Abbreviated 32 Qualitative Analysis Scheme PART I: GROUP CATIONS Record Identifying Cation Used and Your Observations for each Precipitation Reaction. Mark any observed Errors. Cation Reagent Observations Caution ETIMDNT 6izz 6z S Caliont CrCUT Ixmow
The Correct Answer and Explanation is:
It seems you’re referring to a Qualitative Analysis Scheme – Part I: Group Cations, where different cations are identified based on precipitation reactions using specific reagents. The table format you mentioned is common in laboratory reports for qualitative inorganic analysis.
Let’s first define what this involves:
Corrected and Completed Table Entry (Example)
| Cation | Reagent | Observations | Caution / Error |
|---|---|---|---|
| Ag⁺ | HCl | White precipitate formed (AgCl) | No error observed |
| Pb²⁺ | HCl | White precipitate (PbCl₂), soluble in hot water | Handle lead compounds with care |
| Hg₂²⁺ | HCl | White precipitate turns black with NH₄OH (Hg + HgNH₂Cl) | Mercury compounds are toxic |
Explanation
In qualitative analysis, group cations are identified through characteristic precipitation reactions. In Group I (chloride group), cations like silver (Ag⁺), lead (Pb²⁺), and mercury (Hg₂²⁺) form insoluble chlorides when treated with dilute hydrochloric acid (HCl). These are easily separated from other cations due to their low solubility.
When HCl is added:
- Ag⁺ forms a white precipitate of AgCl, which is insoluble in cold water but dissolves in ammonia (NH₄OH).
- Pb²⁺ forms PbCl₂, which is white and sparingly soluble in cold water, but dissolves upon heating, a key identifying feature.
- Hg₂²⁺ forms Hg₂Cl₂, which upon treatment with ammonia turns black due to formation of elemental mercury (Hg) and HgNH₂Cl—a unique and diagnostic color change.
This systematic approach allows chemists to narrow down unknown ions based on observable evidence. Precipitate color, solubility in hot/cold water or ammonia, and any color changes provide essential clues. It is vital to observe carefully and note any errors—for example, failure to dissolve PbCl₂ in hot water could mean the sample was too cold or impure. Additionally, handling mercury and lead compounds must be done cautiously due to their toxicity.
This part of qualitative analysis serves as a foundation for identifying ions in unknown mixtures. The experiment hinges on predictable ionic interactions and the formation of characteristic precipitates, making it a cornerstone technique in analytical chemistry.
