Salt analysis ncert

Introduction to Qualitative Analysis

• Analysis is not just disintegration; it involves understanding substance composition (Qualitative Analysis).

• Focus: Identification of cations and anions in inorganic salts.

Inorganic Salts Formation

• Inorganic salts formed via neutralization:

  • Acid contributes anion.

  • Base contributes cation.

• Examples:

  • CuSO4: Cu2+ (cation), SO4 2– (anion)

  • NaCl: Na+ (cation), Cl– (anion)

Types of Qualitative Analysis

• Macro analysis: 0.1 to 0.5 g of substance with ~20 mL of solution.

• Semimicro analysis: 0.05 g of substance with 1 mL of solution.

• Micro analysis: Requires very small amounts of substance.

• Qualitative reactions can be visually or olfactorily observed:

  • Precipitation formation

  • Color change

  • Gas evolution

Systematic Analysis Steps

1. Preliminary Examination

   • Provides clues for the analysis.

   • General appearance, color, smell, and solubility tests (Dry Tests).

2. Detection of Anions

   • Conduct wet tests to confirm anions.

3. Detection of Cations

   • Perform wet tests for cation confirmation.

Preliminary Tests Overview

• Solubility in water and solution pH reveal ion nature.

  • Acidic/basic solutions indicate potential acid or base origins in salt.

  • For acidic solutions: potential acid salt or weak base salt.

  • Gaseous products during reactions with acids provide insights into anion presence.

Experiment 7.1 Aim

• Detect one cation and one anion from the test ion list:

  • Cations: Pb2+, Cu2+, etc.

  • Anions: CO3 2–, Cl–, etc.

• Exclude insoluble salts.

Theoretical Principles for Analysis

• Solubility Product and Common Ion Effect:

  • The ionic product of salts must remain below solubility thresholds to avoid precipitation.

Experimental Materials List

• Boiling tubes, test tubes, measuring cylinder, test tube stand, corks, filter paper, various reagents.

Systematic Analysis of Anions

Step 1: Preliminary Test with Dilute Sulphuric Acid

• Key reactions with dilute H2SO4 to detect anions:

  • CO3 2– (produces CO2 gas).

  • S2– (produces H2S gas).

  • SO3 2– (produces SO2 gas).

  • NO2– (produces reddish-brown NO2 gas).

  • Acetate CH3COO– produces acetic acid vapours.

Observations & Inferences

Confirmatory Tests for Anions

• Confirm those detected with dilute H2SO4 using sodium carbonate or water extracts based on solubility.

Confirmatory Tests Overview

Step 2: Additional Tests with Concentrated Sulphuric Acid

• Follow similar strategies to determine presence of halides and nitrates through colorimetric or precipitation reactions.

Chemistry of Confirmatory Tests

Carbonate Ion [CO3 2–]

• Reaction with dilute H2SO4 resulting in colorless, odorless gas and milky lime water is confirmatory of carbonate ions.

Sulphide Ion [S2–]

• Reaction follows decomposition into H2S giving characteristic odor and color change on lead acetate.

Additional Tests Summary for Anions

• Specific tests designed for deeper confirmation of common anion radicals illustrate detailed methodology and visual indicators.

Systematic Analysis of Cations

Preliminary Examination of Salt for Cation Identification

1. Color Test: Identify salt color and infer possible cation presence.

2. Dry Heating Test: Observe color changes upon heating the salt for potential cation clues (e.g., color of molten residue).

3. Flame Test: Specific salts create distinct colors in flame tests, leveraging exploitable properties of metal salts.

4. Borax Bead Test: Used for colored salts, confirms metallic borate formation upon heating.

Conclusion

• Detailed experimentation and observation enable identification of both cations and anions in qualitative analysis of salts, vital for understanding salt chemistry in laboratory contexts.

Precautions

• Adhere to safety protocols while performing tests to ensure safety and integrity of results.