By PH Mohamed Hamdy

Analytical chemistrysecond 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.solutionBa** + 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 fromwhite → 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+S4O6ˉˉBy addition of I2 in acidic media (Brown solution ) to Sˉˉ,SO3ˉˉ,S2O3ˉˉ leads 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 thatbut you should also know B and Cso depend on your self to get them

(4)Sulphate SO4ˉˉ :--Parent Acid: H2SO4 Sulphuric Acid-Dry Test:- SO4ˉˉ + 2H* → -ve ( means no rection)

Important notes :.General properties of Sulphuric Acid1- one of the strongest acids 2-Ionizes in dilute solution in 2 stepsH2SO4 ↔ H* + H2SO4ˉH2SO4ˉ↔ H* + SO4ˉˉ3-It has Dehydrating properties :-concerated H2SO4 has great tendency ( قابلية او to (ميلcombine withwater to form stable Hydrates (H2SO4.H2O)

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 +4H2OSOOOOOO NEVER SAY Sulphuric acid act as reducing agentit 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+SO4ˉˉNote that PbSO4 ( lead sulphate) is insoluble in cold.dil.mineral acids but sol.in KIana Ammonium Acetate solution

.Reaction with FeCl3 :(-ve) No reactionthat was about SO4ˉˉLet’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 producedb-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 ofZn[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 prescence of Na2CO3

5-For persulphate S2O8ˉˉ:Depend on their oxidising properties1- S2O8ˉˉ+ 2Iˉ→I2(brow) + SO4ˉˉ ↓starch blue2- 5S2O8ˉˉ+2Mn**(manganous)+ 8H*→2MnO4+ 10SO4ˉˉ+6H* (pink colour)

Analysis of mixtures of Sˉˉ,SO3ˉˉ,S2O3ˉˉ,SO4ˉˉ

YOU should look on these pages in the book 21 , 22,23

المصادر الشروق – ورق الكتاب

ال ه ذالحمدلله الى هدانا كنا ذى ما و االله قدر ان و الله هدانا أن لوال لنهتدى

به تستفيد ان لو ذلك و ابظهر دعوة بها فاسالك واحدة معلومة

الغيب أخــــــــــــــــــــــيــــرا و