Testing For Organic Functional Groups Flashcards
Test for alkenes
Add bromine water
Solution goes from orange -> colourless
Test for an aldehyde
Test with tollens reagent a silver mirror should form
Test with fehlings reagent
Solution goes from blue -> red precipitate
Test for carboxylic acid
Add sodium carbonate
Effervescence of carbon dioxide should evolve
Test for primary alcohols
Warm solution with acidified potassium dichromate
Colour change from Orange -> green
Under distillation primary alcohols oxidise to aldehydes then carboxylic acids
Test for carboxylic acid: add sodium carbonate
If effervescence of co2 then it’s a primary alcohol
Test for aldehyde: Add Tollens reagent
If silver mirror is formed then it’s a primary alcohol
Add fehlings solution
If colour change from blue -> red precipitate then it’s a primary alcohol
Test for secondary alcohols
Warm solution with acidified potassium dichromate
Colour change from Orange -> green
When secondary alcohols are oxidised under reflux a ketone is produced
Test with Fehlings and Tollens a negative results indicates the presence of the ketone and therefore it’s a secondary alcohol
Test for a chloroalkane
Warm with silver nitrate solution (AgNO3)
AgCl (s) -> white precipitate
AgBr (s) -> cream precipitate
AgI (s) -> yellow precipitate
Test for group 2 metal cations
Add dilute sodium hydroxide
MgCl2 + 2NaOH → Mg(OH)2 + 2NaCl
White precipitate formed
CaBr2 + 2NaOH → Ca(OH)2 + 2NaBr
White precipitate formed
SrCl2 + 2NaOH → Sr(OH)2 + 2NaCl
White precipitate
BaCl2 + 2NaOH → Ba(OH)2 + 2NaCl
Colourless solution formed
Test for group 2 metal cations
Add dilute sulphuric acid
MgCl2 + H2SO4 → MgSO4 + 2HCl
Colourless solution
CaBr2 + H2SO4 → CaSO4 + 2HBr
White precipitate
SrCl2 + H2SO4 → SrSO4 + 2HCl
White precipitate
BaCl2 + H2SO4 → BaSO4 + 2HCl
White precipitate formed
Test for ammonium ions
Warm with sodium hydroxide in a fume cupboard
NH4Cl + NaOH → NH3 + NaCl + H2O
Test ammonia gas produced with damp litmus paper the paper should turn blue
Litmus detects alkaline or acidic , Ammonia gas is alkaline therefore it turns blue
Test for carbonate ions in aqueous solution
Add calcium hydroxide (limewater) to sodium carbonate
Limewater solution goes from
colourless -> cloudy
Test for sulphate ions
Add dilute HCl and the barium chloride solution
Solution will turn cloudy and a white precipitate is formed
Test for halide ions in aqueous solution
Add dilute nitric acid followed by silver nitrate
Potassium chloride- white precipitate
Potassium bromide- cream precipitate
Potassium iodide- yellow precipitate
To distinguish between similar colours add ammonia solution
Potassium chloride- dissolves forming colourless solution
Potassium bromide- only dissolves in concentrated ammonia solution
Potassium iodide- doesn’t dissolve at all reminds a yellow precipitate
Testing halide ions using concentrated. H2SO4
Potassium chloride- solution remains white produces effervescence
Potassium bromide- solution turns dark brown
Brown gas /effervescence
Potassium iodide - solution turns bright orange
Effervescence
Period II oxides
Reaction in air Flame
Na2O vigorous Yellow
MgO. vigorous Brilliant white
Al2O3. Slow N/A
SiO2. Slow N/A
P4O10 Spontaneous Brilliant white
Combustion
SO2. Burns steadily. Blue
In aqueous solution
Fe(H2O)6 2+
Green solution
In aqueous solution
Cu(H2O)6 2+
Blue solution
In aqueous solution
Fe(H2O)6 3+
Pale violet but appears orange due to hydrolysis to Fe(H2O)5(OH) 2+
In aqueous solution
Al(H2O)6 3+
Colourless solution
Reaction of Fe(H2O)6 2+ with sodium hydroxide
Fe(H2O)4(OH)2
Green precipitate
Darkens on standing as its oxidised to Fe(H2O)3(OH)3
In excess= no further reaction
Reaction of Cu(H2O)6 2+ with sodium hydroxide
Cu(H2O)4(OH)2
Blue precipitate formed
In excess= no further reaction
Reaction of Fe(H2O)6 3+ with sodium hydroxide
Fe(H2O)3(OH)3
Brown precipitate formed
In excess = no further reaction
Reaction of Al(H2O)6 3+ with sodium hydroxide
Al(H2O)3(OH)3
White precipitate formed
In excess = Al(H2O)2(OH)4 1-
Redissolves to give a colourless solution
Reaction of Metal Aqua ions with NH3
Same as the relations with sodium hydroxide
Except in excess Cu(H2O)4(OH)2 forms Cu(H2O)2(NH3)4 2+
Which is a dark blue solution
Reaction of Fe(H2O)6 2+ with CaCO3
FeCO3
Green precipitate
Reaction of Cu(H2O)6 2+ with CaCO3
CuCO3
Blue-green precipitate
Reaction of Fe(H2O)6 3+ with CaCO3
Fe(H2O)3(OH)3
Brown precipitate and bubbles of gas (CO2)
Reaction of Al(H2O)6 3+ with CaCO3
Al(H2O)3(OH)3
White precipitate and bubbles of gas (CO2)
Substitution reaction of Fe(H2O)6 2+ with HCl
FeCl4 2-
Yellow solution
Substitution reaction of Cu(H2O)6 2+ with HCl
CuCl4 2-
Green solution
Substitution reaction of Fe(H2O)6 3+ with HCl
FeCl4 1-
Yellow solution
Substitution reaction of Al(H2O)6 3+ with HCl 11
AlCl4 1-
Colourless solution
Distinguishing between halogens
Add an aqueous solution of chlorine
Displaces elements that are Lower
Halogen In water With cyclohexane
Cl2 Green. Green
Br2. Orange. Orange
I2. Brown. Violet
Cl2 + 2Br- → Br2 + 2Cl-
Cl2 + 2I- → I2 + 2Cl-
NaF and NaCl with sulfuric acid
NaCl (s) +H2SO4 (l) → NaHSO4 (s) +HCl (g)
Produces steamy HCl fumes
NaF (s) +H2SO4 (l) → NaHSO4 (s) +HF (g)
produces steamy HF fumes
HF & HCl aren’t strong enough reducing agents to reduce sulfuric acid so reaction stops
Not a redox reaction, oxidation states remain the same
NaBr with sulfuric acid
NaBr (s) +H2SO4 (l) → NaHSO4 (s) +HBr (g)
Produces steamy HBr fumes
HBr strong enough to reduce sulfuric acid so it reacts further
2HBr(aq) + H2SO4 (l) → Br2 (g) + SO2 (g) + 2H2O (l)
Choking fumes of SO2
Orange fumes Br2
NaI with sulfuric acid
NaI (s) +H2SO4 (l) → NaHSO4 (s) +HI (g)
Produces steamy HI fumes
HI strong enough to reduce sulfuric acid so it reacts further
2HI(aq) + H2SO4 (l) → I2 (g) + SO2 (g) + 2H2O (l)
HI strongest reducing agent so further reduces SO2
6HI(g) + SO2 (g) → H2S (g) + 3I2 (s) + 2H2O (l)
H2S toxic eggy smell
I2 purple gas/ grey solid
Halogen properties
Colour. State
F2. Pale yellow. Gas
Cl2. Green. Gas
Br2 Red-brown Liquid
I2. Grey Solid
Displacement Reaction with chlorine water
Potassium chloride - no reaction
Potassium bromide - colourless -> orange solution of Br2 formed
Potassium iodide - colourless -> brown solution I2 formed
Displacement reaction with bromine water
Potassium chloride - no reaction
Potassium bromide - no reaction
Potassium iodide - colourless -> brown solution of I2
Displacement reaction with iodine solution
Potassium chloride - no reaction
Potassium bromide - no reaction
Potassium iodide - no reaction
