Question

give me a list of all points regarding group reagents and the subtle details of commmon ion effect and precipitation in salt analysis at a level of jee advanced

Answer 1

Qualitative salt analysis separates cations into groups via selective precipitation. This selectivity is achieved by precisely controlling the concentration of the precipitating anion through:

1. Common Ion Effect: Suppressing the dissociation of weak electrolytes ($\text{H}_2\text{S}$ or $\text{NH}_4\text{OH}$) by adding a strong electrolyte with a common ion, thereby controlling the $[\text{S}^{2-}]$ or $[\text{OH}^-]$ concentration.
   • Group II: High $[\text{H}^+]$ (from $\text{HCl}$) lowers $[\text{S}^{2-}]$, precipitating only very insoluble sulfides.
   • Group III: High $[\text{NH}_4^+]$ (from $\text{NH}_4\text{Cl}$) lowers $[\text{OH}^-]$, precipitating only very insoluble hydroxides.
2. pH Control: Directly influencing the concentration of the precipitating ion (e.g., $\text{S}^{2-}$, $\text{OH}^-$, $\text{CO}_3^{2-}$).
3. Solubility Product ($K_{sp}$): Precipitation occurs when the ionic product ($Q_{sp}$) exceeds $K_{sp}$. Different $K_{sp}$ values allow for selective precipitation.
4. Complex Formation: Used to dissolve specific precipitates (e.g., Group IIB sulfides in yellow ammonium sulfide, $\text{AgCl}$ in $\text{NH}_3$) or prevent precipitation by forming soluble complex ions.
5. Amphoteric Nature: Hydroxides of $\text{Al}^{3+}$, $\text{Cr}^{3+}$, $\text{Zn}^{2+}$, etc., dissolve in excess strong acid/base, which is utilized in identification steps.
6. Interfering Anions: Anions like phosphate, oxalate, borate must be removed to prevent their co-precipitation with cations of higher groups.

Answer 2

Qualitative inorganic analysis, particularly salt analysis, relies heavily on controlled precipitation based on solubility product principles and the common ion effect.

1. Group Reagents and Precipitation Principles

Cations are systematically separated into groups based on their selective precipitation with specific group reagents under controlled conditions (primarily pH).

| Group | Cations Present (Common) | Group Reagent | Principle of Precipitation ALONG WITH THE TEXT.