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Qualitative Inorganic Analysis

Qualitative Inorganic Analysis. Analytical chemistry could be divided into three main parts; qualitative, quantitative and applied. Qualitative analysis deals with detection and identification of different substances singly or in a mixture.

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Qualitative Inorganic Analysis

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  1. Qualitative Inorganic Analysis

  2. Analytical chemistry could be divided into three main parts; qualitative, quantitative and applied. Qualitative analysis deals with detection and identification of different substances singly or in a mixture. This part deals with the qualitative analysis of anions, which could be defined as the negatively charged fragments of salt or compound. Alternatively anions refer to acid radical. An example is Nacl: NaCl Na + + Cl- Cation Anion Basic radical Acid radical

  3. 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

  4. Carbonates and Bicarbonates group CO32- HCO3- I. General characters 1- Parent acid: Carbonic acid (H2CO3) is a very weak volatile acid (stronger than HCN and boric acid) Heating of solution of H2CO3, 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 H2 CO3 H+ + CO32- H+ + HCO3-

  5. 2-Solubility: All carbonated with the exception of those of the alkali metals (Na+ and K+) and of ammonium are insoluble in water. All bicarbonates are soluble in water. II. General Reactions 1- Dry Reactions a- Action of dilute HCl Decomposition with effervescence due to the evolution of CO2 gas, for both CO3-- and HCO3- CO3-- + 2H+ CO2+ H2O NaHCO3+ H+ CO2 + H2O + Na+ This is a type of displacement reaction in which stronger acid liberates the very weak carbonic acid, which spontaneously decomposes to CO2 & H2O.

  6. Test for CO2 gas: 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 a turbidity indicates the presence of carbonates or bicarbonates. CO2 + Ca(OH)2 CaCO3 + H2O CO2 + Ba (OH)2 BaCO3 + H2O With prolonged passage of CO2, the turbidity formed due to the insoluble carbonates, slowly disappears as a result of the formation of a soluble bicarbonate. CaCO3 + CO2 + H2O Ca (HCO3)2 Boiling

  7. 2- Wet Reactions In order to carry out the wet reactions, a solution of the substance in water must be done. Bicarbonates are mostly decomposed on heating with the liberation of CO2. 2HCO3- CO3-- + H2O + CO2  . a- Reaction 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. Ag2CO3 Ag2O +CO2  boiling

  8. b- Reactions with BaCl2, CaCl2 and MgSO4: White precipitates of BaCO3, CaCO3 and MgCO3 will be obtained upon the addition of these reagents to samples of carbonate solution. BaCl2 + NaCO3 BaCO3 + 2 NaCl Ca++ + CO3--CaCO3 Mg++ + CO3--  MgCO3 The precipitate is soluble in mineral acids For HCO3- ; No ppt. on cold since all bicarbonates are soluble in water Ba++ +2HCO3- Ba(HCO3)2 Soluble H2O + CO2+ BaCO3 Boiling

  9. III. 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 CO32- /HCO3- a white ppt. indicates CO3-- , centrifuge or filter Contrifugate White ppt. May be HCO3-CaCO32- H+ CO2 + H2O Confirmatory test: 1) Boil 2) Add ammonia solution white ppt. Ca (HCO3)2 + 2 NH3 CaCO3+ (NH4)2 CO3

  10. Sulphur-containing anions This group of anions, are; 1- Sulphide (S2-) 2- Sulphites (SO32-) 3- Thiosulphate (S2O32-) 4- Sulphates (SO42-) 5- Perasulphate (S2O82-). I. General characters 1- Parent Acids: a- Hydrogren sulphide or Hydrosulphuric acid (H2S) It is a gas with offensive rotten egg odour and poisonous. In solution it gives a weak acid, which ionizes in two steps; H2S H++ HS- (hydrosulphide ion) HS-H++ S-- (sulphide ion) Both HS- and S-- ions give the same reactions.

  11. b- Sulphurous acid:(H2SO3) This acid is only known in solution (like H2CO3). It has moderate strong acidity. Like H2CO3 in water; present in equilibrium as follows: heat H2SO3 H++ HSO3- H2O + SO2 H++ SO3-- Acid sulphite c- Thiosulphuric acid: (H2S2O3) It is not known in the free form, and decomposes to give, H2O, SO2 and S. It's more stronger than sulphurous acid in solutions. It consists of SO32- solution and S, which upon boiling gives S2O32-. d- Sulphuric acid: (H2SO4): It's a colourless oily liquiud (B.P. 3300C). 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)

  12. 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] It is reduced to SO2, while with active reducing agents it may be reduced to So or H2S. heat

  13. 2-Solubility: All Na+, K+ and NH4+ salts of sulphur containing anions are soluble in water. Sulphides : Other sulphides are in-soluble except those of Ca++, Ba++, & Sr2+ dissolve due to hydrolysis. Sulphites: Other sulphites are all in-soluble. Thiosulphates: Most S2O32-are soluble, Ag+, Pb++, Hg2+ & Ba++ salts are slightly soluble. Sulphates: All sulphates are soluble except Pb++, Ba++ and Sr++. Ca++ & Mg++ salts are slightly soluble.

  14. 3-Complexing agent: Thiosulphate form complex with Fe3+ Fe3++ 2S2O3-- (Fe(S2O3)2)- purple color 4-Reducing agent: Sulphides, sulphites and thiosulphates are reducing agents. They reduce solutions of I2, KMnO4 and K2Cr2O7 with varying activities in acidified solutions. H+ I2+S2- 2I-+So lodine (brown) Colourless 2KMnO4+ 5S2-+ 16H+ 2Mn+++ 5SO4--+ 8H2O +2K+

  15. I2+SO32-+H2O SO42-+2I-+2H+ 2 MnO4-+ 5 SO3--+ 6H+ 2Mn+++ 5SO4--+ 3H2O Cr2O7--+ 3SO32-+ 8H+ 2Cr3++ 3SO4--+4H2O I2+2S2O3-- H+ S4O62-+2I- Tetrathionate H+ Fe3++2S2O32- S4O62-+Fe2+ 8MnO4-+ 5 S2O3--+ 14H+ 8Mn+++10SO4--+7H2O 4Cr2O72-+ 3S2O32-+ 26H+ 8 Cr3++6SO4--+ 13 H2O

  16. II. General Reactions 1- Dry Reactions a- Action of dilute HCl • Sulphide; S2- H2S gas; evolved upon adding dil. HCl to a solid sample. The gas evolved has its characteristic rotten egg odour, and could be identified by 1- blackening of filter paper moistened with lead acetate sol. S-- + 2H+ H2S H2S+Pb++ PbS black 2- alternatively, a filter paper moistened with cadmium acetate solution, turns yellow H2S + Cd++ CdS Yellow H2S has reducing character, It reacts with l2 solution, acid KMnO4, acid K2Cr2O7

  17. 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 2- Sulphite: SO32- Upon treatment of SO3-- with dil. HCl, SO2 gas will evolve, due to the decomposition of the liberated unstable H2SO3 SO--3 + 2H+ H2SO3 SO2 +H2O The evolved SO2 gas has a characteristic bunt sulphur odor and turbid lime water (like CO2) due to the formation of the insoluble CaSO3 which is soluble upon prolonged passage of SO2 due to the formation of soluble calcium bisulphite. Ca (OH)2 +SO2 CaSO3 + H2O

  18. CaSO3 + SO2 + H2O Ca(HSO3)2. SO2 like H2S 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 3- Thiosulphate; S2O32- No immediate change on cold, but on warming with dil. HCl or standing, the solution become turbid due to the liberated yellow colloidal sulphur with evolution of SO2 gas. This is due to the decomposition of the produced unstable thiosulphuric acid. S2O3-- + 2H+ H2S2O3 H2O + SO2 + So Thiosulphate has the same action of sulphite with HCl in addition to formation of yellow colloidal precipitate.

  19. 4- Sulphate: SO42- No reaction with dil. HCl. 2- Wet Reactions a- Reaction with BaCl2: Add BaCl2 reagent to neutral sample solution: 1- S2- : No visible reaction 2- SO32- : White ppt. of BaSO3 is formed which is soluble in dil. HCl. Ba+++ SO32- BaSO3 3- S2O3-- : No ppt. in dilute solution, but a ppt. is formed from very concentrated solution. 4- SO4-- : A white ppt. of BaSO4 is formed which is insoluble in dil. HCl, even upon boiling. Ba+++ SO4-- BaSO4 White

  20. b- Reaction with AgNO3: Add AgNO3 reagent to the neutral sample solution 1- S2- : a black ppt. of Ag2S is formed which is soluble in hot dil. HNO3, insoluble in ammonia and KCN solution 2 Ag++ S-- Ag2S black 2- SO32-: A white crystalline ppt. of Ag2SO3 is formed, which on boiling with water undergoes self oxidation reduction with the production of grey ppt. of metallic silver. 2 Ag++ SO32- Ag2SO3 White 2 Ag2SO3 boil 2 Ago + Ag2SO4 + SO2

  21. Silver sulphite is soluble in nitric acid, ammonia and in excess sulphite to give a complex salt, which on boiling gives a grey ppt. of metallic silver Ag2 SO3 + SO3-- 2(AgSO3)- 2(AgSO3)-boiling 2Ago+ SO4-- + SO2 3- S2O3-- : Forms white ppt. of silver thiosulphate which changes its color on standing to yellow, brown and finally black, due to the formation of Ag2S. Ag2S2O3 is soluble in excess S2O3-- to give a complex ion. 2 Ag+ + S2O3-- Ag2 S2O3 Ag2S2O3+ H2O Ag2S + H2SO4 Ag2S2O3+ 3S2O3-- 2(Ag(S2O3)2)3-

  22. 4- SO42- : No ppt. in dil solution, but a ppt. may be formed in a very concentrated solution. c- Reaction with FeCl3: Add FeCl3 reagent to the neutral sample solution 1- S2- : a black ppt. of Fe2S3 is formed which is soluble in dil. HNO3 2Fe3++ 3S-- Fe2S3 black 2- SO3--: A drak red color of ferric sulphite is produced on cold. 2Fe3++ SO3-- Fe2(SO3)3 3- S2O32-: A purple color of complex ferric thiosulphate is produced which disappears on boiling as tetrathionate and Fe2+ are formed from the oxidation of S2O32- with Fe3+, even on cold Fe3++ 2S2O32- (Fe(S2O3)2)- 2 S2O3--+ 2Fe3+ 2Fe+++ S4O6-- 4-SO42- : do not react with FeCl3.

  23. d- Reaction with lead acetate: Adding lead acetate reagent to the neutral sample solution. 1- S--: A black ppt. of PbS is produced Pb+++ S-- PbS 2- SO32-: A with ppt. of lead sulphite which is soluble in cold HNO3. On boiling oxidation to PbSO4 which is a white ppt. occurs. SO3--+ Pb++ PbSO3 3- S2O3--: A white ppt. of lead thiosulphate is formed which is soluble in cold HNO3, on boiling a black ppt. of PbS is formed. Pb+++S2O3-- PbS2O3 4- SO4--: A white ppt. lead suphate, which is insoluble in cold dil. mineral acids, but soluble in ammonium acetate and hydroxide solutions (Na+ and K+)

  24. Pb+++ SO42- PbSO4 PbSO4+ 4 CH3 COO- (Pb (CH3COO)4)2-+ SO42- PbSO4+ 3OH- HPbO2-+ H2O +SO42- Plumbites III. Special Tests • Sulphide; S2- Cadmium carbonate test : The sulphide solution is shaken with CdCO3 powder, a canary yellow ppt. of CdS is produced. S--+ CdCO3 CdS + CO32- This test could be used for the identification and separation of S2- when present in a mixture with other sulphur containing anions, or those anions which do not react with CdCO3.

  25. 2- Sulphite: SO32- Zinc nitroprusside test : Add to cold saturated ZnSO4 solution, equal volume of K4[Fe (CN)6] solution, add few drops of 1% sodium nitroprusside solution. This solution is added to the SO32-solution,a salmon-colored ppt. of zinc nitroprusside is formed Zn (Fe(CN)5 NO). The latter reacts with moist SO2 to give a red ppt. of Na5[Fe(CN)5 SO3] 3- Thiosulphate; S2O32- Formation of thiocyanate : By boiling with KCN solution (poison), in the presence of NaOH, Cool, acidify and add FeCI3, a blood red color of ferric thiocyanate complex is produced. S2O3--+ CN-OH- SCN-+ SO3-- boil Fe3++ SCN-Cool Fe(SCN)2+

  26. 4- Sulphate: SO42- Hepar’s test Sulpate is reduced by carbon to sulphide by heating on a piece of charcoal in the presence of Na2CO3 in the reducing zone of the flame MSO4+ Na2CO3Fusion Na2SO4+ MCO3 Na2SO4+ C Na2S + 4 CO 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

  27. IV. Analysis ofMixtures 1- Mixture of S2-, SO32-, S2O32- and SO42- : Separation is carried first shaking the mixture solution with CdCO3 powder. The centrifugate is allowed to react with BaCl2 solution which will precipitate BaSO4 and BaSO3 leaving S2O32-as soluble centifugate. The precipitated BaSO4 and BaSO3 can be separated by the solubility of BaSO3 in excess dil. HCI. S2-, SO32-, S2O32- , & SO42- Solution + CdCO3 Yellow ppt. Centrifugate S2- + BaCI2 White ppt. Centrifugate BaSO3+BaSO4 S2O32- HCl Heat HCl White PPt SO42- Centrifugate SO32- confirm by reducing character SO2 + So

  28. 2- Mixture of CO32- and SO32- or S2O32- This type of mixtures are considered to be difficult, due to the interference occur upon the addition of dil. HCI which liberates CO2 and SO2 gases which turbides lime water and disappears on prolonged passage. SO2 can be detected by its reducing characters as discussed before, but CO2 has non reducing characters. Therefore SO32- or S2O32- ions must be firstly oxidized into SO42- by an oxidizing agent such as H2O2,K2Cr2O7 or KMnO4 and dil. H2SO4 and warm, CO2 will only evolve which can be test with lime water. 3- 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 H2S gas, SO2 can cause turbidity to lime water

  29. Halides This group of anions, are; 1- Fluoride (F-) 2- Chloride (Cl-) 3- Bromide (Br-) 4- Iodide (I-) Fluorides, chlorides, bromides and iodides are known as halogens. They are characterized by their higher electronegativity As the ionic size increases, the tendency to loose electrons increases and therefore iodide ion is firstly and easily oxidized into free I2 by loosing readily an electron followed by Br - when present in a mixture. However it's difficult to oxidize F- into F2, hence F- ions are highly stable to held strongly a proton. Therefore the order of stronger halogen acid is from HI  HBr  HCl  HF.

  30. I. General characters 1- Parent Acids: a- Hydrofluoric acid; HF : It's coloress fuming highly corrosive and itching liquid (B.P. 19.4oC). Soluble in water producing the weakest acidic solution in the halogen acid series. b- Hydrochloric acid : HCl Colorless gas with irritating odor, fumes in moist air, extremely soluble in water to form acidic solution. Concentrated HCI contains 37% of HCI gas. c- Hydrobromic acids : HBr Colorless gas with irritating odor, fumes in moist air and is extremely soluble in water forming very strongly acidic solution. On standing the solution becomes yellow due to the oxidation to bromine. d- Hydroiodic acid: HI Colorless gas with irritating odor, fumes strongly in moist air, soluble in water forming the strongest acidic solution of the haloacid series. the solution is colorless, becomes brown on standing due to the liberated iodine.

  31. 2-Solubility: All the salts of CI-, Br- and I- are soluble except Ag+, Hg22+, & Cu+ salts, their lead salts are slightly soluble in cold water, soluble in hot water. The alkali metal salts of fluorides, ammonium and silver salts are soluble, other salts are insoluble or sparingly soluble. 3-Reducing agent: Cl- has very weak reducing character. Br- and I- have reducing character, they can react with oxidizing agent like chlorine water to give Br2 or I2. I- has strong reducing power than Br- so it react with FeCl3, H2O2 and nitrite solutions. II. General Reactions 1- Dry Reactions a- Action of dilute HCl Hydrochloric acid shows no reaction upon treatment of the solid sample with it even on heating. This reaction can differentiate carbonate and sulphur group from halides.

  32. b- Action of concentrated H2SO4: Decomposition of the halides occurs upon the addition of the strong non-volatile concentrated H2SO4 to the solid sample, this occurs in the cold, completely on warming with the evolution of HX which can be recognized by a) the fumes evolved. b) Confirmatory chemical test 2X-+ H2SO4 = 2 HX + SO42- X = may be CI-, I-, Br- and F- 1- For Fluoride: • Fluoride gives a characteristic reaction when treated with conc. H2SO4. • Hydrofluoric acid is produced which is colorless and fumes with moist air. • due to the corrosive and itching action of the gas on the glass in presence • of H2O, the test tube or the glass rod subjected to the evolved HF gas • acquire oily appearance due to the formation of silicic acid and • hydrofluorosilicic acid. • This test is considered to be specific for fluoride anion, even in the presence • of other halides. 4HF + SiO2 SiF4+ 2H2O glass 2 F-+ H2SO4 2H F  + SO4-- 3 SiF4+ 3H2O H2 SiO3+ 2 H2 SiF6 silicic acid hydrofluoro silicic acid

  33. 2- For chloride : • HCI gas is evolved upon treatment with conc. H2SO4 which can be • identified by : 2CI-+ H2SO4 2 HCI + SO4-- 1- Formation of white fumes with moist air due the formation of droplets of hydrochloric acid. 2- Pungent irritating odor. 3- Changing a blue moistened litmus paper into red. 4- Formation of white fumes of NH4CI when a glass rod moistened with ammonium hydroxide solution is exposed to the evolved gas. NH4OH + HCI NH4CI + H2O • 3- For Bromide: A mixture of HBr and Br2 may be formed which have characteristic brown color especially on warming. At the same time sulphuric acid will be reduced into SO2, H2S or S 2 Br-+ H2 SO4 2 HBr + SO4-- 2 HBr + H2SO4 Br2 + SO2+ 2 H2O

  34. 4- For iodide: Since HI is the most active reducing agent, so it is readily oxidized to iodine 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 6HI + H2SO4 3 I2 + S + 4H2O 8HI + H2SO4 4 I2 + H2S + 4H2O c- Action of concentrated H2SO4 and MnO2: If the solid halide is mixed with an equal quantity of precipitated manganese dioxide, concentrated H2SO4 added and the mixture gently warmed. Chlorine, bromine and iodine are evolved from CI-, Br- and I- but F- liberates HF since it has no reducing properties. 2X- + 4H++ MnO2 Mn+++ 2H2O +X2 X = may be CI-, Br- and I-

  35. 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 (greenish tint). • 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. CI2+ 2KI 2KCI + I2 Br2+ 2KI 2KBr + I2 2- Wet Reactions a- Reaction with AgNO3: To 1ml of the salt solution add AgNO3 reagent. 1- Fluoride: No precipitate, since AgF is soluble in water. 2- Chloride: A white curdy ppt. of AgCI which is insoluble in nitric acid, soluble in KCN and Na2S2O3 as other silver halides. The precipitated AgCI is soluble in dil. ammonia solution to give the ammine complex.

  36. Ag++ CI- AgCI Silver ammine chloride AgCI + 2NH3 [Ag(NH3)2]CI [Ag(NH3)2] CI + 2H+ 2 NH4++ AgCI AgCI is reprecipitated upon treatment of the ammine complex with acid. AgX + 2CN- [Ag (CN)2]- +X- Soluble complex AgX + 2 S2O3-- [Ag(S2O3)2]3-+X- 3- Bromide: A curdy, pale yellow precipitate of AgBr, sparingly soluble in dilute, but readily soluble in conc. ammonia solution Ag++ Br- AgBr AgBr + 2 NH3 [Ag(NH3)2]++ Br- 4- Iodide: A curdy yellow ppt. of AgI is formed which is insoluble in dil. ammonia but very slightly soluble in conc. ammonia solution. Ag++ I - AgI

  37. There is a periodicity in character of three silver halides. Since AgI is the most insoluble one, followed by AgBr and AgCI. Therefore AgCI will be dissolved in dil. ammonia, followed by AgBr in conc. Ammonia solution but AgI does not This is also attributed to that the conc. of silver ions (Ag+) produced form the dissociation of silver ammine complex according to its instability constant is insufficient to exceed the high solubility product of AgCI, approach that of AgBr (partially soluble) but exceeds that of AgI. Ag++ 2NH3 [Ag(NH3)2]+ Instability constant = (Ag+) (NH3)2 _________________ [Ag(NH3)2]+ Therefore when Br- or iodide solutions are added to AgCI, yellow ppt. of AgBr or AgI are formed. AgCI + Br- (or I-) AgBr (or AgI) + CI- AgBr + I- AgI + Br-

  38. b- Reaction with BaCI2 solution: Only fluoride gives a white gelatinous ppt. when BaCI2 reagent is added to sample solution. Ba+++ 2F- BaF2 The white gelatinous BaF2 ppt. is partially soluble in dil. HCI or HNO3 No ppt. is formed in case of other halides. c- Reaction with FeCI3: Add few drops of FeCI3 reagent to concentrated sample solution. 1- F- : a white crystalline ppt. of the complex salt, which is sparingly soluble in water Fe3++ 6 F‑ [FeF6]3- 2- CI- and Br-: do not react with FeCI3 3- lodide reacts with FeCI3, due to its strong reducing action with the liberation of I2. d- Reaction with lead acetate Precipitates of Pbx2are formed in cold solution when lead acetate reagent is added to sample solutions.

  39. F-, Cl- and Br- form a white ppt with lead acetate, sparingly soluble in cold more soluble in hot water, crystallize on cooling Pb+++ 2 F- PbF2 Pb+++ 2 CI- PbCI2 Pb+++ 2 Br- PbBr2 Iodide forms a bright yellow ppt of PbI2 which is soluble in hot water and crystallizes on cooling as golden spangles. e- Chlorine water test: Chloride and Fluoride do not react with chlorine water . Chlorine water oxidizes I-and Br-into I2 and Br2 which can be extracted with chloroform or carbon tetrachloride as violet color or brown or yellow color of I2 and Br2, respectively. Iodide react first with chlorine water before bromide as it has more reducing character.

  40. Chlorine water reagent is added drop wise to a solution of iodide or bromide as excess chlorine water converts Br2 into yellow bromine monochloride or into colorless hypobromous acid or bromic acid and the organic layer turns pale yellow or colorless. Also, excess chlorine water oxidized I2 to colorless iodic acid. 2Br-+ CI2 Br2+ 2CI- bromine monochloride Br2+ CI2 2 BrCI (yellow) Br2+ CI2 (excess) + 2H2O 2HOBr+2HCI hypobromous acid Colorless Br2+ 5CI2 (excess) + 6H2O 2 HBrO3+10HCI bromic acid 2I- + CI2 I2+ 2CI- I2+ 5CI2 (excess) + 6H2O 2 HIO3+10HCI iodic acid

  41. III. Special Tests 1- For Fluorides: Boron fluoride test: When fluoride is mixed with borax and moisten with conc. H2SO4. The formed HF and boric acid react to produce boronfluoride gas. If the mixture introduced into the flame tinged green by BF3 gas. Na2B4O7+ H2SO4+ 5H2O 4H3BO3+Na2SO4 Borax boric acid 2NaF+ H2SO4 2HF + Na2SO4 H3BO3+ 3HF BF3+ 3H2O 2- For chlorides: Chromyl chloride test: This test is a specific test for chloride even in the presence of other halides. It's classified as dry reactions test because, it is carried out on the solid sample:

  42. The solid chloride is mixed with three times its weight of powdered potassium dichromate in a tube, an equal bulk of concentrated sulphuric acid is added, the tube is attached to another tube by a pent tube, dipped into a NaOH solution. The deep red vapors of chromyl chloride CrO2CI2 which are evolved are passed into sodium hydroxide solution. The resulting yellow solution in the test tube contains sodium chromate; this confirmed by perchromic acid test, which is carried out by acidifying with dil. H2SO4, adding 1-2 ml alcohol or ether, followed by a little H2O2 solution. The organic layer is colored blue. 4CI-+ Cr2O7--+ 6H+ cond. 2CrO2 Cl2 + 3H2O CrO2CI2 + 4OH- CrO4-- + 2CI- + 2H2O 2 CrO4-- + 2H+ Cr2O7--+ H2O Cr2O7--+ 7H2O2 2 CrO83-+ 5H2O + 4H+ Blue in ether or amyl alcohol It is possible to test for CrO4--also by lead acetate CrO4--+ Pb++ Pb CrO4 Yellow

  43. N.B. 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. 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)

  44. 3- For iodides: A) lodide is 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) I- reacts with Cu++ forming a whit ppt. of Cu2I2, the I- being oxidized to free I2. Thus a white ppt. in brown solution is formed on treating I- with CuSO4 solution. 2Cu+++ 4I- Cu2I2+I2 C) I- reacts with mercuric chloride solution mercuric iodide HgI2 will be precipitated as yellow-scarlet red ppt. which dissolves in excess iodide forming soluble colorless complex. HgCI2+ 2I- HgI2 + 2CI- Scarlet red HgI2+ 2I- (HgI4)2- Soluble complex Nessler's reagent

  45. IV. Analysis ofMixtures 1- Mixture of F-, Cl-, Br- and I- : • The F- is separated by treating the mixture solution acidified with • CH3COOH with Ba(NO3)2 or Ca (NO3)2 Centrifuge White PPt. Centrifugate BaF2 CI‑, Br- and I- Confirmed by Conc.H2SO4 test • b) for the centrifugate ( Cl-, Br- and I-), carry out chlorine water test for • both I- and Br – ( or get rid of I- by oxidation to I2 using H2O2 or nitrite and • extract I2 by chloroform then test for Br- in aqueous solution c) For CI-, carry out chromyl test on a solid sample.

  46. 2- Mixture of chlorine / chloride and Br2 / Br-: Chlorine is tested for by its smell, bleaching effect, while Br2 is tested by shaking with chloroform, it give brown color. CI- and Br-could be tested after removal of chlorine and bromine by shaking with metallic mercury (till the smell of CI2 disappears and the liquid doesn't bleach litmus paper). Insoluble Hg2CI2 and/or Hg2Br2 are formed. Test for CI-and or Br-in the clear supernatant (centrifugate(. CI2+ 2Hgo Hg2CI2 Br2+ 2Hgo Hg2Br2 3- Mixture of chloride and iodide: Add AgNO3 to the mixture, AgCl and AgI are precipitated. Add to precipitate dil ammonia solution and filter Filterate Cl- Confirmed by chromyl chloride test Precipitate Yellow ppt. I-

  47. Cyanogen anions This group of anions, are; 1- Cyanide (CN-) 2- Thiocyanate (SCN-) 3- Ferrocyanide [Fe(CN)6]4- 4- Ferricyanide [Fe(CN)6]3- All cyanide containing anions are highly poisonous. In all experiments in which the gas is likely to be evolved or those in which cyanides are heated, should be carried out cautiously in the fume cupboard. I. General characters 1- Parent Acids: a) Hydrocyanic acid:HCN It's very poisonous. It's colorless volatile liquid (B.P. 26.5oC). It has an odor of bitter almonds. It is not stable in solution due the formation of ammonium formate. Any dil. mineral acid can replace HCN in its solution.

  48. On passing CO2 to CN- solution HCN is produced with HCO3-. CN-+ CO2+ H2O HCN + HCO3- b) Thiocyanic acid: HSCN It is colorless toxic liquid (B.P. 85oC) with unpleasant odor. It is as strong as HCI but unstable. It is soluble in ether after the addition of HCI to an aqueous solution of SCN-. On standing its aqueous solution is decomposed to HCN and yellow solid polymer. 3 HCNS HCN + H2N2C2S3 c) Ferrocyanic acid:H4 [FeCN)6] It's white crystalline solid. Its aqueous solution is strongly acidic. The first two protons are nearly completely ionized. d) Ferricyanic acid: H3 [Fe(CN)6] It's browinish crystalline solid, soluble in water to give strongly acids solution. The three protons are nearly completely ionized.

  49. 2-Solubility: CN-: All cyanides are water insoluble except alkali metals (Na+, K+), ammonium salt, alkaline earth metals ( Ba2+, Sr2+ and Ca2+) and mercuric cyanide. SCN-: All thiocyanates are water soluble except AgSCN, Hg2(SCN)2 & Cu2 (SCN)2. Pb (SCN)2 as PbCI2 is sparingly soluble in cold water, but soluble in hot water. Ferro and Ferricyanides: All are insoluble in water except those of alkali metals, ammonium salt and alkaline earth metals. 3-Complexing agent: Cyanide ion has strong tendency to the formation of complexes which may be double cyanides or complex cyanides. 1- Argentocyanide complexes: Double cyanides When a ppt. is formed upon reacting CN- with Ag+, at first white turbidity is formed which is AgCN. According to the medium, if CN- ions are present in excess a soluble complex is formed. AgCN + CN- (Ag (CN)2)-

  50. 2- Complex cyanides: Stable metallo-cyanogen complexes can be formed by reacting FeSO4 with CN- in alkaline medium to give stable ferrocyanide complex. Similar complex is formed with Fe3+ to give ferricyanide. Therefore [Fe(CN)6]4- and [Fe(CN)6]3- are considered to be stable complexes from CN- ions. Also Co++ can form stable complexes with CN-. Fe2++ 6 CN- [Fe(CN)6]4- Fe3++ 6CN- [Fe(CN)6]3- When cyanides are heated with polysulphides (NH4)2Sx or thiosulphate (S­2O3--) they give thiocyanate ion CN-+ (NH4)2Sx (NH4)2Sx-1+ SCN- CN-+ S2O32- SO3--+ SCN- 4-Oxidizing agent: Ferricyanides has oxidizing effect, they can oxidizes I- into I2 5-Reducing agent: Ferrocyanides has mild reducing effect, they can be oxidized to ferricyanide by oxidizing agents, such as MnO4-, NO3-, H2O2 and Cl2

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