Anions PDF

Anions Acid + base →Salt + water HCl + NaOH → NaCl + H2O Na Cl Na+ Cl- Cation Anion Anion: is negative charged fragment of salt The scheme of classification of anions depend on: 1- Dry reactions; Id...

Anions Acid + base →Salt + water HCl + NaOH → NaCl + H2O Na Cl Na+ Cl- Cation Anion Anion: is negative charged fragment of salt The scheme of classification of anions depend on: 1- Dry reactions; Identification of volatile product when salts are treated with acid ( dil HCl, dil H2SO4) ex; HCl and H2SO4 displace carbonic acid. It divided into: A- Involving volatile product upon treatment with dil acid. B- Involving gases with conc H2SO4. 2-Wet reactions: Colour, precipitation, oxidation reduction reactions. 3-Specific and selective reactions for each anions:  Carbonates and bicarbonates CO3-- & HCO3- Parent acid - Carbonic acid (H2CO3): it is weak acid. H2CO3 Heat CO2 + H2O -Bicarbonates decompose on heating and give CO2. 2HCO3- CO3- - + H2O+ CO2 -Bicarbonates are first step of ionization of carbonic acid, while carbonates are second step. H2CO3 H+ + HCO3- H+ + CO3--  Dry reactions 1- Action of dil HCl - Effervescent due to CO2 for carbonate and bicarbonate. Na2CO3 + 2 HCl 2 NaCl + H2CO3 H2CO3 H2O + CO2 Na2CO3 + 2 HCl 2 NaCl + H2O + CO2 -It is displacement reaction. - Neutral carbonates such as FeCO3, (Ca, Mg) CO3 do not react on cold but need heating. -If acid is very dilute, no effervescent observed with carbonate, due to formation of bicarbonate. Na2CO3 + HCl NaHCO3 + NaCl  Turbidity test for CO2 - It is selective test for CO2 and SO2 gases. -CO2 make turbidity to lime water or baryta water. CO2 + Ca (OH)2 CaCO3 + H2O CO2 + Ba (OH)2 BaCO3 + H2O With prolonged passage of CO2, the turbidity disappear due to formation of soluble bicarbonate. CaCO3 + CO2 + H2O  Ca (HCO3) [soluble] This reaction is reversed by boiling 2- Reactions with BaCl2, CaCl2, MgSO4 A- For CO3-- White PPT of BaCO3, CaCO3 and MgCO3. BaCl2 + Na2CO3 BaCO3 + 2 NaCl Ca++ + CO3-- CaCO3 Mg++ + CO3-- MgCO3 B- For HCO3- No PPT on cold due to all bicarbonates are soluble in water Ba++ + 2HCO3- Ba(HCO3)2 soluble On boiling white PPT will be formed Ba(HCO3)2 boil BaCO3 + CO2 + H2O  Mix of CO3-- and HCO3- Interference: both evolve CO2 on treatment with acid. Carbonate precipitate on cold upon addition of CaCl2, BaCl2 and MgSO4, while HCO3- of these metals are soluble. Mix CO3– and HCO3- add excess CaCl2 or BaCl2 or MgSO4 on cold Filtrate may be HCO3- White PPT of Boil CaCO3 or treat with ammonia H+ Bicarbonate CO2 + H2O Ca(HCO3)2 + 2 NH3 CaCO3 + (NH4)3 CO3 carbonate  Sulphur-containing anions Sulphide (S2-), sulphite (SO32-), thiosulphate (S2O32-), sulphate (SO42-) and persulphate (S2O82-). -Sulphur element has tendency to accept electrons, when accept 2 it form the sulphide ion S2-: 2- S xx - Sulphide ions has ability to form covalent bonds with oxygen or with sulphur atoms to form other members. 2- 2- 2- O O O O S O O S O O S O xx O s Sulphite Sulphate Thioulphate  Dry reactions I- Action of dil HCl 1- Sulphide S— H2S gas evolved on cold and rapidly on hot S-- + 2 H+ H2S H2S can be detected by: 1- Rotten egg odor. 2- Blackening of filter paper moistened with lead acetate H2S + Pb++ PbS (Black) Alternatively filter paper moistened with cadmium acetate give yellow color H2S + Cd++ CdS (Yellow) 3- Reducing properties of H2S: H2S behave as reducing agent: A- Bleach pink color of acid KMnO4 5 H2S + 6 H+ + 2 MnO4- 2 Mn2+ + 8 H2O + 5 S B- Bleach the brown color of iodine H2S + I2 2 I- + 2 H+ + S C- Change the orange color of acid K2Cr2O7 into green 3H2S + 8 H+ + Cr2O7-- 2 Cr2+ + 7 H2O + 3 S 2- Sulphite SO3- - SO2 gas evolved due to the decomposition of of the liberated unstable H2SO3 SO3-- + 2 H+ H2SO3 SO2 + H2O Detection of the evolved SO2: 1- Burnt sulphur odor. 2- Turbid lime water due to formation of insoluble CaSO3 which is soluble on prolonged passage of SO2 Ca(OH)2 + SO2 CaSO3 + H2O PPT CaSO3 + SO2 + H2O Ca(HSO3)2 (soluble) 3- Reducing properties of SO2: SO2 behave like H2S as reducing agent: A- Bleach pink color of acid KMnO4 5 SO2 + 6 H+ + 2 MnO4- 2 Mn2+ + 8 H2O + 5 SO3 B- Bleach the brown color of iodine I2 + SO2 + H2O 2 I- + 2 H+ + SO3 C- Change the orange color of acid K2Cr2O7 into green 3 SO2 + 8 H+ + Cr2O7-- 2 Cr2+ + 4 H2O + 3 SO3 3- Thiosulphate S 2O3- - No immediate change on cold. But become turbid solution on warming with dilute HCl or standing due to formation of colloidal sulphur and SO2 gas due to the decomposition of the liberated unstable H2S 2O3 S 2O3-- + 2 H+ H2S 2O3 SO2 + H2O + S Thiosulphuric acid 4- Sulphate SO4- - No reaction with dilute HCl. 5- Persulphate S 2O8- - - No effect on cold. - on boiling with water or persulphates decomposes to give oxygen which oxidized HCl ( the reaction is catalyzed by Ag+). K 2S 2O8 + 2 H2O K2SO4 + H2SO4+ [O] [O] contain ozone which is detected by its odor and by turning KI-starch paper into blue. 2 KI + O3+ H2O I2+ O2 + 2 KOH  Wet reactions Solubility -All Na+, K+ and NH4+ salts of sulphur are soluble in water. Sulphides: Other sulphides are insoluble except those of Ca2+, Ba2+, Sr2+ dissolved due to hydrolysis. Sulphites: Other sulphites are insoluble. Thiosulphates: Most thiosulphates are soluble. Ag+, Pb2+, Hg2+, Ba2+ salts are slightly soluble. Sulphates: All sulphates are soluble except Pb2, Ba2+ , Sr2+ , Ca2+ and Mg2+ salts are slightly soluble. Persulphates: All known persulphates are soluble. 1- reaction with BaCl2: Add BaCl2 reagent to neutral sample solution S-- No Visible reaction SO3-- Ba-- + SO3-- BaSO3 (White PPT) Soluble in dilute HCl and soluble in excess sulphite but reprecipitate on boiling. On standing or warming the PPT or oxidation with H2O2 or Br2 solution, BaSO3 is slowly oxidized to BaSO4 which is insoluble in dilute HCl. S 2O3-- - No PPT in dilute solution.- - But a PPT is formed from very concentrated solution.- SO4-- Ba-- + SO4-- BaSO4 White PPT insoluble in dilute HCl even on boiling S2O8-- No PPT on cold.- - On boiling a white PPT of BaSO4 is formed due to decomposition of - persulphate. Boiling S 2O8-- + 2 H2O SO4-- + H2SO4+ [O]  2- Reducing action Sulphides, polysulphides, sulphites and thiosulphates are reducing agent. A- Iodine solution: S-- Decolorization with turbidity due to precipitation of S- I2 + S-- 2 I- + S SO3-- Decolorization I2 + SO3-- + H2O 2 I- + SO4-- + 2 H+ S2O3-- Weak oxidizing agent such as I2 or Fe2+, oxidize thiosulphate and - decolorize the color of I2. + H I2 + 2 S2O3-- S4O6-- + 2 I- + H Fe3+ + 2 S2O3-- S4O6-- + 2 Fe2+ B- KMnO4: Decolorisation occurs with sulphides, sulphites and thiosulphates. 2 MnO4- + 5 S--+ 6 H+ 2 Mn2+ + 5 SO4--+ 3 H2O colorless Pink 2 MnO4- + 5 SO3--+ 6 H+ 2 Mn2+ + 5 SO4--+ 3 H2O 8 MnO4- + 5 S2O3--+ 14 H+ 8 Mn2+ + 10 SO4--+ 7 H2O B- Cr2O7: Cr2O7 + 3 H2S+ 8 H + 2 Cr2+ + 7H2O + 3S orange green Cr2O7 + SO3--+ 8 H+ 2 Cr2+ + 3 SO4--+ 4 H2O 4 Cr2O7 + 3 S2O3--+ 26 H+ 8 Cr2+ + 6 SO4--+ 13 H2O  Special tests and spot tests 1-Sulphides: Special test for sulphides: The solution is shaken with CdCO3, Canary yellow PPT of CdS is produced. - This test could be used for identification and separation of sulphide when present in a mixture with other sulphur containing anion or those anions which do not react with CdCO3. 3-Thiosulphates S2O3-- : Special test for thiosulphates (formation of thiocyanate): By boiling with KCN solution in the presence of NaOH, cool, acidify and add FeCl3, a blood red color of ferric thiocyanate complex. OH - S2O3-- + CN - SCN - + SO3-- Boil Fe 3+ + SCN - Cool Fe(SCN)2+ 4-Sulphates SO4-- : Special test for sulphates (Hepar test): Sulphate 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. -- Fusion MSO4 + Na2CO3 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 is produced. S-- + H2O 2 OH - + H2O H2S + 2 Ag Ag2S + H2 The formed sulphide can also be tested by any other specific test for sulphides. 5-Persulphates S 2O8-- : Depending on their oxidizing effect: 1. Manganous salts could be oxidized into the pink colored permanganate when boiling managanous salt with persulphate in acid medium (HNO3) using one drop of AgNO3 solution as a catalyst. 2 Mn 2+ + 5 S2O82- + 8 H2O 2 MnO4- + 10 SO42- + 16 H+ pink 2. Persulphate, oxidise I-, solution into I2 which can be identified by: Brown coloration. OR by starch paper. OR can be extracted into chloroform. S2O82- +2I - I2 + SO42-  Analysis of mixture 1-Mixture of S---, SO3--, S2O3– and SO4-- Interference: This mixture is liable to interference upon treatment with dil HCl, due to the common reducing character of H2S and SO2 gases. Separation Separation technique must be done in order to identify each one of them. Separation is carried out by first shaking the mixture solution with CdCO3 powder. The sulphide ion will be precipitated as CdS, centrifuge, the centrifugate is allowed to react with BaCl2 solution which precipitate BaSO4 and BaSO3 leaving BaS2O3as soluble centrifugate. The precipitated BaSO4 and BaSO3 can be separated by the solubility of BaSO3 in excess dil HCl ( by treatment with dil HCl, the acid insoluble residue will be BaSO4 and the filtrate containing SO3– can be tested by oxidation with H2O2 or Br2 water, white PPT of BaSO4 ( which is acid insoluble) indicate a a positive test for sulphite.  S--, SO3-- , S2O3– and SO4– solution + CdCO3 Yellow PPT of CdS. Centrifugate + BaCl2  Sulphide (S2-). White PPT ( BaSO4 and BaSO3) Centrifugate (S2O3--) add dil HCl dil HCl Heat White PPT (BaSO4 SO2 + S Centrifugate SO3-- ). confirmed by oxidation  Thiosulphate (S 2O 3 2-).  Sulphate (SO42- with Br2 or H2O2, which ). give white PPT. 2-Mixture of S---, SO3— and S2O3– Interference and separation: as mentioned before. S--, SO3-- and S2O3– solution + CdCO3 Yellow PPT of CdS. Filtrate + BaCl2  Sulphide (S2-). Filterate (S2O3--) White PPT ( BaSO3) dil HCl dil HCl Heat SO2 SO2 + S  Sulphite (SO 3 2-).  Thiosulphate (S 2O 3 2-).  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. They have similar properties and characters; all are monovalent anions, and they are similar in chemical reaction except fluoride. Regarding the electronegativity , it increases according to the following: Increase electronegativity I - , Br- , Cl - , F - Decrease electronegativity As the ionic size increase, the tendency to lose electrons increases and therefore iodide is firstly and easily oxidized into free I2 by loosing an electron followed by Br- when present in a mixture. However, it is difficult to oxidize F- into F2 ( there is no chemical oxidant which is powerful enough to oxidize F- ions to F2), hence F- ions are highly stable to held strongly a proton that is why HF is the weakest acid, while HI is the strongest hydro halogen acid in this series. HI > HBr > HCl > HF  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 Sulphur containing anions from halides. II- Action of Concentrated H2SO4 Decomposition of the halides occurs upon the addition of conc H2SO4 to specks of the solid sample, 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. 2 X - + H2SO4 2 HX + SO4-- X= may be Cl -, I -, Br-, 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 action of the gas on the glass in presence of water, the HF gas can be detected by expose 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 hexafluorosilicic 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) 2 F - + H2SO4 2 HF + SO4-- 4 HF + SiO2 SiF4 + 2 H2O glass Silicon tetrafluoride 3 SiF4 + 3 H2O H2SiO3 + 2 H2SiF6 silicic acid hydrofluorosilicic acid This test can be considered as specific test for fluoride anion, even in the presence of other halides. 2- For chloride: HCl gas ( which is colorless) is evolved upon treatment with conc H2SO4. 2 Cl - + H2SO4 2 HCl + SO4-- 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 moistured litmus paper into red. 4- Formation of white fumes of NH4Cl when a glass rod moistued with NH4OH is exposed to the evolved gas. NH4OH + HCl NH 4Cl + H2O 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. Since HBr and HI are more active reducing agents than HCl, so as soon as they are formed by the action of conc H2SO4 , they are readily oxidized to free Br2 and I2, respectively and sulphuric acid being reduced to different products ( SO2, H2S or S) according to the degree of reduction. 2 Br - + H2SO4 2 HBr + SO4-- 2 HBr + SO4-- Br2 + SO2 + 2 H2O 4- For iodide: Since HI is the most active reducing agent, so it is readily oxidized to iodine which appear as violet fumes. 2 I - + H2SO4 2 HI + SO4-- 2 HI + H2SO4 I2 + SO2 + 2 H2O 6 HI + H2SO4 3 I2 + S + 4 H2O 8 HI + H2SO4 4 I2 + H2S + 4 H2O I2 can be detected by exposing the evolved gas to paper moistened with starch solution, changes its color into blue. 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. The deep red vapors of chromyl chloride Cr2O2Cl2 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, in contact with NaCl. Thus, the positive test for chromate in yellow sodium hydroxide indicate the presence of chloride in the solid sample.  Cl - + H + HCl Cr2O7-- + 2H+ H2Cr2O7 4 HCl + H2Cr2O7 Condensation 2 CrO2Cl2 + 3 H2O or Condensation 4 Cl- + Cr2O7-- + 6 H+ 2 CrO2Cl2 + 3 H2O CrO2Cl2 + 4 OH - 2 Cl- + CrO4-- + 2 H2O Some Cl2 may also be liberated in the reaction and this decrease the sensitivity of the test. 6 Cl- + Cr2O7-- + 14 H+ 3Cl2 + 2 Cr3+ + H2O  Test for chromate by: 1-Perchromic acid test: It is carried out by acidifying a portion 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 CrO4-- + 2H+ Cr2O7-- + H2O Cr2O7-- + 7 H2O 2 CrO83- + 5H2O + 4 H+ blue in organic layer Test by lead acetate Acidify a portion with acetic acid and treat with lead acetate solution, yellow PPT of lead chromate will be formed. CrO4-- + 2Pb++ PbCrO4 Yellow PPT  ▪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). Flourides give rise to the volatile CrO2F2 which decomposed by water. If the ratio of iodide to chloride exceeds 1:15, the chromly chloride formation is largely prevented and Cl2 is evolved. Nitrites and nitrates interfere, as nitrosyl chloride may be formed.  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 Chloride A white PPT of AgCl which is insoluble in nitric acid , soluble in KCN ana Na2S2O3 as other silver silver halide. The PPT AgCl is soluble in dil ammonia solution to give the amine complex which decomposed by addition of dil acid with re-precipitation of AgCl. Ag+ Cl- AgCl AgCl + 2 NH3 [Ag(NH3)2]Cl silver amine complex [Ag(NH3)2]Cl + 2 H + 2 NH4+ + AgCl Chloride All silver halides PPT are insoluble in dil HNO3. They are soluble in KCN and Na2S2O3 due to the formation of soluble complex. AgX + 2 CN- [Ag(CN)2] - + X - argento cyanide complex [soluble complex] AgX + 2 S2O3-- [Ag(S2O3)2] 3- + X - argento thiosulfate complex [soluble complex] Bromide Pale yellow PPT of AgBr, sparingly soluble in dil but readily soluble in conc ammonia. Ag+ Br- AgBr AgBr + 2 NH3 [Ag(NH3)2]Br silver amine complex Iodide yellow PPT of AgI, insoluble in dil very slightly soluble in conc ammonia. Ag+ I - AgI 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 - 3- solubility in dil ammonia AgCl is completely soluble AgBr is partially soluble. AgI is insoluble. This is also attributed to that the concentration of silver ion (Ag+) produced from the dissociation of silver amine complex according to its instability constant is insufficient to exceed the high solubility product of AgCl (so not precipitated but remain soluble), but approach that of AgBr ( partially soluble) but exceed that of AgI (precipitated and not soluble). [Ag(NH3)2]+ Ag+ + 2 NH3 (Ag+) (NH3)2 Instability constant = [Ag(NH3)2]+ There fore when bromide or iodide solution is added to silver chloride , yellow PPT of AgBr or AgI is formed. AgCl + Br - (or I -) AgBr or AgI AgBr + I AgI + Br - more insoluble lower solubility product Hence if I – solution is added to the solution of AgCl in ammonia (silver amine chloride), yellow PPT of AgI is formed. In concentrated ammonia, AgCl, AgBr are soluble while AgI is slightly soluble. 2- Reaction with BaCl2 solution: when 1 ml of the reagent 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. Ba++ + 2 F - BaF2 Chloride, No PPT is formed. bromide, iodide 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. Fe3+ + 6 F - [FeF6]3- Chloride, Do not react with FeCl3. bromide, Iodide Due to the strong reducing action of I -, iodide react with FeCl3 with liberation of iodine (on warming). 2 Fe 3+ +2I - 2 Fe2+ + I2 5- Chlorine water test: Acidify 3 ml of the sample solution with dil H2SO4, add 1 ml of chloroform or carbon tetrachloride and successive drops of chlorine water drop wise, shake after each addition. Fluoride, No reaction. Chloride Bromide, Chlorine water oxidizes Br -, I- into Br2 or I2 ,respectively, Iodide which are extracted with chloroform or carbon tetrachloride which will be colored yellow to reddish brown with Br2 and violet with I2. - 2 Br + Cl2 Br2 + 2 Cl- - 2 I + Cl2 I2 + 2 Cl -  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. Br2 + Cl2 2 BrCl (yellow) Br2 + Cl2 (excess) + 2 H2O 2 HOBr + 2 HCl ( hypobromous acid colorless) Br2 + 5 Cl2 (excess) + 6H2O 2 HBrO3 + 10 HCl ( bromic acid colorless) with excess chlorine water: I2 is also oxidized to colorless iodic acid. I2 + 5 Cl2 (excess) + 6H2O 2 HIO3 + 10 HCl ( iodic acid colorless) 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 flouride do not interfere with chlorine water test.  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 centrifuge white PPT of BaF2 Centrifugate confirmed by conc H2SO4 Cl-, Br-,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.  Cyanogen Anions (cyanide containing anion) Cyanide (CN-), thiocyanate (SCN-), ferrocyanide ([Fe(CN)6]-4], ferricyanide ([Fe(CN)6]-3]. ▪ 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].  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 HCN gas can be identified by: a- converting HCN gas evolved 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. 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 may occur precipitation of hydroferrocyanic acid and hydroferricyanic acid. [Fe(CN)6]-4 + 4 H+ H4[Fe(CN)6] [Fe(CN)6]-3 + 3 H+ H3[Fe(CN)6]  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 and silver thiocyanate. ▪ 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  Ferrocyanide ▪ Both [Fe(CN)6]-4 and [Fe(CN)6]3- react with AgNO3 and solution, white PPT and orange PPT, respectively. Ferricyanide ▪ The solubility of silver ferricyanide PPT 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]. 4 Ag+ + [Fe(CN)6]-4 Ag4[Fe(CN)6] white PPT insoluble in dil NH3 and dil HNO3 3 Ag+ + [Fe(CN)6]-3 Ag3[Fe(CN)6] Orange PPT soluble in dil NH3 and insoluble dil HNO3 2- Reaction with BaCl2:No observed reaction 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 dissolve in excess cyanide solution to form ferricyanide. 3 CN - Fe3+ + 3 CN - [Fe(CN)6]-3 Fe(CN)3 ferricyanide ferric cyanide 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 structure: Fe3+ + CNS - [Fe(SCN)]2+ or Fe(CNS)3 or [Fe(CN6]3- 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. 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. 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 4- Ferricyanide [Fe(CN)6]3- ▪ A brown color is formed of the non-ionized ferric-ferricyanide. [Fe(CN)6]-3 + Fe3+ Fe[Fe(CN)6] Brown color ▪ This test can be used to differentiate between ferrocyanide and ferricyanide when present in a mixture. 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+ Co + 4 CNS - [Co(CNS)4]2- extracable with ether (blue)  Analysis of mixtures The analysis of a mixture containing 4 cyanide containing anions: CN-, CNS-, [Fe(CN)6]4-, [Fe(CN)6]3- can also be applied for mixture containing 2 or 3 of them. 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.  To the remaining solution, after removal of cyanide, acidify with dil HCl, cool and add FeCl3 solution and centrifuge + dil HCl Cool + FeCl3 centrifugate Deep blue PPT [Fe(CN)6]4- Brown solution Blood red color extractable with ether So, it is thiocyanate SnCl2 Blue PPT so, it is [Fe(CN)6]3- Arsin- and phosphorous containing anions ASO43- & ASO33- , PO4-3  Arsin- and phosphorous containing anions ASO43- & ASO33- , PO43- Identification Dry reaction 1- Action of dil HCl Solid salt + dil HCl, no visible reaction , phosphates, arsenates and arsenites are non-volatile. 2-Action of Conc H2SO4 Solid + conc H2SO4 : Arsenate and phosphate: no visible reaction. Arsenite : being mild reducing agent, some reduction to SO2 may occur on heating. 1- Reaction with AgNO3 solution: Phosphate and Yellow PPT is formed arsenite 3 Ag+ + PO43- Ag3PO4 3 Ag+ + ASO33- Ag3ASO3 Arsenate Chocolate brown PPT 3 Ag+ + ASO43- Ag3ASO4 ▪ All the PPT are soluble in dil HNO3 or NH3 and insoluble in acetic acid. 2- Reaction with Magensia mixture: Magensia mixture reagent: is formed of MgCl2, NH4Cl and NH4OH. MgCl2: introduce the precipitating ion (Mg2+). NH4OH: to make the medium ammonical. NH4Cl: is added to reduce the concentration of OH- (by common ion effect) to be insufficient to PPT Mg(OH)2 but sufficient to make the medium suitable for the precipitation of magnesium ammonium phosphate or arsenate. NH4OH NH4+ + OH - NH4Cl NH4+ + Cl - ▪ Add the solution of the reagent to the sample solution, phosphates and arsenates form white crystalline PPT with Mg2+ in neutral or ammonical solution (of magnesium ammonium phosphate or arsenate). ▪ The PPT is soluble in acetic acid and in mineral acid. ▪ No PPT is formed in case of arsenites. PO43- + Mg2+ + NH4+ Mg(NH4)PO4 magmesium ammonium phosphate ASO43- + Mg2+ + NH4+ Mg(NH4)ASO4 magmesium ammonium arsenate ▪ If the white PPT are treated with AgNO3 (in weak acetic acid medium), that the phosphate will be transformed into yellow PPT, while that of arsenate will be transformed into chocolate PPT. Due the transformation to the less soluble Ag3PO4 and Ag3ASO4 ,respectively. 4- Reaction with ammonium molybdate: ▪ The addition of large excess (2-3 ml) of the ammonium molybdate regent in conc HNO3 to a small volume (0.5 ml) of the test solution, acidified with HNO3 and heat gradually will produce: ▪ A Canary yellow crystalline PPT of ammonium phosphomolybdate (NH4)3PO4.12MoO3 (on warming at 40 ºC) in case of phosphate. ▪ A Canary yellow crystalline PPT of ammonium arseno molybdate (NH4)3ASO4.12MoO3 (on boiling) in case of arsenate. ▪ No PPT is formed with arsenites. ▪ The PPT are soluble in ammonia or alkali hydroxide and in excess phosphates or arsenates respectively and on boiling with ammonium acetate solution and insoluble in HNO3. ▪ MoO3 produced from the action of acid on ammonium molybdate is assumed to be the main reactant.  MoO42- + 2 H+ H2MoO4 H2O + MoO3 3 NH4+ + 12 MoO3+ PO43- (NH4)3PO4.12MoO3 3 NH4+ + 12 MoO3+ ASO43- (NH4)3ASO4.12MoO3 The correct formula of PPT may be : (NH4)3[P (MoO10)4] Where the Mo3O10 group replacing each oxygen atom in phosphate. 3 NH4+ + 12 MoO3+ HPO43- + 23 H+ (NH4)3[P (MoO10)4] + 12 H2O It should be noted that: 1. This is the most delicate test for traces of PO43- or ASO43-. 2. Different formula are given for the PPT but agree with the ratio of P (or As):Mo is 1:12. 3. The solution must not be alkaline (PPT are soluble in ammonia and alkali hydroxide), but the solution must be acidic with HNO3. 4. The reaction is slightly reversible so for complete precipitation add excess NH4+ and MoO3(MoO42- and H+ from HNO3). 5. PPT are poorly formed on cold so warm for phophate and boil for arsenates. 6. Chloride and reducing agent such as S2-, SO32-, [Fe(CN)6]4- and tartarate have destructive effect on molybdate ions, so that they must be absent or destroyed before carrying out the test. 5- Reaction with H2S: Acidify the test solution with dilute HCl and pass H2S, Phosphates: No PPT is formed. Arsenites: produce immediate yellow PPT of arsenious sulphide AS2S3. The PPT is soluble in HNO3 and alkali hydroxides and insoluble in hot conc HCl. H2ASO4- + H2S H2ASO3S- + H2O Arsenates thio arsenate ion H2ASO3S- + H+ HASO2 + H2O + S arsenious acid thio arsenate ion 2 HASO2 + 3 H2S AS2S3 + H2O arsenious acid arsenious sulphide If the acid concentration is high and the stream of H2S is rapid, no preliminary reduction of arsenate to arsenite occurs and arsenic pentasulphide PPT (AS2S5) is produced. H2ASO4- + 5 H2S + 2 H+ AS2S5 + 8 H2O arsenic pentasulphide However, is the solution is heated under the same conditions, mixture of arsenic pentasulphide PPT (AS2S5) and arsenious sulphide (AS2S3) is produced.  Special tests 1- For phosphates Magnesium test: It depends on reduction of the stable phosphate into phosphide (P3-), by mixing with magnesium powder and heat in an ignition tube, moisten the cold mass with water, phosphine gas (PH3) is produced which has unpleasant odor and is inflammable. Heat PO43- + 4 Mg 4 MgO + P3- P3- + H2O PH3 + 3 OH -  2- For arsenate Potassium iodide test: Arsenate is an oxidizing agent so, it will convert I- to I2. Procedure: ▪ 2 ml sample solution + 1 ml chloroform + 3 ml KI solution + 5 ml conc HCl, shake vigrously and allow to settle, a violet color of free I2 appears in the organic layer. H+ ASO43- +2I -+ +4H + ASO2- + I2 + 2 H2O OH - ▪ The test can be used for the detection of arsenate in presence of phosphate and arsenite (in the absence of other oxidizing agent).  3- For arsenite 1-Iodine test: Arsenite has a reducing activity, it reduce I2 to I-. Procedure: ▪ 3 ml sample solution + 0.5 ml saturated NaHCO3 solution + few drops of I2 in KI solution , the brown color of I2 disappears immediately due to the reducing effect of arsenite. ▪ This reaction is the reverse of that for arsenate. alkaline ASO2- + I2 + 2 H2O ASO43- + 2 I - + 4 H+ acidic ▪ In the absence of other reducing agents, this test can be used to distinguish arsenite from phosphate.  Analaysis of mixture 1- Mixture of arsenite and arsenate Ammonical solution of the mixture + magesia mixture and filter white PPT filterate Mg(NH4)ASO4 1- acidify with dil HCl and pass wash with dil NH3 solution H2S, immediate yellow PPT of + AgNO3 acidified with AS2S3. so, it is arsenite. acetic acid, chocolate brown PPT Ag3ASO4. so, it is arsenate Or- add 5-7 ml of 30% H2O2 solution + magnesia mixture by drop (10 ml) with stirring, a white crystalline PPT of Mg (NH4)ASO4 produced by oxidation of arsenite. Or- Addition of NaHCO3 saturated solution + few drops of I2, the brown color of I2 disappears. so, it is arsenite.  2- Mixture of arsenite and phosphate 1. with magnesia mixture (as the mixture of ASO43- and ASO33-) with the only exception that when the PPT of Mg(NH4)PO4 treated with AgNO3 acidified with acetic acid, yellow PPT of Ag3PO4 is produced. 2. Pass H2S in the solution of the mixture, acidified with dil HCl, immediate yellow PPT of AS2S3 indicating ASO33-, filter, drive of excess H2S from the filtrate by boiling and test for phosphate by the general tests.  3- Mixture of arsenate and phosphate Dissolve in Conc HCl (10 ml), boil, Pass H2S for 5 minutes. Dilute with 25 ml H2O and filter. Yellow PPT of Ag2S5 filterate so, it is arsenate Evaporate to dryness. dissolve in conc HNO3 add ammonium molybdate warm canary yellow PPT so it is phosphate  4- Mixture of arsenite , arsenate and phosphate Ammonical solution + magnesia mixture and filter white PPT of Mg(NH4)PO4 and filterate Mg(NH4)ASO4. test for arsenate as in wash with dil NH3 solution mixture 1 dissolve in conc HCl Boil Proceed exactly as mixture 3 of PO43- and ASO43-  Nitogen-containing anion Nitrate (NO3-) Nitrite (NO2-) The nitrate on contains nitrogen in its highest oxidation state of +5, thus react only as oxidizing agent, while nitrite ion contains nitrogen which has oxidation number +3, it can therefore act either as a reducing or as an oxidizing agent. Parent acids 1- Nitric acid (HNO3): ❑ it is colorless liquid. ❑ its solution in water is strongly acidic. ❑ it decomposed on aging to nitrogen dioxide (NO2) 4 HNO3 4 NO2 + O2 + 2 H2O 2- Nitrous acid (HNO2): ❑ it is weak monoprotic acid. ❑ The pure acid never been isolated due to its thermal instability. 2 HNO2 NO + NO2 + H2O ❑ However, on adding strong acid to a solid nitrite or nitrite solution in the cold (at about zero ºC), yields a transient pale- blue liquid (due to the presence of free HNO2 acid or its anhydride, N2O3 and the evolution of brown fumes of NO2.  I- Dry reactions 1- dil HCl ❑ No reaction in case of nitrate. ❑ with nitrite, brown fumes of nitrogen dioxide NO2 evolve and a transient pale blue liquid. 2 NO2- + 2 H+ 2 HNO2 NO + NO2 + H2O ❑ The brown fumes intensify when getting contact with the atmosphere due to combination of NO with O2 of air.  2- Conc H2SO4 Nitrate: ❑ Nitric acid is formed and some of it decomposed with evolution of brown fumes of NO2 with characteristic odor. NO3- + H+ HNO3 4 HNO3 4 NO2 + O2 + 2 H2O ❑ when copper metal is added, and the mixture heated to boiling, the brown fumes of NO2 increased due to the reduction of HNO3 by Cu0 metal which is oxidized to Cu2+ ions, which imparts blue color to the solution. 2 NO3- + 4 H+ + Cu0 2 NO2 + Cu2+ + 2 H2O Nitrite: ❑ The reaction is the same with dil HCl, but it take place with considerable violence. ❑ On adding Cu0 metal, the same occurs as with nitrate.  II- Wet reactions Solubility ❑ All nitrates are soluble in water. ❑ Also, all nitrites are soluble in water, except AgNO2 which is slightly soluble. 1- Reaction with Ag2SO4 Nitrates: No PPT. Nitrite: white crystalline PPT of AgNO3from conc solution. NO2- + Ag+ AgNO2  2- Reaction with BaCl2 Nitrates and Nitrite : No PPT. 3- Reaction with KI Acidify the test solution (3 ml) with dil H2SO4, then add KI solution and few drops of starch solution. Nitrates: No reaction. Nitrite: I2 is liberated which give blue color with starch. 2 NO2- + 2 I - + 4 H+ 2 NO + I2 + 2 H2O  4- Reaction with FeSO4 ❑ To 5 ml of the sample solution acidified with 1 ml dil H2SO4, add 1 ml freshly prepared FeSO4 solution. ❑ Nitrates: No visible change in case of using only dil H2SO4, but on adding conc H2SO4 cautiously down the sides of the test tube, a brown ring is formed at the interface. ❑ Nitrite: Brown color in the whole solution if FeSO4 solution is not cautiously added or a brown ring at the junction of the two liquids, if cautiously added. (the color is formed with dil H2SO4). ❑ FeSO4 reduces nitrate NO3- or nitrite NO2- ions to nitrogen monoxide NO. ❑ Nitrate ion is not reduced except in solutions containing a high H+ ion concentration (in presence of conc H2SO4). ❑ Nitrite ion in contrast is easier in its reduction (only dil H2SO4) or even acetic acid. ❑ The excess Fe2+ ions then combines with the NO produced to form the unstable brownish black complex ion [Fe(NO)]2+, readily decomposed by heat. 3 Fe 2+ + NO3- +4H + 3 Fe3+ + NO + 2 H2O Fe 2+ + NO2- +2H + Fe3+ + NO + H2O Fe2+ + NO [Fe(NO)]2+ ❑ The test differentiates nitrate from nitrite, since nitrite gives the brown ring in presence of dil H2SO4 or even acetic acid, while nitrate ion does not form ring except in presence of conc H2SO4 (NO2-, I- and Br – ions will interfere).  Special tests I- Special test for nitrate Ammonia test: ❑ Metals such as Zn0 or Al0 reduce nitrates in alkaline medium with the formation of NH3 and zincate. ❑ If the solution of NO3- is boiled with Zn0 or Al0 metals in presence of NaOH solution, NH3 will be evolved which can be identified by its odor or with red litmus paper (nitrites interfere). 4 Zn0 + NO3- + 7 OH- 3 [ZnO2]2- + NH3 + 2 H2O zincate ion 8 Al0 + 3 NO3- + 5 OH- + 2H2O 8[AlO2]- + 3NH3 aluminate ion  II- Special test for nitrite Permenganate test: ❑ When dilute KMnO4 solution is added to nitrite solution, acidified with dil H2SO4, its pink color is bleached (NO3- does not interfere). ❑ In this test, KMnO4 reduced by nitrite to colorless manganous salt and the nitrite oxidized to nitrate. 2 MnO4- +5 NO2- +6H + 2 Mn2+ + 5 NO3- + 3 H2O pink colorless  Analysis of mixtures 1- Nitrate and nitrite ❑ Nitrite can be tested for in presence of nitrate )by treatment with dil HCl, KI, KMnO4, FeSO4 in dil H2SO4) and by the special tests for nitrite. ❑ Nitrate can not be tested for in presence of nitrite, since nitrite gives all the reactions of nitrate (conc H2SO4, brown-ring test and ammonia test) therefore nitrite must be removed before testing for nitrate by: ❑ Decomposition of NO2- through it brown complex with FeSO4 formed in dil H2SO4 or acetic acid by heat and shaking. Heat [Fe(NO)]2+ Fe2+ + NO ❑ To the mixture solution acidified with dil H2SO4, or acetic acid, add freshly prepared FeSO4 solution, the solution becomes dark brown. Heat with frequent shaking. The brown complex [Fe(NO)]2+ is decomposed and NO is expelled, the liquid gradually become colorless. Cool, add one more drop of acid and little FeSO4 if, NO2- is decomposed, this addition gives no further color. ❑ Pour conc H2SO4 to the mixture, a brown ring indicates presence of nitrate.