Salt Analysis Practical

Cheatsheet Content

Salt Analysis: Basic Radicals (Cations) Identification of one basic radical from the following list: Group 0: Ammonium ($\text{NH}_4^+$) Group I: Lead ($\text{Pb}^{2+}$) Group II: Copper ($\text{Cu}^{2+}$) Group III: Ferric ($\text{Fe}^{3+}$), Aluminium ($\text{Al}^{3+}$) Group IV: Zinc ($\text{Zn}^{2+}$) Group V: Calcium ($\text{Ca}^{2+}$), Barium ($\text{Ba}^{2+}$) Group VI: Magnesium ($\text{Mg}^{2+}$) Ammonium ($\text{NH}_4^+$) Dry Test: Heat salt with $\text{NaOH}$ solution. Observation: Pungent smell of ammonia gas. Confirmatory: $\text{NH}_3$ gas turns red litmus blue, gives dense white fumes with $\text{HCl}$ rod. Lead ($\text{Pb}^{2+}$) Group Precipitant: Dilute $\text{HCl}$. Observation: White precipitate of $\text{PbCl}_2$. Confirmatory: $\text{PbCl}_2$ is soluble in hot water. Add $\text{KI}$ to hot solution: Yellow precipitate of $\text{PbI}_2$. Add $\text{K}_2\text{CrO}_4$: Yellow precipitate of $\text{PbCrO}_4$. Copper ($\text{Cu}^{2+}$) Group Precipitant: $\text{H}_2\text{S}$ in acidic medium (dilute $\text{HCl}$). Observation: Black precipitate of $\text{CuS}$. Confirmatory: $\text{CuS}$ dissolves in hot dilute $\text{HNO}_3$. Add $\text{NH}_4\text{OH}$ to the solution: Blue precipitate of $\text{Cu}(\text{OH})_2$, dissolves in excess $\text{NH}_4\text{OH}$ to form deep blue solution (due to $[\text{Cu}(\text{NH}_3)_4]^{2+}$). Ferric ($\text{Fe}^{3+}$) Group Precipitant: $\text{NH}_4\text{OH}$ in presence of $\text{NH}_4\text{Cl}$. Observation: Reddish-brown precipitate of $\text{Fe}(\text{OH})_3$. Confirmatory: Precipitate dissolves in dilute $\text{HCl}$. Add $\text{K}_4[\text{Fe}(\text{CN})_6]$: Prussian blue precipitate. Add $\text{KCNS}$: Blood red coloration. Aluminium ($\text{Al}^{3+}$) Group Precipitant: $\text{NH}_4\text{OH}$ in presence of $\text{NH}_4\text{Cl}$. Observation: White gelatinous precipitate of $\text{Al}(\text{OH})_3$. Confirmatory: Precipitate dissolves in $\text{NaOH}$ solution, reprecipitates on adding $\text{HCl}$ and $\text{NH}_4\text{OH}$. Lake test: Add blue litmus solution and then $\text{NH}_4\text{OH}$ dropwise: Blue lake formation. Zinc ($\text{Zn}^{2+}$) Group Precipitant: $\text{H}_2\text{S}$ in presence of $\text{NH}_4\text{OH}$ and $\text{NH}_4\text{Cl}$. Observation: White precipitate of $\text{ZnS}$. Confirmatory: $\text{ZnS}$ dissolves in dilute $\text{HCl}$. Add $\text{K}_4[\text{Fe}(\text{CN})_6]$: White precipitate of $\text{K}_2\text{Zn}_3[\text{Fe}(\text{CN})_6]_2$. Calcium ($\text{Ca}^{2+}$) Group Precipitant: Ammonium oxalate ($\text{(NH}_4)_2\text{C}_2\text{O}_4$) in ammoniacal medium. Observation: White precipitate of $\text{CaC}_2\text{O}_4$. Confirmatory: Precipitate dissolves in dilute $\text{HCl}$. Flame test: Brick red flame. Barium ($\text{Ba}^{2+}$) Group Precipitant: Ammonium carbonate ($\text{(NH}_4)_2\text{CO}_3$) in ammoniacal medium. Observation: White precipitate of $\text{BaCO}_3$. Confirmatory: Precipitate dissolves in dilute $\text{CH}_3\text{COOH}$. Add $\text{K}_2\text{CrO}_4$: Yellow precipitate of $\text{BaCrO}_4$. Flame test: Apple green flame. Magnesium ($\text{Mg}^{2+}$) Group Precipitant: Disodium hydrogen phosphate ($\text{Na}_2\text{HPO}_4$) in ammoniacal medium. Observation: White crystalline precipitate of $\text{MgNH}_4\text{PO}_4$. Confirmatory: Magneson reagent test: Add Magneson reagent and $\text{NaOH}$: Blue precipitate. Salt Analysis: Acid Radicals (Anions) Identification of one acid radical from the following list: Dilute $\text{H}_2\text{SO}_4$ group: Carbonate ($\text{CO}_3^{2-}$), Sulphite ($\text{SO}_3^{2-}$), Acetate ($\text{CH}_3\text{COO}^-$) Concentrated $\text{H}_2\text{SO}_4$ group: Chloride ($\text{Cl}^-$), Bromide ($\text{Br}^-$), Iodide ($\text{I}^-$), Nitrate ($\text{NO}_3^-$) Special group: Sulphate ($\text{SO}_4^{2-}$), Phosphate ($\text{PO}_4^{3-}$), (Acetate is also here) Carbonate ($\text{CO}_3^{2-}$): Dilute $\text{H}_2\text{SO}_4$ Group Test: Add dilute $\text{H}_2\text{SO}_4$ to salt. Observation: Brisk effervescence (colorless, odorless gas). Confirmatory: Gas turns lime water milky ($\text{Ca(OH)}_2 \text{ + CO}_2 \rightarrow \text{CaCO}_3 \downarrow + \text{H}_2\text{O}$). Milky ness disappears with excess $\text{CO}_2$. Sulphite ($\text{SO}_3^{2-}$): Dilute $\text{H}_2\text{SO}_4$ Group Test: Add dilute $\text{H}_2\text{SO}_4$ to salt. Observation: Colorless gas with pungent smell of burning sulphur ($\text{SO}_2$). Confirmatory: Gas turns acidified $\text{K}_2\text{Cr}_2\text{O}_7$ solution green, and turns $\text{KMnO}_4$ solution colorless. Acetate ($\text{CH}_3\text{COO}^-$): Dilute $\text{H}_2\text{SO}_4$ Group & Special Test: Heat salt with dilute $\text{H}_2\text{SO}_4$. Observation: Smell of vinegar. Confirmatory: Ester test: Heat salt with conc. $\text{H}_2\text{SO}_4$ and ethanol: Fruity smell. Ferric chloride test: Neutral $\text{FeCl}_3$ solution gives blood-red coloration. Chloride ($\text{Cl}^-$): Concentrated $\text{H}_2\text{SO}_4$ Group Test: Add conc. $\text{H}_2\text{SO}_4$ to salt. Observation: Colorless pungent gas ($\text{HCl}$) gives dense white fumes with $\text{NH}_3$ rod. Confirmatory: Silver nitrate test: Add $\text{AgNO}_3$ solution to salt extract: White precipitate of $\text{AgCl}$. $\text{AgCl}$ is soluble in $\text{NH}_4\text{OH}$. Bromide ($\text{Br}^-$): Concentrated $\text{H}_2\text{SO}_4$ Group Test: Add conc. $\text{H}_2\text{SO}_4$ to salt. Observation: Reddish-brown fumes of $\text{Br}_2$. Confirmatory: Silver nitrate test: Add $\text{AgNO}_3$ solution to salt extract: Pale yellow precipitate of $\text{AgBr}$. $\text{AgBr}$ is sparingly soluble in $\text{NH}_4\text{OH}$. Layer test: Add $\text{CCl}_4$ and chlorine water: Orange-brown layer. Iodide ($\text{I}^-$): Concentrated $\text{H}_2\text{SO}_4$ Group Test: Add conc. $\text{H}_2\text{SO}_4$ to salt. Observation: Violet fumes of $\text{I}_2$. Confirmatory: Silver nitrate test: Add $\text{AgNO}_3$ solution to salt extract: Yellow precipitate of $\text{AgI}$. $\text{AgI}$ is insoluble in $\text{NH}_4\text{OH}$. Layer test: Add $\text{CCl}_4$ and chlorine water: Violet layer. Nitrate ($\text{NO}_3^-$): Concentrated $\text{H}_2\text{SO}_4$ Group Test: Add conc. $\text{H}_2\text{SO}_4$ to salt, heat gently. Observation: Reddish-brown fumes of $\text{NO}_2$. Confirmatory: Brown Ring Test: Add freshly prepared $\text{FeSO}_4$ solution to salt solution, then carefully add conc. $\text{H}_2\text{SO}_4$ along the side of the test tube: Brown ring at the junction. Sulphate ($\text{SO}_4^{2-}$): Special Group Test: Add $\text{BaCl}_2$ solution to salt extract acidified with dilute $\text{HCl}$. Observation: White precipitate of $\text{BaSO}_4$. Confirmatory: Precipitate is insoluble in conc. $\text{HNO}_3$. Phosphate ($\text{PO}_4^{3-}$): Special Group Test: Add conc. $\text{HNO}_3$ and ammonium molybdate reagent to salt solution, heat. Observation: Yellow precipitate or yellow coloration. Confirmatory: Yellow precipitate of ammonium phosphomolybdate. General Practical Tests Preliminary Tests Colour: Blue/Green: $\text{Cu}^{2+}$ Pink: $\text{Mn}^{2+}$ Light Green: $\text{Fe}^{2+}$ Brown/Yellow: $\text{Fe}^{3+}$ Violet: $\text{Ni}^{2+}$ Smell: Ammoniacal: $\text{NH}_4^+$ Vinegar like: $\text{CH}_3\text{COO}^-$ Rotten egg: $\text{S}^{2-}$ (if present) Solubility: Test solubility in water (cold/hot), then dilute acids, then conc. acids. Dry Heating Test Heat a small amount of salt in a dry test tube. Observations: Gas evolved (color, smell, reaction with litmus/lime water). Sublimate formed (white, yellow, etc.). Residue color changes (hot/cold). E.g., $\text{Zn}^{2+}$ gives yellow hot, white cold residue. $\text{Pb}^{2+}$ gives yellow hot, yellow cold. Flame Test Make a paste of salt with conc. $\text{HCl}$ on a platinum wire. Introduce into non-luminous flame. Observations: Brick Red: $\text{Ca}^{2+}$ Crimson Red: $\text{Sr}^{2+}$ Apple Green: $\text{Ba}^{2+}$ Golden Yellow: $\text{Na}^{+}$ Violet: $\text{K}^{+}$ (view through cobalt glass) Charcoal Cavity Test Mix salt with $\text{Na}_2\text{CO}_3$, heat in a charcoal cavity with blowpipe flame. Observations: Metallic bead (e.g., $\text{Pb}$, $\text{Cu}$). Incinerated mass (e.g., $\text{Al}^{3+}$ gives white mass, glows when hot).