Analytical Chemistry 1 (PAC101) PDF

Analytical Chemistry 1 (PAC101) Qualitative Analytical Chemistry Analysis of Anions  Image result for tall tree clip art Qualitative analysis:...

Analytical Chemistry 1 (PAC101) Qualitative Analytical Chemistry Analysis of Anions  Image result for tall tree clip art Qualitative analysis: Detection and identification of different substances single or in a mixture Next semester What type of samples Quantitative Qualitative we are going to study? What is the sample’s What is the sample’s concentration/amount? name/identity ? Inorganic salts Analytical Chemistry How are Salts formed ? Acid + Base → Salt + Water HCl + NaOH → NaCl + Water Na+Cl- Na+ Cl- Basic part Acid part Cation Anion Metal has +ve charge Nonmetal has -ve charge  Qualitative Chemical Tests Advantages Positive result: Color change or ppt formation → Visual detection Cheap, Quick, Simple Disadvantages Low sensitivity → can NOT detect low sample concentration Low selectivity → Same reagent can give same +ve results with more than one sample → An interference may occur  Qualitative Chemical Tests Applications Present or absent YES or NO Water Analysis Some salts should be present Some salts should be Absent Pharmaceuticals Active ingredient: ( Iron, Calcium, Sodium,…. Etc) Metallic impurity from synthesis procedure Forensic Analysis (for toxic salts) (stomach contents)  Anions Divided into groups according to their parent acid: Carbonate Bicarbonate 1 Carbonate gp. CO32- HCO3- Sulphide Sulphite Thiosulphate Sulphate 2 Sulphur gp. S2- SO32- S2O32- SO42- Fluoride Chloride Bromide Iodide 3 Halide gp. F- Cl- Br- I- Phosphate Arsenate Arsenite 4 Phosphate gp. PO43- AsO43- AsO33- Nitrate Nitrite 5 Nitrogen gp. NO3- NO2-  Anions reactions Dry reactions In dry test tube: 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  1- Carbonates and Bicarbonates group Carbonate CO32- Bicarbonate HCO3- Parent Acid Carbonic acid H2CO3 (Weak unstable acid) H2CO3 H+ + HCO3 - H+ + CO3 2- All are Insoluble Solubility All are soluble except Na+, K+, NH4+ Dry reaction: Strong effervescence and evolution of CO2 gas Solid + dilute (Displacement reaction) HCl Reaction in which strong How can you test for CO2? acid as HCl & H2SO4 Colorless - Odorless liberates the weak acids as Cause turbidity of lime water Ca(OH)2 H2CO3 from their salts (Lime water test)  1- Carbonates and Bicarbonates group Carbonate CO32- Bicarbonate HCO3- Dry reaction: H2CO3 H2CO3 Solid + dilute HCl CO32- + 2 H+→ CO2+ H2O HCO3- + 2 H+→ CO2+ H2O (lime water) Ca(OH)2 (lime water) Ca(OH)2 CaCO3 ↓ CaCO3 ↓ (milky white ppt) (milky white ppt) If long exposure to CO2 If long exposure to CO2 Ca(HCO3)2 Ca(HCO3)2 Soluble Soluble Turbidity decreases Turbidity decreases To identify the evolved gas Lime water test  Carbonate CO32- Bicarbonate HCO3- Dry reaction: Solid + dilute Strong effervescence and evolution of CO2 gas H2SO4 White ppt BaSO4 PbSO4  Carbonate CO32- Bicarbonate HCO3- Wet reaction on cold.. No ppt. is formed White ppt Ag2CO3 since all bicarbonates are soluble in Salt soln. (S.S) + water AgNO3 (silver nitrate) Sol. Product AgHCO3 Differentiate Ag2CO3 Sol. In: & separate 1) Nitric acid: between Heat Ag2CO3 + 2 H+ → 2 Ag+ + CO32- + H2O CO32-& HCO3- White ppt Ag2CO3 in a mixture. 2)Ammonia: Ag2CO3 + NH3 → 2[Ag (NH3)2]+ + CO32- Boil (-CO2) White ppt Ag2CO3 → yellowish brown ppt Ag2O  Carbonate CO32- Bicarbonate HCO3- Wet reaction: Salt soln. (S.S) White ppt BaCO3 Ba2+ +2HCO3- → Ba(HCO3)2 White ppt MgCO3 + BaCl2 Boiling (Barium Chloride) BaCO3 ↓ + CO2 +H2O Or + MgSO4 (Magnesium Differentiate and separate Sulfate) between carbonate and bicarbonate in a mixture. Na2CO3 + MgSO4 → MgCO3 ↓+ Na2SO4 (white ppt) Na2CO3 + BaCl2 → BaCO3 ↓ + 2NaCl (white ppt) How to convert Bicarbonate to Carbonate? Boiling Ba(HCO3)2 + Boil → BaCO3 ↓ + CO2 +H2O Adding ammonia Ba(HCO3)2 + NH3 → BaCO3 ↓ +(NH4)2CO3 Parent Acid 2- Sulfur gp Sulfide S2- Hydrogen sulfide (H2S) - Very weak acid - Rotten egg odor (Toxic) Sulfite SO32- Sulfurous acid (H2SO3) - Weak acid - Unstable, by heating → SO2 ↑ + H2O Thiosulfate S2O32- Thiosulfuric acid H2S2O3 - Never stable → SO2 ↑ + S↓ + H2O - Not known in free form - Its salts solutions decompose upon standing specially in acidic Sulfate SO42- Sulfuric acid (H2SO4) medium - Colorless, oily liquid - Strong acid - Dehydrating agent (cause charring to org. compounds) - Moderate oxidizing agent Sulfide, Sulfite, Thiosulfate are reducing agents → react with oxidizing agents such as Iodine (I2), Pot. dichromate (K2Cr2O7/H+ ) Pot. permanganate (KMnO4/H+ ) I2 + S2- → 2 I- + So Solution of K2Cr2O7 & KMnO4 is 2 KMnO4 + 5 S2-+ 6H+ → 2 Mn2++ 5 So + 8H2O acidified.. why? Cr2O72- + S2- + 8H+ →2 Cr3+ + 3 So + 7H2O bec the oxidation potential of oxidizing agents which contains I2 + SO32-+ H2O → 2I- + SO42-+2H+ O2 increases with H+ ions 2 MnO4-+ 5 SO32- + 6H+ → 2 Mn2+ + 5 SO42- + 3H2O Cr2O72- + 3 SO32-+ 8H+ →2 Cr3+ + 3 SO42- + 4H2O Why S2O32- is oxidized to S4O62- with I2 & oxidized to SO42- with I2 + 2 S2O32- → 2 I- + S4O62- Tetrathionate K2Cr2O7 & KMnO4 ? 8 MnO4-+ 5 S2O32- + 14H+ → 8 Mn+++ 10 SO42- + 7H2O bec. K2Cr2O7 & KMnO4 are strong 4 Cr2O72-+ 3 S2O32-+ 26H+ → 8 Cr3++ 6 SO42- + 13 H2O oxidizing agents have high oxidation potential while I2 is weak oxidizing agent Properties of sulphuric acid: 1) Acid properties H2SO4 → H+ + HSO4¯ (hydrogen sulphate) HSO4¯ → H+ + SO42¯ (sulphate) It reacts with active metals liberating H2 H2SO4 + Zn0 → Zn2+ + SO42- + H2 2) Dehydrating properties - Charring with sugars - Drying agent, highly exothermic reaction. 3) Oxidizing properties - upon reduction it may give SO2 or S0 or even H2S according to the reducing agent. Solubility 2- Sulfur gp Sulfide S2- Sulfite SO32- Insol. in water Insol. in water Except: Except: Na+ K+ NH4+ Na+ K+ NH4+ Ba2+ Ca2+ Sr2+ Thiosulfate S2O32- Sulfate SO42- Sol. in water Sol. in water Except: Except: Pb2+ Ag+ Hg+ Pb2+ Hg+ Ba2+ Ba2+ Ca2+ Sr2+ Nancy Wahid, PhD Dry Reaction 2- Sulfur gp (Solid + dil. HCl) Sulfide S2- Sulfite SO32- H2S gas SO2 gas S2-+ 2H+ → H2S SO32- + 2H+ →H2SO3 → SO2 +H2O Thiosulfate S2O32- Sulfate SO42- warm SO2 gas → S (Yellow colloidal sulfur) No Reaction.. why? S2O32- + 2H+ →H2S2O3 → SO2 + S +H2O Because the parent acid No immediate change on cold, but on warming or is stronger than HCl standing, the sol. become turbid due to the liberated yellow colloidal sulphur with evolution of SO2 gas Dry Reaction (Solid + dil HCl) Sulfide S2- H2S gas How to identify H2S gas? 1- Colorless 2- Rotten egg odor (Toxic) 3- Turn lead acetate paper black H2S + Pb2+ → PbS ↓ black ppt 4- Turn Cadmium acetate paper to yellow H2S + Cd2+ → CdS ↓yellow ppt 5- Reducing Agent Turn I2 soln. paper from brown to colorless Turn K2Cr2O7/H+ paper from orange to green Turn KMnO4/H+ paper from pink to colorless Dry Reaction (Solid + dil HCl) Sulfite SO32- SO2 gas How to identify SO2? 1- Colorless 2- Burnt sulfur odor Ca (OH)2 + SO2 → CaSO3 + H2O 3- Turbid lime water... why? CaSO3 + SO2 + H2O → Ca(HSO3)2 due to CaSO3 ppt. formation but with long passage of SO2 → turbidity decreases 4- Reducing Agent Turn I2 soln. paper from brown to colorless Turn K2Cr2O7/H+ paper from orange to green Turn KMnO4/H+ paper from pink to colorless Wet reaction: Salt soln. (S.S)+ BaCl2 Sulfide S2- Sulfite SO32- No visible reaction White ppt BaSO3 Sol. in dil HCl Thiosulfate S2O3 2- Sulfate SO42- White ppt Ba2S2O3 White ppt BaSO4 if very conc. soln. Insol. in dil HCl As the parent acid of BaSO4 is strong Wet reaction: Salt soln. (S.S)+ AgNO3 Sulfide S2- Sulfite SO32- Sol. in HNO3 Black ppt. Ag2S White ppt. Ag2SO3 Sol. in NH3 (complex) Sol. in hot dil HNO3 Insol in NH3 Ag2SO3 undergoes self-oxidation reduction to produce a grey ppt. of metallic silver boil Thiosulfate S2O3 2- 2 Ag2SO3 → 2 Ago + Ag2SO4 + SO2 White ppt. Ag2S2O3 → turn to black Ag2S Ag2SO3 soluble in excess SO32-(complex formation) On Standing, change its color from white to yellow to brown to black.. why? Ag2SO3 + SO32- → [Ag(SO3)2]3- due to Ag2S formation Ag2S2O3 soluble in excess S2O32- (complex Sulfate SO42- formation) White ppt Ag2SO4 Ag2S2O3 + S2O32- → [Ag(S2O3)2]3- if very conc. soln. Wet reaction: Salt soln. (S.S)+ FeCl3 Mild oxidizing agent Sulfide S2- Sulfite SO32- Black ppt. Fe2S3 Dark Red color Fe2(SO3)3 Thiosulfate S2O32- Sulfate SO42- boil Purple color → disappear Due to formation of complex ferric thiosulfate No Reaction (purple color) which disappear on boiling as tetrathionate and Fe2+ Fe3+ + S2O32- → [Fe(S2O3)2] - boil Fe3+ + S2O32- → 2Fe2+ + S4O62- Wet reaction: Salt soln. (S.S)+ Pb acetate Sulfide S2- Sulfite SO32- Black ppt. PbS White ppt. PbSO3 Sol. in hot HNO3 On boiling → oxidation to PbSO4 Thiosulfate S2O32- Sulfate SO42- boil White ppt. PbSO4 White ppt. Pb2S2O3 → turn to black PbS Insol in mineral acids Soluble in ammonium acetate PbSO4+ CH3COO- → Pb (CH3COO)2+ SO42- soluble in hydroxide solutions PbSO4+ 4 OH- → [Pb(OH)4]2− +SO42 Special Tests Sulfide S2- 1- Cd2+ + S2- → CdS↓ 2- Add sodium nitroprusside solution to the alkaline sulphide solution using NaOH or NH4OH, a purple colour is produced. S2- + [Fe(CN)5NO]2- →[Fe(CN)5NOS]4- Thiosulfate S2O32- Sulfate SO42- Hepar test for sulphate: S2O32- + KCN → SCN- MSO4 + Na2CO3 → Na2SO4 + MCO3 Fe3+ + SCN- → [Fe(SCN)]2+ Na2SO4 + C → Na2S + 4CO Blood red color S2- + 2H2O → 2OH- + H2S H2S + 2 Ag0 → Ag2S + H2 Brownish black  Mixture of S2-, SO32-, S2O32- and SO42- + CdCO3 Filtration or Ppt. Filtrate (Soluble) centrifugation Yellow ppt S2- SO32-, S2O32- and SO42- + BaCI2 BaSO3+ BaSO4 Ppt. Filtrate (Soluble) + HCl S2O32- Confirm by White ppt Filtrate (Soluble) Heat HCl BaSO3 BaSO4 confirm by reducing character SO2 + S