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..…………pharmaza..…………… اسرة فرسان صيدلة اسرة فرسان صيدلة …..…..pharmaza

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Analytical Chemistry II Anions are divided into six groups:

1- Carbonates and Bicarbonates group

2- Sulphur-containing anions

3- Halides

4- Cyanogen anions

5- Arsinic and phosphorous containing anions

6- Nitrogen- containing anions

1. Carbonates and Bicarbonates group, CO32-, HCO3

-

CO3

2- HCO3

-

Parent acid Carbonic acid (H2CO3) is a very weak acid, Heating of solution of H2CO3, CO2 will evolve.

H2CO3 ⇋ CO2 + H2O

Solubility Insoluble in water except (Na+, K+, NH4+) Soluble in water

1- Dry Reactions

a) dilute HCl

b) sulphuric acid

Decomposition with effervescence due to the evolution of CO2 gas, for both CO3 2- and HCO3

-

CO3-- + 2H+ ⇋ CO2 + H2O

NaHCO3+ H+ ⇋ CO2 + H2O + Na+

As HCl, eff. In addition the formation insoluble sulphate (with gp v metals)

BaCO3 +H2SO4 ⇋ ↓BaSO4 + ↑SO2 + H2O 2- wet reaction

a- with AgNO3

A white precipitate of silver carbonate is immediately formed.

CO3 -- +2Ag+ Ag2CO3

The precipitate is soluble in mineral acids (nitric acid) and in ammonia.

Ag2CO3 + 2H+ 2 Ag+ + CO2 + H2O

Ag2CO3+4NH3 2[Ag (NH3)2]+ + CO32-

The precipitate becomes yellow or brown if the mixture is boiled.


2

Ag2CO3 ⇋ Ag2O +CO2

boiling

b- with BaCl2,

CaCl2 and MgSO4:

White precipitates of BaCO3, CaCO3 and MgCO3 will be

obtained with carbonate solution.

BaCl2 + NaCO3 BaCO3 + 2 NaCl

Ca++ + CO3 -- CaCO3

Mg++ + CO3 -- MgCO3

The precipitate is soluble in mineral acids

No ppt. on cold since all HCO3- are

soluble in water.

Mixture of CO32- & HCO-3

Both anions haves similar reactions, but CO32- form precipitates immediately on cold upon the addition of

CaCl2, BaCl2 or MgSO4, while the bicarbonates of these metals are soluble. Separation: Add excess CaCl2 (BaCl2 or MgSO4) to a solution of the mixture CO3

2- /HCO3- a white ppt.

indicates CO3--

, centrifuge or filter

Ca (HCO3)2 + 2 NH3 ⇋ CaCO3+ (NH4)2 CO3


3

2. Sulphur-containing anions

Sulphide (S2-) Sulphites (SO32-) Thiosulphate

(S2O32-

)

Sulphates

(SO42-)

Parent

acid

H2S H2SO3

H2S2O3Decompos

es to give, H2O,

SO2 and S.

H2SO4

1- Dry

Reactions

a- Action

of dilute

HCl

H2S gas; evolved has rotten egg odour,

1- blackening of filter paper moistened with

lead acetate sol

2- turns filter paper moistened with

cadmium acetate solution, yellow

It bleaches the brown color of l2 solution,

changes the pink color of acid KMnO4 into

colorless and changes the orange color of

acid K2Cr2O7 into green.

H2S + l2 ⇋ 2l- + 2H+ +So

5H2S + 6H+ +2 MnO4- ⇋ 2Mn++ + 8H2O + 5So

3H2S + 8H+ + Cr2O7-- ⇋ 2Cr3+ + 7H2O + 3So

SO2 gas evolved has bunt

sulphur odor and turbid lime

water due to the formation

of the insoluble CaSO3

Ca (OH)2 +SO2 ⇋ CaSO3 +

H2O

SO2 has reducing character,

bleaches the brown color of

iodine, reacts with acid

KMnO4 and acid K2Cr2O7.

l2 + SO2 + H2O ⇋ SO3 +

2H++ 2l-

2 MnO4- + 5 SO2 +

6H+⇋2Mn++ + 5SO3 + 3H2O

Cr2O72- +3 SO2 + 8H+

⇋ 2Cr3++ 3SO3 + 4H2O

The solution

becomes turbid

due to the

liberated yellow

colloidal sulphur

with evolution of

SO2 gas.

S2O3-- + 2H+

⇋

H2S2O3 ⇋ H2O

+ SO2 + So↓

No reaction

with dil. HCl


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2- Wet

Reactions

Reaction

with BaCl2:

No visible

reaction

White ppt. of BaSO3 is

formed which is soluble in dil.

HCl.

Ba+++SO32- =BaSO3

No ppt. in dilute

solution, but a ppt. is

formed from very

concentrated solution

A white ppt. of BaSO4 is formed

which is insoluble in dil. HCl, even

upon boiling.

Ba+++ SO4-- = BaSO4 ↓ White

Reaction

with

AgNO3

a black ppt. of

Ag2S soluble in

hot dil. HNO3,

insoluble in

ammonia an

2 Ag++ S-- ⇋

Ag2S black

A white crystalline ppt. of

Ag2SO3, which on boiling with

water undergoes self redox

with the production of grey

ppt. of metallic silver.

2 Ag++ SO32-⇋ Ag2SO3

2 Ag2SO3 boil→2 Ago + Ag2SO4

↓ + SO2 ↑

White ppt. which changes

its color on standing to

yellow, brown and finally

black, due to the formation

of Ag2S.

2 Ag+ + S2O3--⇋ Ag2 S2O3

Ag2S2O3+ H2O ⇋ Ag2S +

H2SO4

No ppt. in dil solution, but a

ppt. may be formed in a very

concentrated solution.

Reaction

with FeCl3

a black ppt. of Fe2S3 is

formed which is soluble

in dil. HNO3

2Fe3++ 3S-- → Fe2S3

A drak red color of ferric

sulphite is produced on

cold.

2Fe3++ SO3-- → Fe2(SO3)3

A purple color of complex

disappears on boiling

Fe3++ 2S2O32- → (Fe(S2O3)2)-

2 S2O3--+ 2Fe3+ ⇋ 2Fe+++ S4O6

-

-

do not react with FeCl3

Reaction

with lead

acetate:

A black ppt. of

PbS is produced

Pb+++ S-- → PbS

A with ppt. soluble in

cold HNO3. On boiling

oxidation to PbSO4.

SO3--+ Pb++ →PbSO3

A white ppt. is soluble in

cold HNO3, on boiling a

black ppt. of PbS is formed.

Pb+++S2O3-- →PbS2O3

A white ppt. lead suphate, which is

insoluble in cold dil. mineral acids,

but soluble in ammonium acetate and

hydroxide solutions


5

Special

Tests

Cadmium

carbonate test

S--+ CdCO3

→ CdS + CO32-

Zinc nitroprusside

test :

Add ZnSO4 + K4[Fe

(CN)6] + 1% sodium

nitroprusside

solution. salmon-

colored ppt. of zinc

nitroprusside

is formed Zn

(Fe(CN)5 NO).

Formation of thiocyanate :

By boiling with KCN +

NaOH, Cool, acidify and add

FeCI3, a blood red color of

ferric thiocyanate complex

is produced.

S2O3--+ CN- OH- →SCN-+

SO3-

Fe3++ SCN- Cool →Fe(SCN)2+

Hepar’s test

Sulpate is reduced by carbon to

sulphide

Transfer the fusion product to a

silver coin and moisten with a little

water, a brownish black stain of

Ag2S results.


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3. Halides

Fluoride (F-) Chloride (Cl-) Bromide (Br-) Iodide (I-)

Therefore the order of stronger halogen acid is from HI HBr HCl HF. Parent Acids: HF:coloress fuming highly corrosive

and itching liquid

HCl Colorless gas

with irritating

odor, fumes in

moist air,

HBr Colorless gas

with irritating odor,

fumes in moist air

HI Colorless gas

with irritating

odor, fumes

strongly in moist

air,

Dry Reactions

a- dilute HCl

Hydrochloric acid shows no reaction .This reaction can differentiate

carbonate and sulphur group from halides.

b- conc. H2SO4 2X-+ H2SO4 = 2 HX + SO42- X = may be CI-, I-, Br- and F-

HF colorless fumes, the glass

rod acquire oily appearance

due to the formation of silicic

acid and hydrofluorosilicic

acid.

2 F-+ H2SO4 → 2H F +

SO4—

4HF+SiO2→SiF4+ 2H2O

3 SiF4+ 3H2O → H2 SiO3+ 2

H2 SiF6

HCI gas is evolved

2CI-+H2SO4 → 2 HCI +

SO4--

identified by :

Formation of white

fumes of NH4CI when a

glass rod moistened

with ammonium

hydroxide

NH4OH + HCI

→ NH4CI + H2O

A mixture of HBr

and Br2 have

characteristic

brown color

2 Br-+ H2SO4 → 2

HBr + SO4--

2 HBr + H2SO4

→ Br2 + SO2+ 2

H2O

I2 which appears as

violet fumes. I2 can

be detected by

exposing the evolved

gas to paper

moistened with starch

solution, it changes

into blue.

2I-+ H2SO4 →2 HI +

SO42-

2HI + H2SO4 → I2 +

SO2 + 2H2O


7

Conc.H2SO4 &

MnO2:

2X- + 4H++ MnO2 ⇋ Mn+++ 2H2O +X2

X = may be CI-, Br- and I-

The free halogen, (X2) could be detected by: 1- Bleaching of a moistened colored litmus paper.

2- Suffocating, and irritating odor. 3- Characteristic color of Br2 (brown), I2 (violet) and CI2 gas

4- I2 changes starch paper into blue, Br2 turns it orange. 5- CI2 and Br2 change a starch – KI into

blue due to the oxidation of I- to I2 produce a blue adsorption complex.

2- Wet Reactions

a- Reaction with

AgNO3:

No precipitate A white curdy ppt. insoluble in

nitric acid, soluble in KCN and

dil. ammonia solution to give

the ammine complex.

AgCI + 2NH3 →

[Ag(NH3)2]CI

A curdy, pale yellow

precipitate , sparingly

soluble in dilute, but readily

soluble in conc. ammonia

solution

AgBr + 2 NH3 →

[Ag(NH3)2]++ Br-

A curdy yellow ppt.

insoluble in dil.

ammonia but very

slightly soluble in

conc. ammonia

solution.

b- Reaction with

BaCI2 solution:

The white gelatinous BaF2 ppt. is partially

soluble in dil. HCI or HNO3

No ppt. is formed

c- Reaction with

FeCI3:

a white crystalline ppt. of the complex

salt, which is sparingly soluble in water

Fe3++ 6 F- → [FeF6]3-

CI - and Br - : do not react

with FeCI3

Reacts with FeCI3, due to

its strong reducing action

with the liberation of I2.

Reaction with lead

acetate

F-, Cl- and Br- form a white ppt with lead acetate, sparingly

soluble in cold more soluble in hot water, crystallize on

cooling

forms a bright yellow ppt of PbI2

which is soluble in hot water

and crystallizes on cooling as golden

spangles


8

Chlorine water

test

Chloride and Fluoride do not

react with chlorine water

2Br-+ CI2 → Br2+ 2CI-

Br2+ CI2 →2 BrCI (yellow)

Br2+ CI2 (excess) + 2H2O

→2HOBr+2HCI Colorless

2I- + CI2 → I2+ 2CI-

I2+ 5CI2 (excess) + 6H2O

→ 2 HIO3+10HCI

Special Tests Boron fluoride test:

fluoride + borax and conc.

H2SO4.→ boronfluoride gas.

Na2B4O7 + H2SO4+ 5H2O →

4H3BO3 +Na2SO4

2NaF + H2SO4 → 2HF +

Na2SO4 H3BO3+3HF→

BF3+ 3H2O

Chromyl chloride test:

The solid chloride + powder potassium

dichromate in a tube, + conc. sulphuric acid.

The deep red vapors of chromyl chloride

CrO2CI2 are passed into sodium hydroxide

solution.→

Yellow color;

4CI-+ Cr2O7--+ 6H+ cond.→ 2CrO2 Cl2 + 3H2O

CrO2CI2 + 4OH- → CrO4-- + 2CI- + 2H2O

I- reacts with Cu++

forming a whit ppt.

of Cu2I2,

2Cu+++4I- ⇋ Cu2I2

+I2

..…………pharmaza..…………… اسرة فرسان صيدلة pharmaza..…..…اسرة فرسان صيدلة

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