Practical No. 01: Identification of Cations
XIII. Interpretation of Results
Qualitative analysis successfully identified cations using group separation and confirmatory tests. Characteristic precipitates and colour reactions confirmed the presence of respective cations in the sample solutions.
XIV. Conclusions and Recommendations
- Conclusion: Systematic group-wise separation effectively identifies cations in unknown solutions.
- Recommendation: Clean glassware, dropwise reagent addition, and careful confirmatory tests are recommended to avoid false results.
XV. Practical Related Questions & Answers
Q1. Identify the basic radical present in the given solution ‘A’ by observing the formation of a black precipitate with diluted hydrochloric acid (HCl) and the evolution of hydrogen sulfide (H₂S) gas.
- Answer: The basic radical present is Cu²⁺ (Copper). A black precipitate of CuS is formed in group II when H₂S gas is passed through the solution containing Cu²⁺ ions in an acidic medium. Copper belongs to group II of qualitative analysis.
Q2. Explain the process for identifying either the Ba²⁺ or Ca²⁺ radical in the unknown solution.
- Answer: To distinguish between Ba²⁺ and Ca²⁺, add K₂CrO₄ solution to the original solution. Ba²⁺ gives a yellow precipitate of BaCrO₄, while Ca²⁺ gives no precipitate.
- Alternative: Alternatively, perform a flame test — Ba²⁺ gives an apple green flame, and Ca²⁺ gives a brick red flame. Ammonium oxalate gives a white precipitate with Ca²⁺ which is insoluble in acetic acid.
Q3. Identify the cation in solution ‘X’ by recognizing its pale green colouration, and when combined with sodium hydroxide, observe the formation of a dirty green-coloured precipitate.
- Answer: The cation is Fe²⁺ (Ferrous ion). The pale green colour indicates Fe²⁺ ions. With NaOH, Fe²⁺ forms a dirty green precipitate of Fe(OH)₂. This can be confirmed by K₃[Fe(CN)₆] which gives a deep blue precipitate (Turnbull’s blue) with Fe²⁺.
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