BT-101 Engineering Chemistry - Jun 2023 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aExplain the formation and composition of scales in boilers. How are they different from sludge's? What are bad affects?
   How to answer

   • Definition and formation mechanism of scales (precipitation of sparingly soluble salts like $CaSO_4$, $CaCO_3$, magnesium silicate)
   • Chemical composition of typical boiler scales
   • Key differences between scales (hard, adhering coatings) and sludges (loose, slimy precipitates)
   • Disadvantages/bad effects: wastage of fuel, overheating and tube failure, decreased efficiency, boiler explosion hazards
2. 7 Marks
   bA water sample contains the following impurities per liter $\text{CaCl}_2 = 222\text{ mg}$; $\text{Mg(HCO}_3)_2 = 73\text{ mg}$; $\text{CaSO}_4 = 6.8\text{ mg}$, $\text{NaCl} = 58.5\text{mg}$; $\text{Ca(NO}_3)_2 = 162\text{ mg}$ and $\text{MgSO}_4 = 73\text{ mg}$. The sample of lime available is 74% pure and soda is 90% pure. 20% excess chemicals have to be added. Calculate the amount lime and soda required for the treatment of 10000 liters of water.
   How to answer

   • Convert each impurity into $CaCO_3$ equivalents (NaCl does not consume chemicals)
   • Identify salts reacting with lime: $\text{Mg(HCO}_3)_2$, $\text{MgSO}_4$
   • Identify salts reacting with soda: $\text{CaCl}_2$, $\text{CaSO}_4$, $\text{Ca(NO}_3)_2$, $\text{MgSO}_4$
   • Calculate theoretical lime and soda requirement
   • Adjust for purity (74% for lime, 90% for soda) and add 20% excess
   • Multiply by total volume (10000 L) to state final quantities in kg or grams
3. 7 Marks
   aExplain the hot lime-soda process. What are its advantages?
   How to answer

   • Operating temperature ($80^\circ\text{C}-100^\circ\text{C}$) and operating principle of hot lime-soda process
   • Chemical equations for removal of temporary and permanent hardness
   • Schematic diagram of hot lime-soda softening plant
   • Key advantages: faster reaction rate, low residual hardness (15-30 ppm), no coagulant needed, dissolved gases ($CO_2$, $O_2$) expelled, rapid filtration
4. 7 Marks
   bWrite an note on ion-exchange process.
   How to answer

   • Principle of deionization/demineralization using synthetic organic resins
   • Cation exchanger reactions: $2RH + Ca^{2+} \rightarrow R_2Ca + 2H^+$
   • Anion exchanger reactions: $R'OH + Cl^- \rightarrow R'Cl + OH^-$
   • Regeneration of exhausted resins with dil. $HCl/H_2SO_4$ and dil. $NaOH$
   • Advantages and disadvantages (produces water of zero hardness, but costly equipment)
5. 7 Marks
   aDescribe the mechanism of lubrication that is applied to delicate instruments.
   How to answer

   • Identification of lubrication mechanism applicable to delicate instruments: boundary lubrication / thin-film lubrication
   • Physical/chemical adsorption of polar organic molecules on metal surfaces (monomolecular or polymolecular layer)
   • Action mechanism preventing metal-to-metal contact under low speeds and low loads
   • Examples of lubricants used (fatty acids, mineral oils blended with vegetable oils, synthetic lubricants, silicones) and instruments (watches, scientific balances, sewing machines)
6. 7 Marks
   bExplain about aniline point and saponification Number.
   How to answer

   • Aniline Point: Definition (lowest temperature at which equal volumes of oil and aniline are completely miscible), determination, and significance (measure of aromatic content; higher aniline point indicates lower aromaticity and better lubricating quality)
   • Saponification Number: Definition (mg of KOH required to saponify 1 g of oil/fat), determination by titration, and significance (differentiates animal/vegetable oils from mineral oils)
7. 7 Marks
   aWrite a short note on the following. i) Functionality ii) free radical chain polymerization iii) ionic polymerization.
   How to answer

   • Functionality: definition (number of bonding sites per molecule), effect on polymer structure (bifunctional gives linear, polyfunctional gives branched/cross-linked)
   • Free radical chain polymerization: three distinct steps — initiation (initiators like benzoyl peroxide), propagation, and termination (coupling and disproportionation)
   • Ionic polymerization: cationic (initiated by Lewis acids like $BF_3$, carbocation intermediate) and anionic (initiated by bases like $NaNH_2$, carbanion intermediate) mechanisms
8. 7 Marks
   bWrite a note on preparation, properties and uses of the following i) Phenol-formaldehyde resin ii) Buna-S
   How to answer

   • Phenol-formaldehyde resin (Bakelite): preparation from phenol and formaldehyde with acid/base catalyst, stages (Novolac to cross-linked Bakelite), properties (electrical insulator, hard, heat-resistant), uses (electrical switches, plugs, handles)
   • Buna-S (Styrene-Butadiene Rubber): preparation by copolymerization of 75% 1,3-butadiene and 25% styrene in presence of peroxide catalyst, properties (high abrasion resistance, load-bearing capacity), uses (automobile tires, conveyor belts, shoe soles)
9. 14 Marks
   Describe the following with suitable examples. i) Chemical corrosion and Electro chemical corrosion ii) Phase diagram of one-component water system.
   How to answer

   • Chemical (dry) corrosion: direct chemical attack by gases ($O_2$, $Cl_2$, $SO_2$), mechanism of oxide film formation, Pilling-Bedworth ratio, examples
   • Electrochemical (wet) corrosion: occurrence in conductive liquids/moisture, anodic oxidation and cathodic reduction (hydrogen evolution / oxygen absorption mechanism), examples like rusting of iron
   • Phase diagram of water system: P-T diagram showing sublimation curve (OA), vaporization curve (OB), fusion curve (OC), and metastable curve ($OA'$)
   • Application of Gibbs Phase Rule ($F = C - P + 2$) for areas ($F=2$), curves ($F=1$), and triple point ($F=0$, $T=0.0098^\circ\text{C}, P=4.58\text{ mm Hg}$)
10. 14 Marks
    Discuss principle, instrumentation and applications of vibrational and rotational spectroscopy.
    How to answer

    • Rotational (Microwave) Spectroscopy: principle (permanent dipole moment requirement, selection rule $\Delta J = \pm 1$), energy levels, instrumentation overview, applications (bond length, moment of inertia determination)
    • Vibrational (Infrared) Spectroscopy: principle (change in dipole moment during vibration, selection rule $\Delta v = \pm 1$), fundamental modes of vibration
    • Instrumentation: IR/microwave source, monochromator/interferometer, sample cell, detector, recorder
    • Applications: functional group identification, finger-print region analysis, detecting hydrogen bonding, purity testing
11. 7 Marks
    aHow do you explain electro negativity, ionic sizes and electron affinity of s, p-block elements?
    How to answer

    • Electronegativity: definition, general trends across periods (increases) and down groups (decreases) in s and p-blocks due to effective nuclear charge and screening effect
    • Ionic sizes (radii): cation vs. anion sizes compared to neutral atoms, trends across periods (decrease) and down groups (increase)
    • Electron affinity: definition, trends across periods (generally increases/more negative) and down groups (decreases), anomalies in groups 15 and 16 (e.g., F vs Cl, O vs S)
12. 7 Marks
    bState and explain beer-Lambert's Law.
    How to answer

    • Statement of Lambert's law and Beer's law individually
    • Mathematical formulation: $-\frac{dI}{dx} = k I c$
    • Integration leading to $\ln(I_0/I) = k' c l$ or $A = \log_{10}(I_0/I) = \epsilon c l$
    • Define all terms: $A$ (absorbance), $\epsilon$ (molar extinction coefficient), $c$ (concentration), $l$ (path length)
    • Limitations/deviations from the law (high concentration, polychromatic light, chemical equilibria)
13. 14 Marks
    Write brief note on (Any two) i) Eutectic point ii) Flash point & Fire point iii) Caustic Embrittlement iv) Polarizability
    How to answer

    • Eutectic point: definition of eutectic mixture and lowest freezing temperature of a two-component condensed system, degrees of freedom at eutectic point ($F=0$)
    • Flash point & Fire point: definitions of flash point (lowest temperature at which oil gives off sufficient vapors to ignite momentarily) and fire point (burns continuously for at least 5 seconds), Pensky-Martens/Abel apparatus, practical significance for storage and transport
    • Caustic Embrittlement: form of stress corrosion cracking in high-pressure boilers due to high NaOH concentration in hairline cracks/rivets, prevention by adding sodium phosphate or tannin
    • Polarizability: ability of an electron cloud of an atom/molecule to be distorted by an external electric field, relation to induced dipole moment $\mu = \alpha E$, role in intermolecular forces and optical properties