SALT ANALYSIS Physical appearance of salt EXPERIMENT
OBSERVATION
INFERENCE
1. Colour of the salt is noted
White colour
Pb2+,Al3+, Zn2+ ,Ca2+,Mg2+,NH4+ salts Cu2+ or Ni2+ salts Fe2+,Ni2+ salts Fe3+ salts Mn2+ salts NH4+ salt Cl- or NO3-
Bluish of bluish green colour Light green colour Yellowish colour Light pink/ buff colour Smell of ammonia Deliquescent nature 2. Nature
(i) (ii)
Amorphous Crystalline
May be carbonate May be nitrate,sulphate and chlorides
3. Action of heat i) Colourless, odourless gas is evolved Pinch of salt is heated which turns lime water milky in a dry test tube ii) Colourless pungent gas, turns acidified potassium dichromate paper in to green. iii) Reddish brown gas is evolved, which turns ferrous sulfate solution into brown or black. i) Yellow when hot, white when cold. ii) Brown when hot, yellow Residue is observed when cold. after heating. iii) Original light green salt changes into reddish brown. iv) Pale brown changes to black. v) Green changes to yellow. vi) Residue is black in colour. vii) Decrepitating sound viii) Condensation of water vapours
May be salt contains carbonate ion. May be salt contains sulphite ion.
4. Flame test:
Ca2+ Sr2+ Ba2+ Cu2+ ZnSO4, MnCl2 Pb2+, Sn2+ Absence of the above mentioned cations.
Salt is mixed with conc. HCl and made in to paste which is subjected to flame test
i) ii) iii) iv) v) vi) vii)
Brick red Crimson red Light green/apple green Bluish green Green flashes Bluish white No characteristic colour
1
May be salt contains nitrate ion. Zn2+ Pb2+ Fe2+ Fe3+ Ni2+ May be Cu2+, Fe3+ Mn2+, Co 2+ Lead nitrate or barium nitrate. May be hydrated salts like copper sulfate, nitrate etc.,
EXPERIMENT 5. Solubility test Salt mixture + water
Salt mixture + dill HCl
OBSERVATION
INFERENCE
i)
Soluble
ii)
Insoluble
May be nitrate, sulfate and chloride salts May be carbonate sulfide and sulfite(except amm.carbonate). May be carbonate or sulfite or sulfide
Soluble
Preparation of sodium carbonate extract: Take 0.5 g of the given salt mixture + 5g sodium carbonate + 20 ml of distilled water and boil this content for about 10 minutes and then filter. The filtrate is used for the anion analysis and also for the confirmatory test. The filtrate is sodium carbonate extract Group –I anions 2Anions identified by using dilute H2SO4 ( CO3 , SO32- NO2- CH3COO-and S2-)
EXPERIMENT OBSERVATION Little salt mixture is i) Colourless, odourless gas treated with dilute H2SO4, is released observed in cold and after ii) Vinegar like smell warming. Limewater turns milky. The liberated gas is passed thorough limewater.
The liberated gas is checked with acidified pot dichromate and pot permanganate paper.
ii) Colourless, pungent selling gas is evolved. Pink colour of pot. Permanganate disappears and dichromate paper turns to green. iii) Reddish brown gas is evolved
Gas is passed though ferrous sulphate solution. Liberated gas is checked with lead acetate paper W.E or S.E + sodium nitroprusside solution is added S.E or W.E + dil. HCl is added till all
INFERENCE May be CO32-, May be CH3COO – CO32- is confirmed. May be SO32SO32- is confirmed.
May be NO2-
Ferrous sulphate solution turns to dark brown or black.
NO2- is confirmed.
iii)
May be S2-
Rotten egg smell gas is evolved.
Lead acetate paper turns to silvery black.
S2- is confirmed.
Purple or violet colour formation.
S2- is confirmed.
iv) vinegar smell
May be acetate
Blood red colour solution formation.
CH3COO – is confirmed
2
carbonates are removed then add neutral FeCl3.
Group II anions; Identified by using conc. H2SO4 (Cl , Br , I , NO3-, CH3COO-). -
EXPERIMENT Little salt mixture is heated with conc. H2SO4, observed in cold and also after warming. Add MnO2 and heat it Confirmatory test S.E or W.E + dil HNO3 till effervescence ceases + AgNO3 solution.
-
-
OBSERVATION i) Colourless gas with pungent smell is evolved.
INFERENCE May be Cl-
Greenish yellow coloured gas is evolved.
May be Cl-
White curdy ppt, soluble in excess of ammonium hydroxide solution.
Cl- is confirmed.
ii)
May be I-, May be I-,
Violet vapours appear.
Violet vapours intensify May be I-, Turns to blue-black Yellow ppt is formed which is insoluble in excess of amm.hydroxide
3
I- is confirmed.
Add MnO2 and heat it. . Check the gas with starch paper. Confirmatory test S.E or W.E + dil HNO3 till effervescence ceases + AgNO3 solution.
Add piece of copper turning or paper ball. Confirmatory test S.E or W.E + dil HNO3 till effervescence ceases + AgNO3 solution Confirmatory test S.E or W.E + dil H2SO4 is added till all carbonates are removed then add freshly prepared FeSO4 solution, then add con H2SO4 through the sides of the test tube.
Reddish brown gas is evolved. Reddish brown gas intensifies Reddish brown gas does not intensify
May be NO3-, Br-
Yellow ppt, dissolves in excess of amm.hydroxide solution.
Br – is confirmed.
Brown ring at the junction of two liquids.
NO3- is confirmed.
iv)
May be CH3COO –
iii)
Smell of vinegar.
May be NO3May be Br-
CH3COO – is confirmed.
Pleasant odour
Blood red colour solution formation. CH3COO – is confirmed. Red- brown ppt
Add about 1ml of ethyl alcohol. Confirmatory test S.E or W.E + dil HCl is added till all carbonates are removed then add neutral FeCl3. -- Heat the red colour solution. SO42- is the 10th anion in the syllabus W.E / SE acidified with White ppt insoluble in dil HCl dil HCl .Boil off to expell CO2 .Add BaCl2 soln
SO42- confirmed
Note : In all CT for anions the order should be WE or SE ,as only SE has to be acidified with acid (to remove the CO32- which would otherwise give ppt with any reagent ) .if WE is used you do not need to acidify 4
CATION ANALYSIS Preparation of original solution for cation analysis: original solution is prepared by dissolving the salt mixture in any one of the following solvent.1. Water 2. dil. HCl 3. dil. HNO3 4. conc. HCl EXPERIMENT OBSERVATION INFERENCE 0. Salt mixture + NaOH Gas evolved turns moist red litmus Group 0 present. NH4+ solution and heat. blue and gives dense white fumes may be present. with glass rod dipped in conc.HCl Confirmatory test Reddish brown precipitate. NH4+ is confirmed. Salt + NaOH, pass the gas evolved through Nessler’s reagent.
1
2
EXPERIMENT O.S + excess dill HCl
OBSERVATION White ppt
INFERENCE Group I present. Cations of Pb2+ or Ag+ may be present.
No ppt Confirmatory test for Pb2+ Boil the precipitate with the distilled water and divide in to two parts Part I of the hot filtrate + KI solution.
Precipitate dissolves
Absence of group I radicals. Pb2+ may be present
Yellow precipitate.
Pb2+ is confirmed.
Part II of the hot filtrate + K2Cr2O7 it should be K2CrO4 solution.(This is a common mistake seen during correction ) Filtrate of group I +H2S
Yellow precipitate.
Pb2+ is confirmed.
Black colour ppt Brown colour ppt
Group II present. Cu2+, Pb2+, Hg2+ Sn2+ may be present.
5
Confirmatory test for Cu2+ Boil the precipitate with 5 ml of 50% nitric acid. Divide the solution in to two parts. Part I + NH4OH soln. little and then in excess.
Blue colored solution is formed
Cu2+ may be present
Pale blue ppt, dissolves in excess of amm.hydroxide solution.
Cu2+ is confirmed.
Part II + potassium ferocyanide solution Confirmatory test for Hg2+ Boil the precipitate with 5ml of 50% nitric acid. Treat the ppt with aqua regia and heat to dryness then dissolve it in water. Divide the content in to two parts. Part I + excess of KI solution.
Chocolate brown ppt.
Cu2+ is confirmed.
Ppt does not dissolve.
Hg2+ may be present
Red ppt of HgI2, which dissolves in excess of KI solution.
Hg2+ is confirmed.
Part II +freshly prepared stannous chloride (SnCl2) solution.
White ppt formed which turns black.
Hg2+ is confirmed.
Confirmatory test for Sn2+ Boil the ppt with yellow ammonium sulphide solution.(NH4)2S Divide in to two parts
Brown ppt dissolves
Sn2+ may be present
Part I + mercuric chloride (HgCl2).
White ppt
Sn2+ is confirmed.
Part II + dil HCl +H2S
Brown ppt
Sn2+ is confirmed.
6
Boil the filtrate of group II to expel H2S. Add few drops conc. HNO3 + pinch of NH4Cl(s) +NH4OH solution in excess.
Precipitate colour: Gelatinous white Brown Bluish green or grey green
Confirmatory test for Al3+ Dissolve the pt with minimum quantity of dill HCl and then and divide in to A white ppt formed which two parts. dissolves on adding excess of To the first part add NaOH NaOH. drop wise A blue lake floating in clear liquid is seen. To the second part add blue litmus solution then add NH4OH solution. Blood red colouration 2+ Confirmatory test for Fe Dissolve the brown ppt with dil HCl. Then add potassium thiocyanide (KCNS) Dirty green preciptate
Group III present. Al3+,Fe2+, Fe3+ Cr3+
Al3+is confirmed.
Al3+ is confirmed.
May be Fe2+or Fe3+
Fe2+ is confirmed.
O.S + NaOH. Solution.
Pale blue ppt
Fe2+ is confirmed.
O.S + pot. Ferricyanide
No ppt
Fe2+ is confirmed.
Blood red colouration
May be Fe2+or Fe3+
O.S + NaOH. Solution.
Reddish brown ppt
Fe3+ is confirmed.
O.S + pot. Ferricyanide
No ppt
Fe3+ is confirmed.
O.S + pot. Ferrocyanide
Blue ppt
Fe3+ is confirmed.
Confirmatory test for Cr3+ Treat the ppt with 1ml of NaOH and bromine water.
Formation of yellow solution.
Cr3+ is confirmed.
Formation of yellow ppt of lead chromate.
Cr3+ is confirmed.
O.S + pot. Ferrocyanide Confirmatory test for Fe3+ Dissolve the brown ppt with dil HCl. Then add potassium thiocyanide (KCNS)
To the yellow solution formed add 1 ml of lead acetate solution.
7
Filtrate of group III + pinch of NH4Cl(s) +NH4OH + H2S gas.
Precipitate formation Grayish white Black Buff coloured
Group IV is present Zn2+,Ni2+,Mn2+ may be present
White ppt forms which dissolves in excess of NaOH
Zn2+ is confirmed.
Bluish white ppt is formed.
Zn2+ is confirmed.
A cherry red colouration.
Ni2+ is confirmed.
White ppt is formed, which slowly turns to brown on standing.
Mn2+ is confirmed.
Pink colour developed in solution.
Mn2+ is confirmed.
Confirmatory test for Zn2+ Dissolve the ppt with dil HCl , boil the content to remove H2S. Cool and divide the solution in to two parts. st
To the 1 part add NaOH drop wise and then in excess To the second part add pot ferro cyanide solution. Confirmatory test for Ni2+ Dissolve the ppt in minimum quantity of aqua regia , and evaporate to dry mass. Extract the residue with water. Add 1-2 ml of Dimethyl glyoxime (DMG) solution. Then add NH4OH solution. Confirmatory test for Mn2+ Divide the buff ppt into two parts Dissolve the 1st part in least quantity of dil HCl. Boil to expel H2S. Add NaOH solution drop wise. Dissolve the 2nd part in con HNO3. Add 1 gm lead dioxide boil the content. Dilute it with water.
8
Boil off H2S from filtrate of group IV and reduce the volume of the solution to 1/3 by heating. Now add pinch of NH4Cl(s) +NH4OH solution + excess of ammonium carbonate solution. Dissolve the ppt with hot acetic acid and divide in to four parts.
White ppt
Group V is present May be Ba2+, Sr 2+ , Ca2+
Ba2+ is confirmed. To the 1st part add pot.chromate.
Yellow ppt of barium chromate is formed. Ba2+ is confirmed.
nd
To the 2 part add dil H2SO4. White ppt is formed. Insoluble in all mineral acid. To the 3rd part add 1ml of concentrated ammonium Formation white ppt of strontium sulphate solution and warm. sulfate. To the 4th part add 1ml of ammonium oxalate solution. The white ppt is dissolved in dil HCl and then add few drops of KMnO4 solution. Perform flame test with the ppt.
Sr2+ is confirmed.
Ca2+ is confirmed. White ppt is formed. Pink colour of KMnO4 is discharged.
A brick red flame. A crimson red flame A light green/apple green flame
To the filtrate of group V add White ppt is formed ammonium phosphate or di sodium hydrogen phosphate solution + 2ml of ethyl alcohol. Scratch the wall of the test tube with glass rod.
Not to be done or written
Ca2+ is confirmed. Sr2+ is confirmed. Ba2+ is confirmed. Group VI present. Mg2+ is confirmed.
Note : 1. In Gp V –if you have to follow the order of Ba2+, Sr 2+ , Ca2+ eg , if your salt contains Sr 2+ , then you have to write the tests for Ba2+ and say ppt not observed , hence Ba2+absent .Then go on to write test for Sr 2+ . 2.CT for Mg2+ ----Boil the filtrate of group V to reduce the volume .Filter ,if necessary .To the clear solution add an excess of disodium hydrogen phosphate and a few drops of ammonium hydroxide. Shake well and scratch the walls of the test tube with a glass rod → White crystalline ppt on standing
9
