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These viva questions are frequently asked during lab sessions and mid-term viva. Click any question to expand the answer hint.
💧 Water Chemistry (CO2)
1. What is the EDTA method for hardness determination? Write the chemical equation.
EDTA (Ethylenediaminetetraacetic acid, Na₂H₂Y) forms stable 1:1 complexes with Ca²⁺ and Mg²⁺ ions at pH 10. Reaction: M²⁺ + H₂Y²⁻ → [MY]²⁻ + 2H⁺. EBT indicator shows wine-red → blue at endpoint. Hardness (mg/L as CaCO₃) = (V_EDTA × M_EDTA × 100,000) / V_sample
2. Distinguish between temporary and permanent hardness with examples.
Temporary hardness: Caused by Ca(HCO₃)₂ and Mg(HCO₃)₂. Removed by boiling. Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. Permanent hardness: Caused by CaSO₄, MgSO₄, CaCl₂, MgCl₂. Cannot be removed by boiling. Removed by ion exchange, lime-soda process, or EDTA.
3. What are the BIS permissible limits for water hardness, alkalinity, dissolved oxygen, and acidity?
As per IS 10500 (BIS Drinking Water Standards): Total Hardness: 300 mg/L (max 600) | Total Alkalinity: 200 mg/L (max 600) | Dissolved Oxygen: ≥ 6 mg/L | pH: 6.5–8.5 | Residual Chlorine: 0.2–0.5 mg/L. Values in mg/L as CaCO₃ unless otherwise stated.
4. What is Winkler's method for dissolved oxygen?
Winkler's iodometric method: DO oxidizes Mn²⁺ to Mn³⁺ in alkaline solution. In acid, Mn³⁺ oxidizes I⁻ to I₂. I₂ is titrated with Na₂S₂O₃ using starch indicator. Reactions: 4Mn(OH)₂ + O₂ → 4Mn(OH)₃; 2Mn(OH)₃ + 2KI + 3H₂SO₄ → I₂ + ...; I₂ + 2Na₂S₂O₃ → Na₂S₄O₆ + 2NaI. DO (mg/L) = V × N × 8000 / V_sample
🔬 Analytical Techniques (CO1)
5. What is the Rf value in chromatography? What is its range?
Rf (Retention Factor) = Distance travelled by component / Distance travelled by solvent front. Range: 0 to 1 (never > 1). Rf = 0: Component stays at origin. Rf = 1: Component travels with solvent front. Ideal Rf for identification: 0.3–0.7. Each compound has a characteristic Rf for a given solvent system.
6. What is iodometric titration? Give two examples from the syllabus.
Iodometric titration: An oxidizing agent (analyte) liberates I₂ from KI, and the liberated I₂ is titrated with Na₂S₂O₃ (titrant). Indicator: Starch (blue → colourless at endpoint). Examples: (1) Dissolved oxygen determination (Winkler's method, Lab 5) — DO liberates I₂ indirectly. (2) Determination of K₂Cr₂O₇ strength (Lab 15) — Cr₂O₇²⁻ + KI → I₂, titrated with Na₂S₂O₃. (3) Residual chlorine (Lab 3).
7. What is iodine value? How does it classify oils?
Iodine value = grams of I₂ absorbed by 100 g of oil. Measures degree of unsaturation (C=C bonds). Classification: Drying oils (IV > 130): linseed, tung oil — dry on exposure to air forming hard films (used in paints). Semi-drying (100–130): cottonseed, sunflower — partially dry. Non-drying (< 100): coconut, castor, groundnut — do not form films. Higher IV = more unsaturated = greater tendency to oxidize/rancidify.
🔥 Fuel Analysis (CO3)
8. What is proximate analysis? What are the four components determined?
Proximate analysis determines: (1) Moisture (M%): Loss at 105°C, 1h in air. (2) Volatile Matter (VM%): Loss at 925°C, 7 min in covered crucible (subtract M). (3) Ash (A%): Residue after combustion at 750°C. (4) Fixed Carbon (FC%): 100 – (M + VM + A). Fixed carbon is the actual combustible carbon content. High FC + low ash = high quality coal. Anthracite: FC > 90%; Bituminous: FC 60–80%; Lignite: FC < 40%.
9. Define flash point and fire point. What apparatus is used?
Flash point: Lowest temperature at which vapour momentarily ignites when flame applied (but doesn't sustain burning). Fire point: Temperature at which vapour burns continuously for ≥ 5 seconds. Fire point > Flash point (by ~5–40°C). Apparatus: Pensky Martin's closed cup (for FP > 50°C, e.g., diesel, lubricating oils) or Abel's apparatus (for FP < 50°C, e.g., petrol). Low flash point = more flammable = greater fire hazard.
🌊 Physical Properties (CO4)
10. What is viscosity? Why does viscosity of liquids decrease with temperature?
Viscosity is the resistance of a fluid to flow due to internal friction between its layers. For liquids: viscosity arises from intermolecular cohesive forces. As temperature increases, kinetic energy increases, molecules have enough energy to overcome intermolecular attractions → viscosity decreases. For gases: viscosity arises from molecular momentum transfer; as temperature increases, momentum transfer increases → viscosity increases. Andrade equation: log η = A + B/T.
11. What is surface tension? Name three phenomena caused by surface tension.
Surface tension (γ) = Force per unit length at the surface of a liquid (N/m or mN/m). Caused by unbalanced intermolecular cohesive forces at the surface. Phenomena: (1) Insects walking on water (Gerris sp.), (2) Capillary action (water rising in plants, wicking), (3) Spherical shape of liquid drops (minimum surface area), (4) Detergent action — soaps reduce surface tension, (5) Mercury forming convex meniscus. Surface tension decreases with temperature and addition of surfactants.
🧬 Polymer Synthesis (CO6)
12. Explain the mechanism of urea-formaldehyde resin synthesis in two stages.
Stage 1 (Addition, Alkaline pH 8–9): Urea reacts with formaldehyde to form methylol urea: NH₂CONH₂ + HCHO → HOCH₂NHCONH₂ (mono-methylol urea) → (HOCH₂NH)₂CO (di-methylol urea). Stage 2 (Condensation, Acidic pH 4–5): Methylol groups condense with –NH– groups eliminating water to form –CH₂– bridges: –NHCH₂OH + H₂N– → –NHCH₂NH– + H₂O. Continued condensation forms cross-linked 3D network (thermosetting). Properties: Hard, rigid, resistant to heat and solvents, cannot be re-melted.
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Mid-Term Viva questions test conceptual understanding. Prepare definitions, formulae, and mechanisms for each experiment performed.
Mid-Term Viva Topics — Water Analysis (Labs 1–3, 5, 14)
- Define hardness. Types and causes. EDTA method — principle, indicators, formulae.
- Alkalinity — phenolphthalein and total alkalinity. Relationship between P and T alkalinity and types of alkalinity present.
- Residual chlorine — importance in drinking water. Methods of chlorination.
- Dissolved oxygen — Winkler's method, significance, BOD relationship.
- Acidity — mineral vs CO₂ acidity, sources, effects.
- BIS standards for all parameters (IS 10500).
Mid-Term Viva Topics — Fuels & Physical Properties (Labs 6, 8, 10, 12)
- Surface tension — definition, units, measurement by drop-weight method.
- Viscosity — definition, dynamic vs kinematic, Redwood viscometer, temperature effect.
- Proximate analysis — four parameters, significance, coal classification.
- Flash point vs fire point — definition, Pensky Martin's apparatus, safety significance.
Mid-Term Viva Topics — Analytical Chemistry (Labs 7, 9, 11, 13, 15)
- Chromatography — types, stationary phase, mobile phase, Rf value calculation.
- Water of crystallization — definition, examples, gravimetric determination.
- KMnO₄ titrations — acidic medium, self-indicator, temperature effect.
- Iodine value — definition, Wijs method, oil classification.
- K₂Cr₂O₇ — primary standard, n-factor, iodometric titration principle.
Mid-Term Viva Topics — Polymer Synthesis (Lab 4)
- Thermosetting vs thermoplastic polymers — differences and examples.
- UF resin synthesis — two-stage mechanism, role of pH.
- Properties and applications of UF resin.
- Environmental concerns (formaldehyde emission) and green alternatives.
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End Semester Examination (ESE) consists of practical performance (70 marks). You will be asked to perform one experiment and give a viva. Practice all 15 experiments thoroughly.
| ESE Pattern | Marks | Description |
|---|---|---|
| Practical Performance | 40 | Perform the given experiment: setup, procedure, observations, calculations, result |
| Lab Record / Report | 15 | Evaluation of your lab record book (all 15 experiments) |
| Viva-Voce | 15 | Oral examination on the experiment performed and related theory |
| Total (ESE) | 70 | 70% of total course marks |
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Important: All 15 experiments must be completed and recorded in the lab record book before the ESE. Incomplete records will result in mark deduction.
Q1. What is an indicator? Give two examples used in this course with the experiments they are used in.
[Hint: EBT (hardness), phenolphthalein (alkalinity, acidity), methyl orange (alkalinity, acidity), starch (iodometric titrations)]
[Hint: EBT (hardness), phenolphthalein (alkalinity, acidity), methyl orange (alkalinity, acidity), starch (iodometric titrations)]
Q2. Define normality. Calculate the normality of 9.8 g H₂SO₄ dissolved in 1 litre of solution. (M = 98, n-factor = 2).
[Hint: N = 9.8/(98/2) = 0.2 N]
[Hint: N = 9.8/(98/2) = 0.2 N]
Q3. What is a primary standard? Mention three primary standards used in quantitative analysis.
[Hint: Oxalic acid, K₂Cr₂O₇, Na₂CO₃, Mohr's salt]
[Hint: Oxalic acid, K₂Cr₂O₇, Na₂CO₃, Mohr's salt]
Q4. Why is the Redwood viscometer heated slowly and uniformly? What is the heating rate?
[Hint: 5–6°C/min; rapid heating gives inaccurate readings due to temperature gradients]
[Hint: 5–6°C/min; rapid heating gives inaccurate readings due to temperature gradients]
Q5. What happens if excess KI is not added in the K₂Cr₂O₇ iodometric titration?
[Hint: Incomplete reduction of Cr₂O₇²⁻ → less I₂ liberated → underestimation of K₂Cr₂O₇ strength]
[Hint: Incomplete reduction of Cr₂O₇²⁻ → less I₂ liberated → underestimation of K₂Cr₂O₇ strength]
Q6. The iodine value of linseed oil is 180. Classify this oil and explain its industrial use.
[Hint: IV > 130 = drying oil. Used in paints, varnishes, linoleum. Dries by oxidative polymerization of C=C bonds on exposure to air.]
[Hint: IV > 130 = drying oil. Used in paints, varnishes, linoleum. Dries by oxidative polymerization of C=C bonds on exposure to air.]
Q7. In proximate analysis, why must the VM crucible have a tight-fitting lid during heating at 925°C?
[Hint: Prevent air entry → volatile gases would burn if oxygen present → results would be wrong (combustion ≠ volatilisation)]
[Hint: Prevent air entry → volatile gases would burn if oxygen present → results would be wrong (combustion ≠ volatilisation)]
Q8. What is Mohr's salt? Why is it preferred as a source of Fe²⁺ over FeSO₄?
[Hint: Mohr's salt = (NH₄)₂Fe(SO₄)₂·6H₂O. More stable than FeSO₄ — doesn't oxidize to Fe³⁺ as quickly in air. Used as primary standard for KMnO₄ standardisation.]
[Hint: Mohr's salt = (NH₄)₂Fe(SO₄)₂·6H₂O. More stable than FeSO₄ — doesn't oxidize to Fe³⁺ as quickly in air. Used as primary standard for KMnO₄ standardisation.]