This lesson covers the techniques used to identify ions and compounds (qualitative analysis) and to determine exact amounts of substances (quantitative analysis). It includes tests for cations, anions, gases, titrations, and instrumental methods.

1. Core Concepts (Short Notes)

27.1 Qualitative Analysis

Used to identify ions and substances. Includes:

• Flame tests

• Precipitation reactions

• Gas identification tests

27.2 Quantitative Analysis

Used to measure amounts of substances. Includes:

• Volumetric analysis (titrations)

• Gravimetric analysis

• Instrumental analysis (AAS, colorimetry)

2. Qualitative Analysis: Identifying Ions

27.3 Flame Tests (Metal Ions)

• Li⁺ → crimson red

• Na⁺ → bright yellow

• K⁺ → lilac

• Ca²⁺ → brick red

• Ba²⁺ → apple green

• Cu²⁺ → blue-green

27.4 Tests for Cations

Using sodium hydroxide (NaOH) or ammonia (NH₃):

(a) Aluminium (Al³⁺):

• White ppt, dissolves in excess NaOH

(b) Calcium (Ca²⁺):

• White ppt, insoluble in excess

(c) Copper (Cu²⁺):

• Blue ppt with NaOH

• Deep blue complex with NH₃ (excess)

(d) Iron(II) (Fe²⁺):

• Green ppt → turns brown (oxidation)

(e) Iron(III) (Fe³⁺):

• Brown ppt

(f) Ammonium (NH₄⁺):

• Heating with NaOH → ammonia gas produced (turns red litmus blue)

27.5 Tests for Anions

(a) Carbonate (CO₃²⁻):

• Add acid → effervescence (CO₂)

(b) Sulfate (SO₄²⁻):

• Add BaCl₂ after acidifying → white ppt of BaSO₄

(c) Chloride (Cl⁻):

• Add AgNO₃ → white ppt of AgCl (soluble in NH₃)

(d) Nitrate (NO₃⁻):

• Brown ring test using FeSO₄ + concentrated H₂SO₄

27.6 Gas Tests

• H₂: pops with lighted splint

• O₂: relights glowing splint

• CO₂: turns limewater milky

• NH₃: turns damp red litmus blue

• Cl₂: bleaches litmus

• SO₂: turns acidified KMnO₄ from purple → colorless

3. Quantitative Analysis

27.7 Titrations

Used to determine concentration. Essential components:

• Burette (titrant)

• Pipette (analyte)

• Indicator

Types:

• Acid–base titrations

• Redox titrations

Indicators:

• Phenolphthalein → colorless to pink (alkali end point)

• Methyl orange → red to yellow (acid-base)

Titration Formula

27.8 Gravimetric Analysis

Substance is converted to an insoluble solid, filtered, dried, and weighed. Example: Determining sulfate by precipitation as BaSO₄.

4. Instrumental Methods

27.9 Colorimetry

Measures absorbance of colored solutions.

• More color → higher concentration.

28.0 Atomic Absorption Spectroscopy (AAS)

• Identifies metals at very low concentrations.

• Used for water testing (Pb, Hg, Cd).

5. Tips & Tricks for Exams

• Always acidify when testing for sulfate or halides.

• Use excess ammonia to differentiate AgCl, AgBr, AgI.

• Record burette readings to 2 decimal places.

• Use concordant titration values (within 0.1 cm³).

• Choose the correct indicator based on acid/base strength.

• Flame test colors are highly examinable.

6. Important Points to Remember

• Qualitative analysis identifies ions; quantitative measures amounts.

• Precipitation reactions are used to confirm presence of specific ions.

• Titrations must be performed carefully with accurate readings.

Modern techniques like AAS are more sensitive and accurate.