Analytical Chemistry 1 (PAC101) Lecture Notes PDF

# Analytical Chemistry 1 (PAC101) ## Qualitative Analytical Chemistry ### Analysis of Anions - Anions are divided into groups according to their parent acid. - There are 5 groups: - **Carbonate**: Carbonate $CO_3^{2-}$, Bicarbonate $HCO_3^-$ - **Sulfur**: Sulfide $S^{2-}$, Sulfite $SO_3^...

# Analytical Chemistry 1 (PAC101) ## Qualitative Analytical Chemistry ### Analysis of Anions - Anions are divided into groups according to their parent acid. - There are 5 groups: - **Carbonate**: Carbonate $CO_3^{2-}$, Bicarbonate $HCO_3^-$ - **Sulfur**: Sulfide $S^{2-}$, Sulfite $SO_3^{2-}$, Thiosulfate $S_2O_3^{2-}$, Sulfate $SO_4^{2-}$ - **Halide**: Fluoride $F^-$, Chloride $Cl^-$, Bromide $Br^-$, Iodide $I^-$ - **Phosphate**: Phosphate $PO_4^{3-}$, Arsenate $AsO_4^{3-}$, Arsenite $AsO_3^{3-}$ - **Nitrogen**: Nitrate $NO_3^-$, Nitrite $NO_2^-$ ## Qualitative Analysis: - Detection and identification of different substances single or in a mixture. - **What type of samples we are going to study?** Inorganic salts. ## How are Salts formed? - **Acid + Base → Salt + Water** - *Example*: $HCl + NaOH → NaCl + Water$ ## 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. ### Applications - **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 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 $CO_3^{2-}$ - **Parent Acid**: Carbonic acid $H_2CO_3$ (Weak unstable acid) - $H_2CO_3 \rightleftharpoons H^+ + HCO_3^- \rightleftharpoons H^+ + CO_3^{2-}$ - **Solubility**: All are insoluble except $Na^+$, $K^+$, $NH_4^+$ - **Dry reaction**: Solid + dilute HCl → Strong effervescence and evolution of $CO_2$ gas (Displacement reaction) - **How can you test for $CO_2$?** - Colorless - Odorless - Cause turbidity of lime water $Ca(OH)_2$ - **Dry reaction**: Solid + dilute $H_2SO_4$ → Strong effervescence and evolution of CO₂ gas + White ppt $BaSO_4$, $PbSO_4$ - **Wet reaction**: - Salt soln. (S.S) + $AgNO_3$ (silver nitrate) → White ppt $Ag_2CO_3$ - $Ag_2CO_3$ Sol. In: - Nitric acid: $Ag_2CO_3 + 2 H^+ → 2 Ag^+ + CO_3^{2-} + H_2O$ - Ammonia: $Ag_2CO_3 + NH_3 → 2[Ag(NH_3)_2]^+ + CO_3^{2-}$ - Boil (-$CO_2$) → White ppt $Ag_2CO_3$ → yellowish brown ppt $Ag_2O$ - Salt soln. (S.S) + $BaCl_2$ (Barium Chloride) or $MgSO_4$ (Magnesium Sulfate) → White ppt $BaCO_3$, $MgCO_3$ - $Na_2CO_3 + MgSO_4 → MgCO_3↓+ Na_2SO_4$(white ppt) - $Na_2CO_3 + BaCl₂ → BaCO_3↓ + 2NaCl$ (white ppt) ### Bicarbonate $HCO_3^-$ - **Parent Acid**: Carbonic acid $H_2CO_3$ - **Solubility**: All are soluble - **Wet reaction**: On cold - No ppt. is formed since all bicarbonates are soluble in water - Salt soln. (S.S) + $BaCl_2$ (Barium Chloride) → $Ba^{2+} +2HCO_3 → Ba(HCO_3)_2$ - Boil → $BaCO_3↓ + CO_2 +H_2O$ - **Differentiate & separate between $CO_3^{2-}$ & $HCO_3^-$ in a mixture.** - **How to convert Bicarbonate to Carbonate?** - **Boiling**: $Ba(HCO_3)_2 + Boil → BaCO_3↓ + CO_2 +H_2O$ - **Adding ammonia**: $Ba(HCO_3)_2 + NH_3 → BaCO_3↓ +(NH_4)_2CO_3$ ## 2- Sulfur gp ### Sulfide $S^{2-}$ - **Parent Acid**: Hydrogen sulfide ($H_2S$) - Very weak acid - Rotten egg odor (Toxic) - **Solubility**: Insol. in water Except: $Na^+$, $K^+$, $NH_4^+$, $Ba^{2+}$, $Ca^{2+}$, $Sr^{2+}$ - **Dry Reaction**: Solid + dil. HCl → $H_2S$ gas - $S^{2-} + 2H^+ → H_2S$ - **How to identify $H_2S$ gas?** - Colorless - Rotten egg odor (Toxic) - Turn lead acetate paper black $H_2S + Pb^{2+} → PbS↓$ black ppt - Turn Cadmium acetate paper to yellow $H_2S + Cd^{2+} → CdS ↓$yellow ppt - Reducing Agent: - Turn $I_2$ soln. paper from brown to colorless - Turn $K_2Cr_2O_7/H^+$ paper from orange to green - Turn $KMnO_4/H^+$ paper from pink to colorless - **Wet reaction**: Salt soln. (S.S)+ $BaCl_2$ → No visible reaction - **Wet reaction**: Salt soln. (S.S)+ $AgNO_3$ → Black ppt. $Ag_2S$ - Sol. in hot dil $HNO_3$ - Insol in $NH_3$ - **Wet reaction**: Salt soln. (S.S)+ $FeCl_3$ → Black ppt. $Fe_2S_3$ ### Sulfite $SO_3^{2-}$ - **Parent Acid**: Sulfurous acid ($H_2SO_3$) - Weak acid - Unstable, by heating → $SO_2↑ + H_2O$ - **Solubility**: Insol. in water Except: $Na^+$, $K^+$, $NH_4^+$ - **Dry Reaction**: Solid + dil. HCl → $SO_2$ gas - $SO_3^{2-} + 2H^+ →H_2SO_3 → SO_2 +H_2O$ - **How to identify $SO_2$?** - Colorless - Burnt sulfur odor - Turbid lime water... why? due to CaSO3 ppt. formation - $Ca (OH)_2 + SO_2 → CaSO_3 + H_2O$ - $CaSO_3 + SO_2 + H_2O → Ca(HSO_3)_2$ - Reducing Agent: - Turn $I_2$ soln. paper from brown to colorless - Turn $K_2Cr_2O_7/H^+$ paper from orange to green - Turn $KMnO_4/H^+$ paper from pink to colorless - **Wet reaction**: Salt soln. (S.S)+ $BaCl_2$ → White ppt $BaSO_3$, Sol. in dil HCI - **Wet reaction**: Salt soln. (S.S)+ $AgNO_3$ → White ppt. $Ag_2SO_3$, Sol. in $HNO_3$, Sol. in $NH_3$ (complex) - $Ag_2SO_3$ undergoes self-oxidation reduction to produce a grey ppt. of metallic silver - $2 Ag_2SO_3 → 2 Ag° + Ag_2SO_4 + SO_2$ - **Wet reaction**: Salt soln. (S.S)+ $FeCl_3$ → Dark Red color $Fe_2(SO_3)_3$ ### Thiosulfate $S_2O_3^{2-}$ - **Parent Acid**: Thiosulfuric acid $H_2S_2O_3$ - Never stable → $SO_2↑ + S↓ + H_2O$ - Not known in free form - Its salts solutions decompose upon standing specially in acidic medium - **Solubility**: Sol. in water Except: $Pb^{2+}$, $Ag^+$, $Hg^+$, $Ba^{2+}$ - **Dry Reaction**: Solid + dil. HCl → $SO_2$ gas → $S$ (Yellow colloidal sulfur) - $S_2O_3^{2-} + 2H^+ → H_2S_2O_3 → SO_2 + S +H_2O$ - No immediate change on cold, but on warming or standing, the sol. become turbid due to the liberated yellow colloidal sulfur with evolution of SO2 gas - **Wet reaction**: Salt soln. (S.S)+ $BaCl_2$ → White ppt $Ba_2S_2O_3$ if very conc. soln. - **Wet reaction**: Salt soln. (S.S)+ $AgNO_3$ → White ppt. $Ag_2S_2O_3$, turn to black $Ag_2S$ - On Standing, change its color from white to yellow to brown to black .. why? due to $Ag_2S$ formation - $Ag_2S_2O_3$ soluble in excess $S_2O_3^{2-}$ (complex formation) - $Ag_2S_2O_3 + S_2O_3^{2-} → [Ag(S_2O_3)_2]^{3-}$ - **Wet reaction**: Salt soln. (S.S)+ $FeCl_3$ → Purple color → boil → disappear - Due to formation of complex ferric thiosulfate (purple color) which disappear on boiling as tetrathionate and $Fe^{2+}$ - $Fe^{3+} + S_2O_3^{2-} → [Fe(S_2O_3)_2]^{-}$ - $Fe^{3+} + S_2O_3^{2-} → 2Fe^{2+} + S_4O_6^{2-}$ - **Special Tests**: - $S_2O_3^{2-} + KCN → SCN^-$ - $Fe^{3+} + SCN^-→ [Fe(SCN)]^{2+}$ Blood red color ### Sulfate $SO_4^{2-}$ - **Parent Acid**: Sulfuric acid ($H_2SO_4$) - Colorless, oily liquid - Strong acid - Dehydrating agent (cause charring to org. compounds) - Moderate oxidizing agent - **Properties of sulfuric acid:** - Acid properties: - $H_2SO_4 \rightleftharpoons H^+ + HSO_4^-$ (hydrogen sulphate) - $HSO_4^- \rightleftharpoons H^+ + SO_4^{2-}$ (sulphate) - It reacts with active metals liberating $H_2$ - $H_2SO_4 + Znº → Zn^{2+} + SO_4^{2-} + H_2$ - Dehydrating properties: - Charring with sugars - Drying agent, highly exothermic reaction. - Oxidizing properties: - upon reduction it may give $SO_2$ or $S^{0}$ or even $H_2S$ according to the reducing agent. - **Solubility**: Sol. in water Except: $Pb^{2+}$, $Hg^+$, $Ba^{2+}$, $Ca^{2+}$, $Sr^{2+}$ - **Dry Reaction**: Solid + dil. HCl → No Reaction.. why? Because the parent acid is stronger than HCl - **Wet reaction**: Salt soln. (S.S)+ $BaCl_2$ → White ppt $BaSO_4$, Insol. in dil HCI (As the parent acid of $BaSO_4$ is strong) - **Wet reaction**: Salt soln. (S.S)+ $AgNO_3$ → White ppt. $Ag_2SO_4$, if very conc. soln. - **Wet reaction**: Salt soln. (S.S)+ $FeCl_3$ → No Reaction - **Wet reaction**: Salt soln. (S.S)+ Pb acetate → White ppt. $PbSO_4$ - Insol in mineral acids - Soluble in ammonium acetate $PbSO_4+ CH_3COO^- → Pb (CH_3COO)_2+ SO_4^{2-}$ - Soluble in hydroxide solutions $PbSO_4+ 4 OH^- → [Pb(OH)_4]^{2-} +SO_4^{2-}$ - **Special Tests**: Hepar test for sulphate - $MSO_4 + Na_2CO_3 → Na_2SO_4+ MCO_3$ - $Na_2SO_4 + C → Na_2S + 4CO$ - $S^{2-} + 2H_2O → 2OH^-+ H_2S$ - $H_2S + 2 Agº → Ag_2S + H_2$ Brownish black ## Mixture of $S^{2-}$, $SO_3^{2-}$, $S_2O_3^{2-}$ and $SO_4^{2-}$ - **Add $CdCO_3$** - **Filtration or centrifuguation**: - **Ppt**: Yellow ppt $S^{2-}$ - **Filtrate (soluble)**: $SO_3^{2-}$, $S_2O_3^{2-}$ and $SO_4^{2-}$ - **Add $BaCl_2$** - **Ppt**: $BaSO_3 + BaSO_4$ - **Add HCI** - **White ppt**: $BaSO_4$ - **Filtrate (soluble)**: $BaSO_3$ confirm by reducing character - **Filtrate (soluble)**: $S_2O_3^{2-}$ - **Confirm by Heat + HCI**: $SO_2 + S$ # Thank you The drawing shows a positive image of a cat and a negative one of an onion. The text describes a positive connotation to cats and a negative one to onions.