PC-101 Lecture 4 Anions Part 1 Carbonate and Sulfur Containing 2024 PDF

PC101-Anions part 1 Carbonate/bicarbonates and sulfur containing anions Dr. Hatem Mokhtar Lecturer of Analytical Chemistry Faculty of Pharmacy sinaiuniversity.net  Anions Part I Carbonate/Bica...

PC101-Anions part 1 Carbonate/bicarbonates and sulfur containing anions Dr. Hatem Mokhtar Lecturer of Analytical Chemistry Faculty of Pharmacy sinaiuniversity.net  Anions Part I Carbonate/Bicarbonates Sulfur containing anions @Sinaiunieg [email protected] www.su.edu.eg Salts composition: Anions and cations 𝑨𝒄𝒊𝒅 + 𝑩𝒂𝒔𝒆 → 𝑺𝒂𝒍𝒕 + 𝑾𝒂𝒕𝒆𝒓 𝑯𝑪𝒍 + 𝑵𝒂𝑶𝑯 → 𝑵𝒂𝑪𝒍 + 𝑯𝟐 O 𝑯+ 𝑪𝒍− + 𝑵𝒂+ 𝑶𝑯− → 𝑵𝒂+ 𝑪𝒍− + 𝑯𝟐 𝑶 Color code: Cations - Anions Salt: ionic compound formed from the assembly of anions and cations. It is the result of reaction between acid and base or between metal and nonmetal Anion: the negative ion fragment of the salt, contributed by an acid. Cation: the positive ion fragment of the salt, contributed by a base. Acid: An anion + 𝑯+ , a molecule donating hydrogen ions. Base: A cation + 𝑶𝑯− , a molecule donating a hydroxyl ion or accepting hydrogen ion. @Sinaiunieg [email protected] www.su.edu.eg 3  Anions qualitative analysis The scheme of anions identification depends on: 1- Dry reactions; 2-Wet reactions: 3-Specific and selective reactions for each anions: @Sinaiunieg [email protected] www.su.edu.eg 4  Anions qualitative analysis 1- Dry reactions; Identification of volatile product when solid salts are treated with acids ex; HCl and H2SO4 displace carbonic acid to form carbon dioxide as effervescence. It is divided into: – Step A: Addition of Dilute acid (HCl) to the dry solid salt and observation of evolving volatile products. – Step B: Addition of Conc. H2SO4 to the dry solid salt and observation of evolving volatile products. @Sinaiunieg [email protected] www.su.edu.eg 5  Anions qualitative analysis 2-Wet reactions: – Reaction between salt solution and group reagents. The result would be: – Color – Precipitation – Oxidation reduction reactions (results also in color change). 3-Specific and selective reactions for each anions: @Sinaiunieg [email protected] www.su.edu.eg 6 Carbonates and bicarbonates @Sinaiunieg [email protected] www.su.edu.eg  Key to study equations This equation is important, you must study it and keep it with its weights Info This equation is for information but you should know the name and structures of reactants and products @Sinaiunieg [email protected] www.su.edu.eg 8  Carbonates and bicarbonates Salts of Carbonic acid. The anion radical is a polyatomic ion Carbonate: 𝑪𝑶𝟑 −𝟐 Bicarbonate: 𝑯𝑪𝑶𝟑 −𝟏 @Sinaiunieg [email protected] www.su.edu.eg 9  Carbonates and bicarbonates Carbonic acid, carbonates and bi carbonates 𝐶𝑂2 (𝑔) + 𝐻2 𝑂 (𝑙𝑖𝑞. ) ⇌ 𝐻2 𝐶𝑂3 (𝐴𝑞.) ∆,−𝑷 1st 2nd Info ionization ionization step step @Sinaiunieg [email protected] www.su.edu.eg 10 Carbonates and bicarbonates I-Solubility Carbonates ✓ All carbonate salts are insoluble except: ▪ alkali (Na, K, Li) and ammonium carbonate Bicarbonates: ✓ Alkali (Na, K, Li) , Ammonium and Alkali earth; (Mg, Ba, Ca, Sr) bicarbonates are water soluble. @Sinaiunieg [email protected] www.su.edu.eg 11 Carbonates and bicarbonates II-Dry reaction A- Dil HCl Effervescence upon dilute HCL addition. For either carbonate : 𝑁𝑎2 𝐶𝑂3 + 2𝐻𝐶𝑙 → 2𝑁𝑎𝐶𝑙 + 𝐻2 𝑂 + 𝐶𝑂2 ↑ and bicarbonate: 𝑁𝑎𝐻𝐶𝑂3 + 𝐻𝐶𝑙 → 𝑁𝑎𝐶𝑙 + 𝐻2 𝑂 + 𝐶𝑂2 ↑ Very dilute acid addition to carbonates does not produce effervescence as it converts carbonates to bicarbonates. Salts other than alkali need warming e.g. Mg, Fe. @Sinaiunieg [email protected] www.su.edu.eg 12 Carbonates and bicarbonates II-Dry reaction The evolved gas (CO2) renders lime water [Ca(OH)2 solution] or baryta water [Ba(OH)2 solution] turbid. 𝐶𝑂2 + 𝐶𝑎 𝑂𝐻 2 → 𝑪𝒂𝑪𝑶𝟑 ↓ +𝐻2 𝑂 Salt + Lime or Excess carbon dioxide gas re-dissolves the PPT (PPT= precipitate). Dil HCl baryta water 𝐶𝑂2 + 𝐻2 𝑂 + 𝑪𝒂𝑪𝑶𝟑 ↓ → 𝐶𝑎 𝐻𝐶𝑂3 2 (𝒔𝒐𝒍𝒖𝒃𝒍𝒆) PPT forms again upon boiling. △ 𝐶𝑎 𝐻𝐶𝑂3 2 → 𝐶𝑂2 + 𝐻2 𝑂 + 𝑪𝒂𝑪𝑶𝟑 ↓ The PPt dissolves in dilute HCl or acetic acid 𝐶𝑎𝐶𝑂3 ↓ +2𝐻𝐶𝑙 → 𝐶𝑎𝐶𝑙2 + 𝐶𝑂2 ↑ + 𝐻2 𝑂 +𝑪𝑶𝟐 @Sinaiunieg [email protected] www.su.edu.eg 13 Carbonate and bicarbonate II-Wet reactions A- Barium chloride, BaCl2 solution Carbonate: white PPT soluble in dilute HCl and acetic acid. 𝐵𝑎𝐶𝑙2 + 𝑁𝑎2 𝐶𝑂3 → 2𝑁𝑎𝐶𝑙 + 𝑩𝒂𝑪𝑶𝟑 ↓ Bicarbonate: No PPT on cold – PPT on boiling 𝐵𝑎𝐶𝑙2 + 2𝑁𝑎𝐻𝐶𝑂3 → 2𝑁𝑎𝐶𝑙 + 𝑩𝒂(𝑯𝑪𝑶𝟑 )𝟐 (𝒔𝒐𝒍𝒖𝒃𝒍𝒆) ∆ 𝑩𝒂(𝑯𝑪𝑶𝟑 )𝟐 → 𝑩𝒂𝑪𝑶𝟑 ↓ + 𝑯𝟐 𝑶 + 𝑪𝑶𝟐 ↑ The same reactions occurs for Calcium chloride; CaCl2 and Magnesium chloride; MgCl2 solutions for both of carbonates and bicarbonates. @Sinaiunieg [email protected] www.su.edu.eg 14 Carbonate and bicarbonate II-Wet reactions B- Calcium chloride, CaCl2 solution Carbonate: white PPT soluble in dilute HCl and acetic acid. C𝑎𝐶𝑙2 + 𝑁𝑎2 𝐶𝑂3 → 2𝑁𝑎𝐶𝑙 + 𝑪𝒂𝑪𝑶𝟑 ↓ Bicarbonate: No PPT on cold – PPT on boiling 𝐶𝑎𝐶𝑙2 + 2𝑁𝑎𝐻𝐶𝑂3 → 𝑁𝑎𝐶𝑙 + 𝑪𝒂(𝑯𝑪𝑶𝟑 )𝟐 (𝒔𝒐𝒍𝒖𝒃𝒍𝒆) ∆ 𝑪𝒂(𝑯𝑪𝑶𝟑 )𝟐 → 𝑪𝒂𝑪𝑶𝟑 ↓ + 𝑯𝟐 𝑶 + 𝑪𝑶𝟐 ↑ C- Magnesium chloride, MgCl2 solution Carbonate: white PPT soluble in dilute HCl and acetic acid. Mg𝐶𝑙2 + 𝑁𝑎2 𝐶𝑂3 → 2𝑁𝑎𝐶𝑙 + 𝑴𝒈𝑪𝑶𝟑 ↓ Bicarbonate: No PPT on cold – PPT on boiling 𝑀𝑔𝐶𝑙2 + 2𝑁𝑎𝐻𝐶𝑂3 → 𝑁𝑎𝐶𝑙 + 𝑴𝒈(𝑯𝑪𝑶𝟑 )𝟐 (𝒔𝒐𝒍𝒖𝒃𝒍𝒆) ∆ 𝑴𝒈(𝑯𝑪𝑶𝟑 )𝟐 → 𝑴𝒈𝑪𝑶𝟑 ↓ + 𝑯𝟐 𝑶 + 𝑪𝑶𝟐 ↑ @Sinaiunieg [email protected] www.su.edu.eg 15 How to identify Carbonates and bicarbonates in their mixtures Interference: both carbonates and bicarbonates evolve CO2 on addition of dilute acid solution. How to separate and identify each of them separately: Add either CaCl2, BaCl2 or MgSO4 On Cold: – Carbonates precipitate on cold while bicarbonates of these metals are soluble. The PPT is soluble in dilute acids Then filter and boil the filtrate or add dilute ammonia to the filtrate: – If bicarbonates are present it will PPT on hot or upon addition of dilute ammonia as carbonate – Ca(HCO3)2 + 2 NH3 CaCO3 ↓ + (NH4)3 CO3 @Sinaiunieg [email protected] www.su.edu.eg 16 Hoe to identify Carbonates and bicarbonates in their mixtures Mixture of CO3– and HCO3- add excess CaCl2 or BaCl2 or MgSO4 on cold Filtrate may be HCO3- White PPT of CaCO3 on Boil cold, soluble in dil. acid or add ammonia H+ CO2 + H2O If PPT (of carbonate) is formed on hot or with dil. ammonia ∴ Bicarbonate is present Carbonate @Sinaiunieg [email protected] www.su.edu.eg 17 Revision Carbonates and bicarbonates Reaction Carbonates Bicarbonates Dry Reaction-Dil HCl Effervescence: CO2 Effervescence: CO2 Turbidity when pass in lime Turbidity when pass in lime water; Ca(OH)2or baryta water or baryta water water; Ba(OH)2 Wet reactions BaCl2 (or MgCl2 or CaCl2) White PPT on Cold No PPT on Cold (negative) White PPT on HOT @Sinaiunieg [email protected] www.su.edu.eg  Sulphur-containing anions @Sinaiunieg [email protected] www.su.edu.eg Sulphur-containing anions Sulfide (S2-) Sulfite (SO32-) Thiosulfate (S2O32-) Sulfate (SO42-) Info Persulfate (S2O82-). @Sinaiunieg [email protected] www.su.edu.eg 20 Dry reactions Addition of dilute HCl 1- Sulfide S2- 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) @Sinaiunieg [email protected] www.su.edu.eg 21 Dry reactions Addition of dilute HCl Sulfide: Detection of H2S (cont.) 3- Reducing properties of H2S: H2S behaves as reducing agent: A- Bleaching pink color of acid KMnO4 + Info 5 H2S + 6 H + 2 MnO4- 2 Mn 2+ + 8 H2O + 5 S B- Bleach the brown color of iodine H2S + I2 2 I- + 2 H+ + S Info C- Change the orange color of acid K2Cr2O7 into green 3H2S + 8 H+ + Cr2O7-- 2 Cr3+ 2+ + 7 H2O + 3 S ↓ ** Info - @Sinaiunieg [email protected] www.su.edu.eg 22 Dry reactions Addition of dilute HCl 2- Sulfite; SO32- SO2 gas evolved due to the decomposition of the liberated unstable sulfurous acid; H2SO3 --2 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) @Sinaiunieg [email protected] www.su.edu.eg 23 Dry reactions Addition of dilute HCl Sulfite; detection of SO2 gas (Cont.) 3- Reducing properties of SO2: A- Bleach pink color of acid KMnO4 5 SO2 + 6 H+ + 2 MnO4- 2 Mn2+ + 8 H2O + 5 SO3 Info B- Bleach the brown color of iodine I2 + SO2 + H2O 2 I- + 2 H+ + SO3 Info C- Change the orange color of acid K2Cr2O7 into green + Info 3 SO2 + 8 H + Cr2O72-- 2 Cr3+ 2+ + 4 H2O + 3 SO3 @Sinaiunieg [email protected] www.su.edu.eg 24 Dry reactions Addition of dilute HCl 3- Thiosulfate; S2O32- 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 2O23-- + 2 H+ H2S 2O3 SO2 + H2O + S ↓ Thiosulphuric acid 4- Sulphate SO42- No reaction with dilute HCl @Sinaiunieg [email protected] www.su.edu.eg 25 Dry reactions Addition of dilute HCl 5- Persulfates, S2O82- No effect on cold. On boiling with water persulphates decomposes to give oxygen ( the reaction is catalyzed by Ag+). K 2S 2O8 + 2 H2O K2SO4 + H2SO4+ [O] [O] reacts with atmospheric oxygen to produce ozone which is detected by its odor and by turning KI-starch paper into blue. 2 KI + O3+ H2O I2+ O2 + 2 KOH @Sinaiunieg [email protected] www.su.edu.eg 26 Wet reactions Solubility: All Na+, K+ and NH4+ salts of sulfur are soluble in water except the following Sulfides: – Other sulfides are insoluble except those of Ca2+, Ba2+, Sr2+ dissolved due to hydrolysis. Sulfites: – Other sulfites are insoluble. Thiosulfates: – Most thiosulfates are soluble. – Ag+, Pb2+, Hg2+, Ba2+ salts are slightly soluble. Sulfates: – All sulfates are soluble except Pb2, Ba2+ , Sr2+ , Ca2+ and Mg2+ salts are slightly soluble. Persulfates: – All known persulfates are soluble. @Sinaiunieg [email protected] www.su.edu.eg 27 Wet reactions 1- reaction with BaCl2: Add BaCl2 reagent to neutral sample solution Anion Reaction S-2 No Visible reaction SO32- Ba2+ -- + SO3--2 BaSO3 (White PPT) Soluble in dilute HCl and soluble in excess sulfite but re-precipitate on boiling. On standing or warming or oxidation with H2O2 or Br2 solution, the PPT; BaSO3 is slowly oxidized to BaSO4 which is insoluble in dilute HCl. S 2O32- -- No PPT in dilute solution. - But a PPT of BaS2O3 is formed from very concentrated solution. SO42- 2+ Ba-- + SO4--2 BaSO4 White PPT insoluble in dilute HCl even on boiling S2O82- -No PPT on cold. -- On boiling a white PPT of BaSO4 is formed due to decomposition of persulfate. Boiling 2 S 2O8--2+ 2 H2O SO4-- + H2SO4+ [O] @Sinaiunieg [email protected] www.su.edu.eg 28 Wet reactions 2- Reducing action Sulfides, polysulfides, sulfites and thiosulfates are reducing agent. A- Iodine solution (weak oxidizing agent): Anion Reaction 2 S-2 I2 + S-- 2 I- + S Info -Decolorization with turbidity due to precipitation of S SO3-2 I2 + SO3--2+ H2O 2 I- + SO4--2+ 2 H+ Info Decolorization S2O3-2 - Weak oxidizing agent such as I2 or Fe2+, oxidize thiosulphate and decolorize the color of I2. H+ I2 + 2 S2O3-- 2 S4O6--2 + 2 I- 2 H+ Info Fe 3+ + 2 S2O3-- S4O6--2+ 2+ 2 Fe @Sinaiunieg [email protected] www.su.edu.eg 29 Wet reactions 2- Reducing action B- KMnO4: Info Decolorisation occurs with sulfides, sulfites and thiosulfates. 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 -2 C- Cr2O7: -2 Cr2O7 + 3 H2S+ 8 H+ 2 Cr3+ 2+ + 7H2O + 3S Info orange green -2 Cr2O7 + SO3--+ 8 H+ 2 Cr3+ 2+ + 3 SO4--+ 4 H2O -2 3+ 4 Cr2O7 + 3 S2O3--+ 26 H+ 8 Cr2+ + 6 SO4--+ 13 H2O @Sinaiunieg [email protected] www.su.edu.eg 30 Special tests and spot tests 1-Sulfides: Test with Cadmium carbonate The solution is shaken with CdCO3, Canary yellow PPT of CdS is produced. - This test could be used for identification and separation of sulfide when present in a mixture with other sulfur containing anion or those anions which do not react with CdCO3. @Sinaiunieg [email protected] www.su.edu.eg 31 Special tests and spot tests 2-Thiosulphates S2O32- : 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--2 + CN - SCN - + SO3--2 Boil Fe 3+ + SCN - Cool Fe(SCN)2+ @Sinaiunieg [email protected] www.su.edu.eg 32 Special tests and spot tests 3-Sulfates SO42- : Hepar test Sulfate is reduced by carbon to sulfide by heating on a piece of charcoal in the presence of Na2CO3 in the reducing zone of the flame. Fusion MSO4-- + Na2CO3 Na2SO4 + MCO3 Info 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. The formed sulfide can also be tested by any other specific test for sulfides. @Sinaiunieg [email protected] www.su.edu.eg 33 5-Persulfates S 2O82- : Depending on their oxidizing effect: 1. Manganous salts could be oxidized into the pink colored permanganate when boiling manganous salt with persulfate in acid medium (HNO3) using one drop of AgNO3 solution as a catalyst. Info 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. 2- S2O82- +2I - I2 + SO4 OR by starch paper. OR can be extracted into chloroform. @Sinaiunieg [email protected] www.su.edu.eg 34 Analysis of mixtures 1- Mixture of Sulfide, Sulfite, Thiosulfate and Sulfate 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 sulfide ion will be precipitated as CdS. Centrifuge, the centrifugate is reacted 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. @Sinaiunieg [email protected] www.su.edu.eg 35  S2-, SO32- , S2O32- and SO42- solution + CdCO3 Yellow PPT of CdS. Centrifugate + BaCl2  Sulfide (S2-). White PPT ( BaSO4 and BaSO3) Centrifugate (S2O3--) add dil HCl dil HCl Heat White PPT (BaSO4 ). SO2 + S Centrifugate: Sulfite  Sulfate (SO42-).  Thiosulfate (S 2O 3 2-). confirmed by oxidation with Br2 or H2O2, which @Sinaiunieg give white PPT. [email protected] www.su.edu.eg 36 2-Mixture of Sulfide, Sulfite and Thiosulfate Interference and separation: as mentioned before. S2-, SO32- and S2O32- solution + CdCO3 Yellow PPT of CdS. Filtrate + BaCl2  Sulfide (S2-). Filterate (S2O32-) White PPT ( BaSO3) dil HCl dil HCl Heat SO2 SO2 + S  Sulfite (SO 3 2-).  Thiosulfate (S 2O 3 2-). 37 Revision-Sulfur containing compounds Reaction Sulfide Sulfite Thiosulfate Sulfate Persulfate Dry Reaction- H2S SO2 On standing or Negative Negative on Cold Dil HCl Rotten egg odor Burnt sulfur odor heating: On boiling: [O] Black to Pb acetate Turbidity to lime or SO2 + S PPT Forms ozone with Yellow to Cd baryta water Atmospheric acetate Reducing properties oxygen Reducing Turns KI-starch properties paper into blue Wet reactions BaCl2 (or Negative White PPT on cold, Negative from dil Positive Negative on cold MgCl2 or soluble in dil acids solutions CaCl2) On boiling with H2O2 Positive from On boiling: white the PPT becomes Conc solution PPT of Ba SO4 insol. in acids Special test Shaking with - Boiling with KCN- Hepar test Turns iodide into CdCO3 NaOH Fusion with Charcoal and iodine (brown) Canary yellow Add FeCl3 in acid sodium carbonate then Turns manganous color medium on cold wetting the residue on into permanganate Blood red silver surface (Pink) @Sinaiunieg Fe(SCN)2+ [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