Lab Worksheet for Identifying Acidic (Anion) and Basic (Cation) Molecules
1. Name of the Experiment:
Identification of basic (cations) and acidic (anions) radicals of the given unknown inorganic sample.
Preparation of Original Solution / Stock Solution:
A small amount of the unknown inorganic salt sample was taken in a clean test tube, and a required volume of distilled water was added to it. The mixture was shaken thoroughly to prepare a clear solution. This is the Original Solution (Stock Solution) for the experiment.
Experimental Procedure: Small portions of the prepared original solution were taken in separate clean test tubes to perform specific confirmatory tests for various cations and anions.
1. Identification of Cations (Basic Radicals) in Solution
Original Solution + 1-2 drops of NH4OH (Ammonium Hydroxide) solution → a light blue precipitate (precipitate forms) of Cu(OH)2 is obtained. Upon adding excess NH4OH solution dropwise to this light blue precipitate, it dissolves to form a deep blue solution of [Cu(NH3)4]2+ (tetraamminecopper(II)) ion.
Cu(OH)2 + 4NH4OH → [Cu(NH3)4]2+ (Deep Blue Solution) + 2OH– + 4H2O
Original Solution + 1-2 drops of NaOH (Sodium Hydroxide) solution → a gelatinous white precipitate (precipitate forms) of Al(OH)3 is formed. Adding excess NaOH dissolves the precipitate to form a clear solution of NaAlO2 (Sodium Aluminate). Adding excess solid NH4Cl (Ammonium Chloride) to this clear solution and heating it brings back the white precipitate (precipitate forms) of Al(OH)3.
Al(OH)3 + NaOH → NaAlO2 (Clear Solution) + 2H2O
NaAlO2 + H2O + NH4Cl → Al(OH)3↓ (White Precipitate) + NaCl + NH3↑
(a) Original Solution + 1-2 drops of K3[Fe(CN)6] (Potassium Ferricyanide) solution → a deep blue precipitate (precipitate forms) of KFe[Fe(CN)6] (Turnbull’s Blue) is formed.
(b) Original Solution + 1-2 drops of K4[Fe(CN)6] (Potassium Ferrocyanide) solution → a light blue precipitate (precipitate forms) of K2Fe[Fe(CN)6] is formed.
(c) Original Solution + 1-2 drops of NH4OH solution → a green precipitate (precipitate forms) of Fe(OH)2 is formed.
(b) Fe2+ + K4[Fe(CN)6] → K2Fe[Fe(CN)6]↓ (Light Blue Precipitate) + 2K+
(c) Fe2+ + 2NH4OH → Fe(OH)2↓ (Green Precipitate) + 2NH4+
(a) Original Solution + 1-2 drops of NH4SCN (Ammonium Thiocyanate) solution → a blood-red solution of Fe(SCN)3 is produced.
(b) Original Solution + 1-2 drops of K3[Fe(CN)6] solution → a brown precipitate (precipitate forms) of Fe[Fe(CN)6] is produced.
(c) Original Solution + 1-2 drops of K4[Fe(CN)6] solution → a deep blue precipitate (precipitate forms) of Fe4[Fe(CN)6]3 (Prussian Blue) is produced.
(b) Fe3+ + K3[Fe(CN)6] → Fe[Fe(CN)6]↓ (Brown Precipitate)
(c) 4Fe3+ + 3K4[Fe(CN)6] → Fe4[Fe(CN)6]3↓ (Deep Blue Precipitate) + 12K+
Original Solution + 1-2 drops of NaOH solution → a white precipitate (precipitate forms) of Zn(OH)2 is obtained. Adding excess NaOH dissolves it to form a clear solution of Na2ZnO2 (Sodium Zincate). Passing H2S (Hydrogen Sulfide) gas through this clear solution yields a white precipitate (precipitate forms) of ZnS.
Zn(OH)2 + 2NaOH → Na2ZnO2 (Clear Solution) + 2H2O
Na2ZnO2 + H2S → ZnS↓ (White Precipitate) + 2NaOH
Original Solution + 1-2 drops of (NH4)2C2O4 (Ammonium Oxalate) solution → a white precipitate (precipitate forms) of CaC2O4 (Calcium Oxalate) is formed. Adding dilute HCl dropwise dissolves the precipitate to form a clear solution.
CaC2O4 + 2HCl → CaCl2 (Clear Solution) + H2C2O4
Original Solution + dropwise alkaline K2[HgI4] (Nessler’s Reagent) → a brown precipitate (precipitate forms) of iodide of Millon’s base [NH2(Hg2I3)] is obtained.
Original Solution + dropwise K2H2Sb2O7 (Potassium Pyroantimonate) solution → a crystalline white precipitate (precipitate forms) of Na2H2Sb2O7 (Sodium Pyroantimonate) is formed.
2. Identification of Anions (Acidic Radicals) in Solution
Original Solution + 1-2 drops of Ba(NO3)2 (Barium Nitrate) solution → a white precipitate (precipitate forms) of BaSO4 (Barium Sulfate) is obtained. This white precipitate remains completely insoluble (unchanged) upon adding dilute HCl.
BaSO4 + HCl → No reaction occurs (Insoluble)
Original Solution + 1-2 drops of Ba(NO3)2 solution → a white precipitate (precipitate forms) of BaCO3 (Barium Carbonate) is obtained. This white precipitate dissolves completely with effervescence, releasing CO2 gas, upon adding dilute HCl.
BaCO3 + 2HCl → BaCl2 (Soluble Solution) + CO2↑ (Effervescence) + H2O
Original Solution + 1-2 drops of AgNO3 (Silver Nitrate) solution → a curdy white precipitate (precipitate forms) of AgCl is formed. Adding excess NH4OH solution dissolves this white precipitate to form a clear solution of [Ag(NH3)2]Cl (diamminesilver(I) chloride).
AgCl + 2NH4OH → [Ag(NH3)2]Cl (Clear Solution) + 2H2O
