qualitative analysis of cations and anions

7/27/2019 Qualitative Analysis of cations and anions

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INORGANIC PRESENTATION

TOPIC: THEORITICAL ASPECTS OFANIONS

SUBMITTED BY: NIDHI CHAUDHARYB.Sc(H) CHEMISTRY

VI SEMESTER


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QUALITATIVEINORGANIC

ANALYSISIt is the analysis (i.e. detection and

identification) of the cations andanions present in given compoundor salt mixture.


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IDENTIFICATION OF ANIONS

AND CATIONS

Identification of anions/cations is done through

a series of tests, broadly divided into :

Preliminary tests : provide us with the idea of

the cation/anion present in the compound.

Confirmatory tests : confirm the presence of the

cation/anion in a given compound.


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ANIONS

Anion is an ion with more electrons thanprotons, giving it a net negativecharge (since electrons are negatively

charged and protons are positivelycharged).

Anions are contributed by acids, therefore,they are called as acid radicals.

For example, the anion (or acid radical) Cl-

in a water solution of salt sodium chloride(NaCl) comes from the hydrochloric acid(HCl) and the cation (or basic radical) Na+from the base sodium hydroxide (NaOH).


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PREPARING TEST

SOLUTIONS

Most of the confirmatory tests of the cations/anions are not

carried out with the solid mixture but with their solutions :

Water Extract: If the given compound is soluble in water,

then 1-2 g of mixture is dissolved in distilled water (10-20ml).

Sodium Carbonate (soda) Extract: If the compound is

insoluble in water, then 1 g of mixture is taken along with

2 g Na2CO3 in distilled water (15-20 ml) and heated for

15 minutes. Solution is filtered and the filterate is soda

extract.


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CLASSIFICATION OF ANIONS

Anions can not be classified into specificgroups but their action with sulphuricacid divides them into threecategories:

Dilute Sulphuric Acid: CO32-, NO2

-,CH3COO

-, S2-, SO32-

Conc. Sulphuric Acid: Cl-, Br-, I-, NO3-, Independent Radicals: SO4

2-,PO43-

,BO33-, C2O4

2-


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SNo EXPERIMENT OBSERVATIONS INFERENCE

1. TEST FOR CARBONATE(CO3

2-)

Pre. Test : To a pinch of

mixture add few drops of

dilute sulphuric acid.

Con. Test : Pass the gas

evolved in the above step

through lime water.

Colorless gas evolves

with brisk

effervescence.

2 H+ + CO32- H2O +

CO2

Lime water turns

milky.

M(OH)2 + CO2 MCO3+ H2O

May be CO32- .

CO32-

confirmed.


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SNo. EXPERIMENT OBSERVATIONS INFERENCE

2. TEST FOR NITRITE

(NO2-)

Pre. Test : To a pinch of

mixture in test tube, add

dilute sulfuric acid.

Con. Test : (a) To the abovesolution, add 0.5 ml of

potassium iodide solution

followed by 0.5 ml of pure

starch solution.

(b) Take water extract or soda

extract of the compound and

add dilute sulfuric acid

followed by freshly prepared

ferrous sulphate solution.

Reddish brown vapors

observed.

2MNO2

+ H2SO

4M

2SO

4+ HNO2

3MNO2 H20 + HNO3 +

NO

NO + O2 NO2 (brown

fumes)

A deep blue colorationobserved.

2KI + 2MNO2 + H2SO4

K2SO4 + I2 + NO + H2O

I2 + STARCH BLUE

COLORED COMPLEX

A dark brown or black

coloration obtained.

MNO2 + H2SO4 MSO4 +

HNO2

HNO2 HNO3 + NO

FeSO4 + NO FeSO4.NO

May be NO2- .

NO2- confirmed.

NO2- confirmed.


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3. TEST FOR ACETATE

(CH3COO-)

Pre. Test : A pinch of mixture

is treated with dilute

sulphuric acid .

OR,

1-1.5 g of mixture is taken in

watch glass to which a pinch

of oxalic acid and a few drops

of water were added.

Con. Test: (a) 1 ml of

water/soda extract is

neutralized with dilute acetic

acid followed by addition offerric chloride solution.

Vinegar like smell is

obtained.

M(CH3COO) + H2SO4CH3COOH + MSO4

Vinegar like smell is

obtained.

Deep red colored

precipitate is observed

due to formation of a

complex.

CH3COO- + Fe3+ + H2O

[Fe3(OH)2(CH3COO)6]+ +

2H+

[Fe3(OH)2(CH3COO)6]+ +

H2O CH3COOH +

[Fe(OH)2(CH3COO)] + H+

May beCH3COO- .

CH3COO- confirmed.


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(b)

(c)

To 1 ml of water/soda

extract lithium nitrate

solution and potassiumiodide solution were added.

After this, few drops of

dilute ammonia solution was

added and the resultant

solution was heated.

Equal volume of soda/water

extract and pure calcium

hydroxide is taken in a test

tube. Heat the solution and

pass the evolved vapors

into a solution of 2,4 DNP

hydrazine.

Blue color is obtained.

Yellow precipitate is

obtained.

Ca(OH)2 + M(CH3COO)

CH3COCH3

CH3COCH3 +H2NHC6H5(NO2)

(CH3)2CNNHC6H5(NH2)2

CH3COO-

confirmed.

CH3COO-

confirmed.


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4.

(b)

(c)

TEST FOR SULPHIDE

(S2-)

Pre. Test: Take a pinch ofmixture in a test tube and

add dilute sulphuric acid.

Con Test: a) Pass the above

gas in cadmium acetate.

Acidify 1-2 ml of soda/water

extract with dilute acetic

acid and boil the solution toexpel carbon dioxide. To this

add 1-2 ml of lead acetate

solution.

Add 1-2 ml of freshly

prepared sodium

nitroprusside solution to the

soda/water extract.

A colorless gas evolveswhich smells like rotten

egg.

S2- + H2SO4 H2S + SO42-


obtained.Cd(CH3COO)2 + H2S CdS

+ CH3COOH

Black precipitate obtained.

H2S + Pb(CH3COO)2 PbS

+ CH3COOH

Violet coloration obtained.

S2- + Na2[Fe(CN)5NO]

Na4[Fe(CN)5NOS]

May be S2- .

S2- confirmed.

S2- confirmed.

S2- confirmed.


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SNO EXPERIMENT OBSERVATIONS INFERENCE

5.

(b)

TEST FOR SULPHITE

(SO32-)

Pre. Test: Take a pinch of

mixture and add 2-3 ml of

dilute sulphuric acid.

Con.Test: (a) Take 1-2 ml of

soda/water extract; add 2-3

ml of dilute sulphuric acidand few drops of potassium

dichromate solution.

Take a pinch of mixture and

add 2-3 ml of dilute

hydrochloric acid.Pass the gas evolved

through lime water.

A colorless and pungent

smelling gas evolves.

A green color is obtained.

3Na2SO3 + K2Cr2O7 +4H2SO4 Cr2(SO4)3

(Green color) + 3Na2SO4 +

4H2O + K2SO4

Sulphur dioxide is evolved.

White precipitate is

obtained.

May beSO32-

SO32- confirmed.

SO32-

confirmed.


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SNo EXPERIMENT OBSERVATIONS INFERENCE

6. TEST FOR CHLORIDE

(Cl-)

Pre Test: To a pinch of

mixture, add 1-2 ml of conc.

sulphuric acid.

Bring a glass rod dipped in

ammonium hydroxide near

the mouth of the above test

tube.

Con. Test: (a) To the

water/soda extract, add dilute

nitric acid and few drops ofsilver nitrate.

Greenish yellow gas having

pungent smell evolves.

Dense white fumes observed.

NaCl + H2SO4 NaHSO4 +

HCl

HCl + NH4OH NH4Cl +

H2O

White precipitate formed

which is soluble in excess of

ammonium hydroxide.

AgNO3 + NaCl AgCl +

NaNO3

AgCl + 2NH4OH

[Ag(NH3)2Cl] (soluble

complex) + 2H2O

May be Cl- .

Cl- confirmed.


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(b) Chromyl Chloride Test -

Take about 0.2 g of mixture

in a test tube and add about0.3 g of solid potassium

dichromate and 2 ml of

conc. sulphuric acid. Heat

the mixture and pass the

gas evolved into a tube

containing sodium

hydroxide solution. Add 1 ml

of lead acetate solution.

Yellow precipitate is formed.

K2Cr2O7 + 4NaCl + 6H2SO4

2CrO2Cl2(chromyl chloride) + 2KHSO4

+ 4NaHSO4 + 3H2O

CrO2Cl2 + 4NaOH

Na2CrO4 + 2NaCl + 2H2O

Na2CrO4 + Pb(CH3COO)2

PbCrO4 (yellow) +

2CH3COONa

Cl- confirmed.


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7. TEST FOR BROMIDE

(Br-)

Pre. Test: To a pinch of

mixture, add conc.

sulphuric acid.

Con Test: (a) Take 0.5 ml of

soda/water extract and

then add 0.5 ml of dilute

nitric acid and few drops

of silver nitrate solution.

Reddish brown vapors

with a pungent smell

evolved.

KBr + H2SO4 KHSO4 +

HBr

2HBr + H2SO4 Br2 + SO2

+ 2H2O

Yellow precipitate obtained

which is sparingly soluble

in ammonium hydroxide.

NaBr + AgNO3

AgBr

+ NaNO3

AgBr + 2NH4OH

[Ag(NH3)2]Br + 2H2O

May be Br-.

Br- confirmed.


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(b) Take 0.5 ml of soda/water

extract of the mixture and

add 0.5 ml of carbon

tetrachloride or chloroform

followed by 1 ml of conc.

nitric acid or chlorine

water. Warm the mixture

and shake the test tube.

Organic solvent layer

attains orange color due to

dissolution of evolved

bromine in it.

NaBr + HNO3 NaNO3 +

HBr

2HBr + 2HNO3 Br2 +

2NO2 + 2H2O

Br- confirmed.


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8. TEST FOR IODIDE

(I-)Pre. Test: To a pinch of

mixture, add conc sulphuric

acid.

Con Test: (a) Take 0.5 ml of

soda/water extract and then

add 0.5 ml of dilute nitric

acid followed by 0.5 ml of

silver nitrate solution.

Violet vapors of iodine

evolved due to partial

decomposition of the

formed HI.

KI + H2SO4 KHSO4 +

HI2HI + H2SO4 I2 + SO2 +

2H2O

Yellow precipitate

obtained which isinsoluble in ammonium

hydroxide.

NaI + AgNO3 AgI +

NaNO3

May be I-.

I- confirmed.


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(b) Take 0.5 ml of soda/water

extract of the mixture and

add 0.5 ml of carbontetrachloride or chloroform

followed by 1 ml of conc.

Nitric acid or chlorine water.

Warm the mixture and shake

the test tube vigorously.

Organic solvent layer

attains violet color

due to dissolution ofiodine in it.

NaI + HNO3 NaNO3 +

HI

4HI + O2 2I2 + 2H2O

I- confirmed.


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9. TEST FOR NITRATE

(NO3-)

Pre. Test: To a pinch of

mixture, add conc sulphuric

acid.

Con Test: Take around 1 ml

of soda/water extract and

acidify with dilute sulphuricacid. Add 2-3 ml of freshly

prepared ferrous sulphate

solution and then pour

conc. sulphuric acid slowly

in thin stream along the

sides of the test tube.

Light brown fumes

observed which intensify

on heating the mixture

with copper turnings.

NaNO3 + H2SO4

NaHSO4 + HNO3

4HNO3 4NO2 + O2 +2H2O

A brown black ring at the

junction of two layers is

formed.

NaNO3 + H2SO4NaHSO4 + HNO3

2HNO3 + 6FeSO4 +

3H2SO4 3Fe2(SO4)3 +

2NO + 4H2O

FeSO4 + NO

FeSO4.NO(brown ring)

May be NO3-

NO3- confirmed.


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10. TEST FOR OXALATE

(C2O42-)

Pre. Test: Add concsulphuric acid(1-2 ml) to a

pinch of given mixture(0.1 g)

and heat the solution. .Bring the mouth of the test

tube near the flame.Also pass the gas in the

lime water.

Con Test: (a) Acidify 1 ml of

soda/water extract of themixture with dilute acetic

acid and boil the solution.

Then add 1 ml of calcium

chloride solution and shake

the test tube.

Evolved gas burns with ablue flame.

(COONa)2 + H2SO4

Na2SO4 + (COOH)2

(COOH)2 CO + CO2 +

H2O

Lime water turns milky.

White precipitate obtained.(COONa)2 + H2SO4

Na2SO4 + (COOH)2

(COOH)2 + CaCl2

(COO)2Ca + 2HCl

May be C2O42-.


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(b)

Dissolve the precipitate in

minimum quantity of dilutesulphuric acid and then addpotassium permanganate

solution drop wise.

Acidify soda/water extract

with dilute acetic acid and

boil the solution. Add ferrous

sulphate solution.

Pink color of potassium

permanganate gets

discharged.(COO)2Ca + H2SO4(COOH)2 + CaSO4

2KMnO4 + 3H2SO4 +

5(COOH)2 2MnSO4 +

K2SO4 + 10CO2 + 8H2O

Yellow precipitate

obtained.

C2O42- + Fe2+

[Fe(C2O4)]2-

C2O42- confirmed.

C2O42- confirmed.


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11. TEST FOR FLUORIDE

(F-)

Pre. Test: Take 0.1 g of themixture and add 1 ml of

conc. sulphuric acid.

Con Test: Add a pinch of

sand to the above reaction

mixture. Heat it. Bring a

glass rod moistened with

water near the mouth ofthe test tube.

Oily droplets are formedalong the sides of the test

tube.

2NaF + H2SO4 Na2SO4 +

2HF

White gelatinous deposit

on the glass rod observed.

4NaF + H2SO4 + SiO2

SiF4 + 2Na2SO4 + 2H2O

3SiF4 + 4H2O H4SiO4 +2H2SiF6 (hydrofluorosilicic

acid; waxy appearance)

May be F-

F- confirmed.


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12.

13.

TEST FOR SULPHATE

(SO42-)

To the soda/water extract (1

ml) add dilute hydrochloricacid (1 ml) so as to remove

the carbonate (if present).

Add 1 ml of barium chloride

solution.

TEST FOR PHOSPHATE

(PO43-)

Take a pinch of the given

mixture in a test tube andadd about 1 ml of conc nitric

acid. Boil the contents and

add excess of ammonium

molybdate solution.

White precipitate obtained

which is insoluble in conchydrochloric acid.

Na2SO4 + BaCl2

BaSO4 + 2NaCl


obtained.

PO43- + 12MoO4

2- + 24H+

PMo12O403- + 12H2O

SO42- confirmed.

PO43- confirmed.


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14. TEST FOR BORATE(BO3

3-)

In a porcelain dish, take a

small amount of the mixture,

say 0.2-0.3 g, and add nearly

1 ml of conc sulphuric acidfollowed by 1 ml of ethyl

alcohol. Heat the dish and

bring a burning paper over

it.

Green flame is observed.

Na3BO3 + 3H2SO4

Na2SO4 + 2H3BO3

H3BO3 + C2H5OH

B(OC2H5)3 + H2O

BO33- confirmed.

qualitative analysis of cations and anions

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