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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

Gas Evolved

Possible Anion

CO2

CO3 2–

H2S

S2–

SO2

SO3 2–

NO2

NO2–

CH3COOH

CH3COO–

Confirmatory Tests for Anions

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

Confirmatory Tests Overview

Anion Name

Test Procedure

Expected Result

CO3 2–

Dilute H2SO4 leads to CO2 gas

Milky lime water changes

S2–

H2SO4 produces H2S

Black precipitate on lead acetate

SO3 2–

Produces SO2 with H2SO4

Discoloration of KMnO4

NO2–

Red-brown gas evolved with warm H2SO4

Turns starch solutions blue

CH3COO–

Fruity smell when reacting with H2SO4

Deep red solution formation

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.