PRACTICAL CHEMISTRY LECTURE

2025 CHEMISTRY PRACTICAL EXAM LECTURE

1. Volumetric Analysis (Titration)

Volumetric analysis involves using a solution of known concentration (titrant) to determine the concentration of another solution (analyte).

Titration Table Example

Acid: HCl, Base: NaOH

Titration	Initial Reading (cm3)	Final Reading (cm3)	Volume Used (cm3)
Rough	0.0	24.8	24.8
1st	24.8	49.5	24.7
2nd	49.5	74.3	24.8
3rd	74.3	99.0	24.7

Average Volume: (24.7 + 24.8 + 24.7)/3 = 24.73 cm³

Titration Calculations

1. Molarity: M1V1 = M2V2 → M1 = (M2*V2)/V1
2. Convert volume to dm³: 24.73 cm³ = 0.02473 dm³
3. Example: Molarity HCl = (0.1*0.025)/0.02473 = 0.101 mol/dm³
4. Concentration in g/dm³ = 0.101 * 36.46 = 3.68 g/dm³
5. Mole ratio of acid to base: HCl + NaOH → NaCl + H2O → 1:1
6. Percentage purity = (Actual mass / Theoretical mass) * 100
7. Impure sample correction: subtract impurity mass from total before calculating molarity
8. Multiple titration example calculations included for students to practice.

2. Qualitative Analysis: Test for Ions

Cations

Cation	Reagent / Treatment	Observation	Inference
Na+	Flame Test	Yellow flame	Presence of Na+
K+	Flame Test	Lilac flame	Presence of K+
Ca2+	Na2CO3	White ppt	CaCO3 formed
Mg2+	NaOH	White ppt, soluble in excess	Mg(OH)2
Al3+	NaOH	White ppt, soluble in excess	Al(OH)3
Fe2+	NaOH	Green ppt	Fe(OH)2
Fe3+	NaOH	Brown ppt	Fe(OH)3

Anions

Anion	Reagent / Treatment	Observation	Inference
Cl-	AgNO3	White ppt	AgCl formed
SO42-	BaCl2 + HCl	White ppt	BaSO4 formed
CO32-	HCl, effervescence	Gas evolved, fizzing	CO32- present
NO3-	FeSO4 + H2SO4, warm	Brown ring at interface	NO3- detected
PO43-	Ammonium molybdate + HNO3	Yellow ppt	PO43- present

Special Cases

• Solution A + water → observe color, clarity, effervescence
• Residue + NaOH → white ppt, soluble/insoluble, heat if needed
• Residue + NH3 → formation of complex ions, solubility tests
• Observation: gas evolution, color change, precipitate formation
• Inference: determine ion identity and concentration

Functional Group Tests

• Alcohol: Acidified dichromate orange → green
• Alkanoic acid: Reacts with NaHCO3 → effervescence
• Alkene: Decolorizes bromine water
• Reducing sugars: Benedict's solution → red ppt

3. Practical Skills and Observations

• Accurate use of burettes, pipettes, measuring cylinders.
• Recording initial/final readings for titration.
• Calculating average titres, molarity, g/dm³, percentage purity.
• Observation: color change, effervescence, ppt formation, gas evolution.
• Inference: derive chemical composition, molarity, and purity from observations.
• Preparation of clear tables for titration, cation, anion, and functional group tests.

This lecture provides detailed guidance on volumetric analysis with calculations, ion identification, functional group tests, and practical observations to prepare students comprehensively for the 2025 Chemistry Practical Exam.