Mn(H2O)6]2+ pale pink
Pale brown ppt in a few drops of NaOH or NH3 (Mn(OH)2), no reaction with excess NaOH or NH3
Aldehyde or ketone test
Add 2,4-DNP (Brady’s reagent), orange precipitate formed
Aldehyde test
Add Tollen’s reagent, silver mirror formed
Carboxylic acid test
Add sodium carbonate, effervescence, test gas using lime water, colourless to cloudy
Benzene test
No reaction with bromine water, sooty flame when burned
