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Qualitative Inorganic Analysis
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-, HCO3Parent acid
CO32HCO3Carbonic acid (H2CO3) is a very weak acid, Heating of solution of H 2CO3,
CO2 will evolve.
H2CO3 ⇋ CO2 + H2O
Bicarbonates are considered to be the first step of ionization of carbonic
acid, while in the second step carbonates are formed
H2CO3 ⇋ H+ + HCO3- ⇋ H+ + CO32-
Solubility
Insoluble in water except (Na+, K+, NH4+)
1- Dry Reactions
a) dilute HCl
Decomposition with effervescence due to the evolution of CO 2 gas, for
both CO3 2- and HCO3CO3-- + 2H+ ⇋ CO2 + H2O
NaHCO3+ H+ ⇋ CO2  + H2O + Na+
# (Test for CO gas)
Soluble in water
2
b) sulphuric acid
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 ppt. is soluble in mineral acids (nitric acid) and in ammonia.
Ag2CO3 + 2H+  2 Ag+ + CO2 + H2O
Ag2CO3+4NH3  2[Ag (NH3)2]+ + CO32The precipitate becomes yellow or brown if the mixture is boiled.
Ag2CO3 →
 Ag2O +CO2 
𝐁𝐨𝐢𝐥𝐢𝐧𝐠
White precipitates of BaCO3, No ppt. on cold since all HCO3- are
CaCO3 and MgCO3 will be obtained soluble in water.
with carbonate solution.
BaCl2 + NaCO3 BaCO3 + 2 NaCl
Ca++ + CO3 --  CaCO3
Mg++ + CO3 --  MgCO3
The precipitate is soluble in mineral
acids
III. Mixture of CO32-, HCO3-: 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.
b- with BaCl2,
CaCl2 and MgSO4:
1
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Separation: Add excess CaCl2 (BaCl2 or MgSO4) to a solution of the mixture CO 32- /HCO3- a white
ppt. indicates CO3--, centrifuge or filter
Ca (HCO3)2 + 2 NH3 ⇋ CaCO3+ (NH4)2 CO3
# Test for CO gas:
2
The solid substance is placed in a test tube, dilute HCl is added, which immediately displaced the gas,
which is evolved (upon warming) and passed into lime water or baryta water contained in another test
tube.
The production of turbidity indicates the presence of carbonates or bicarbonates.
CO + Ca(OH)  CaCO + H O
2
2
3
2
CO + Ba (OH)  BaCO + H O
2
2
3
2
With prolonged passage of CO , the turbidity formed due to the insoluble carbonates, slowly
2
disappears as a result of the formation of soluble bicarbonate.
CaCO + CO + H O
→
Ca (HCO3)2
3
2
2
𝐁𝐨𝐢𝐥𝐢𝐧𝐠
Sulphur-containing anions
This group of anions are;
1- Sulphide (S2-)
2- Sulphites (SO32-)
3- Thiosulphate (S2O32-)
4- Sulphates (SO42-)
5- Perasulphate (S2O82-).
2
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2. Sulphur-containing anions
Sulphide (S2-)
Parent acid
Reducing
agent:
Hydrogren
sulphide
or
Hydrosulphuric acid (H2S)
Gas with offensive rotten
egg odour and poisonous.
In solution it gives a weak
acid, which ionizes in two
steps;
H2S ⇋ H++ HSHS- ⇋ H++ S-Sulphides, sulphites and
thiosulphates are reducing
agents. They reduce
solutions of I2, KMnO4 and
K2Cr2O7
I2+S2→
2I-+So
lodine (brown)
Colourless
22KMnO4+ 5S + 16H+ →
2Mn+++ 5 SO4--+ 8H2O +2K+
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
S-- + 2H+ → H2S↑
H2S+Pb++ →PbS ↓ black
Sulphites (SO32-)
Sulphurous acid:(H2SO3)
H2O + SO2 →
H2SO3 ⇋
Thiosulphate (S2O32-)
Sulphates (SO42-)
Thiosulphuric
acid:
(H2S2O3)
Decomposes to give, H2O,
SO2 and S.
Sulphuric acid: (H2SO4)
(general properties #)
I2+SO32-+H2O → SO42-+2I+2H+
2 MnO4-+ 5 SO3--+ 6H+ →
2Mn+++ 5SO4--+ 3H2O
Cr2O7--+ 3SO32-+ 8H+ →
2Cr3++ 3SO4--+4H2O
I2+2S2O3-+2I-
------
SO2 gas evolved has bunt
sulphur odor and turbid lime
water due to the formation
of the insoluble CaSO3
Ca (OH)2 +SO2 ⇋ CaSO3 +
H 2O
SO2 has reducing character,
bleaches the brown color of
The solution becomes turbid
due to the liberated yellow
colloidal
sulphur
with
evolution of SO2 gas.
S2O3-- + 2H+ ⇋ H2S2O3
⇋
o
H2O + SO2 + S ↓
+
-
𝐇𝐞𝐚𝐭
+
H + HSO3 ⇋ H + SO3
--
3
H+
→
S4O62-
Tetrathionate
Fe3++2S2O32- → S4O62-+Fe2+
8MnO4-+ 5 S2O3--+ 14H+
→8Mn+++10SO4--+7H2O
4Cr2O72-+ 3S2O32-+ 26H+ →
8 Cr3++6SO4--+ 13 H2O
No reaction with dil. HCl
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2- Wet
Reactions
Reaction
with BaCl2:
Reaction
with AgNO3
Reaction
with FeCl3
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2turns
filter
paper
moistened with cadmium
acetate solution, yellow
H2S + Cd++ →CdS ↓ 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
No visible reaction
a black ppt. of Ag2S soluble
in hot dil. HNO3, insoluble in
ammonia an
2 Ag++ S-- ⇋ Ag2S black
a black ppt. of Fe2S3 is
formed which is soluble in
dil. HNO3
2Fe3++ 3S-- → Fe2S3
iodine, reacts with acid
KMnO4 and acid K2Cr2O7.
l2 + SO2 + H2O ⇋ SO3 + 2H++
2l2 MnO4- + 5 SO2 + 6H+⇋2Mn++
+ 5SO3 + 3H2O
Cr2O72- +3 SO2 + 8H+
⇋ 2Cr3++ 3SO3 + 4H2O
White ppt. of BaSO3 is
formed which is soluble in dil.
HCl.
Ba+++SO32- =BaSO3
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 ↑
A drak red color of ferric
sulphite is produced on cold.
2Fe3++ SO3-- → Fe2(SO3)3
4
Complexing agent:
Thiosulphate form
complex with Fe3+
Fe3++ 2S2O3-- → (Fe(S2O3)2)purple color
No ppt. in dilute solution, but
a ppt. is formed from very
concentrated solution
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
A purple color of complex
disappears on boiling
Fe3++ 2S2O32- → (Fe(S2O3)2)2 S2O3--+ 2Fe3+ ⇋ 2Fe+++
S4O6--
A white ppt. of BaSO4 is
formed which is insoluble in
dil. HCl, even upon boiling.
Ba+++ SO4-- = BaSO4 ↓ White
No ppt. in dil solution, but a
ppt. may be formed in a very
concentrated solution.
do not react with FeCl3
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Reaction
with lead
acetate:
A black ppt. of PbS
produced
Pb+++ S-- → PbS
is
Special
Tests
Cadmium carbonate test
S--+ CdCO3 → CdS + CO32Canary yellow ppt.
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
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-
Hepar’s test
Sulpate is reduced by
carbon to sulphide
Fe3++ SCN-
Transfer the fusion product
to a silver coin and moisten
with a little water, a
brownish black stain of Ag2S
results.
S--+ 2H2O → 2 OH-+ H2S
H2S + 2 Ag →Ag2S +H2
5
Cool
→Fe(SCN)2+
MSO4+
Na2CO3
Na2SO4+ MCO3
𝐹𝑢𝑠𝑖𝑜𝑛
→
Na2SO4+ C → Na2S + 4 CO
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# General properties of H2SO4
1- Acid properties;
It is one of the strongest acids; ionize in dilute solutions in two steps,
H2SO4 → H++ HSO4- (hydrogen sulphate
HSO4- → H++ SO4-- (sulphate)
Metals can liberate hydrogen from H2SO4 solution
H2SO4+ Zno → ZnSO4+ H2
Being a strong acid can replace weak acids like, boric acids,
hydrocyanic acid and volatile acids or their decomposition products due to its high B.P.
2NaCl + H2SO4 ⇋ Na2SO4+ 2HCl
2- Dehydrating properties;
Conc. H2SO4 has a great tendency to combine with water to from stable hydrates
H2SO4.x H2O. So it is used as a dehydrating agent for certain substance, and used mostly in
the dissectors.
It causes charring for certain organic substances as sugars due to the vigorous abstracting
of water from theses substances.
3- Oxidizing properties:
It's considered to be as moderately strong oxidizing agent when heated with most reducing
agents
H2SO4 →
H2O + SO2 + [O]
𝐇𝐞𝐚𝐭
It is reduced to SO2, while with active reducing agents it may be reduced to S o or H2S.
2. Mixture of H2S and SO2 gases:
In order to differentiate between these two gases which evolve upon the addition of dil. HCI to
sulphides, sulphites and thiosulphates and having similar reducing properties. A paper moistened
with lead acetate solution changes into black when exposed to H 2S gas, SO2 can cause turbidity to
lime water
6
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3. Halides
Fluoride (F-)
Parent Acids:
Dry Reactions
a- dilute HCl
b- conc. H2SO4
Conc.H2SO4 & MnO2:
Chloride (Cl-)
Therefore the order of stronger halogen acid is from HI  HBr
HF:coloress fuming highly HCl Colorless gas with
corrosive and itching liquid
irritating odor, fumes in moist
air,
Bromide (Br-)
Iodide (I-)
 HCl  HF.
HBr Colorless gas with
irritating odor, fumes in
moist air
HI Colorless gas
with
irritating
odor,
fumes
strongly in moist
air,
Hydrochloric acid shows no reaction .This reaction can differentiate carbonate and sulphur group from halides.
2X-+ H2SO4 = 2 HX + SO42X = may be CI-, I-, Br- and FHF colorless fumes, the glass HCI gas is evolved
A mixture of HBr and
rod acquire oily appearance 2CI-+H2SO4 → 2 HCI + SO4-- Br2 have characteristic
due to the formation of silicic identified by :
brown color
acid and hydrofluorosilicic Formation of white fumes of
acid.
NH4CI when a glass rod 2 Br-+ H2SO4 → 2 HBr +
—
2 F + H2SO4 → 2H F  + SO4
moistened with ammonium SO4-4HF+SiO2→SiF4+ 2H2O
hydroxide
2
HBr
+
H2SO4
3 SiF4+ 3H2O → H2 SiO3+ 2 H2
NH4OH + HCI
→ → Br2 + SO2+ 2 H2O
SiF6
NH4CI + H2O
silicic acid & hydrofluoro
silicic acid
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 +
SO422HI + H2SO4 → I2 +
SO2 + 2H2O
2X- + 4H++ MnO2 ⇋ Mn+++ 2H2O +X2
X = may be CI-, Br- and IThe free halogen, (X2) could be detected by: 1- Bleaching of a moistened colored litmus paper.
2- Suffocating, and irritating odor.
3- Characteristic color of Br 2 (brown), I2 (violet) and CI2 gas
4- I2 changes starch paper into blue, Br 2 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.
CI2+ 2KI → 2KCI + I2
Br2+ 2KI → 2KBr + I2
7
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2- Wet Reactions
aReaction
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 yellow ppt.
insoluble in dil. ammonia
but very slightly soluble
in
conc.
ammonia
solution.
Ag++ I - → AgI
b- Reaction with BaCI2
solution:
The white gelatinous
BaF2 ppt. is partially
soluble in dil. HCI or
HNO3
Ba+++ 2F- → BaF2
A curdy, pale yellow
precipitate , sparingly
soluble in dilute, but
readily soluble in conc.
ammonia solution
AgBr + 2 NH3 →
[Ag(NH3)2]+ + BrNo ppt. is formed
cReaction
FeCI3:
with
Reacts with FeCI3, due
to its strong reducing
action
with
the
liberation of I2.
Reaction
acetate
lead
a white crystalline ppt.
CI -and Br -: do not react with FeCI3
of the complex salt,
which
is
sparingly
soluble in water
Fe3++ 6 F- → [FeF6]3F-, Cl- and Br- form a white ppt with lead acetate, sparingly soluble in cold more soluble
in hot water, crystallize on cooling
Silver ammine chloride
with
Chlorine water test
Chloride and Fluoride do not react with chlorine water
8
2Br-+ CI2 → Br2+ 2CIBr2+ CI2 →2 BrCI (yellow)
Br2+ CI2 (excess) + 2H2O
→2HOBr+2HCI Colorless
forms a bright yellow
ppt of PbI2  which is
soluble in hot water
and crystallizes on
cooling
as
golden
spangles
2I- + CI2 → I2+ 2CII2+ 5CI2 (excess) +
6H2O
→ 2
HIO3+10HCI
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Special Tests
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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
# N.B.(for Chromyl chloride test)
1- Some CI2 may also be liberated owing to the reacting.
6CI- + Cr2O7--+ 14H+ → 3CI2+ 2Cr3++ 7H2O
and this decreases the sensitivity of the test.
2- Fluorides give rise to the volatile CrO2F2 which is decomposed
by water,
and hence should be absent or removed.
3- Nitrites and nitrates interfere, as nitrosyl chloride may be
formed.
IA) readily oxidized in acid solution
(dil. H2SO4) with nitrite solution
or H2O2 into free l2
2I-+ 2NO2-+ 4H+ → I2+ 2NO + 2H2O
2I-+H2O2+ 2H+ → I2+ 2H2O
B) reacts with Cu++ forming a whit ppt.
of Cu2I2,
2Cu+++4I- ⇋ Cu2I2 +I2
4- Bromides and iodides give rise to the free halogens, which yield
colorless or pale yellow solution with NaOH.
6 Br-+ Cr2O7--+ 14H+ → 2 Cr3++ 3Br2+ 7H2O
6 I-+ Cr2O7--+ 14H+ → 2Cr3++ 3I2+ 7H2O
Br2+ 2OH- → OBr-+ Br-+ H2O (hypobromide)
I2+ 2OH- → OI-+ I-+ H2O
(hypoiodide)
9
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‫‪10‬‬
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Pharmaza ------
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4. Cyanogen anions
Cyanide (CN-)
Thiocyanate (SCN-)
Ferrocyanide
[Fe(CN)6]4-
Ferricyanide
[Fe(CN)6]3-
1-Parent Acids:
Hydrocyanic acid :HCN has an odor of
bitter almonds.
On passing CO2 to CN- solution HCN is
produced with HCO3CN-+ CO2+ H2O → HCN + HCO3-
Thiocyanic acid: HSCN colorless
toxic liquid
On standing its aqueous solution is
decomposed to HCN and yellow
solid polymer.
3 HCNS → HCN + H2N2C2S3
H4[FeCN)6] white
crystalline solid.
H3
[Fe(CN)6]
browinish
crystalline solid.
Complexing
agent:
Cyanide ion has strong tendency to the formation of complexes which
1- Argentocyanide complexes: Double cyanides
CN- + Ag+, at first white turbidity is formed which is AgCN, if CN- ions are present in excess a soluble complex is
formed. . AgCN + CN- →(Ag (CN)2)2- Complex cyanides:
Stable metallo-cyanogen complexes can be formed by reacting FeSO 4 with CN- in alkaline medium to give stable
ferrocyanide complex. Similar complex is formed with Fe3+ to give ferricyanide.
Fe2++ 6 CN- → [Fe(CN)6]4and
Fe3++ 6CN- → [Fe(CN)6]3When cyanides are heated with polysulphides (NH4)2Sx or thiosulphate (S2O3--) they give thiocyanate ion
CN-+ (NH4)2Sx →(NH4)2Sx-1+ SCNCN-+ S2O32- → SO3--+ SCN-
4-Oxidizing
Ferricyanides has oxidizing effect, they can oxidizes I- into I2
agent:
11
Pharmaza ------
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5-Reducing
Ferrocyanides has mild reducing effect, they can be oxidized to ferricyanide by oxidizing agents, such as MnO4-, NO3-
agent:
, H2O2 and Cl2
2. Dry
Reactions
a- dilute HCl
HCN gas evolved with characteristic bitter almond odor and can be tested:
1- Converting HCN evolved into SCN-, by exposing the evolved HCN gas to a paper
moistened with ammonium polysulphide. The resulted SCN- can be tested by adding dil.
HCI and a drop of FeCI3 solution, a blood red color is produced.
2- By passing the evolved gas into AgNO3 solution, a white ppt. of AgCN is formed
insoluble in dil. HNO3, soluble in ammonia solution.
HCN + AgNO3 →AgCN + HNO3
AgCN + 2NH3 → (Ag(NH3)2)CN
conc. H2SO4:
2Wet
Reactions
a- Silver nitrate
solution:
No
reaction
as SCNis
as
strong
as HCl
With cold dil. HCI,
no gases, but may
be precipitation of
hydro ferrocyanic
and
hydroferricyanic
acid occur.
(Fe(CN)6)4-+
4H+
→ H4(Fe(CN)6)
(Fe(CN)6)3-+ 3H+ →
H3(Fe(CN)6)
3-Prussian blue test: The evolved HCN gas is passed into NaOH solution, add drops
of FeSO4 solution, heat to boiling, the HCN is converted into ferrocyanide which can
be tested by adding drops of FeCl3 solution to produce a Prussian blue ppt.
decomposed
on SCN-+ 4H++ 2SO4--+
On heating, CO will be evolve which burns with a blue flame. SO 2
+
heating
H2O → NH4 + 2HSO4 + is produced in case of ferrocyanide.
CN- +2H++ H2O
→ COS Carbonyl Sulphide (Fe(CN)6)4-+ 6H2O +22H++ 10 SO42- → Fe2++6NH4++ 10 HSO4-+ 6 CO

NH4+ +CO
2Fe2++ 4H++ SO4--→ SO2+ 2H2O + 2Fe3+
(Fe(CN)6)3-+ 6H2O + 22H++ 10 SO42- → Fe3++ 6NH4++ 10 HSO4-+ 6CO

CN- & SCN- : form white ppts. AgCN is soluble
in excess CN-, ammonia solution, but insoluble in
dil. HNO3
Ag++ SCN- →  AgSCN
Ag++ CN- →  AgCN → CN- (Ag(CN)2)- H+→HCN+
AgCN
Both [Fe(CN)6]4-and [Fe(CN)6]3- form white ppt. and orange red ppt.,
respectively
4 Ag++ [Fe(CN)6]4- →  Ag4[Fe(CN)6]
Insoluble in dil. Ammonia and dil. HNO3
+
3 Ag + [Fe(CN)6]3- →  Ag3[Fe(CN)6] Orange red ppt.
Insoluble in dil. HNO3 and Soluble in dil. Ammonia
12
Pharmaza ------
reaction
FeCI3:
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with
iron (III) cyanide dissolved in excess
cyanide forming ferricyanide.
Fe3++ 3CN- → Fe (CN)33CN-→
.
[Fe(CN)6]3Ferricyanide
blood red color
Fe3++ SCN- →
[Fe(SCN)]++
or Fe(SCN)3
or [Fe(SCN)6]3-
Prussian
blue
ppt.
insoluble in dil. HCI, but
soluble in NaOH
3[Fe(CN)6)4-+
4Fe3+
→ Fe4[Fe(CN)6] Prussian
blue
d) Reaction with
FeSO4 reagent:
yellow brown ppt. at first which is
then form ferrocyanide,
2CN-+ Fe2+
→Fe(CN)2 4CN-→
[Fe(CN)6]4-
No reaction.
[Fe(CN)6]3++Fe2+ → Fe3++ [Fe(CN)6]4Turanbull's blue
Prussian blue
Reaction
CuSO4
with
form soluble complex cuprocyanide and cyanogen in acid
medium
2Cu+++ 8CN2[Cu (CN)3]2-+ (CN)2
In alkaline medium cyanogen is converted to CN- &
cyanate CNO-.
(CN)2+ 2OHCN-+ CNO-+ H2O
Reaction
with
Cobalt Nitrate:
Co2++ 2CN-+ 2H2O
2H2O 4CN-→
(CN)6]4complex.
Special Tests
Prussian blue test
→ Co (CN)2.
[Co
soluble
brown color is formed
Fe3++ [Fe(CN)6]3→
Fe[Fe(CN)6] Brown color
This test used to differentiate
between
ferro
and
ferricyanide
Ferrocyanide forms white ppt.
2K++Fe+++ [Fe(CN)6]4- → K2Fe[Fe(CN)6]
Cu+++ SCN- →Cu (SCN)2 green
2 Cu (SCN)2  unstable →  Cu2 (SCN)2+ (SCN)2
decomposition
white
gummy mass
4[Fe(CN)6] + 2Cu++ → Cu2[Fe(CN)6]
Brown
2 [Fe(CN)6]3-+ 3Cu++ → Cu3[Fe(CN)6]2
green
Vogel's Reaction
2Co2++ [Fe(CN)6]4- → Co2[Fe(CN)6]
characteristic blue color
greyish green
extractable with ether or amyl alcohol
Co2++ 4SCN- →[Co (SCN)4]23 Co2++ 2[Fe(CN)6]3- → Co3[Fe(CN)6]2
Extractable with ether (blue)
red ppt.
Vogel's Reaction
As mild reducing agents
As oxidizing agents
2[Fe(CN)6]4-+ CI2
→ 2[Fe(CN)6]3-+
2I2[Fe(CN)6]3-+ 2CI→ 2[Fe(CN)6]4-+I2
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‫اسرة فرسان صيدلة‬
IV. Analysis of Mixtures
1- Mixture of CN-, SCN-, [Fe(CN)6]4- & [Fe (CN)6]3a- Passing CO2 in the mixture solution using acetic acid or NaHCO3
and heat, until no more HCN evolved.
To the remaining solution, after removal of CN-, acidify with dil.
HCI, cool and add FeCI3 solution and centrifuge
2- Mixture of SCN-, CI-, Br- and ISCN- is tested for by reacting with FeCI3, to give blood red color which is extractable
with ether and removed. In presence of I-, I2 is also formed which can be extracted with
CHCI3 (Violet color).
The blue complex formed with Co2+ can also be used to detect and remove SCN - by
extraction with ether or amyl alcohol.
The halides are tested for in the usual way after the removal of SCN-, since it interferes
with their precipitation.
After testing for SCN-, it is removed by igniting the mixture till no more blackening or no
odor of burnt sulphur is observed.
The residue will contain only CI-, Br-, I-, and test for CI- by chromyl chloride test for Iand Br-, carry out chlorine water test.
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‫اسرة فرسان صيدلة‬
5. Arsinic and phosphorous containing anions
Arsenate (AsO43-)
Arsenite (AsO33-)
Phosphate (PO43-)
1- Parent Acids:
1- Dry Reactions
a- dilute HCl
Orthoarsenic acid :H3AsO4
On hot arsenate ion oxidises HCI into free
CI2, while it will be reduced to arsenite
2CI-+ AsO43-+ 4H+ ⇋ CI2  +AsO2- + 2H2O
Arseneous acid :H3AsO3
Arsenite will react and vapour of
arsenious chloride is evolved
AsO2-+ 3CI- + 4H+ ⇋ AsCI3  + 2H2O
Orthophosphoric acid :H3PO4
no visible reaction
Redox-reaction
with I2/I-:
Aresnate has oxidizing effect and aresnite has reducing effect
Arsenate (AsO43-) ions oxidises iodide into iodine; but the redox reaction is reversible due to the narrow difference
in Eo values of the two redox systems.
2- Wet Reactions
a- Silver nitrate
solution:
All the precipitates are soluble in ammonia
solution, due to the formation of the complex ion
[Ag (NH3)2]+,
Reaction
with
Magensia Mixture:
reagent is formed
of MgCI2, NH4CI
and NH4OH
The reagent solution form white crystallineprecipitate with phosphates and arsenates in neutral or ammoniacal
solution. The precipitate is soluble in acetic acid and in mineral acids.
No precipitate is formed with arsenites.
PO43-+Mg2++ NH4+ → Mg (NH4) PO4
[magnesium ammonium phosphate]
32+
+
AsO4 + Mg + NH4 → Mg(NH4)AsO4 [magnesium ammonium arsenate]
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Reaction
ammonium
molybdate
with
‫اسرة فرسان صيدلة‬
reagent + conc. HNO3 + test solution heat gradually, = a canary yellow crystalline precipitates of ammonium
phosphomolybdate (NH4)3PO4. 12MoO3 (on warming to 40oC) and of ammonium arsnomolybdate (NH4)3 AsO4. 12MoO3
(on boiling) in case of phosphates and arsenates respectively.
No precipitate is formed with arsenites.
Reaction with H2S
yellow ppt. of arsenious sulphide
As2S3.
The ppt. is soluble in HNO3 and alkali
hydroxides insoluble in hot conc. HCI.
2H2AsO4-+ 5H2S +2H+ → As2S5 
+8H2O
not immediate, but after prolonged
passage of H2S, yellow ppt. of AS2S3 is produced.
No precipitate
Reaction
with
CuSO4 solution:
green ppt. of the cupric arsenate, or
CuHAO4,
The ppt. is soluble in mineral acids and
in ammonia.
yellowish green ppt. of copper arsenite CuHAsO3
The ppt. is soluble in excess
NaOH to give deep blue color of CuO.HAsO2. On
boiling red ppt. is formed due to the reduction of
CuO into cuprous oxide (Cu2O), the arsenious acid is
simultaneously partially-oxidised to arsenic acid.
Cu2++ AsO2-+ OH-→ CuHAsO3 = [CuO.HAsO2]
2[CuO.HAsO2] + H2O → Cu2O+ H3AsO4 + HAsO2
Bluish
ppt
of
CuHPO4,
The ppt. is soluble in
mineral acids and in
ammonia.
g) Uranyl acetate
solution:
Light yellow, gelatinous precipitate of uranyl ammonium phosphate Uo2(NH4) PO4 or arsenate UO2 (NH4) AsO4 in case
of phosphates and arsenates repectively, in the presence of excess ammonium acetate. The precipitate is soluble in
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‫اسرة فرسان صيدلة‬
mineral acids, but insoluble in acetic acid. This test provides an excellent method of distinction of phosphate and
arsenate from arsenite, which does not give a precipitate with the reagent.
PO43-+ UO22++ NH+4 → UO2(NH4)PO4
Special Tests
Potassium iodide test
AsO43-+ UO22++ NH4+ →UO2(NH4) AsO4
a) Bettendorf's test:
test solution + 4ml of conc. HCI, and 1 ml of
stannous chloride = dark brown and finally black
ppt. of arsenic is formed.
3 Sn2++ 8H++ 2AsO2- (heat) → 2As  +3Sn4++ 4H2O
b) Iodine test:
NaHCO3 solution + sample solution.+ few drops
of I2 solution. The brown color of I2 disappears
immediately due to the reducing effect of
arsenite. this test can be used to distinguish
arsenite from arsenate or phosphate.
c) Marsh's reaction: [for small amounts of
arsenic.]
In acidic solution arsenic (III) and (V)
compounds are reduced by
hydrogen to the poisonous hydrogen arsenide
gas (H3As) with garlic like
odor which when heated dissociates to
elementary arsenic and hydrogen:
17
Magnesium test:
It depends on reduction
of the stable phosphates
into phosphide (P3-),
(heat)
PO43++ 4Mg
→
34MgO + P
P3-+ 3H2O → PH3  +
3OH-
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‫اسرة فرسان صيدلة‬
6. Nitrogen- containing anions
Parent Acids
Dry Reactions
a- Action of dilute
HCl
Action of conc. H2SO4
Wet Reactions
with Ag2SO4 solution
with KI solution:
with Fe SO4 solution.
Nitrate (NO3-)
Nitric acid :HNO3 decomposes (NO2).
4HNO3 → 4NO2  + O2  +2H2O
No reaction
Nitrite (NO2-)
Nitrous acid :HNO2
2HNO2 → NO  + NO2  + H2O
2NO2-+ 2H+ → 2HNO2 →NO  + NO2  +H2O
2NO  + O2  → 2NO2 
Nitric acid is formed and some of it decomposed with evolution of brown As in dil HCl
fumes of NO2.
NO3-+ H+ → HNO3
4HNO3 → 4NO2  + O2  + 2H2O
No ppt.
White crystalline ppt. of AgNO2.
NO2-+ Ag+ → AgNO2
No reaction
I2 is liberated give blue color to the starch.
2NO2-+ 2I-+ 4H+ → 2NO  + I2+ 2H2O
(Brown Ring Test):Acidify the test solution (5ml) with dil. H2SO4, add (1ml) freshly prepared
FeSO4 solution. This test differentiates NO3- ion from NO2- ion, since the latter gives the brown ring in presence of dil.
H2SO4 or even acetic acid, while NO3- ion dose not form the ring except in presence of conc. H 2SO4.
(NO2-, I- and Br- ions will interfere)
3Fe2++ NO3-+ 4H+ → 3Fe3++ NO  + 2H2O
Fe2++ NO2-+ 2H+ → Fe3++ NO + H2O
Fe2++ NO  → [Fe (NO)]2+
Ammonia test
1- Permanganate test:
o
o
If solution of NO3 is boiled with Zn or Al metals and NaOH permanganate is reduced by the nitrite into colorless
solution, NH3 will be evolved which can identified by its odor or manganous salt and the nitrite is oxidized into nitrate.
with red litmus paper (nitrites interfere).
2MnO4-+ 5NO2-+ 6H+ → 2Mn2++ 5NO3-+ 3H2O
Pink
colorless
2- Urea test:
CO (NH2)2+ 2HNO2 → 2N2 + CO2 +3H2O
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‫اسرة فرسان صيدلة‬
IV. Analysis of Mixtures
1- Mixture of Nitrate and Nitrite:
Nitrite can be tested for in presence of nitrate (by treatment with dil HCI,
KI, KMnO4, FeSO4 in dil. H2SO4); and by the special tests for nitrite.
Nitrate cannot be tested for in presence of nitrite, since nitrite gives all the reactions of
nitrate (conc. H2SO4, brown-ring test and ammonia test).
Therefore nitrite be removed before testing for nitrate by:1- Decomposition of NO2- through its brown complex with FeSO4 formed in dil. H2SO4 or
acetic acid by heat and shaking.
[Fe (NO)]2+ heat → NO
+ Fe2+
2- Decomposition of NO2- through its reduction to nitrogen by boiling with
NH4CI or warming with urea and few drops of dilute H 2SO4 or warming with little
sulphamic acid.
HO.SO2. NH2+ HNO2 → N2 + H2SO4+ H2O
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