Edexcel A level Chemistry - Chemical Tests (In Progress)
Important chemical tests to know from across the Edexcel A-Level Chemistry syllabus.
- Created by: Amelia Mackay
- Created on: 25-08-20 09:44
Testing for Carbon Dioxide
Testing for Carbon Dioxide
- Method-
- Bubble the gas through limewater (saturated aqueous solution of calcium hydroxide)
- Observe the change occurring
- Positive Result-
- White precipitate
- The carbon dioxide reacts to form calcium carbonate which is insoluble in water and is the white precipitate
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
Testing for Sulfate Ions
Testing for Sulfate Ions
-Method-
- Add dilute nitric acid to the aqueous solution containing the sulfate ions
- Add barium chloride or barium nitrate
- Observe the change
-Positive Result-
- A white precipitate will form
- The sulfate ions in the solution will react with the added barium ions to form an insoluble white precipitate of barium sulfate
Ba2+(aq) + SO42-(aq) → BaSO4(s)
Flame Tests
Flame Tests
-Method-
- Wear safety glasses and a lab coat
- Add a few drops of concentrated HCl to the solid to dissolve the solid
- Dip a clean nichrome wire into the mixture
- Pass the wire through a lit bunsen burner in a fume cupboard
- Observe the colours produced
-Colours-
Li+- Red Rb+- Red/purple Ca2+ - Brick red
Na+- Yellow/orange Cs+ - Blue/Violet Sr2+ - Crimson red
K+- Lilac Be2+ and Mg2+ - no colour Ba2+ - Apple green
Testing for Ammonium Ions
Testing for Ammonium Ions
-Method-
- Add sodium hydroxide solution
- Warm the mixture
- Smell the gas produced
-Positive Result-
- Damp red litmus paper will turn blue in the presence of the gas
- HCl gas reacts with ammonia to form white fumes of ammonium chloride
NH4 (aq) + OH- (aq) → NH3 (g) + H2O (l)
Testing for Halide Ions
Testing for Halide Ions
-Method-
- Add dilute nitric acid to the halide solution
- Add a solution of silver nitrate
- Observe the precipitate formed
-Results-
- Cl- - White ppt, soluble in dilute and concentrated aqueous ammonia
- Br- - Cream ppt, insoluble in dilute aqueous ammonia, soluble in concentrated aqueous ammonia
- I- - Yellow ppt, insoluble in dilute and concentrated aqueous ammonia
Ag+(aq) + X-(aq) → AgCl(s)
Testing for Alkenes
Testing for Alkenes
-Method-
- Add bromine water to the organic compound
- Shake the mixture
- Observe the colour change
-Positive Result-
- The mixture changes colour from orange to colourless
- The bromine has been decolourised by the C=C bond
Example:
C2H4 + Br2 → C2H4Br2
Testing for Aldehydes
Testing for Aldehydes
-Method-
- Add one of the reagents below to oxidise the aldehyde to a carboxylic acid
- Observe the colour change
-Reagents and Positive Results-
- Acidified potassium dichromate (IV) - Orange solution to green solution
- Fehling's solution - Deep blue solution to red precipitate
- Benedict's solution - Deep blue solution to red precipitate
- Tollens' reagent - Colourless solution to silver mirror
Test for CH3CO Group
Test for CH3CO Group
-Method-
- Add a carbonyl compound to an alkaline solution of iodine
- Warm the mixture and cool it
- Observe whether a precipitate is formed
-Positive Result-
- A yellow precipitate of insoluble CHI3
- This indicates that the compound is ethanal or a methyl ketone
Testing for Carbonyl Compounds
Testing for Carbonyl Compounds
-Method-
- Add Brady's reagent (2,4-dinitrophenylhydrazine) to the compound
- Observe the colour change
-Positive Result-
- A brightly coloured orange solid will be produced
- This derivative can be analysed to identify the specific carbonyl compound
Colours of Complexes - Copper II
Colours of Complexes - Copper II
- [Cu(H2O)6]2+ - Pale blue solution
- [Cu(H2O)4(OH)2] - Pale blue precipitate
- Formed during the reaction with aqueous sodium hydroxide
- Formed during the reaction with aqueous ammonia
- [Cu(NH3)4(H2O)2]2+ - Deep blue precipitate
- Formed during the reaction with excess ammonia
- [CuCl4]2- - Yellow solution
- Formed during the reaction with concentrated HCl
Colours of Complexes - Iron II
Colours of Complexes - Iron II
- [Fe(H2O)6]2+ - Pale green solution
- [Fe(H2O)4(OH)2] - Green precipitate
- Formed during the reaction with aqueous sodium hydroxide
- Formed during the reaction with aqueous ammonia
- [Fe(H2O)3(OH)3] - Brown precipitate
- Formed upon the standing of [Fe(H2O)4(OH)2]
- Formed during the reaction with excess ammonia
Colours of Complexes - Iron III
Colours of Complexes - Iron III
- [Fe(H2O)6]3+ - Yellow/brown solution
- [Fe(H2O)3(OH)3] - Brown precipitate
- Formed during the reaction with aqueous sodium hydroxide
- Formed during the reaction with aqueous/excess ammonia
Colours of Complexes - Cobalt II
Colours of Complexes - Cobalt II
- [Co(H2O)6]2+ - Pink solution
- [Co(H2O)4(OH)2] - Blue precipitate (pink precipitate on standing)
- Formed during the reaction with aqueous sodium hydroxide
- Formed during the reaction with aqueous ammonia
- [Co(NH3)6]2+ - Brown solution
- Formed during the addition of excess ammonia
Colours of Complexes - Cobalt II Continued
Colours of Complexes - Cobalt II Continued
- [Co(NH3)6]3+ - Yellow precipitate
- Formed upon the standing of [Co(NH3)6]2+
- [CoCl4]2- - Blue solution
- Formed during the reaction with concentrated HCl
Colours of Complexes - Chromium
Colours of Complexes - Chromium
- [Cr(H2O)6]3+ - Green or violet solution
- [Cr(H2O)3(OH)3] - Green precipitate
- Formed during the reaction with aqueous sodium hydroxide
- Formed during the reaction with aqueous ammonia
- [Cr(H2O)2(OH)4]- - Green solution
- Formed during the reaction with excess aqueous sodium hydroxide
- [Cr(OH)6]3- - Green solution
- Formed during the reaction with concentrated sodium hydroxide
Colours of Complexes - Chromium Continued
Colours of Complexes - Chromium Continued
- [Cr(NH3)6]3+ - Violet or purple solution
- Formed during the reaction with excess ammonia
- CrO42- - Yellow solution, Cr7O42- - Orange solution
- Formed during the addition of H2O2/OH- to [Cr(OH)6]3-, then the addition of H+
- [Cr(H2O)6]3+ - Green or violet solution, [Cr(H2O)6]2+ - Blue solution
- Formed during the addition of Zn/H+ from CrO42- and [Cr(H2O)6]3+ respectively
The Chemistry of Vanadium
The Chemistry of Vanadium
V2+ (Vanadium (II)) - Purple
V3+ (Vanadium (III)) - Green
VO2+ (Oxovanadium (IV)) - Blue
VO2+ (Dioxovanadium (V)) - Yellow
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