By PH Mohamed Hamdy
Analytical chemistry
second part of lecture (2)
lecturer : Dr.Magda
In this lecture we take about :
(3)ThioSulphate (S2O3ˉˉ):-Parent acid :H2S2O3 Thiosulphuric acid
-DryTest :S2O3ˉˉ + 2H* → H2S2O3
↓∆
H2O+SO2↑+S˚↓
Thiosulphuric acid easily decomposed to give colloidal
sulphur with yellow colour
thiosulphuric acid has Reducing Properties
-Wet Reactions :.Reaction with BaCl2 :It gives No ppt in Dil.solution
But ppt is formed in conc.solution
Ba** + conc.S2O3 → BaS2O3↓
↓Boil
BaSO4↓
( white ppt )
.Reaction with AgNO3 :2Ag* + S2O3ˉˉ → Ag2S2O3 ↓White ppt
↓H2O
H2SO4 + Ag2S↓↓
(Black ppt)
It gives white ppt of (Ag2S2O3) silver thio
sulphate which changes its colour on
standing from
white → yellow →Brown → Black
.Reaction with Pb(Ac)2:Pb** + S2O3ˉˉ→PbS2O3 ↓
↓Boil
PbS ↓↓(Black ppt
.It gives white ppt of lead thiosulphate (PbS2O3)
which is soluble in cold.HNO3
.On Boiling give black ppt of (PbS)
.Reaction with FeCl3 :Fe*** + 2S2O3ˉˉ → [Fe(S2O3)2]ˉ
(purple complex)
↓∆
2Fe** + S4O6ˉˉ
.It gives purple colour of
[Fe(S2O3)2]ˉcomplex ferric thiosulphate
.on Boiling purple colour Disappear and
formation of Fe** and tetrathionate
S4O6ˉˉ
Q:prove that Sˉˉ,SO3ˉˉ,S2O3ˉˉHave
Reducing properties ???
A-Reaction with I2(iodine):Sˉˉ
SO3ˉˉ
S2O3ˉˉ
↓I2/H*
↓I2/H*
↓I2/H*
2Iˉ+S˚ 2Iˉ+SO4ˉˉ S˚+2Iˉ+S4O6ˉˉ
By addition of I2 in acidic media
Brown solution ) to Sˉˉ,SO3ˉˉ,S2O3ˉˉ
eads to discolouration of brown colour
of I2 solution and give colours solution
You also can prove that by
B-Reaction with K2Cr2O7 :C-Reaction with KMnO4
(pot.permenganate)
Dr.Magda said that you can use A or B
or C to prove that
but you should also know B and C
so depend on your self to get them 
(4)Sulphate SO4ˉˉ :-Parent Acid: H2SO4 Sulphuric Acid
-Dry Test:SO4ˉˉ + 2H* → -ve ( means no
rection)
.General properties of Sulphuric Acid
1- one of the strongest acids
2-Ionizes in dilute solution in 2 steps
H2SO4 ↔ H* + H2SO4ˉ
H2SO4ˉ↔ H* + SO4ˉˉ
3-It has Dehydrating properties :concerated H2SO4 has great
tendency (‫ )ميل او قابلية‬to combine
with
H2SO4 ALSO :
can extract H2O from certain
substances
C2H5-OH + H2SO4 →C2H4+
H2SO4.H2O (Hydrated sulphuric a)
and cause charring to sugars due to
removing water from them
4-H2SO4 Has Oxidising properties :
It is moderately oxidising agent
when heated with most reducing
agents
H2SO4(▲)→H2O + SO2+[O]
H2SO4+8HI→H2S + 4I2 +4H2O
SOOOOOO
NEVER SAY
Sulphuric acid act as reducing agent
it is oxidising agent (ok?????)
-Wet Reactions:.Reaction with BaCl2:
Ba** + SO4ˉˉ→ BaSO4↓(white ppt)
Note that BaSO4 is insoluble in
dil.HCl even upon boiling
.Reaction with AgNO3:
2Ag* + SO4ˉˉ(conc.)→Ag2SO4 ↓
(white ppt)
.Reactions with Pb(Ac)2:
Pb** + SO4ˉˉ→ PbSO4↓↓white ppt
PbSO4 + 3OHˉ→HPbO2ˉ+H2O
+SO4ˉˉ
Note that
PbSO4 ( lead sulphate) is insoluble
in cold.dil.mineral acids but sol.in KI
ana Ammonium Acetate solution
.Reaction with FeCl3 :
(-ve) No reaction
that was about SO4ˉˉ
Let’s see what next
(5)PerSulphate S2O8ˉˉ:
All Reactions of S2O8ˉˉon cold is –
ve (negative) No reaction occur
.Dry Test:
S2O8ˉˉ + H2O (▲)→SO4ˉˉ +
H2SO4+[O]
↓HCl
↑ Cl2
-Wet Reactions:
.Reaction of BaCl2:
S2O8ˉˉ+H2O(▲)→SO4ˉˉ
↓Ba**
BaSO4↓white ppt
.Reactions with AgNO3:
S2O8ˉˉ+2H2O+2Ag*(▲)→Ag2O2↓
+2H2SO4
(black ppt)
.Reaction with Pb(Ac)2:
No reaction on cold, on boiling
Brown pt of Hydrated peroxide
appear
.Reaction with FeCl3:
NO REACTION
SPECIAL TEST : ( SO IMPORTANT)
1-For Sˉˉ:
a-Cadmium carbonateTest:
Cd** + Sˉˉ→CdS ↓yellow ppt
sulphide solution is shaken with
CdCO3 →yellow ppt of CdS produced
b-Sodium Nitro Prusside Test:
Sˉˉ+[Fe(CN)5NO]ˉˉ→
[Fe(CN)5NOS]ˉˉˉˉ (purple colour)
2-for Sulphite SO3ˉˉ:
Zinc Nitro prusside Test:
ZnSO4+K4[Fe(CN)6]+ Sod.nitro
prusside + SO3ˉˉ→Red colour of
Zn[Fe(CN)5NO]+ moist SO2 →
Na5[Fe(CN)5SO3] (red complex)
3-For ThioSulphate S2O3ˉˉ:
Thiocyanate test:
S2O3ˉˉ+CNˉ(boiling alkaline)
→ SCNˉ+SO3ˉˉ
H* ↓Fe***
Fe(SCN)3 or [Fe(SCN)]**
(red blood colour)
4-For sulphate SO4ˉˉ:
Hepar’s Test:
MSO4 + Na2CO3(fusion)→Na2SO4
+ MCO3
↓carbon
Na2S+4CO↑
↓H2O
Ag2S ←Ag*+H2S
(black ppt)
SO4ˉˉis reduced by (C) to Sˉˉ by
heating on piece of charcoal in
5-For persulphate S2O8ˉˉ:
Depend on their oxidising properties
1S2O8ˉˉ+ 2Iˉ→I2(brow) + SO4ˉˉ
↓starch
blue
25S2O8ˉˉ+2Mn**(manganous)+
8H*→2MnO4+ 10SO4ˉˉ+6H*
(pink colour)
Analysis of mixtures of Sˉˉ,SO3ˉˉ,
S2O3ˉˉ,SO4ˉˉ
Sˉˉ,SO2ˉˉ,S2O3ˉˉ,SO4ˉˉ
Centrifugate
+
BaCl2
White ppt
BaSO4 +
BaSO3+Dil.Hcl
White ppt
BaSO4
SO4ˉˉ
Centrifugate
SO3ˉˉ
Cnfirmed by oxidation with Br2
or H2O into SO4ˉˉ
CdS
Yellow ppt
Centrifugate
BaS2O3
+
Dil.HCl
↓▲
↑SO2=S
YOU should look on these
pages in the book
21 , 22,23
‫المصادر‬
‫ورق الشروق –الكتاب‬
‫الحمدهلل الذى هدانا الى هذا و ما كنا لنهتدى لوال‬
‫أن هدانا هللا و ان قدر هللا لك ان تستفيد بهذا و لو‬
‫معلومة واحدة فاسالك بها دعوة بظهر الغيب‬
‫و أخــــــــــــــــــــــيــــرا‬