Qualitative Inorganic Analysis

Transcription

1 اسرة فرسان صيدلة pharmaza اسرة فرسان صيدلة Anions are divided into six groups: 1 Carbonates and Bicarbonates group Sulphurcontaining anions 3 Halides Qualitative Inorganic Analysis 4 Cyanogen anions 5 Arsinic and phosphorous containing anions 6 Nitrogen containing anions 1. Carbonates and Bicarbonates group, CO3, HCO3 CO 3 HCO 3 Parent acid Carbonic acid (H CO 3) is a very weak acid, Heating of solution of H CO 3, CO will evolve. H CO 3 CO + H O Bicarbonates are considered to be the first step of ionization of carbonic acid, while in the second step carbonates are formed H CO 3 H + + HCO 3 H + + CO 3 Solubility Insoluble in water except (Na +, K +, NH 4 + ) Soluble in water 1 Dry Reactions a) dilute HCl Decomposition with effervescence due to the evolution of CO gas, for both CO 3 and HCO 3 CO 3 + H + CO + H O NaHCO 3+ H + CO + H O + Na + # (Test for CO gas) b) sulphuric acid As HCl, eff. In addition the formation insoluble sulphate (with gp v metals) BaCO 3 +H SO 4 BaSO 4 + SO + H O wet reaction a with AgNO 3 A white precipitate of silver carbonate is immediately formed. CO 3 +Ag + Ag CO 3 The ppt. is soluble in mineral acids (nitric acid) and in ammonia. Ag CO 3 + H + Ag + + CO + H O Ag CO 3+4NH 3 [Ag (NH 3) ] + + CO 3 The precipitate becomes yellow or brown if the mixture is boiled. Ag CO 3 Ag Boiling O +CO b with BaCl, CaCl and MgSO 4: White precipitates of BaCO 3, CaCO 3 and MgCO 3 will be obtained with carbonate solution. BaCl + NaCO 3 BaCO 3 + NaCl Ca ++ + CO 3 CaCO 3 Mg ++ + CO 3 MgCO 3 The precipitate is soluble in mineral acids 1 No ppt. on cold since all HCO 3 are soluble in water. III. Mixture of CO 3, HCO 3 : Both anions haves similar reactions, but CO 3 form precipitates immediately on cold upon the addition of CaCl, BaCl or MgSO 4, while the bicarbonates of these metals are soluble.

2 اسرة فرسان صيدلة pharmaza اسرة فرسان صيدلة Separation: Add excess CaCl (BaCl or MgSO 4) to a solution of the mixture CO 3 /HCO 3 a white ppt. indicates CO 3, centrifuge or filter Ca (HCO 3) + NH 3 CaCO 3+ (NH 4) CO 3 # Test for CO 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 turbidity indicates the presence of carbonates or bicarbonates. CO CO + Ca(OH) + Ba (OH) CaCO + H O 3 BaCO 3 + H O With prolonged passage of CO, the turbidity formed due to the insoluble carbonates, slowly disappears as a result of the formation of soluble bicarbonate. CaCO 3 + CO + H O Ca (HCO 3) Boiling Sulphurcontaining anions This group of anions are; 1 Sulphide (S ) Sulphites (SO 3 ) 3 Thiosulphate (S O 3 ) 4 Sulphates (SO 4 ) 5 Perasulphate (S O 8 ).

3 اسرة فرسان صيدلة pharmaza اسرة فرسان صيدلة. Sulphurcontaining anions Sulphide (S ) Sulphites (SO3 ) Thiosulphate (SO3 ) Sulphates (SO4 ) Parent acid Hydrogren sulphide or Hydrosulphuric acid (H S) Gas with offensive rotten egg odour and poisonous. In solution it gives a weak acid, which ionizes in two steps; H S H + + HS Reducing agent: HS H + + S Sulphides, sulphites and thiosulphates are reducing agents. They reduce solutions of I, KMnO 4 and K Cr O 7 I +S I +S o lodine (brown) Colourless KMnO 4+ 5S + 16H + Mn SO 4 + 8H O +K + Sulphurous acid:(h SO 3) H O + SO H Heat SO 3 H HSO 3 H + SO3 I +SO 3 +H O SO 4 +I +H + MnO SO 3 + 6H + Mn SO 4 + 3H O Cr O 7 + 3SO 3 + 8H + Cr SO 4 +4H O Thiosulphuric acid: (H S O 3) Decomposes to give, H O, SO and S. I +S O 3 H+ S 4O 6 +I Tetrathionate Fe 3+ +S O 3 S 4O 6 +Fe + 8MnO S O H + 8Mn SO 4 +7H O 4Cr O 7 + 3S O 3 + 6H + 8 Cr 3+ +6SO H O Sulphuric acid: (H SO 4) (general properties #) 1 Dry Reactions a Action of dilute HCl H S gas; evolved has rotten egg odour, 1 blackening of filter paper moistened with lead acetate sol S + H + H S H S+Pb ++ PbS black SO gas evolved has bunt sulphur odor and turbid lime water due to the formation of the insoluble CaSO 3 Ca (OH) +SO CaSO 3 + H O SO has reducing character, bleaches the brown color of The solution becomes turbid due to the liberated yellow colloidal sulphur with evolution of SO gas. S O 3 + H + H S O 3 H O + SO + S o No reaction with dil. HCl 3

4 اسرة فرسان صيدلة pharmaza اسرة فرسان صيدلة Wet Reactions Reaction with BaCl : Reaction with AgNO 3 Reaction with FeCl 3 turns filter paper moistened with cadmium acetate solution, yellow H S + Cd ++ CdS Yellow It bleaches the brown color of l solution, changes the pink color of acid KMnO 4 into colorless and changes the orange color of acid K Cr O 7 into green. H S + l l + H + +S o 5H S + 6H + + MnO 4 Mn H O + 5S o 3H S + 8H + + Cr O 7 Cr H O + 3S o No visible reaction a black ppt. of Ag S soluble in hot dil. HNO 3, insoluble in ammonia an Ag + + S Ag S black a black ppt. of Fe S 3 is formed which is soluble in dil. HNO 3 Fe S Fe S 3 iodine, reacts with acid KMnO 4 and acid K Cr O 7. l + SO + H O SO 3 + H + + l MnO SO + 6H + Mn SO 3 + 3H O Cr O 7 +3 SO + 8H + Cr SO 3 + 4H O White ppt. of BaSO 3 is formed which is soluble in dil. HCl. Ba ++ +SO 3 =BaSO 3 A white crystalline ppt. of Ag SO 3, which on boiling with water undergoes self redox with the production of grey ppt. of metallic silver. Ag + + SO 3 Ag SO 3 Ag SO boil 3 Ag o + Ag SO 4 + SO A drak red color of ferric sulphite is produced on cold. Fe 3+ + SO 3 Fe (SO 3) 3 Complexing agent: Thiosulphate form complex with Fe 3+ Fe 3+ + S O 3 (Fe(S O 3) ) 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 Ag S. Ag + + S O 3 Ag S O 3 Ag S O 3+ H O Ag S + H SO 4 A purple color of complex disappears on boiling Fe 3+ + S O 3 (Fe(S O 3) ) S O 3 + Fe 3+ Fe ++ + S 4O 6 A white ppt. of BaSO 4 is formed which is insoluble in dil. HCl, even upon boiling. Ba ++ + SO 4 = BaSO4 White No ppt. in dil solution, but a ppt. may be formed in a very concentrated solution. do not react with FeCl 3 4

5 اسرة فرسان صيدلة pharmaza اسرة فرسان صيدلة Reaction with lead acetate: A black ppt. of PbS is produced Pb ++ + S PbS A with ppt. soluble in cold HNO 3. On boiling oxidation to PbSO 4. SO 3 + Pb ++ PbSO 3 A white ppt. is soluble in cold HNO 3, on boiling a black ppt. of PbS is formed. Pb ++ +S O 3 PbS O 3 A white ppt. lead suphate, which is insoluble in cold dil. mineral acids, but soluble in ammonium acetate and hydroxide solutions Special Tests Cadmium carbonate test S + CdCO 3 CdS + CO 3 Canary yellow ppt. Zinc nitroprusside test : Add ZnSO 4 + K 4[Fe (CN) 6] + 1% sodium nitroprusside solution. salmoncolored ppt. of zinc nitroprusside is formed Zn (Fe(CN) 5 NO). Formation of thiocyanate : By boiling with KCN + NaOH, Cool, acidify and add FeCI 3, a blood red color of ferric thiocyanate complex is produced. S O 3 + CN OH SCN + SO 3 Hepar s test Sulpate is reduced by carbon to sulphide MSO 4+ Na CO 3 Na SO 4+ MCO 3 Fusion Na SO 4+ C Na S + 4 CO Fe 3+ + SCN Cool Fe(SCN) + Transfer the fusion product to a silver coin and moisten with a little water, a brownish black stain of Ag S results. S + H O OH + H S H S + Ag Ag S +H 5

6 اسرة فرسان صيدلة pharmaza اسرة فرسان صيدلة # General properties of H SO 4 1 Acid properties; It is one of the strongest acids; ionize in dilute solutions in two steps, H SO 4 H + + HSO 4 (hydrogen sulphate HSO 4 H + + SO 4 (sulphate) Metals can liberate hydrogen from H SO 4 solution H SO 4+ Zn o ZnSO 4+ H 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. NaCl + H SO 4 Na SO 4+ HCl Dehydrating properties; Conc. H SO 4 has a great tendency to combine with water to from stable hydrates H SO 4.x H O. 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 H SO 4 H Heat O + SO + [O] It is reduced to SO, while with active reducing agents it may be reduced to S o or H S.. Mixture of H S and SO 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 S gas, SO can cause turbidity to lime water 6

7 اسرة فرسان صيدلة pharmaza اسرة فرسان صيدلة 3. Halides Fluoride (F ) Chloride (Cl ) Bromide (Br ) Iodide (I ) Therefore the order of stronger halogen acid is from HI HBr HCl HF. HCl Colorless gas with HBr Colorless gas with HI Colorless gas irritating odor, fumes in moist irritating odor, fumes in with irritating air, moist air odor, fumes strongly in moist air, Hydrochloric acid shows no reaction.this reaction can differentiate carbonate and sulphur group from halides. Parent Acids: HF:coloress fuming highly corrosive and itching liquid Dry Reactions a dilute HCl b conc. H SO 4 X + H SO 4 = HX + SO 4 X = may be CI, I, Br and F HF colorless fumes, the glass rod acquire oily appearance due to the formation of silicic acid and hydrofluorosilicic acid. F + H SO 4 H F + SO 4 4HF+SiO SiF 4+ H O 3 SiF 4+ 3H O H SiO 3+ H SiF 6 silicic acid & hydrofluoro silicic acid HCI gas is evolved CI +H SO 4 HCI + SO 4 identified by : Formation of white fumes of NH 4CI when a glass rod moistened with ammonium hydroxide NH 4OH + HCI NH 4CI + H O A mixture of HBr and Br have characteristic brown color Br + H SO 4 HBr + SO 4 HBr + H SO 4 Br + SO + H O I which appears as violet fumes. I can be detected by exposing the evolved gas to paper moistened with starch solution, it changes into blue. I + H SO 4 HI + SO 4 HI + H SO 4 I + SO + H O Conc.H SO 4 & MnO : X + 4H + + MnO Mn ++ + H O +X X = may be CI, Br and I The free halogen, (X ) could be detected by: 1 Bleaching of a moistened colored litmus paper. Suffocating, and irritating odor. 3 Characteristic color of Br (brown), I (violet) and CI gas 4 I changes starch paper into blue, Br turns it orange. 5 CI and Br change a starch KI into blue due to the oxidation of I to I produce a blue adsorption complex. CI + KI KCI + I Br + KI KBr + I 7

8 اسرة فرسان صيدلة pharmaza اسرة فرسان صيدلة Wet Reactions a Reaction with AgNO 3: b Reaction with BaCI solution: No precipitate The white gelatinous BaF ppt. is partially soluble in dil. HCI or HNO 3 Ba ++ + F BaF A white curdy ppt. insoluble in nitric acid, soluble in KCN and dil. ammonia solution to give the ammine complex. AgCI + NH 3 [Ag(NH 3) ]CI Silver ammine chloride A curdy, pale yellow precipitate, sparingly soluble in dilute, but readily soluble in conc. ammonia solution AgBr + NH 3 [Ag(NH 3) ] + + Br No ppt. is formed A curdy yellow ppt. insoluble in dil. ammonia but very slightly soluble in conc. ammonia solution. Ag + + I AgI c Reaction with FeCI 3: Reaction with lead acetate a white crystalline ppt. CI and Br : do not react with FeCI 3 of the complex salt, which is sparingly soluble in water Fe F [FeF 6] 3 F, Cl and Br form a white ppt with lead acetate, sparingly soluble in cold more soluble in hot water, crystallize on cooling Chlorine water test Chloride and Fluoride do not react with chlorine water Br + CI Br + CI Br + CI BrCI (yellow) Br + CI (excess) + H O HOBr+HCI Colorless Reacts with FeCI 3, due to its strong reducing action with the liberation of I. forms a bright yellow ppt of PbI which is soluble in hot water and crystallizes on cooling as golden spangles I + CI I + CI I + 5CI (excess) + 6H O HIO 3+10HCI 8

9 اسرة فرسان صيدلة pharmaza اسرة فرسان صيدلة Special Tests Boron fluoride test: fluoride + borax and conc. H SO 4. boronfluoride gas. Na B 4O 7 + H SO 4+ 5H O 4H 3BO 3 +Na SO 4 NaF + H SO 4 HF + Na SO 4 H 3BO 3+3HF BF 3+ 3H O Chromyl chloride test #: The solid chloride + powder potassium dichromate in a tube, + conc. sulphuric acid. The deep red vapors of chromyl chloride CrO CI are passed into sodium hydroxide solution. Yellow color; 4CI + Cr O 7 + 6H + cond. CrO Cl + 3H O CrO CI + 4OH CrO 4 + CI + H O I A) readily oxidized in acid solution (dil. H SO 4) with nitrite solution or H O into free l I + NO + 4H + I + NO + H O I +H O + H + I + H O B) reacts with Cu ++ forming a whit ppt. of Cu I, Cu ++ +4I Cu I +I # N.B.(for Chromyl chloride test) 1 Some CI may also be liberated owing to the reacting. 6CI + Cr O H+ 3CI + Cr H O and this decreases the sensitivity of the test. Fluorides give rise to the volatile CrO F 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 + Cr O H + Cr Br + 7H O 6 I + Cr O H+ Cr I + 7H O Br + OH OBr + Br + H O (hypobromide) I + OH OI + I + H O (hypoiodide) 9

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11 اسرة فرسان صيدلة Pharmaza 4. Cyanogen anions 1Parent Acids: Cyanide (CN ) Thiocyanate (SCN ) Ferrocyanide [Fe(CN)6] 4 Hydrocyanic acid :HCN has an odor of bitter almonds. On passing CO to CN solution HCN is produced with HCO 3 CN + CO + H O HCN + HCO 3 Thiocyanic acid: HSCN colorless toxic liquid On standing its aqueous solution is decomposed to HCN and yellow solid polymer. 3 HCNS HCN + H N C S 3 H 4[FeCN) 6] white crystalline solid. Ferricyanide [Fe(CN)6] 3 H 3 [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) ) Complex cyanides: Stable metallocyanogen complexes can be formed by reacting FeSO 4 with CN in alkaline medium to give stable ferrocyanide complex. Similar complex is formed with Fe 3+ to give ferricyanide. Fe CN [Fe(CN) 6] 4 and Fe CN [Fe(CN) 6] 3 When cyanides are heated with polysulphides (NH 4) S x or thiosulphate (S O 3 ) they give thiocyanate ion CN + (NH 4) S x (NH 4) S x1+ SCN CN + S O 3 SO 3 + SCN 4Oxidizing agent: Ferricyanides has oxidizing effect, they can oxidizes I into I 11

12 اسرة فرسان صيدلة Pharmaza 5Reducing agent: Ferrocyanides has mild reducing effect, they can be oxidized to ferricyanide by oxidizing agents, such as MnO 4, NO 3, H O and Cl. 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 FeCI 3 solution, a blood red color is produced. By passing the evolved gas into AgNO 3 solution, a white ppt. of AgCN is formed insoluble in dil. HNO 3, soluble in ammonia solution. HCN + AgNO 3 AgCN + HNO 3 AgCN + NH 3 (Ag(NH 3) )CN 3Prussian blue test: The evolved HCN gas is passed into NaOH solution, add drops of FeSO 4 solution, heat to boiling, the HCN is converted into ferrocyanide which can be tested by adding drops of FeCl 3 solution to produce a Prussian blue ppt. conc. H SO 4: decomposed on heating CN +H + + H O + NH 4 +CO SCN + 4H + + SO 4 + H O NH HSO 4 + COS Carbonyl Sulphide No reaction as SCN is 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 + H 4(Fe(CN) 6) (Fe(CN) 6) 3 + 3H + H 3(Fe(CN) 6) On heating, CO will be evolve which burns with a blue flame. SO is produced in case of ferrocyanide. (Fe(CN) 6) 4 + 6H O +H SO 4 Fe + +6NH HSO CO Fe + + 4H + + SO 4 SO + H O + Fe 3+ (Fe(CN) 6) 3 + 6H O + H SO 4 Fe NH HSO 4 + 6CO Wet Reactions a Silver nitrate solution: CN & SCN : form white ppts. AgCN is soluble in excess CN, ammonia solution, but insoluble in dil. HNO 3 Ag + + SCN AgSCN Ag + + CN AgCN CN (Ag(CN) ) 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 Ag 4[Fe(CN) 6] Insoluble in dil. Ammonia and dil. HNO 3 3 Ag + + [Fe(CN) 6] 3 Ag 3[Fe(CN) 6] Orange red ppt. Insoluble in dil. HNO 3 and Soluble in dil. Ammonia 1

13 اسرة فرسان صيدلة Pharmaza reaction FeCI 3: with iron (III) cyanide dissolved in excess cyanide forming ferricyanide. Fe CN Fe (CN) 3 3CN [Fe(CN) 6] 3. Ferricyanide blood red color Fe 3+ + 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 + 4Fe 3+ Fe 4[Fe(CN) 6] Prussian blue brown color is formed Fe 3+ + [Fe(CN) 6] 3 Fe[Fe(CN) 6] Brown color This test used to differentiate between ferro and ferricyanide d) Reaction with FeSO 4 reagent: Reaction CuSO 4 with Reaction with Cobalt Nitrate: yellow brown ppt. at first which is then form ferrocyanide, CN + Fe + Fe(CN) 4CN [Fe(CN) 6] 4 form soluble complex cuprocyanide and cyanogen in acid medium Cu CN [Cu (CN) 3] + (CN) In alkaline medium cyanogen is converted to CN & cyanate CNO. (CN) + OH CN + CNO + H O Co + + CN + H O Co (CN). H O 4CN [Co (CN) 6] 4 soluble complex. No reaction. [Fe(CN) 6] 3+ +Fe + Fe 3+ + [Fe(CN) 6] 4 Turanbull's blue Vogel's Reaction characteristic blue color extractable with ether or amyl alcohol Co + + 4SCN [Co (SCN) 4] Extractable with ether (blue) Prussian blue Ferrocyanide forms white ppt. K + +Fe ++ + [Fe(CN) 6] 4 K Fe[Fe(CN) 6] Cu ++ + SCN Cu (SCN) green unstable Cu (SCN) Cu (SCN) + (SCN) decomposition white gummy mass [Fe(CN) 6] 4 + Cu ++ Cu [Fe(CN) 6] Brown [Fe(CN) 6] 3 + 3Cu ++ Cu 3[Fe(CN) 6] green Special Tests Prussian blue test Vogel's Reaction As mild reducing agents [Fe(CN) 6] 4 + CI [Fe(CN) 6] 3 + CI Co + + [Fe(CN) 6] 4 Co [Fe(CN) 6] greyish green 3 Co + + [Fe(CN) 6] 3 Co 3[Fe(CN) 6] red ppt. As oxidizing agents [Fe(CN) 6] 3 + I [Fe(CN) 6] 4 +I 13

14 اسرة فرسان صيدلة Pharmaza IV. Analysis of Mixtures 1 Mixture of CN, SCN, [Fe(CN) 6] 4 & [Fe (CN) 6] 3 a Passing CO in the mixture solution using acetic acid or NaHCO 3 and heat, until no more HCN evolved. To the remaining solution, after removal of CN, acidify with dil. HCI, cool and add FeCI 3 solution and centrifuge Mixture of SCN, CI, Br and I SCN is tested for by reacting with FeCI 3, to give blood red color which is extractable with ether and removed. In presence of I, I is also formed which can be extracted with CHCI 3 (Violet color). The blue complex formed with Co + 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 I and Br, carry out chlorine water test. 14

15 اسرة فرسان صيدلة Pharmaza 5. Arsinic and phosphorous containing anions Arsenate (AsO4 3 ) Arsenite (AsO3 3 ) Phosphate (PO4 3 ) 1 Parent Acids: Orthoarsenic acid :H 3AsO 4 Arseneous acid :H 3AsO 3 Orthophosphoric acid :H 3PO 4 1 Dry Reactions no visible reaction a dilute HCl On hot arsenate ion oxidises HCI into free CI, while it will be reduced to arsenite CI + AsO H + CI +AsO + H O Arsenite will react and vapour of arsenious chloride is evolved AsO + 3CI + 4H + AsCI 3 + H O Redoxreaction with I /I : Aresnate has oxidizing effect and aresnite has reducing effect Arsenate (AsO 4 3 ) ions oxidises iodide into iodine; but the redox reaction is reversible due to the narrow difference in E o values of the two redox systems. Wet Reactions a Silver nitrate solution: All the precipitates are soluble in ammonia solution, due to the formation of the complex ion [Ag (NH 3) ] +, Reaction with Magensia Mixture: reagent is formed of MgCI, NH 4CI and NH 4OH 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. PO 3 4 +Mg NH 4 Mg (NH 4) PO 4 [magnesium ammonium phosphate] AsO Mg NH 4 Mg(NH 4)AsO 4 [magnesium ammonium arsenate] 15

16 اسرة فرسان صيدلة Pharmaza Reaction ammonium molybdate with reagent + conc. HNO 3 + test solution heat gradually, = a canary yellow crystalline precipitates of ammonium phosphomolybdate (NH 4) 3PO 4. 1MoO 3 (on warming to 40 o C) and of ammonium arsnomolybdate (NH 4) 3 AsO 4. 1MoO 3 (on boiling) in case of phosphates and arsenates respectively. No precipitate is formed with arsenites. Reaction with H S yellow ppt. of arsenious sulphide As S 3. The ppt. is soluble in HNO 3 and alkali hydroxides insoluble in hot conc. HCI. H AsO 4 + 5H S +H + As S 5 +8H O not immediate, but after prolonged passage of H S, yellow ppt. of AS S 3 is produced. No precipitate Reaction with CuSO 4 solution: green ppt. of the cupric arsenate, or CuHAO 4, The ppt. is soluble in mineral acids and in ammonia. yellowish green ppt. of copper arsenite CuHAsO 3 The ppt. is soluble in excess NaOH to give deep blue color of CuO.HAsO. On boiling red ppt. is formed due to the reduction of CuO into cuprous oxide (Cu O), the arsenious acid is simultaneously partiallyoxidised to arsenic acid. Cu + + AsO + OH CuHAsO 3 = [CuO.HAsO ] [CuO.HAsO ] + H O Cu O + H 3AsO 4 + HAsO Bluish ppt of CuHPO 4, The ppt. is soluble in mineral acids and in ammonia. g) Uranyl acetate solution: Light yellow, gelatinous precipitate of uranyl ammonium phosphate Uo (NH 4) PO 4 or arsenate UO (NH 4) AsO 4 in case of phosphates and arsenates repectively, in the presence of excess ammonium acetate. The precipitate is soluble in 16

17 اسرة فرسان صيدلة Pharmaza 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. PO UO + + NH + 4 UO (NH 4)PO 4 AsO UO + + NH 4 + UO (NH 4) AsO 4 Special Tests Potassium iodide test 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 Sn + + 8H + + AsO (heat) As +3Sn H O b) Iodine test: NaHCO 3 solution + sample solution.+ few drops of I solution. The brown color of I disappears immediately due to the reducing effect of arsenite. this test can be used to distinguish arsenite from arsenate or phosphate. Magnesium test: It depends on reduction of the stable phosphates into phosphide (P 3 ), PO 3+ (heat) 4 + 4Mg 4MgO + P 3 P 3 + 3H O PH 3 + 3OH 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 (H 3As) with garlic like odor which when heated dissociates to elementary arsenic and hydrogen: 17

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19 اسرة فرسان صيدلة Pharmaza 6. Nitrogen containing anions Nitrate (NO 3 ) Nitrite (NO ) Parent Acids Nitric acid :HNO 3 decomposes (NO ). 4HNO 3 4NO + O +H O Dry Reactions No reaction a Action of dilute HCl Action of conc. H SO 4 Nitric acid is formed and some of it decomposed with evolution of brown fumes of NO. NO 3 + H + HNO 3 4HNO 3 4NO + O + H O Wet Reactions with Ag SO 4 solution Nitrous acid :HNO HNO NO + NO + H O NO + H + HNO NO + NO +H O NO + O NO As in dil HCl No ppt. White crystalline ppt. of AgNO. NO + Ag + AgNO with KI solution: No reaction I is liberated give blue color to the starch. NO + I + 4H + NO + I + H O with Fe SO 4 solution. (Brown Ring Test):Acidify the test solution (5ml) with dil. H SO 4, add (1ml) freshly prepared FeSO 4 solution. This test differentiates NO 3 ion from NO ion, since the latter gives the brown ring in presence of dil. H SO 4 or even acetic acid, while NO 3 ion dose not form the ring except in presence of conc. H SO 4. (NO, I and Br ions will interfere) 3Fe + + NO 3 + 4H + 3Fe 3+ + NO + H O Fe + + NO + H + Fe 3+ + NO + H O Fe + + NO [Fe (NO)] + Ammonia test If solution of NO 3 is boiled with Zn o or Al o metals and NaOH solution, NH 3 will be evolved which can identified by its odor or with red litmus paper (nitrites interfere). 1 Permanganate test: permanganate is reduced by the nitrite into colorless manganous salt and the nitrite is oxidized into nitrate. MnO 4 + 5NO + 6H + Mn + + 5NO 3 + 3H O Pink colorless Urea test: CO (NH ) + HNO N + CO +3H O 19

20 اسرة فرسان صيدلة Pharmaza 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, KMnO 4, FeSO 4 in dil. H SO 4); 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. H SO 4, brownring test and ammonia test). Therefore nitrite be removed before testing for nitrate by: 1 Decomposition of NO through its brown complex with FeSO 4 formed in dil. H SO 4 or acetic acid by heat and shaking. [Fe (NO)] + heat NO + Fe + Decomposition of NO through its reduction to nitrogen by boiling with NH 4CI or warming with urea and few drops of dilute H SO 4 or warming with little sulphamic acid. HO.SO. NH + HNO N + H SO 4+ H O 0