Tests for anions, cations, functional groups... Flashcards
Test for acid/base character
acid- red
base- blue
Flame test for Li+
Red
Flame test Na+
orange/yellow
Flame test K+
lilac
Flame test Rb+
red
Flame test Cs+
blue
Flame test Mg2+
no color
Flame test Ca2+
brick-red
Flame test Sr2+
crimson red
Flame test Ba2+
green
Test for CO32- and HCO3-
add acid(aq)
bubbles of co2 observed
use delivery tube to pass gas through limewater
limewater turns cloudy, CaCO3 formed
Test for NH4+ ions
add NaOH(aq) and warm gently
pungent smell given off
turns damp red litmus paper blue
Test for SO42-
Add BaCl2
white ppt of BaSO4 formed
Test for Halides
HNO3 followed by AgNO3
Cl-:white ppt soluble in ammonia
Br-: cream ppt soluble in excess ammonia
I-: yellow ppt insoluble in ammonia
Test for Mg2+
Add NaOH: white suspension
Add more NaOH: insoluble
Test for Ca2+
Add NaOH: white suspension
Add more NaOH: partially in soluble
Test for Sr2+ and Ba2+
Add NaOH: soluble
Add more NaOH: soluble
Test for Zn2+
Add NaOH: white ppt soluble in NH3
Add more NaOH:ppt dissolves
Zn is amphoteric
Test for Al3+
Add NaOH: white ppt
Add more NaOH: ppt dissolves
Al is amphoteric
Test for Ag+
Add NaOH: dark brown ppt soluble in NH3
Add more NaOH: insoluble
Test for Cu2+
Add NaOH: blue ppt soluble in excess ammonia blue solution
Add more NaOH: insoluble
Test for Fe2+
Add NaOH: white/green ppt slowly turns brown when exposed to air
Add more NaOH: insoluble
Test for Fe3+
Add NaOH: brown ppt
Add more NaOH: insoluble
Test for Cr3+
Add NaOH: blue-green ppt soluble in NH3 to give violet solution
Add more NaOH:ppt dissolves to give green solution
Test for Co2+
Add NaOH: blueish ppt slowly turns pink, dissolves in NH3 light brown solution
Add more NaOH:insoluble
Test for Ni2+
Add NaOH: green ppt soluble in NH3 to give blue solution
Add more NaOH: ppt doesn’t dissolve
Test for Mn2+
Add NaOH: off-white ppt turns brown in exposure to air
Add more NaOH:insoluble
Test for halides with conc H2SO4
Cl-: steamy fumes of HCl
Br-: steamy fumes, brown vapour
I-: steamy fumes, purple vapour, black solid
Test for bromides
add chlorine water
orange solution
Effervescence may be produced
Test for alkenes
add some bromine water
color change from orange to colourless
Test for -OH groups (not phenols)
add PCl5 misty fumes of HCl or add a small piece of sodium effervescence
Test for carboxylic acids
litmus paper turns red-ish.
Add a carbonate/HCO3 −
Effervescence (CO2 )
Test for aldehydes and ketones
Add 2,4-DNP (Brady’s reagent).
An orange precipitate is formed upon reaction with C=O group of aldehyde or ketone.
Test to distinguish aldehydes from ketones
Add Tollen’s Solution(ammoniacal AgNO3).
Aldehydes give a positive test and a silver mirror is observed.
Ketones cannot be oxidised, so no change observed)
or
Fehling’s test.
Aldehydes give a positive test and form a brick red precipitate.
Ketones don’t react so the solution stays deep blue).
Test for methylketones, ethanal, ethanol, and methyl secondary alcohols
Iodoform Reaction
Warm with iodine and sodium hydroxide.
Yellow precipitate.
Antiseptic smell (triiodomethane, iodoform).
Test for primary/secondary alcohol and aldehydes
warm with acididfied K2Cr2O7
color change from orange to green
Esterification test
Gently warm an alcohol and carboxylic acid in presence of conc. H2 S O4
Should produce a compound with a characteristic smell
Solubility Test
Compounds with groups that can form H-bonds may be soluble in water, (e.g. amines, alcohols, carboxylic acids etc.)
Some carboxylic acids may not be soluble in water, but may be soluble in alkaline solution (due to formation of RCOO− ) .
Same goes with amines. Some may not be soluble in water, but will be soluble in acidic solution (e.g. formation of RNH3 + )
