Salt analySiS

Chapter 20Salt analySiS

20.1 INTRODUCTION

Qualitative analysis of inorganic compounds involves the identification of radicals (cations and anions) in an inorganic salt or in a mixture of salt. A salt consists of two parts known as radicals. The positively charged part of a salt (cation), derived from a base is termed as a basic radical and the negatively charged part of the salt (anion) derived from an acid is termed as an acidic radical.

E.g., Zn Cl2 Zn (OH)2 + 2 HCl → ZnCl2 + 2H2O Base Acid SaltSo, the salt ZnCl2 contains Zn2+ as the basic radical and Cl- as the acidic radical.

20.1.1 Physical Appearance of Inorganic Salt

S. No. Inorganic Salt Colour S. No. Inorganic Salt Colour

1. Cu+2 Blue 2. Cr+3 , Cr+6 Dark green3. Fe+2 Green 4. Fe+3 Yellow or brown5. Mn+2 Light pink 6. Co+2 Pink7. Ni+2 Green or blue 8. HgO, HgI2, Pb3O4 Red9. Salt of Pb, Hg, Bi and Ba Relatively heavier.

Heavier salts are salts of Pb, Hg, Bi and Ba.Lighter salts are carbonates of Be, Mg, Al, Zn, Ca and Sr.Deliquescent substances are CdCl2, ZnCl2, MgCl2, MnCl2, nitrites and nitrates.

20.1.2 Characteristic Colour Changes in Hot and Cold

Cold Hot Inference Cold Hot Inference

Red Chocolate Pb3O4 Red Black HgOScarlet Black HgS Crimson Yellow HgI2

Yellow Brown Bi2O3 White Yellowish brown SnO2

Chemistry at a Glance Final.pdf 238Chemistry at a Glance Final.pdf 238 4/1/2014 12:26:16 PM4/1/2014 12:26:16 PM

Salt Analysis 20.233

Cold Hot Inference Cold Hot Inference

White Orange is yellow ZnO Violet Green Chromic saltsYellow Brownish black FeCl3

.6H2O Red Violet CoI2.6H2O

Red Green CoBr2.6H2O Blue White CuSO4

.5H2O

20.1.3 Action of Heat

1. All carbonates except (Na, K, Rb and Cs) decompose on heating, giving CO2.

Li2CO3 ∆→ Li2O + CO2 MgCO3

∆→ MgO + CO2

2. All bicarbonates decompose to give carbonates and CO2. 2 NaHCO3 ∆→ Na2CO3 + H2O + CO2

3. Halides are normally stable to heat; however, some halides decompose as 2FeCl3

∆→ 2FeCl2 + Cl2 MgCl2.6H2O ∆→ MgO + 2HCl + 5H2O

Hg2Cl2 ∆→ HgCl2 + Hg NH4Cl ∆→ NH3 + HCl

4. Nitrates decompose on heating NH4NO3 → N2O + 2H2O 2MNO3 → 2MNO2 + O2 (except Li) (M ≡ alkali metal) 2LiNO3 → Li2O + 2NO2 + ½O2 2Mg(NO3)2 → 2MgO + 4NO2 + O2

2Cu(NO3)2 → 2CuO + 4NO2 + O2 Hg(NO3)2 → Hg + 2NO2 + O2

5. Silver salt on heating gives Ag. Ag2CO3 → 2Ag + CO2 + ½O2 2AgNO3 → 2Ag + 2NO2 + O2

20.1.4 Solubility of Salts

(i) Nitrates, acetates and nitrites of all the metals are water soluble. (ii) All sulphates except (Pb, Ba and Sr) are water soluble. CaSO4 is slightly soluble in water. (iii) Halides of Ag, Pb, mercurous and cuprous forms are insoluble. The order of their solubility is

fluoride > chloride > bromide > iodide. (iv) CaF2 is insoluble in water, other halides of Ca are soluble.

20.1.5 Colour of the Sublimate

If the substance sublimes and the colour of the sublimate is

S. No. Colour Name of Sublimate

1. White HgCI2, Hg2CI2, As2O3, Sb2O3

2. Yellow AICI3 and NH4X(where X is F, CI, Br or I)As2S3 and Hgl2 (turns red when rubbed with glass rod)

3. Grey HgO, Hg(NO3)2

4. Blue-black or violet Iodides5. Black As, Sb, Hg sulphides and iodides


20.234 Chemistry at a Glance

20.2 DRY TESTS

20.2.1 Classification of OresOres may be divided into four groups. Following tests are performed in dry state.

(i) Flame test (ii) Borax bead test (iii) Charcoal cavity test (iv) Micro cosmic salt bead test (v) Cobalt nitrate charcoal test

20.2.2 Flame testSome volatile salts impart characteristic colour to the non-luminous flame. The platinum wire fused in a glass rod is heated in the flame till it imparts colourless flame. The tip of the wire is now dipped in conc. HCl and then into the substance. The tip of the wire is strongly heated in the non-luminous flame and the colour of the flame is observed by the naked eye.

S. No. Observation Inference1. Substance melts Salts of alkali metals and salts

having water of cystallization.2. Substance decripitates (crackling noise) NaCI, Kl, Pb(NO3)2 and Ba(NO3)2

3. Substance swells (due to loss of water following crystallization)

Alums, borates and phosphates

4. Gas is evolved(a) Colourless and odourless (i) O2 - rekindles a glowing splinter Alkali nitrates

(2KNO3 → 2KNO2 + O2) (ii) CO2 - turns lime water milky Carbonates and oxalates

(CaCO3 → CaO + CO2) (iii) N2 Ammonium nitrite

(NH4NO2N2 + 2H2O)(b) Colourless gas with odour (i) NH3 - turns red litmus blue and mercurous

nitrate paper blackAmmonium salts (NH4)2SO4 → NH4HSO4 + NH3

(ii) SO2 - Smell of burning sulphur, turns acidified K2Cr2O7 paper green

Sulphites and thiosulphatesCaSO3 → CaO + SO2

(iii) HCI - Pungent smell, white fumes with NH3 Hydrated chlorides CaCI2.6H2O → Ca(OH)2 + 4H2O + 2HCI

(iv) H2S - Smell of rotten eggs, turns lead acetate paper black

Sulphides Na2S + 2H2O → 2NaOH + H2S

(c) Coloured gas (i) NO2 - Brown, turns starch iodide paper blue Nitrites and nitrates of heavy metals

2Cu(NO3)2 → 2CuO + 4NO2 + O2(Continued)



S. No. Observation Inference

(ii) Br2 - Reddish brown (A) Turns starch paper yellow (B) Turns starch iodide paper blue

Bromides 2CdBr2 + 02 → 2CdO + 2Br2

(iii) l2 - Violet, turns starch paper blue Iodides 2Cdl2 + 02 → 2 CdO + 2I2

(iv) Cl2-greenish yellow (A) Bleaches moist litmus paper (B) Bleaches indigo solution (C) Turns starch iodide paper blue

Chlorides CuCI2 + H20 → CuO + 2HCI CuO + 2HCI → Cu + H2Q + Cl2

S. No. Colour of salt Inference

1. Pale greenish Lead 2. Green with a blue centre Cu salt, BO3

3–

3. Brick red Ca 4. Red Li 5. Golden yellow Na 6. Violet (lilac) K 7. Violet (redish) Rb 8. Violet (bluish) Cs 9. Crimson red Sr10. Apple green Ba

Be and Mg do not give flame test.Flame test should not be performed in the presence of As, Sb, Bi, Sn and Pb as these radicals form an

alloy with platinum and hence, the wire is spoiled.The white salt with colourless solution cannot have Cu, Ni, Co, Fe, Mn, Cr, etc.

20.2.3 Borax Bead Test

On heating borax (Na2B4O7 . 10H2O) on a loop of platinum wire, a transparent colourless glassy bead of sodium metaborate and boric anhydride is formed.

2 4 2 2 4 7 2 2 3

Glassy bead

Na B O 10H O Na B O 2NaBO B O∆ ∆⋅ → → +

On heating coloured salt on the glassy bead, a coloured metaborate is formed in the oxidizing flame.CuSO4 → CuO + SO3; CuO + B2O3 → Cu(BO2)2

Copper metaborate (blue) Similarly, CoO + B2O3 → Co(BO2)2.

Cobalt metaborate (blue)The metaborates posses different characteristic colours in oxidizing flame and reducing flame.


20.236 Chemistry at a Glance

The different colours, in the reducing flame may be due to different reactions. E.g., copper metaborate may be reduced to colourless cuprous metaborate or to metallic copper which appears red and opaque.

2Cu(BO2)2 + C → 2CuBO2 + B2O3 + C 2Cu(CO2)2 + 2C → 2Cu + 2B2O3 + 2CO

Metal

Colour of bead in

Oxidizing Flame Reducing Flame

Hot Cold Hot Cold

Copper (Cu+2) Green Blue Colourless Brown redIron (Fe+2) Yellowish brown Pale yellow Bottle green Bottle greenChromium (Cr+3) Green Green Green GreenCobalt (Co+2) Blue Blue Blue BlueManganese (Mn+2) Violet Amethyst red Grey GreyNickel (Ni+2) Violet Grey Grey Grey

20.2.4 Charcoal Cavity Test

This test is carried out on a charcoal block having a small cavity in it. Little substance is mixed with anhy-drous Na2CO3 or fusion mixture is placed in the cavity. The mass is moistened with a drop of water and heated in a reducing flame with the blow pipe. Metallic salt on heating with Na2CO3 gives metal carbonate which decomposes into metal.

E.g., CuCl2 + Na2CO3 → CuCO3 + 2 NaCl CuCO3 → CuO + CO2 CuO + C → Cu + CO

S. No. Observation Inference1. Formation of metallic bead

(a) Lustrous white, malleable Ag(b) Greyish white, marks paper Pb(c) White, does not mark paper Sn(d) Red Cu

2. Incrustation with metal(a) White incrustation, brittle metal Sb(b) Yellow incrustation, brittle metal B(c) Yellow incrustation, malleable metal Pb

3. Incrustation without metal(a) White and yellow when hot ZnO,SnO(b) Yellow and orange when hot BiO(c) Brown CdO(d) White (volatile, garlic odour) As2O3

20.2.5 Microcosmic Salt Bead TestWhen microcosmic salt is heated on a loop of Pt wire, a colourless transparent bead of sodium metaphosphate is formed.



4 4 2 3 4 4 4 2 3 3 4(bluebead)Transparent Sodiummeta

bead Phosphate

Na(NH )HPO ,4H O Na (NH )HPO NaPO H O NH NaPO CoO NaCOPO∆ ∆→ → + ↑ + ↑ + →

Sodium metaphosphate combines with metallic oxides to form orthophosphates which are usually coloured.

Metal

Colour of bead in

Oxidizing Flame Reducing Flame

Hot Cold Hot Cold

Copper (Cu+2) Green Blue Colourless RedIron (Fe+2) Yellow or reddish Brown Yellow Yellow ColourlessChromium (Cr+3) Green Green Green GreenManganese (Mn+2) Violet Violet Colourless ColourlessCobalt (Co+2) Blue Blue Blue BlueNickel (Ni+2) Brown Brown — Grey

20.2.6 Cobalt Nitrate Charcoal TestA small amount of the substance with twice its bulk of sodium carbonate is placed in the charcoal cavity. A drop of water is added and the mass is heated in an oxidizing flame with the help of a blow pipe. After cooling, one or two drops of cobalt nitrate solution are added and the mass is again heated in the oxidizing flame.

By heating the salt with sodium carbonate, the oxide is formed which on heating with cobalt nitrate form a mixed oxide of a characteristic colour.

ZnSO4 + Na2CO3 → ZnCO3 + Na2SO4 ZnCO3 → ZnO + CO2 2Co(NO3)2 → 2CoO + 4NO2 + O2 ZnO + CoO → CoZnO2 (Cobalt zincate) (green)The colour produced in cavity is noticed.

Observation Inference

(a) Blue mass Aluminium(b) Green residue Zinc(c) Pink residue Magnesium(d) Bluish green Tin

20.2.7 Mirror Test

1. As/Sb + Zn/H2SO4 Heat→ AsH3/SbH3.

When passed through a heated glass tube, AsH3 and SbH3 give a silver mirror due to decomposition of unstable hydrides. SbH3, being more unstable, gives a mirror (of Sb) before the flame only and AsH3 gives a mirror(of arsenic) after the flame.

2. Hydrazine (N2H4) and hydrazinium salts (containing N2H5+) give silver and copper mirrors with Ag+

or Cu2+ solutions, e.g., N2H4 + 2CuSO4 → Cu + N2 + 2H2SO4.


20.238 Chemistry at a Glance20.3

T

ES

T F

OR

AC

ID R

AD

ICA

LS

1.

Add

dil.

HC

l/H2SO

4 to a

smal

l am

ount

of s

ubst

ance

and

war

m g

ently

. Obs

erve

.

Rad

ical

VTe

st/O

bser

vati

on/A

naly

sis

Rea

ctio

n1.

CO

3-2

(c

arbo

nate

) (i

) Br

isk e

fferv

esce

nce

of co

lour

less

gas

(CO

2) (i

i) Th

e ga

s tur

ns li

me

wat

er m

ilky

(iii)

Exce

ss o

f pas

sage

of g

as th

roug

h lim

e w

ater

rem

oves

milk

ines

s

CaC

O3+H

2SO4 →

CaS

O4 +

H2O

+ C

O2

CO

2 + C

a(O

H) 2 →

CaC

O3↓

+ H

2O m

ilky

CaC

O3 +

CO

2 + H

2O →

Ca(

HC

O3) 2 (

solu

ble)

2. S

O3-2

(s

ulph

ite)

(i)

Col

ourle

ss g

as w

ith su

ffoca

ting

odou

r of b

urni

ng su

lphu

r (SO

2) (i

i) Th

e ga

s tur

ns m

oist

ened

pap

er w

ith a

cidi

fied

K2C

r 2O7 g

reen

(iii)

The

sulp

hite

s also

giv

e a

whi

te p

pt. w

ith B

aCl 2, s

olub

le in

dil.

H

Cl

CaS

O3+H

2SO4→

CaS

O4+H

2O +

SO

2 K

2Cr 2O

7+H2SO

4+2SO

2 → K

2SO4+C

r 2(SO

4) 3+H2O

(gre

en)

Na 2SO

3 + B

aCl 2 →

2N

aCl +

BaS

O3 ↓

3. S

-2

(s

ulph

ide)

Col

ourle

ss g

as w

ith sm

ell o

f rot

ten

eggs

(H2S)

The

gas t

urns

lead

ace

tate

pap

er b

lack

The

sulp

hide

also

turn

s sod

ium

nitr

opru

ssid

eso

lutio

n vi

olet

CaS

+ H

2SO4 →

CaS

O4 +

H2S

(CH

3CO

O) 2 P

b +

H2S

→ P

bS↓

+ 2C

H3C

OO

H

(b

lack

)N

a 2S+N

a 2[FeN

O(C

N) 5] →

Na 4[F

e(N

OS)

(CN

) 5]

(vio

let)

4. C

H3C

OO

- –(a

ceta

te)

Smel

l of v

ineg

ar co

mes

out

, may

be

acet

ate

The

acet

ate

give

s blo

od re

d co

lour

with

neu

tral

FeC

l 3

solu

tion

(afte

r rem

ovin

g C

O32-

, SO

32-, P

O43-

and

I- ,io

ns b

y ad

ding

AgN

O3, s

ince

thes

e al

so co

mbi

ne w

ith F

e3+)

(CH

3CO

O) 2C

a+H

2SO4 →

2C

H3C

OO

H+C

aSO

3

(v

ineg

ar sm

ell)

3(CH

3CO

O) 2 C

a + 2

FeCl

3 →2F

e(C

H3C

OO

) 3 + 3

CaC

l 2

blo

od re

d co

lora

tion

5. N

O2–

(nitr

ite)

(i) R

eddi

sh b

row

n va

pour

s of N

O2 co

me

out,

may

be

nitr

ite(ii

) The

gas t

urns

aci

difie

d K

I + S

tarc

h pa

per b

lue

2KN

O2 +

H2SO

4 → K

2SO4 +

2H

NO

2

3HN

O2 →

HN

O3 +

2N

O +

H2

2NO

+ O

2 → 2

NO

2 2K

I+2N

O2→

2KN

O2+I

2 St

arch

+I2→

Blue

colo

ur

Rem

embe

r! If

catio

n (e

.g.,

Pb2+

, Ba2+

, etc

.) fo

rms

an in

solu

ble

prec

ipita

te w

ith H

Cl a

nd/o

r H

2SO4

, the

rea

ctio

n m

ay s

top

after

som

etim

e, e.g

., if

dil.

H2SO

4 is ad

ded

to P

bCO

3 or B

aCO

3, effe

rves

cenc

e will

be o

bser

ved

initi

ally

but

reac

tion

will

stop

qui

ckly

bec

ause

of f

orm

atio

n of

a la

yer o

f PbS

O4 o

r BaS

O4 o

n ca

rbon

ate.

CA

CO

3 will

diss

olve

in d

il. H

Cl (

since

CaC

l 2 is w

ater

solu

ble)

but

not

in d

il. H

2SO4 (s

ince

CaS

O4 w

ill

cove

r the

surf

ace

and

prev

ent f

urth

er re

actio

n). I

n su

ch c

ases

, dil.

HN

O3 sh

ould

be

used

.

SO

2 also

turn

s lim

e w

ater

milk

y du

e to

form

atio

n of

CaS

O3. M

ilkin

ess d

isapp

ears

on

prol

onge

d pa

ssag

e du

e to

form

atio

n of

solu

ble

calc

ium

bi

sulp

hite

Ca(

HSO

3) 2.



2. A

dd C

onc.

H2SO

4 to a

smal

l am

ount

of t

he su

bsta

nce

and

war

m g

ently

. Obs

erve

.

Rad

ical

VTe

st/O

bser

vati

on/A

naly

sis

Rea

ctio

n6.

Cl-

(Chl

orid

e) (

i) C

olou

rless

fum

ing

gas (

HC

l) w

ith p

unge

nt sm

ell

(ii)

The

chlo

rides

giv

e w

hite

pre

cipi

tate

with

AgN

O3 so

lubl

e in

N

H4O

H.

Whi

te p

reci

pita

te o

f AgC

l rea

ppea

rs o

n ad

ding

HN

O3

(iii)

Chr

omyl

chlo

ride t

est (

not g

iven

by

cova

lent

chlo

rides

, e.g

., H

g 2Cl 2)

(a)

on h

eatin

g ch

lorid

e sa

lt w

ith K

2Cr 2O

7 and

Con

c. H

2SO4 or

ange

re

d va

pour

s of c

hrom

yl ch

lorid

e (C

rO2C

l 2) com

e ou

t

(b

) ch

lorid

e (C

rO2C

l 2) whi

ch o

n pa

ssin

g th

roug

h N

aOH

giv

e ye

llow

solu

tion

(c)

Aci

difie

d so

lutio

n of

Na 2C

rO4 g

iven

yel

low

ppt

. with

2NaC

l + H

2SO4 →

Na 2SO

4 +

2HC

l N

aCl +

AgN

O3 →

AgC

l ↓ +

NaN

O3 w

hite

ppt

.

AgC

l + 2

NH

4OH

→ A

g(N

H3) 2C

l + 2

H2O

(sol

uble

) A

g(N

H3) 2C

l +2H

NO

3 → A

gCl +

2N

H4N

O3

(a)

4NaC

l + K

2 Cr 2O

7 + 3

H2SO

4 →

2C

rO2C

l 2 +

2Na 2SO

4 + K

2SO4 +

3H

2O(b

) C

rO2C

l 2+4N

aOH

→N

a 2CrO

4 +2

NaC

l +2H

2O(c

) N

a 2CrO

4+(C

H3C

OO

) 2Pb→

2CH

3CO

ON

a +

(CH

3CO

O) 2Pb

+ P

bCrO

4↓ (

yello

w p

pt.)

7. B

r-(a

) Br

own

vapo

urs (

Br2) c

ome

out (

Br- o

r NO

3- po

ssib

le)

(inte

nsifi

ed o

n ad

ding

littl

e M

nO2)

(b)

The

brom

ide

give

s lig

ht y

ello

w p

reci

pita

te w

ith A

gNO

3 that

is

part

ially

solu

ble

in N

H4O

H(c

) Br

own

vapo

urs o

f Br 2 o

n pa

ssin

g in

H2O

giv

e br

own

colo

ur

whe

reas

of N

O2 d

oes n

ot im

part

any

colo

ur to

H2O

(d)

Sodi

um c

arbo

nate

ext

ract

of b

rom

ine

on a

dditi

on o

f CH

Cl 3 a

nd

chlo

rine

wat

er g

ives

bro

wn

laye

r to

CH

Cl 3

(

exce

ss ch

lorin

e wat

er d

ecol

ouriz

es it

due

to fo

rmat

ion

of H

BrO

)

2NaB

r + H

2SO4 →

Na 2SO

4 + 2

HBr

2HBr

+ H

2SO4 →

Br 2 +

2H

2O +

SO

2

NaB

r + A

gNO

3 → A

gBr ↓

+ N

aNO

3 (li

ght y

ello

w)

2KBr

+ C

l 2(wat

er) →

2KC

l + B

r 2Br

2+Chl

orof

orm

→ B

row

n-co

lour

ed

chlo

rofo

rm8.

I- I

odid

e(a

) D

ark

viol

et fu

mes

(I2) c

ome

out

(b)

Iodi

ne tu

rns s

tarc

h bl

ue(c

) Io

dide

s giv

e ye

llow

ppt

. with

AgN

O3 in

solu

ble

in N

H4O

H(d

) Si

mila

r to

Br -

2Nal

+ H

2SO4 →

Na 2SO

4 + 2

HI

2HI +

H2SO

4 → I 2 +

2H

2O +

SO2 (

viol

et)

I 2 + S

tarc

h →

Blu

e-co

lour

ed co

mpl

exN

aI +

AgN

O3 →

AgI

↓ +

NaN

O3 (y

ello

w)

2KI+

Cl2

(H2O

) →2K

Cl+

I2+

chlo

rofo

rm

viol

et co

lour

ed9.

NO

3-(a

) Br

own

fum

es co

me o

ut (i

nten

sified

on

addi

ng co

pper

turn

ings

)(b

) Br

own

ring

test

An

aque

ous s

olut

ion

of sa

lt is

mix

ed w

ith fr

eshl

y pr

epar

ed F

eSO

4 an

d co

nc. H

2SO4 is

pou

red

in a

test

tube

from

side

s, br

own

ring

is de

velo

ped.

(c)

Boili

ng n

itrat

e with

Al o

r Zn

in C

onc.

NaO

H am

mon

ia is

evol

ved.

(n

ot a

CT)

(NO

2- , Br- o

r I- m

ay in

terfe

re w

ith th

is te

st)

NaN

O3 +

H2SO

4 → N

aHSO

4 + H

NO

34H

NO

3 → 2

H2O

+ O

2 + 4

NO

2 N

aNO

3 + H

2SO4 →

NaH

SO4 +

HN

O3

6FeS

O4 +

2H

NO

3 + 3

H2SO

4 → 3

Fe2(S

O4) 3 +

2N

O +

4H

2OFe

SO4 +

NO

→ [F

e(N

O)]

SO4 (b

row

n ri

ng)

Nitr

osof

erro

us su

lpha

teN

O3- +

8H

→ O

H- +

2H

2O +

NH

3(C

ontin

ued)


20.240 Chemistry at a GlanceR

adic

alV

Test

/Obs

erva

tion

/Ana

lysi

s R

eact

ion

10.

C2O

42-

Oxa

late

(a)

Col

ourle

ss g

as (C

O +

CO

2) com

es o

ut(b

) Th

ese

gas b

urn

with

blu

e fla

me

at th

e m

outh

of t

est t

ube

(c)

A so

lutio

n of

oxa

late

s giv

es

(i) W

hite

ppt

. with

CaC

l 2 solu

tion

(ii) Th

is pp

t. ge

ts d

issol

ved

in d

il. H

2SO4

Na 2C

2O4 +

H2SO

4 → H

2O +

CO

+ C

O2 +

Na 2SO

42C

O +

O2 →

2C

O2

(i)

Na 2C

2O4+C

aCl 2→

CaC

2O4↓

+2N

aCl (

whi

te)

(ii)

CaC

2O4+H

2SO4 →

CaS

O4+H

2C2O

4 2K

MnO

4 +

3H2SO

4 + 5

H2C

2O4 →

2M

nSO

4 + K

2SO4 +

8H

2O

+ 10

CO

2

11.

SO4-2

Sulp

hate

A sm

all a

mou

nt o

f sub

stan

ce +

Con

c. H

NO

3; hea

t thi

s mix

ture

and

add

Ba

Cl 2. W

hite

ppt

. ins

olub

le in

any

aci

d or

alk

ali,

sulp

hate

is co

nfirm

ed.

(Ag+ o

r Pb2+

, if p

rese

nt, w

ill a

lso g

ive

ppt.

with

(Cl- )

Na 2SO

4+2H

NO

3 → 2

NaN

O3 +

H2SO

4H

2SO4 +

BaC

l 2 → B

aSO

4↓ +

2H

Cl (

whi

te)

12.

PO4-3

Phos

phat

e(a

) A

dd C

onc.

HN

O3 to

smal

l am

ount

of s

ubst

ance

, hea

t and

(b

) th

en a

dd a

mm

oniu

m e

xces

s mol

ybda

te y

ello

w p

pt. c

onfir

ms t

he

pres

ence

of p

hosp

hate

. (•

ppt.

diss

olve

s in

exce

ss p

hosp

hate

) (•

as a

lso g

ives

yel

low

ppt

. of (

NH

4) 3·AsO

4·12M

oO3)

(a)

Na 3PO

4+3H

NO

3 → 3

NaN

O3+H

3PO4

(b)

H3PO

4 + 1

2(N

H4) 2M

O4 +

21H

NO

3

Am

m. m

olyb

date

→

(NH

4) 3.PO

412M

oO3↓

+12H

2O+

21N

H4N

O3

A

mm

. pho

spho

mol

ybda

te (y

ello

w p

pt.)

Grp

. No.

Rad

ical

VTe

st/O

bser

vati

on/A

naly

sis

Rea

ctio

n

I Gro

upH

g+2, A

g+ , Pb+2

Add

dil.

HC

l to

clea

r sol

utio

n of

subs

tanc

e w

hite

pp

t. in

dica

tes t

he p

rese

nce

of H

g+ ,Ag+ o

r Pb2+

2HgN

O3 +

2H

Cl →

Hg 2C

l 2↓ +

2H

NO

3

AgN

O3

+ H

Cl →

AgC

l↓ +

HN

O3

Pb(N

O3) 2 +

2H

Cl →

PbC

l 2 ↓ +

2H

NO

3

Imp.

PbC

l 2 is so

lubl

e in

hot

wat

er (b

ut in

solu

ble

in co

ld w

ater

) whi

le A

gCl a

nd H

g 2Cl 2 a

re in

solu

ble.

(a)

Pb+2

Pb+2

ions

giv

es y

ello

w p

pt. w

ith K

2CrO

4 and

KI

sepa

rate

lyPb

Cl 2 +

K2C

rO4 →

PbC

rO4↓

+ 2

KCl (

yello

w)

PbC

l 2 + 2

KI →

PbI

2↓ +

2KC

l (ye

llow

)

(b)

Hg 22+

Hg 22+

ions

giv

es b

lack

ppt

. with

NH

3H

g 2Cl 2 +

2N

H4O

H →

Hg(

NH

2)Cl +

Hg↓

(bla

ck) +

N

H4C

l + 2

H2O

(c)

Ag+

1. A

gCl i

s sol

uble

in N

H4O

H2.

Ag+ io

ns g

ive

(a) y

ello

w p

pt. w

ith K

I 3.

Red

ppt

. with

K2C

rO4

AgC

l + 2

NH

4OH

→ [A

g(N

H3) 2]C

l + 2

H2O

Ag+ +

I- → A

gI↓

(yel

low

)K

2CrO

4 + 2

Ag+ →

Ag 2C

rO4 +

2K

+ (r

ed)

(Con

tinue

d)


Salt Analysis 20.241G

rp. N

o.R

adic

alV

Test

/Obs

erva

tion

/Ana

lysi

s R

eact

ion

II G

roup

Hg+2

, Pb+2

, Cu+2

,Cd2+

Bi+3

(IIA

), A

s+3, S

b+3

Sn+2

, Sn+4

(IIB

)C

d+2, A

s+3, S

n+4

Sb+3

Sn+2

Hg+2

, Pb+2

, Bi+3

Cu+2

On

pass

ing

H2S

in p

rese

nce

of H

Cl t

hrou

gh a

so

lutio

nco

ntai

ning

thes

e io

ns, f

ollo

win

g su

lphi

des p

re-

cipi

tate

.Ye

llow

ppt

.; (C

dS, A

s 2S 3, SnS

2)O

rang

e pp

t; (S

b 2S 3)Br

own

ppt.;

(SnS

)Bl

ack

ppt.;

(HgS

, PbS

, Bi 2S 3, C

uS)

The

ppt.

obta

ined

can

be

dist

ingu

ished

by

trea

ting

with

yel

low

am

mon

ium

sulp

hide

(NH

4) 2S x to g

ive

inso

lubl

e IIA

and

solu

ble

IIB

part

s.II

A(d

) H

g+2H

g+2 io

n in

solu

tion,

on

addi

tion

of S

nCl 2,

give

whi

te p

pt. t

urni

ng b

lack

copp

er tu

rnin

gs

in H

gCl 2 g

ive

grey

dep

osit

2Hg+2

+ S

nCl 2 →

Sn+4

+ H

g 2Cl 2↓

Whi

teH

g 2Cl 2 +

SnC

l 2 → S

nCl 4 +

2H

g↓

Blac

k(e

) Pb

+21.

Pb+2

ions

in so

lutio

n gi

ve w

hite

ppt

. with

H

2SO4

2. P

b+2 io

ns in

solu

tion

give

yel

low

ppt

. with

K

2CrO

4 an

d K

I (se

para

tely

)

Pb+2

+ H

2SO4 →

PbS

O4 ↓

+ 2

H+

Pb+2

+ C

rO4-2

→ P

bCrO

4↓(y

ello

w)

Pb+2

+ 2

I- → P

bI2 (y

ello

w)

(f)

Cu+2

1. Th

ese

ions

in so

lutio

n gi

ve d

eep

blue

colo

ur

with

exc

ess o

f NH

4OH

2. C

u+2 io

ns g

ive

choc

olat

e pp

t. w

ith

K4Fe

(CN

) 6

Cu+2

+ 4

NH

4OH

→ C

u(N

H3) 4+2

+ 4H

2O

(d

eep

blue

in co

lour

)2C

u+2+K

4Fe(C

N) 6→

Cu 2[F

e(C

N) 6]↓

+4K

+

choc

olat

e or

red

brow

n pp

t.(g

) Bi

+31.

Bi g

ives

whi

te p

pt. w

ith N

H4O

H so

lubl

e in

di

lute

HC

l

2. B

i+3 io

ns in

solu

tion

of H

Cl o

n ad

ditio

n of

w

ater

wat

er g

ive

whi

te cl

oudy

ppt

.

BiC

l 3 + 3

NH

4OH

→ B

i(OH

) 3 +3N

H4C

BiC

l 3 + H

2O →

BiO

Cl↓

+ 2

HC

l W

hite

bis

mut

h ox

ychl

orid

e2B

iCl 2 +

3N

a 2SnO

2 + 6

NaO

H →

2B

i↓ +

3Na 2Sn

O3+

6NaC

l +3H

2O(S

od. s

tann

ite)

(h)

Cd+2

Cad

miu

m g

ives

solu

ble

com

plex

with

NH

4OH

Cd2+

ions

giv

e ye

llow

ppt

. on

pass

ing

H2S

(bla

ck) s

od. s

tann

ate

CdS

O4+4

NH

4OH

→[C

d(N

H3) 4]S

O4+4

H2O

Tet

ram

ine

Cad

. sul

phat

e co

lour

less

)[C

d(N

H3) 4]S

O4+H

2S→ C

dS↓+

(NH

4) 2SO4+2

NH

3

(yel

low

)(C

ontin

ued)


20.242 Chemistry at a GlanceG

rp. N

o.R

adic

alV

Test

/Obs

erva

tion

/Ana

lysi

s R

eact

ion

II B

(i) A

s+3

As+3

ions

in so

lutio

n gi

ve y

ello

w p

pt. w

ith

amm

oniu

m m

olyb

date

and

HN

O3

As+3

3H

NO

Oxi

datio

n→

As+5

(as H

3AsO

4)H

3AsO

4 +

12(N

H4) 2M

oO4 +

21H

NO

3→

(NH

4) 3AsO

4. 12M

oO3↓

+ 2

1NH

4NO

3 + 1

2H2O

(y

ello

w)

(j) S

n+2Sn

+2 io

ns in

solu

tion

as S

nCl 2 g

ive

whi

te p

pt. w

ith

HgC

l 2 tu

rnin

g bl

ack

on st

andi

ngSn

Cl 2 +

2H

gCl 2 →

SnC

l 4 + H

g 2Cl 2↓

(Whi

te)

Hg 2C

l 2 + S

nCl 2 →

SnC

l 4 + 2

Hg↓

(Bla

ck)

(k)

Sn+4

alum

iniu

m re

duce

s Sn+4

to S

n+2 io

n th

en te

sted

Sn

Cl 4 +

by

HgC

l 2 →

No

reac

tion

3SnC

l 4 + 2

AI →

2A

lCl 3 +

3Sn

Cl 2\

SnC

l 2 +

HgC

l 2 →

SnC

l 4 + H

g (B

lack

)(l)

Sb+3

Sb+3

ions

in so

lutio

n as

SbC

l 3 on

addi

tion

of w

ater

gi

ves w

hite

ppt

.Sb

Cl 3 +

H2O

→ S

bOC

l↓ +

2H

Cl w

hite

III G

roup

Fe+3

, Cr+3

& A

l+3Th

ese

ions

are

pre

cipi

tate

d as

hyd

roxi

des o

n ad

ditio

n of

NH

4Cl a

nd N

H4O

HFe

+3 +

3O

H- →

Fe(

OH

) 3 (red

ppt

.)C

r+3 +

3O

H- →

Cr(

OH

) 3 (gre

en p

pt.)

Al+3

+ 3

OH

- → A

l(OH

) 3 (whi

te p

pt.)

Few

dro

ps o

f con

c. H

NO

3 is a

lso a

dded

bef

ore

test

of I

II g

r to

oxid

ise F

e+2 to

Fe+3

.(m

) A

l+3W

hite

ppt

. of A

l(OH

) 3 is so

lubl

e in

NaO

H

prec

ipita

te re

appe

ars o

n bo

iling

with

NH

4Cl.

Al(O

H) 3 +

NaO

H →

2H

2O +

NaA

lO2

Sod.

met

alum

inat

eN

aAlO

2 + N

H4C

l + H

2O →

Al(O

H) 3+N

aCl +

NH

3(n

) Cr+3

Gre

en p

pt. o

f Cr(

OH

) 3 is so

lubl

e in

N

aOH

+ B

r 2 w

ater

and

add

ition

of B

aCl 2 to

th

is so

lutio

n gi

ves y

ello

w p

pt

Br2 +

H2O

→ 2

HBr

+ O

2Cr(

OH

) 3 + 4

NaO

H +

3O

→ 2

Na 2C

rO4+

5H2O

Na 2C

rO4 +

BaC

l 2 → B

aCrO

4↓ +

2N

aCl

Ye

llow

ppt

.(o

) Fe+3

(i

) (a

) Bro

wn

ppt.

of F

e(O

H) 3 is

diss

olve

d in

HC

l an

d (b

) add

ition

of K

CN

S to

this

soln

. giv

es

bloo

d re

d co

lour

(ii

) A

lso o

n ad

ditio

n of

K4[F

e(C

N) 6] t

o th

is

solu

tion

a pr

ussia

n bl

ue co

lour

is o

btai

ned

Fe(O

H) 3 +

3H

Cl →

FeC

l 3+ 3H

2OFe

Cl3

+3KC

NS→

Fe(C

NS)

3+3K

Cl

Ferr

ic th

iocy

anat

e(b

lood

red

colo

ur)

IV G

roup

Zn+2

, Mn+2

, C

o+2, N

i+2

Co+2

, Ni+2

,Zn

+2

Mn+2

Thes

e io

ns a

re p

reci

pita

ted

as su

lphi

des o

n pa

ss-

ing

H2S

in p

rese

nce

of N

H4O

HBl

ack

(CoS

, NiS

) ppt

. (so

lubl

e in

aqu

a re

gia)

Whi

te (Z

nS) (

solu

ble

in H

Cl)

Pink

(MnS

) sol

uble

in H

Cl o

r buff

colo

ured

2FeC

l 3 + 3

K4[F

e(C

N) 6]→

Fe4[F

e(C

N) 6] 3 +

12K

Cl

Ferr

icfe

rroc

yani

de (P

russ

ian

blue

)M

Cl 2 +

H2S

→ M

S↓ +

2H

Cl

(Con

tinue

d)


Salt Analysis 20.243G

rp. N

o.R

adic

alV

Test

/Obs

erva

tion

/Ana

lysi

s R

eact

ion

Solu

tion

with

Ni2+

or C

o2+ +

NaH

CO

3 + b

rom

ine

wat

erAp

ple

gree

n co

lour

confi

rms C

o2+. I

f no

ppt.

heat

.

CoC

l 2+6N

aHC

O3 →

N

a 4Co(

CO

3) 3 + 3

H2O

+ 2

NaC

l + 3

CO

2

2Na 4C

o(C

O3) 3+H

2O

2Ofr

omBr

wat

er→

2N

a 3Co(

CO

3) 3

(gre

en co

lora

tion)

NiC

l 2 + 2

NaH

CO

3→N

iCO

3 + 2

NaC

l+H

2O+

CO

2

2NiC

O3 +

O →

Ni 2O

3 + 2

CO

2 (b

lack

)(p

) Ni+2

Nic

kel s

alt r

eact

s with

dim

ethy

l gly

oxim

e (D

MG

) in

pre

senc

e of

NH

4OH

to g

ive

red

ppt.

of n

icke

l di

met

hyl

+ N

iCl 2

+ N

H4O

H

3 3(D

MG

)

CH

CN

OH

|C

HC

NO

H

−=

−=

+ N

iCl 2

+ N

H4O

H

Nic

kel d

imet

hylg

lyox

ime (

red

ppt.)

(q) C

o+2 (i

) C

obal

tous

salts

giv

es b

lue

colo

ur w

ith

NH

4CN

S(ii

) C

H3C

OO

H +

KN

O2 +

Co2+

→ y

ello

w p

pt.

CoC

l 2+4N

H4C

NS→

(NH

4) 2[CO

(CN

S)4]+

2NH

4Cl

Am

m. c

abal

toth

iocy

anat

e (b

lue

colo

ur)

7KN

O2+2

CH

3CO

OH

+CO

Cl 2

→K

3CO

(NO

2) 6

Ye

llow

+ 2K

Cl +

2C

H3C

OO

K +

NO

+ H

2O(r

) Zn+2

Zn+2

ions

in so

ln. g

ive

whi

te p

pt. w

ith N

aOH

, w

hich

diss

olve

s in

exce

ss o

f NaO

HZn

+2 +

2N

aOH

→ Z

n(O

H) 2↓

+ 2

Na+

W

hite

Zn(O

H) 2 +

2N

aOH

→ N

a 2ZnO

2 + 2

H2O

Solu

ble

sod.

zinc

ate

(s) M

n+2(a

) M

n+2 io

ns in

soln

.giv

e pi

nk p

pt. w

ith N

aOH

(b)

Turn

ing

blac

k or

bro

wn

on h

eatin

g a

, b, g

Mn+2

+ 2

NaO

H →

Mn(

OH

) 2↓ +

2N

a+

Mn(

OH

) 2 + O

∆→

MnO

2+ H

2OBr

own

or b

lack

(Con

tinue

d)


20.244 Chemistry at a GlanceG

rp. N

o.R

adic

alV

Test

/Obs

erva

tion

/Ana

lysi

s R

eact

ion

V G

roup

Ba

+2, S

r+2

Ca+2

Thes

e io

ns a

re p

reci

pita

ted

as c

arbo

nate

s on

addi

-tio

n of

(NH

4) 2CO

3 solu

tion

M+2

+ (N

H4) 2C

O3 →

MC

O3 +

2N

H4+

BaC

O3, C

aCO

3, SrC

O3 (w

hite

) sol

uble

in

CH

3CO

OH

(t) B

a+2Ba

+2 io

ns in

solu

tion

give

(i)

Yello

w p

pt. w

ith K

2CrO

4

(ii)

Whi

te p

pt. w

ith (N

H4) 2SO

4

(iii)

Whi

te p

pt. w

ith (N

H4) 2C

2O4

Ba+2

+ K

2CrO

4 → B

aCrO

4↓ +

2K

+ ye

llow

Ba+2

+(N

H4) 2SO

4 → B

aSO

4↓ +

2N

H4+ (w

hite

)Ba

+2 +

(NH

4) 2C2O

4 → B

aC2O

4 + 2

NH

4+ (whi

te)

(u)

Sr+2

Sr+2

ions

giv

e w

hite

ppt

. with

(i)

(NH

4) 2SO4→

(ii)

(NH

4) 2C2O

4 →

Sr+2

+ (N

H4) 2SO

4 → S

rSO

4↓ +

2N

H4+ (w

hite

ppt

.)Sr

+2 +

(NH

4) 2C2O

4 → S

rC2O

4 + 2

NH

4+ (whi

te p

pt.)

(v)

Ca2+

Ca+2

ions

giv

e w

hite

ppt

. with

onl

y (N

H4) 2C

2O4

Ca+2

+ (N

H4) 2C

2O4 →

CaC

2O4 +

2N

H4+

(w

hite

)V.

Imp.

: Th

ese

are

test

ed in

the

orde

r Ba+2

then

Sr+2

th

en C

a+2

VI G

roup

Zero

grou

p

(w)

Mg+2

Mg+2

ions

giv

e w

hite

ppt

. with

NH

4OH

and

(N

H4) 2H

PO4 (w

hite

)M

g+2 +

(NH

4) 2HPO

4 + N

H4O

H →

MgN

H4PO

4↓+

2NH

4+ + H

2O

(x)

NH

4+ (i

) (a

) A

ll am

mon

ium

salts

on

trea

ting

with

any

al

kali

(e.g

., N

aOH

) giv

e sm

ell o

f NH

3.

(b

) Th

e ga

s com

ing

out (

NH

3) sho

ws w

hite

fu

mes

with

HC

l

(c

) O

n pa

ssin

g th

is ga

s to

Hg 2(N

O3) 2, a

bla

ck

colo

ur is

form

ed

(d

) w

ith N

essle

r’s re

agen

t, a

brow

n pp

t. is

notic

ed. 2

K2H

gI4 +

4KO

H +

NH

4Cl

(a) N

H4C

l + N

aOH

∆

→

NaC

l+N

H3 +

H2O

(b) N

H3 +

HC

l → N

H4C

l (w

hite

fum

es)

Hg 2(N

O3) 2+

2NH

3→H

g+H

g(N

H2)N

O3+N

H4N

O3

(Bla

ck)

Nes

sler’s

reag

ent

Iodi

de o

f Mill

on’s

base

(bro

wn

ppt.)


Documents

Salt analySiS