PC-101-Lecture 5 Anions Part 2 Halides and Cyanogen Anions 2024 PDF

Anions-Part II Halides + Cyanogen anions Dr. Hatem Mokhtar Lecturer of Analytical Chemistry Faculty of Pharmacy sinaiuniversity.net  Halides F-, Cl-, Br-, I- @Sinaiunieg [email protected] DENTISTRY/ second year/ SU/ lect 6 www.su.ed...

Anions-Part II Halides + Cyanogen anions Dr. Hatem Mokhtar Lecturer of Analytical Chemistry Faculty of Pharmacy sinaiuniversity.net  Halides F-, Cl-, Br-, I- @Sinaiunieg [email protected] DENTISTRY/ second year/ SU/ lect 6 www.su.edu.eg Halides F-, Cl-, Br-, I- F-, Cl-, Br-, I- known as halogens. They are characterized by their higher electronegativity i.e: their tendency for gaining electrons is very great, when these anions gain one electron, each one attains the inert gas structure (octet rule). They have similar properties and characters, all are monovalent anions and they are similar in chemical reaction except fluoride. Regarding the electronegativity , it increase according to the following: Electronegativity: @Sinaiunieg [email protected] www.su.edu.eg Halides As the ionic size increase, the tendency to lose electrons increases and therefore iodide is firstly and easily oxidized (lose electron) into free I2 by loosing an electron followed by Br- when present in a mixture. @Sinaiunieg [email protected] www.su.edu.eg Halides However it is difficult to oxidize F- into F2 ( there is no chemical oxidant which is powerful enough to oxidize F- ions to F2). F- ions are highly stable to hold strongly a proton that is why HF is the weakest halogen acid, while HI is the strongest hydrohalogen acid in this series. (strongest acid)HI > HBr > HCl > HF (weakest acid) @Sinaiunieg [email protected] www.su.edu.eg Scheme I-Dry reactions – 1- Dil. HCl – 2- Conc. H2SO4 II-Wet Reactions – 1-Silver Nitrate (AgNO3) – 2- Barium Chloride(BaCl2) – 3- Ferric Chloride (FeCl3) – 4- Chlorine water test III- Specific tests (Chromyl chloride for Chloride) @Sinaiunieg [email protected] www.su.edu.eg Dry reactions I- Action of dil HCl HCl shows no reaction upon treatment of the solid sample with it , even on heating. This reaction can differentiate carbonate and Sulfur containing anions from halides. @Sinaiunieg [email protected] www.su.edu.eg Dry Reactions II- Action of Concentrated (Conc.) H2SO4 Decomposition of the halides occurs upon the addition of conc H2SO4 to specks of the solid sample. 2 X - + H SO 2 H X + SO -- 24 4 -- - - X = ma yb eC l, I , Br, F This occurs in the cold, completely on warming with evolution of HX which can be detected by: 1. The fumes evolved. 2. Confirmatory chemical test. @Sinaiunieg [email protected] www.su.edu.eg Dry Reactions II- Action of Concentrated (Conc.) H2SO4 1- For fluoride: Fluoride gives a characteristic reaction when treated with conc H2SO4 , hydrofluoric acid (HF) is produced, which is colorless and fumes with moist air. Due to the corrosive action of the gas on the glass in presence of water, the HF gas can be detected by exposing the gas to glass rod with a drop of water at its tip in the evolving gas, the glass acquire oily appearance due to formation of silicic acid and hydrofluoric acid. ( Silicon dioxide of the glass will react with HF producing, silicon tetrafluoride which in contact with water is hydrolyzed with the formation of gelatinous silicic acid and hexafluorosilicic acid) @Sinaiunieg [email protected] www.su.edu.eg Dry Reactions II- Action of Concentrated (Conc.) H2SO4 1- For fluoride: - -- 2 F + H 2S O 4 2 H F + S O 4 4 H F + S iO 2 S iF 4 + 2 H 2O g la s s S ilic o n te tr a flu o r id e 3 S iF + 3 H 2O H 2S iO 3 + 2 H 2S iF 6 4 s ilic ic a c id Hexafluorosilicic h y d r o f l u o r o s i l i c iacid c a c id This test can be considered as specific test for fluoride anion, even in the presence of other halides. @Sinaiunieg [email protected] www.su.edu.eg Dry Reactions II- Action of Concentrated (Conc.) H2SO4 2- For chloride: HCl gas ( which is colorless) is evolved upon treatment with conc H2SO4. - - - 2 C l + H 2S O 42H C l + S O4 HCl gas can be identified by: 1- It form white fumes with moist air due to the formation of droplet of HCl. 2- It’s pungent irritating odor. 3- Changing a blue moistened litmus paper into red. 4- Formation of white fumes of NH4Cl when a glass rod moistened with NH4OH is exposed to the evolved gas. N H O H + H 4l N C H C l + H 4 2O @Sinaiunieg [email protected] www.su.edu.eg Dry Reactions II- Action of Concentrated (Conc.) H2SO4 2- For chloride: Ammonium Fumes with air chloride fumes @Sinaiunieg [email protected] www.su.edu.eg Dry Reactions II- Action of Concentrated (Conc.) H2SO4 For bromide and iodide: HBr and HI are more active reducing agents than HCl. When they are formed by the action of conc H2SO4 , they are readily oxidized by Sulfuric acid to free Br2 and I2, respectively. Sulfuric acid is in this reaction reduced to different products ( SO2, H2S or S) according to the degree of reduction. @Sinaiunieg [email protected] www.su.edu.eg Dry Reactions II- Action of Concentrated (Conc.) H2SO4 3- For bromide: A mixture of HBr and Br2 may be formed which have characteristics brown color especially on warming. The same will be occur with iodide. - - - 2 B r+ H 2S O 4 2 H B r+ S O4 - -+ B r + SO +2 H OBromine upon sulfuric 2 H B r+ S O+ 2H 4 222 addition @Sinaiunieg [email protected] www.su.edu.eg Dry Reactions II- Action of Concentrated (Conc.) H2SO4 4- For iodide: Fumes with sulfuric Since HI is the most active reducing agent, so it is readily oxidized to iodine which appear as violet fumes. - -- 2 I + H 2S O 4 2 H I + SO 4 2 H I + H 2S O 4 I2 + S O 2 + 2 H 2O 6 H I + H 2S O 4 3 I2 + S + 4 H 2O Starch paper test 8 H I + H 2S O 4 4 I2 + H 2S + 4 H 2O I2 can be detected by exposing the evolved gas to paper moistened with starch solution, changes its color into blue. @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 1-Reaction with AgNO3 To 1 ml of the salt solution, add silver nitrate reagent; Fluoride – No PPT , since AgF is soluble in water @Sinaiunieg [email protected] www.su.edu.eg Wet Rreactions 1-Reaction with AgNO3 All other silver halides PPTs are insoluble in dil HNO3. They are soluble in KCN and Na2S2O3 due to the formation of soluble complex. - [Ag(CN) ] - +X - A gX + 2 C N 2 a r g e n to c y a n id e c o m p le x [s o lu b le c o m p le x ] -- 3- - A gX + 2 S 2O 3 [Ag(S O ) 2 3 2 ] +X a r g e n to th io s u lfa te c o m p le x [s o lu b le c o m p le x ] @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 1-Reaction with AgNO3 Chloride A white PPT of AgCl which is: Insoluble in nitric acid Soluble in KCN Soluble in Na2S2O3 As other silver halides. AgCl PPT @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 1-Reaction with AgNO3 Chloride The PPT AgCl is soluble in dil ammonia solution to give the Silver amine complex which decomposes by addition of dil. acid with re- precipitates AgCl. A g + C l- AgCl A gC l + 2 N H [Ag(NH 3 ) 2 ]Cl 3 s ilv e r a m in e c o m p le x + [Ag(NH )]Cl + 2 + 2 HN H4+A gC l 32 @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 1-Reaction with AgNO3 Bromide Pale yellow PPT of AgBr, sparingly soluble in dil but readily soluble in conc ammonia. + - A g B r AgBr A gB r + 2 N H [Ag(NH 3)2 ]Br 3 s ilv e r a m in e c o m p le x AgBr PPT @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 1-Reaction with AgNO3 Iodide yellow PPT of AgI, insoluble in dil very slightly soluble in conc ammonia. + - A g I AgI AgI PPT @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 1-Reaction with AgNO3 There is a periodicity in character of the 3 silver halides: 1- color: AgCl is white, AgBr is pale yellow, AgI is yellow. 2- solubility in water: AgCl is most soluble AgBr is less soluble. AgI is least soluble. They can replace each other in the order: AgCl + Br - (or I -) AgBr or AgI AgBr + I AgI + Br - more insoluble lower solubility product @Sinaiunieg [email protected] www.su.edu.eg Wet Rreactions 1-Reaction with AgNO3 3- PPT solubility in dil ammonia AgCl AgBr AgI Dil Ammonia Soluble Slightly soluble insoluble Conc. Ammonia Soluble Soluble Very slightly soluble @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 1-Reaction with AgNO3 3- PPT solubility in dil ammonia Silver amine complex is formed upon addition of ammonia to silver containing solutions according to the following reaction. + + [Ag(NH ) 3 2] A g+ 2N H3 + 2 ( Ag)( NH) 3 I ns t abi l it yco n st an t= + [Ag(NH ) 3 2] the formed complex is stable and therefore, the concentration of free Ag+ in the solution becomes very low. @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 1-Reaction with AgNO3 3- PPT solubility in dil ammonia The concentration of silver ion (Ag+) produced from the dissociation of silver amine complex is lower than the high solubility product Ksp of AgCl. Therefore AgCl could not be precipitated in presence of ammonia as the ion product of Ag+ and Cl- remains below AgCl Ksp On the other hand, The concentration of silver ion (Ag+) produced from the dissociation of silver amine complex is higher than the low solubility product Ksp of AgI. Therefore AgI PPT is formed in presence of ammonia as the ion product of Ag+ and I- Exceeds AgI Ksp. @Sinaiunieg [email protected] www.su.edu.eg Wet reactions 2-Reaction with Barium Chloride when 1 ml of the reagent BaCl2 is added to 1 ml of the sample. Fluoride A white gelatinous PPT of BaF2 which is partially soluble in dil HCl or HNO3, and insoluble in acetic acid. + +- B a + 2F BaF 2 Chloride, bromide, iodide: No reaction @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 3- Reaction with FeCl3 solution Add few drops of FeCl3 reagent is added to concentrated sample solution. Fluoride A white crystalline PPT of complex salt which is sparingly soluble in water. 3 + -3 [F F e + 6 F] 6 @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 3- Reaction with FeCl3 solution Chloride, bromide – Do not react with FeCl3. Iodide Due to the reducing action of I -, iodide react with FeCl3 with liberation of iodine (on warming). 3 + -2+ 2 F e + 2 I2 I 2+ @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 4- Chlorine water test Acidify 3 ml of the sample solution with dil H2SO4 – Add 1 ml of chloroform or carbon tetrachloride. – Add successive drops of chlorine water drop wise, shake after each addition. Fluoride, Chloride – No reaction. @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 4- Chlorine water test Bromide, Iodide Chlorine water oxidizes Br -, I- into Br2 or I2 ,respectively, which are extracted with chloroform or carbon tetrachloride which will be colored yellow to reddish brown with Br2 and violet with I2. 𝑪𝒍𝟐 + 𝟐𝑩𝒓− → 𝟐𝑪𝒍− + 𝑩𝒓𝟐 Chlorine water test using hexane as 𝑪𝒍𝟐 + 𝟐𝑰− → 𝟐𝑪𝒍− + 𝑰𝟐 organic layer (Upper) @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 4- Chlorine water test 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. So add chlorine water drop wise. @Sinaiunieg [email protected] www.su.edu.eg Wet Reactions 4- Chlorine water test with excess chlorine water: I2 is also oxidized to colorless iodic acid. I + 25 C l 2( e x ce s s )+ 6 H O 2 2 H IO + 31 0H Cl ( i o di c ac i dc o l o rl e s s) if Br- and I- are together, chlorine water first displace I2 which give violet color to chloroform, adding more chlorine water the color disappears(HIO3 is colorless). Further addition of Cl2 water give brown color of Br2. Chloride and fluoride do not interfere with chlorine water test. @Sinaiunieg [email protected] www.su.edu.eg Specific test for Chloride (Dry reaction) 4- Chromyl chloride test It is specific test for chloride even in the presence of other halides. It is classified as one of the dry reaction because it is carried out on the solid sample. The solid chloride is mixed with 3 times its weight of powdered K2Cr2O7 in a tube. An equal volume of conc H2SO4 is added. The tube is attached to another tube by a delivery tube, dipped into NaOH solution, then heat gently. @Sinaiunieg [email protected] www.su.edu.eg Specific test for Chloride (Dry reaction) 4- Chromyl chloride test The deep red vapors of chromyl chloride CrO2Cl2 are evolved (in the presence of chloride), then pass this vapors into NaOH solution in another test tube. The NaOH solution turns yellow and give a positive test for chromate. Chromyl chloride is produced by condensation of HCl with H2Cr2O7. Thus the positive test for chromate in yellow sodium hydroxide indicate the presence of chloride in the solid sample. @Sinaiunieg [email protected] www.su.edu.eg Chromyl Chloride test Test for chromate by: 1-Perchromic acid test: It is carried out by acidifying a portion of the solution containing chromates with dil H2SO4, adding 2 ml amyl alcohol (or ether) followed a little H2O2 solution and shake a blue color in the organic layer of perchromic acid -- + indicates chromate. 2 C r O 4 + 2 H C r 2 O 7 -- + H 2 O -- 3- + C r2O 7 + 7 H 2O 2 2 C rO 8 + 5 H 2O + 4 H b lu e in o r g a n ic la y e r @Sinaiunieg [email protected] www.su.edu.eg Chromyl Chloride test Test for chromate by: 2-Test by lead acetate Acidify a portion with acetic acid and treat with lead acetate solution, yellow PPT of lead chromate will be formed. - -+ + C r O + 2 4P bPb 4 Y e l l o w PP T @Sinaiunieg [email protected] www.su.edu.eg Chromyl Chloride test-interferences Bromide and iodide do not behave similar to chloride, as they are strong reducing agents, oxidation rather condensation occurs to give free halogen (HBr and HI being very actively oxidizable to reddish Br2and violet I2). Fluorides give rise to the volatile CrO2F2 which decomposes by water. If the ratio of iodide to chloride exceeds 1:15, the chromyl chloride formation is largely prevented and Cl2 is evolved. Nitrites and nitrates interfere, as nitrosyl chloride may be formed. @Sinaiunieg [email protected] www.su.edu.eg Analysis of mixture 1- mixture of F-, Cl-, Br-, I- A- The F- is separated firstly by treating the mixture solution which is acidified with acetic acid by addition of Ba(NO3)2 or Ca(NO3)2 c e n tr ifu g e w h ite P P T o f B a F 2 C e n tr ifu g a te c o n fir m e d b y c o n c H 2S O 4 C l-, B r -,I - B- For the centrifugate: carry out chlorine water test for both I- and Br -. C- For Cl-: carry out chromylchloride test on a solid sample [ but in the presence of large amount of I- and Br -, they may exhaust the dichromate used in chromylchloride test in that case]. So, one must use larger amount of dichromate. @Sinaiunieg [email protected] www.su.edu.eg  Cyanogen Anions Cyanide containing anions @Sinaiunieg [email protected] DENTISTRY/ second year/ SU/ lect 6 www.su.edu.eg Cyanogen Anions Cyanide (CN-) Thiocyanate (SCN-) Ferrocyanide ([Fe(CN)6]-4] Ferricyanide ([Fe(CN)6]-3]. @Sinaiunieg [email protected] www.su.edu.eg Cyanogen Anions ▪ All Cyanide containing anions are highly toxic. ▪ In all experiments in which the gas is evolved (such as when cyanide are heated), should be carried out cautiously in the fume cupboard). ▪ Cyanide ion has strong tendency to the formation of complexes which may be: 1- Double cyanide. e.g. argentocyanide complex (Ag(CN)2)- 2- Complex cyanide. ferrocyanide ([Fe(CN)6]-4], ferricyanide ([Fe(CN)6]-3]. @Sinaiunieg [email protected] www.su.edu.eg Cyanogen anions-Scheme I-Dry reactions – Dil HCl – Conc. H2SO4 II- Wet reactions – Silver Nitrate; AgNO3 – Barium Chloride; BaCl2 – Ferric Chloride; FeCl3 – Ferrous sulfate, FeSO4 – Cobalt Nitrate, Co(NO3)2 III- Specific tests: NA @Sinaiunieg [email protected] www.su.edu.eg Dry reactions 1- Action of dil HCl The solid is treated dil HCl (do not try to smell the evolved gases). 1- For Cyanide: HCN gas is evolved with bitter almond odor. - + HCN CN + H @Sinaiunieg [email protected] www.su.edu.eg Dry reactions: I-Dilute HCl addition HCN gas can be identified by: a- Converting the evolved HCN gas to SCN- by exposing the evolved HCN gas to a paper moistened with ammonium polysulphide. HCN + (NH4)2SX (NH4)2SX-1 + HCNS The resulted SCN- can be tested by adding a drop of FeCl3 solution acidified with dil HCl to prevent the formation of Fe2S3, a blood red color is produced. 𝑭𝒆𝟑+ + 𝑺𝑪𝑵− → [𝑭𝒆 𝑺𝑪𝑵 ]𝟐+ @Sinaiunieg [email protected] www.su.edu.eg Dry reactions: I-Dilute HCl addition b- By passing the evolved gas through AgNO3 solution, a white PPT of AgCN is formed which is insoluble in dil HNO3 but soluble in ammonia solution. 𝑯𝑪𝑵 + 𝑨𝒈𝑵𝑶𝟑 → 𝑨𝒈𝑪𝑵 ↓ +𝑯𝑵𝑶𝟑 𝑨𝒈𝑪𝑵 + 𝟐 𝑵𝑯𝟑 → 𝑨𝒈 𝑵𝑯𝟑 𝟐 𝑪𝑵 @Sinaiunieg [email protected] www.su.edu.eg Dry reactions: I-Dilute HCl addition 2- For SCN-:No reaction. 3- For ferrocyanide [Fe(CN)6]-4 and ferricyanide [Fe(CN)6]3-: With cold dil HCl , no gases, but a precipitation may occur of hydroferrocyanic acid and hydroferricyanic acid respectively. [Fe(CN)6]-4 + 4 H+ H4[Fe(CN)6] -3 + H3[Fe(CN)6] [Fe(CN)6] + 3 H @Sinaiunieg [email protected] www.su.edu.eg Dry reactions 2- Action of Conc H2SO4 1-For Cyanide: All cyanides are decomposed on heating with conc. (N gives ammonium bisulfite, C is transformed to carbon monoxide and the metal (M) is transformed to its sulfate. 𝑴(𝑪𝑵)𝟐 + 𝟑 𝑯𝟐 𝑺𝑶𝟒 + 𝟐𝑯𝟐 𝑶 → 𝑴𝑺𝑶𝟒 + 𝟐 𝑵𝑯𝟒 𝑯𝑺𝑶𝟑 + 𝟐𝑪𝑶 ↑ @Sinaiunieg [email protected] www.su.edu.eg Dry reactions 2- Action of Conc H2SO4 2-For CNS-: Decomposes with the evolution of carbonyl sulfide COS which burns with a blue flame. - + 2- CNS + 4 H + 2 SO4 + H2O NH4+ + 2HSO4- + COS @Sinaiunieg [email protected] www.su.edu.eg Dry reactions 2- Action of Conc H2SO4 3- For ferrocyanide [Fe(CN)6]-4 and ferricyanide [Fe(CN)6]3-: Both ions are decomposed with the evolution of carbon monoxide CO which burns with a blue flame. Fe2+ ion is produced in case of ferrocyanide which is further oxidized by H2SO4 and some SO2 gas was produced. 2+ + - 2 [Fe(CN)6]-4 + 6 H2O+ 22 H+ + 10 SO42- Fe + 6 NH4 + 10 HSO 4 + 6 CO 2 Fe2+ + 4 H+ + SO42- SO2 + 2 H2O + 2 Fe3+ -3 + [Fe(CN)6] + 6 H2O+ 22 H + 10 SO42- Fe3+ + 6 NH4+ + 10 HSO 4- + 6 CO @Sinaiunieg [email protected] www.su.edu.eg Wet reactions 1- Reaction with AgNO3 To 1 ml of the salt solution, add silver nitrate reagent; CN- and CNS- ▪Form white PPT of silver cyanide AgCN and silver thiocyanate AgSCN. ▪These PPT are soluble in excess cyanide, ammonia solution, but insoluble in dil HNO3. ▪Excess CN- dissolve AgCN due to the formation of argentocyanide complex, AgCN is precipitated again, if excess Ag+ is added to the complex. + CN - Ag Ag+ + CN - AgCN [Ag(CN)2]- 2 AgCN argentocyanide complex @Sinaiunieg [email protected] www.su.edu.eg Wet reactions 1- Reaction with AgNO3 Ferrocyanide and Ferricyanide ▪Both [Fe(CN)6]-4 and [Fe(CN)6]3- react with AgNO3 solution, white PPT and orange PPT, respectively. ▪PPT of Ag ferrocyanide is insoluble in both dil. Ammonia and dil. Nitric acid 4 Ag+ + [Fe(CN)6]-4 Ag 4[Fe(CN)6] Ferro white PPT insoluble in dil NH3 and dil HNO3 3 Ag+ + [Fe(CN)6]-3 Ag 3[Fe(CN)6] Ferri Orange PPT soluble in dil NH3 and insoluble dil HNO3 @Sinaiunieg [email protected] www.su.edu.eg Wet reactions 1- Reaction with AgNO3 Ferrocyanide and Ferricyanide ▪The solubility of silver ferricyanide PPT in dil. ammonia solution can be used for the separation of ferrocyanide and ferricyanide when present in a mixture. ▪Oxidation of the white PPT Ag4 [Fe(CN)6] by warming with few drops of conc HNO3, it turns into orange red PPT of Ag3 [Fe(CN)6] which become soluble in dil ammonia (due to oxidation to Ag3 [Fe(CN)6]. @Sinaiunieg [email protected] www.su.edu.eg 2- Reaction with BaCl2 No observed reaction @Sinaiunieg [email protected] www.su.edu.eg 3- Reaction with FeCl3 This reaction is very important, since it is differentiating reaction. Procedure: The dilute sample solution is added dropwise to 1 ml of FeCl3 reagent. 1- CN - With dilute solution, a PPT of ferric cyanide will be formed which dissolves in excess cyanide solution to form ferricyanide. 3 CN - Fe3+ + 3 CN - [Fe(CN)6]-3 Fe(CN)3 ferricyanide ferric cyanide @Sinaiunieg [email protected] www.su.edu.eg 3- Reaction with FeCl3 2-CNS-: This reaction is specific for ferric iron only(but not for ferrous) with CNS- in the absence of other interfering ions. Procedure: A cold acidic solution of CNS- (with dil HCl) is treated with FeCl3 reagent, a blood red color which is extractable with ether. The formed color is subjected to have the following structures: 3+ - 2+ 3- Fe + CNS [Fe(SCN)] or Fe(CNS)3 or [Fe(CN6] @Sinaiunieg [email protected] www.su.edu.eg 3- Reaction with FeCl3 In order to increase the sensitivity of the test, the following precautions must be done: 1. Ensure the presence of iron in the ferric (Fe3+) state. 2. Acidification of the medium (by dil HCl is preferable). 3. Addition of excess CNS-. 4. Cooling of the solution before testing. 5. By extracting the color with ether. 6. Removal of interfering ions by precipitation or complexation (e.g. Fluoride, Iodide …. @Sinaiunieg [email protected] www.su.edu.eg 3- Reaction with FeCl3 Interference: 1. Presence of ions that capture Fe3+ to more stable complex e.g. F-, PO43-, oxalate and tartarate that bleach the color (in neutral but not in moderately acidic solutions). So, these ions must be absent. Fe3+ + 6 F - [Fe(F)6]3- stable complex 2. Presence of ions reacting with CNS- e.g. Hg2+ decolorize the solution by forming unionized Hg(CNS)2 which is colorless. 3. Iodide (I-) interfere by being oxidized by Fe3+ into brown I2. 3+ - 2+ 2 Fe +2I 2 Fe + I2 4. The color is bleached by heating. @Sinaiunieg [email protected] www.su.edu.eg 3- Reaction with FeCl3 3- Ferrocyanide [Fe(CN)6]4- ▪ A Prussian blue characteristic PPT (dark blue PPT) which is formed when Fe3+ is added to acidic solution of ferrocyanide. ▪ This blue PPT is insoluble in dil HCl but soluble in alkali hydroxide. 3 [Fe(CN)6]-4 + 4 Fe3+ Fe4[Fe(CN)6]3 prussian blue PPT Or Fe3+ + K+ + [Fe(CN)6]4- K Fe[Fe(CN)6] prussian blue PPT @Sinaiunieg [email protected] www.su.edu.eg 3- Reaction with FeCl3 4- Ferricyanide [Fe(CN)6]3- ▪ A brown color (in solution) is formed of the non-ionized ferric- ferricyanide. -3 3+ [Fe(CN)6] + Fe Fe[Fe(CN)6] Brown color ▪ This test can be used to differentiate between ferrocyanide and ferricyanide when present in a mixture. @Sinaiunieg [email protected] www.su.edu.eg 4- Reaction with FeSO4 It is similar to the reaction of FeCl3 reagent with cyanogen salts, but differ in being the iron in the ferrous state. Procedure: The 1 ml of freshly prepared FeSO4 solution, add the dilute salt solution gradually. CN- Cyanide form yellow brown PPT which is ferrocyanide. This reaction is enhanced by heating or addition of alkali. 4CN - -4 Fe 2+ + 2 CN - [Fe(CN)6] Fe(CN)2 @Sinaiunieg [email protected] www.su.edu.eg 4- Reaction with FeSO4 CNS- – No reaction Ferrocyanide It forms white PPT of potassium ferrous ferrocyanide. 2+ + 4- Fe + 2 K + [Fe(CN)6] K2 Fe[Fe(CN)6] @Sinaiunieg [email protected] www.su.edu.eg 4- Reaction with FeSO4 Ferricyanide Ferricyanide forms with FeSO4 reagent , a similar blue PPT (Turnbulls blue) or (Potassium ferrous ferricyanide) as that of Prussian blue, but differ in the distribution of iron-different oxidation state is varied 2+ + 3- Fe + K + [Fe(CN)6] K Fe[Fe(CN)6] @Sinaiunieg [email protected] www.su.edu.eg 4- Reaction with FeSO4 It is suggested that the prussian blue and turnbull’s blue PPT are identical corresponding in composition to Kfe[Fe(CN)6]. Both oxidation state of iron are present, but their distribution is governed by the oxidation –reduction equilibrium. -3 2+ -4 3+ [Fe(CN)6] + Fe [Fe(CN)6] + Fe Turnbulls blue prussian blue @Sinaiunieg [email protected] www.su.edu.eg 6- Reaction with cobalt nitrate Co(NO3)2 Add excess Co(NO3)2 reagent to the sample solution CNS- (vogel’s reaction): The reaction of Co2+ with CNS- to produce a characteristic blue color extractable with ether or amyl alcohol due to the formation of [CO(CNS)4]2-. This reaction is known as Vogel’s reaction. Other cyanogen anions form PPT with Co(NO3)2 reagent. 2+ - 2- Co + 4 CNS [Co(CNS)4] extracable with ether (blue) @Sinaiunieg [email protected] www.su.edu.eg Analysis of mixtures 1- Mixture of CN-, CNS-, [Fe(CN)6]4-and [Fe(CN)6]3- : Generally; if CN- present in any anion mixture, it should be first tested, then removed from the mixture. This is done depending on its strong affinity to protons, low ionization and volatility of HCN. The following procedure could be applied: A- this is done by passing CO2 in the mixture solution, using acetic acid and sodium bicarbonate and heat until no more HCN evolved. Test for HCN by; 1- passing in AgNO3 solution, acidified with dil HNO3 gives a white PPT. ↓ 2- passing in NaOH, adding FeSO4 solution , heating, followed by FeCl3 ↓ solution, a Prussian blue PPT is formed. @Sinaiunieg [email protected] www.su.edu.eg To the remaining solution, after removal of cyanide, will contain Thiocyanates, ferrocyanide and ferricyanide acidify with dil HCl, cool and add FeCl3 solution and centrifuge + dil HCl Cool + FeCl3 Filter ↓ Filtrate or centrifugate Deep blue PPT [Fe(CN)6]4- Shake with ether Brown solution Blood red color extractable with ether So, it is thiocyanate SnCl2 Blue PPT so, it is [Fe(CN)6]3- ↓ Cyanogen anions, Dry reactions Reaction Cyanide Thiocyanate Ferrocyanide Ferricyanide CN- SCN- [Fe(CN)6]4- [Fe(CN)6]3- Dry Reaction- HCN Gas Negative Negative Negative Dil HCl Detected by White PPT when passed May PPT the free acid May PPT the free into AgNO3 Solution acid Ammonium polysulfides then FeCl3 in acid medium: Blood red color Dry reaction- Decompose on heating to CO, NH4+ Decompose on heating Decompose on heating Decompose on conc sulfuric to COS, NH4+ to Fe 2+, CO, NH4+ heating to Fe3+, Fe 2+ is oxidized to Fe 3+ CO, NH4+ with evolution of SO2 gas @Sinaiunieg [email protected] www.su.edu.eg Cyanogen anions, Wet reactions Reaction Cyanide Thiocyanate Ferrocyanide Ferricyanide CN- SCN- [Fe(CN)6]4- [Fe(CN)6]3- BaCl2 Negative Negative Negative Negative Silver Nitrate White PPT AgCN Sol. in excess White PPT AgSCN White PPT Orange PPT AgNO3 Cyanide ↓ ↓ ↓ Ferric chloride PPT sol. In excess cyanide Blood red color Prussian blue PPT Brown color in acid solution solution solution FeCl3 ↓ ↓ Ferrous sulfate, Yellowish brown PPT sol. In excess Negative White PPT Turnbull blue PPT FeSO4 cyanide ↓ ↓ ↓ Cobalt nitrate PPT Blue color extractable PPT PPT Co(NO3)2 in amyl alcohol @Sinaiunieg ↓ [email protected] ↓ www.su.edu.eg ↓  THANK YOU For any questions feel free to contact me by mail [email protected] Dr Hatem Mokhtar Lecturer of Analytical Chemistry