Pharmaceutical Analytical Chemistry 1 (PA 101) PDF

# Pharmaceutical Analytical Chemistry 1 (PA 101) ## Analysis of Anions - Part 2 ### Anions: Anions are divided into groups according to their parent acid. | Group | Group Name | Anions | |---|---|---| | 1 | Carbonate gp. | CO₃^2-, HCO₃^- | | 2 | Sulphur...

# Pharmaceutical Analytical Chemistry 1 (PA 101) ## Analysis of Anions - Part 2 ### Anions: Anions are divided into groups according to their parent acid. | Group | Group Name | Anions | |---|---|---| | 1 | Carbonate gp. | CO₃^2-, HCO₃^- | | 2 | Sulphur gp. | S^2-, SO₃^2-, S₂O₃^2-, SO₄^2-| | 3 | Halide gp. | F^-, Cl^-, Br^-, I^- | | 4 | Phosphate gp. | PO₄^3-, AsO₄^3-, AsO₃^3- | | 5 | Nitrogen gp. | NO₃^-, NO₂^- | ### Anion Reactions Anion reactions can be divided into three categories: * **Dry Reactions:** Solid powder + acid * **Wet Reactions:** Salt solution + reagent → ppt or color * **Special Test:** Salt solution + special reagent → ppt or color; selective reagent for selected one or two anions ### 3 - Halide gp * **Ionic size:** Increases down the group * **Electron affinity:** Decreases down the group. * **Tendency to lose electrons (gets oxidized):** Increases down the group. Iodide ion is firstly and easily oxidized into free I₂ by losing readily an electron followed by Br^-. It's difficult to oxidize F^- into F₂, as F^- ions are highly stable. ### Reducing & Oxidizing Properties of the Halide gp | Anion | Reducing Properties | Oxidizing Properties | |---|---|---| | Chloride Cl^- | Very weak reducing | Chlorine Cl₂ | | Bromide Br^- | | Bromine Br₂ - Brown color in both aqueous and organic solutions | | Iodide I^- | Strongest reducing properties among halide gp, reducing properties increases down the group | Iodine I₂ - Brown color in aqueous solution, violet color in organic solution, blue color in starch solution | ### Parent Acid - 3 - Halide gp | Anion | Parent Acid | Properties | |---|---|---| | Fluoride F^- | Hydrofluoric acid HF | Highly corrosive | | Chloride Cl^- | Hydrochloric acid HCl | Colorless gas with irritating odor fumes in moist air. | | Bromide Br^- | Hydrobromic acids HBr | Colorless gas with irritating odor fumes in moist air. | | Iodide I^- | Hydroiodic acid: HI | Colorless gas with irritating odor fumes in moist air. Strongest acidic solution of the halogen series | The order of stronger halogen acid is from HI > HBr > HCl > HF ### Solubility - 3 - Halide gp | Anion | Solubility | Exceptions | |---|---|---| | Fluoride F^- | Insoluble in water | Na⁺, K⁺, NH₄⁺, Ag⁺ | | Chloride Cl^- | Soluble in water | Pb²⁺, Ag⁺, Hg⁺, Cu²⁺ | | Bromide Br^- | Soluble in water | Pb²⁺, Ag⁺, Hg⁺, Cu²⁺ | | Iodide I^- | Soluble in water | Pb²⁺, Ag⁺, Hg⁺, Cu²⁺ | ### Dry Reaction (Solid + dil HCI) | Anion | Observations | |---|---| | CO₃^2- | Strong effervescence CO₂ gas | | HCO₃^- | Strong effervescence CO₂ gas | | S^2- | H₂S gas | | SO₃^2- | SO₂ gas | | S₂O₃^2- | SO₂ gas + Colloidal S | | SO₄^2- | No reaction | | F^- | No reaction | | Cl^- | No reaction | | Br^- | No reaction | | I^- | No reaction | ### Dry Reaction (Solid + Conc. H₂SO₄) | Anion | Observations | |---|---| | F^- | HF acid | | Cl^- | HCl gas. How to identify HCl gas? <br> 1. Form white fumes with moist air due the formation of droplets of HCl acid. <br>2. Pungent irritating odor. <br>3. Change a moistened litmus paper from blue into red. <br> 4. Formation of white clouds of NH₄Cl when a glass rod moistened with ammonium hydroxide solution is exposed to the evolved gas <br> NH₄OH + HCl → NH₄Cl + H₂O | | Br^- | HBr gas + Br₂ gas. How to identify Br₂ gas? <br> 1. Brown color. <br> 2. Suffocating & irritating odor <br> 3. Turn starch paper to brown | | I^- | HI gas + I₂ gas. How to identify I₂ gas? <br> 1. Violet color <br> 2. Suffocating & irritating odor <br> 3. Turn starch paper to blue | ### 1- Concentrated H2SO4 +MnO2 Mix the solid halide with an equal amount of MnO₂, add concentrated sulphuric acid, and warm gently. HCl, HBr, and HI can be reduced in acidic medium by strong oxidizing agents such as MnO₄^-, MnO₂ and higher heavy metals oxides producing elemental halogens. 2X + 4H⁺ + MnO₂ → X₂ + Mn²⁺ + H₂O ### 2- Chromyl chloride test - Specific test for chloride Solid Cl^- + solid K₂Cr₂O₇ + conc. H₂SO₄ → CrO₂Cl₂ (chromyl chloride gas), deep red fumes 4 Cl^- + Cr₂O₇^2- + 6 H⁺ → 2 CrO₂Cl₂↑ + 3H₂O CrO₂Cl₂↑ + 4 OH^- → CrO₄^2- + 2 Cl^- + 2H₂O 1. CrO₄^2- + Pb²⁺ → PbCrO₄ ppt 2. CrO₄^2- + H⁺ → Cr₂O₇^2- 3. Cr₂O₇^2- + H₂O₂ → CrO₈^3- - Blue in ether layer (perchromic acid) Classified as dry reactions test because it is carried out on the solid sample ### Wet reaction: Salt soln. (S.S)+ AgNO₃ | Anion | Observations | |---|---| | Fluoride F^- | No ppt. AgF is soluble in water.| | Chloride Cl^- | White ppt. AgCl. <br> - Insoluble in HNO₃. <br> - Soluble in NH₃ (complex). <br> - Soluble in cyanides (complex). <br> - Soluble in S₂O₃^2- (complex). | | Bromide Br^- | Yellowish white ppt. AgBr. Sparingly Soluble in NH₃ (complex). | | Iodide I^- | Yellow ppt. AgBr. Insoluble in NH₃. | There is a periodicity in character of three silver halides. AgCl will be dissolved in dilute ammonia, followed by AgBr in concentrated ammonia, but AgI does not. Why is AgI ppt. insoluble in NH₃? Because the concentration of Ag⁺ produced from dissociation of silver ammine complex (according to its instability constant) is very high and sufficient to exceed the very small value of the solubility product of AgI. AgI + NH₃ → 2[Ag(NH₃)₂]⁺ + I^- Ag⁺ + NH₃ → AgI ### Wet reaction: Salt soln. (S.S)+ BaCl₂ | Anion | Observations | |---|---| | Fluoride F^- | White ppt. BaF₂. Ba²⁺ + 2F^- → BaF₂ | | Chloride Cl^- | No reaction | | Bromide Br^- | No reaction | | Iodide I^- | No reaction | ### Wet reaction: Salt soln. (S.S) + FeCl₃ - Mild oxidizing agent | Anion | Observations | |---|---| | Fluoride F^- | White ppt. of the complex salt [FeF₆]^3-. Fe³⁺ + 6F^- → [FeF₆]^3- | | Chloride Cl^- | No reaction. Due to its weak reducing action. | | Bromide Br^- | No reaction. Due to its relatively weak reducing action. | | Iodide I^- | Brown color of I₂. Fe³⁺ + I^- → Fe²⁺ + I₂. Due to strong reducing action of iodide. | ### Wet reaction: Salt soln. (S.S)+ Pb acetate | Anion | Observations | |---|---| | Fluoride F^- | White ppt. PbF₂ | | Chloride Cl^- | White ppt. PbCl₂ | | Bromide Br^- | White ppt. PbBr₂ | | Iodide I^- | yellow ppt. Pbl₂ | All lead halides are soluble in hot water and precipitate on cooling. ### Wet reaction: Salt soln. (S.S)+ Chlorine water | Anion | Observations | |---|---| | Fluoride F^- | No reaction | | Chloride Cl^-| No reaction | | Bromide Br^- | Chlorine water oxidizes Br^- into Br₂. The liberated Br₂ can be extracted with chloroform as brown or yellow color in chloroform layer. <br> 2KBr + Cl₂ → Br₂ + 2KCl | | Iodide I^- | Chlorine water oxidizes I^- into I₂. The liberated I₂ can be extracted with chloroform as **violet** color in chloroform layer. <br> 2KI + Cl₂ → I₂ + 2KCl | If iodide and bromide are in a mixture, iodide reacts first with chlorine water before bromide as it has more reducing character. 1. Mixture + chloroform + dps chlorine water → **violet** color in chloroform 2. On the same test tube: Take aqueous part + chloroform + dps chlorine water → **Brown** color in chloroform Chlorine water reagent is added drop wise to a solution of iodide or bromide. * Excess chlorine water converts Br₂ into colorless bromic acid (more oxidation). * Excess chlorine water converts I₂ to colorless iodic acid (more oxidation). Br₂ + 5 Cl₂ (excess) + 6 H₂O → 2 HBrO₃ + 10 HCl (bromic acid) I₂ + 5 Cl₂ (excess) + 6H₂O → 2 HIO₃ + 10 HCl (iodic acid) ### Special Tests **Fluoride F^-** **Boron fluoride test:** Mix the fluoride with borax and moisten with concentrated H₂SO₄: Na₂B₄O₇ + H₂SO₄ + 5H₂O -> 4H₃BO₃ + Na₂SO₄ 2NaF + H₂SO₄ -> 2HF + Na₂SO₄ 3HF + H₃BO₃ -> BF₃ (boronfloride gas, green in flame) **Iodide I^-** * **Nitrite or hydrogen peroxide test:** Oxidized in acid solution with nitrite solution or hydrogen peroxide into free iodine. * **Cupper sulphate test:** White precipitate of Cu₂I₂ and free iodine. * **Mercuric chloride test:** Mercuric iodide will be precipitated as yellow-scarlet red ppt. which dissolves in excess iodide forming soluble colorless complex. ### Mixture of Cl^- and I^- * Add AgNO₃ and NH₃ * Filter or centrifuge * Ppt. will contain AgI. Confirmed by concentrated H₂SO₄ test * Filtrate will contain Cl^-. ### Dry Reaction (Solid + dil HCI) | Anion | Observations | |---|---| | CO₃^2- | Strong effervescence CO₂ gas | | HCO₃^- | Strong effervescence CO₂ gas | | S^2- | H₂S gas | | SO₃^2- | SO₂ gas | | S₂O₃^2- | SO₂ gas + Colloidal S | | SO₄^2- | No reaction | | F^- | No reaction | | Cl^- | No reaction | | Br^- | No reaction | | I^- | No reaction | ### Dry Reaction (Solid + Conc. H₂SO₄) | Anion | Observations | |---|---| | F^- | HF | | Cl^- | HCl gas | | Br^- | HBr gas + Br₂ gas | | I^- | HI gas + I₂ gas | ### Wet reaction: Salt soln. (S.S)+ AgNO₃ | Anion | Observations | |---|---| | CO₃^2- | White ppt of Ag₂CO₃ (Sol in NH₃) | | HCO₃^- | No ppt (Soluble AgHCO₃) | | S^2- | Black ppt Ag₂S (Insol in NH₃) | | SO₃^2- | White ppt Ag₂SO₃ (Sol in NH₃). Self-oxidation reduction. Ag₂SO₃ soluble in excess SO₃^2- | | S₂O₃^2- | White ppt. Ag₂S₂O₃ → turn to black Ag₂S. Ag₂S₂O₃ soluble in excess S₂O₃^2- | | SO₄^2- | White ppt Ag₂SO₄ | | F^- | No ppt | | Cl^- | White ppt AgCl (sol in NH₃) | | Br^- | Yellowish white ppt AgBr (sparingly sol. In NH₃) | | I^- | **Yellow** ppt (Insol in NH₃) | ### Wet reaction: Salt soln. (S.S)+ BaCl₂ | Anion | Observations | |---|---| | CO₃^2- | White ppt of Ba₂CO₃ | | HCO₃^- | No ppt Soluble Ba(HCO₃)₂ | | S^2- | No ppt | | SO₃^2- | White ppt BaSO₃ (Sol in dil. HCI) | | S₂O₃^2- | White ppt Ba₂S₂O₃ (if very conc. Soln.) | | SO₄^2- | White ppt BaSO₄ (Insol in dil HCI) | | F^- | White ppt BaF₂ | | Cl^- | No ppt | | Br^- | No ppt | | I^- | No ppt | ### Wet reaction: Salt soln. (S.S) + FeCl₃ | Anion | Observations | |---|---| | CO₃^2- | - | | HCO₃^- |- | | S^2- | Black ppt. Fe₂S₃ | | SO₃^2- | **Dark Red** color Fe₂(SO₃)₃ | | S₂O₃^2- | **Purple** color → disappear | | SO₄^2- | No reaction | | F^- | white ppt of complex [FeF₆]^3- | | Cl^- | No reaction | | Br^- | No reaction | | I^- | **Brown** color of I₂ | ### Wet reaction: Salt soln. (S.S)+ Pb acetate | Anion | Observations | |---|---| | CO₃^2- | - | | HCO₃^- |- | | S^2- | Black ppt. PbS | | SO₃^2- | White ppt. PbSO₃ | | S₂O₃^2- | White ppt. Pb₂S₂O₃ → turn to black PbS | | SO₄^2- | White ppt. PbSO₄ <br>Insoluble in mineral acids <br> Soluble in ammonium acetate <br> Soluble in hydroxide solutions (complex) | | F^- | White ppt. PbF₂ | | Cl^- | White ppt. PbCl₂ | | Br^- | White ppt. PbBr₂ | | I^- | **Yellow** ppt. Pbl₂ | ### Complex formation * Ag⁺ + NH₃ → 2[Ag(NH₃)₂]⁺ * Ag₂SO₃ + SO₃^2- → [Ag(SO₃)₂]^3- * Ag₂S₂O₃ + S₂O₃^2- → [Ag(S₂O₃)₂]^3- * Fe³⁺ + S₂O₃^2- → [Fe(S₂O₃)₂]^- * Fe³⁺ + 6 F^- →[FeF₆]^3- * PbSO₄ + 4 OH^- → [Pb(OH)₄]^2- +SO₄^2- ## Thank you! The document contains a diagram of 6 test tubes with various coloured liquids. It also contains a diagram of a Hulk and Shrek character.