Engineering Chemistry Essentials

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1. Water Technology 1.1 Hardness of Water Temporary Hardness: Due to bicarbonates of Ca & Mg ($Ca(HCO_3)_2$, $Mg(HCO_3)_2$). Removed by boiling. Permanent Hardness: Due to chlorides & sulfates of Ca & Mg ($CaCl_2$, $MgCl_2$, $CaSO_4$, $MgSO_4$). Units of Hardness: ppm, mg/L, French degrees ($1^\circ Fr = 10 \text{ mg } CaCO_3/L$), Clark degrees ($1^\circ Cl = 14.3 \text{ mg } CaCO_3/L$). EDTA Method: Complexometric titration using EBT indicator. $$Hardness = \frac{V_{EDTA} \times M_{EDTA} \times 100}{V_{sample}} \text{ mg/L as } CaCO_3$$ 1.2 Water Treatment Lime-Soda Process: Removes $Ca^{2+}$ and $Mg^{2+}$ by precipitation. Cold Lime-Soda: Efficient for large scale. Hot Lime-Soda: Faster, more complete removal, deaeration. Zeolite Process (Permutit): Ion exchange. $Na_2Ze + Ca^{2+} \rightarrow CaZe + 2Na^{+}$. Regeneration with NaCl. Ion-Exchange Process (Demineralization): Cation Exchanger: $RH_2 + Ca^{2+} \rightarrow RCa + 2H^+$. Anion Exchanger: $R'OH_2 + Cl^- \rightarrow R'Cl + OH^-$. $H^+ + OH^- \rightarrow H_2O$. Reverse Osmosis (RO): Pressure applied to overcome osmotic pressure, forcing water through semi-permeable membrane. 2. Corrosion and its Control 2.1 Types of Corrosion Definition: Deterioration of a metal by chemical or electrochemical reaction with its environment. Dry (Chemical) Corrosion: Direct attack by atmospheric gases (e.g., oxidation, halogen corrosion). Wet (Electrochemical) Corrosion: Occurs in presence of conducting liquid (electrolyte). Differential Aeration Corrosion: Areas with less oxygen act as anode. Pitting Corrosion: Localized attack, forms pits. Crevice Corrosion: Occurs in narrow gaps. 2.2 Factors Affecting Corrosion Nature of Metal: Electrode potential, purity, overvoltage, surface film. Nature of Environment: pH, temperature, humidity, presence of impurities, conductivity. 2.3 Corrosion Control Protective Coatings: Metallic Coatings: Galvanizing (Zn on Fe), Tinning (Sn on Fe), Electroplating. Organic Coatings: Paints, varnishes. Inorganic Coatings: Phosphate, chromate. Cathodic Protection: Sacrificial Anodic Protection: Connect more active metal (Mg, Zn, Al) to object. Impressed Current Cathodic Protection: Apply external current to force object to be cathode. Corrosion Inhibitors: Substances that reduce corrosion rate (e.g., chromates, phosphates). Design & Material Selection: Avoid dissimilar metals, crevices, sharp bends. 3. Electrochemistry and Batteries 3.1 Electrochemical Cells Galvanic Cell: Converts chemical energy to electrical energy (spontaneous reaction). $$E_{cell} = E_{cathode} - E_{anode}$$ Nernst Equation: Relates cell potential to concentration. $$E = E^0 - \frac{RT}{nF} \ln Q$$ At $25^\circ C$: $E = E^0 - \frac{0.0592}{n} \log Q$ Electrolytic Cell: Converts electrical energy to chemical energy (non-spontaneous reaction). 3.2 Batteries (Cells) Primary Batteries (Non-rechargeable): Dry Cell (Leclanché): Anode: Zn, Cathode: Carbon rod in $MnO_2/C$ paste. Electrolyte: $NH_4Cl/ZnCl_2$. Alkaline Battery: Anode: Zn, Cathode: $MnO_2$. Electrolyte: KOH. Longer shelf life. Secondary Batteries (Rechargeable): Lead-Acid Battery: Anode: Pb, Cathode: $PbO_2$. Electrolyte: $H_2SO_4$. Discharge: $Pb + PbO_2 + 2H_2SO_4 \rightarrow 2PbSO_4 + 2H_2O$. Ni-Cd Battery: Anode: Cd, Cathode: NiO(OH). Electrolyte: KOH. Longer cycle life, toxic. Lithium-ion Battery: Anode: Graphite, Cathode: $LiCoO_2$ or $LiFePO_4$. Electrolyte: Lithium salt in organic solvent. High energy density. Fuel Cells: Convert chemical energy of fuel directly into electrical energy. H$_2$-O$_2$ Fuel Cell: Anode: $H_2$, Cathode: $O_2$. Electrolyte: KOH or $H_3PO_4$. Products: $H_2O$. 4. Engineering Materials 4.1 Polymers Thermoplastics: Can be repeatedly softened by heating and hardened by cooling (e.g., PE, PVC, PS). Thermosets: Undergo irreversible chemical change upon heating, form rigid cross-linked structure (e.g., Bakelite, Epoxy resins). Elastomers: Amorphous polymers with good elasticity (e.g., Natural rubber, SBR). Polymerization Types: Addition Polymerization: Monomers add to each other in chain reaction (e.g., PE from ethene). Condensation Polymerization: Monomers combine with elimination of small molecules (e.g., Nylon-6,6, PET). 4.2 Composites Definition: Material made from two or more constituent materials with significantly different physical or chemical properties, which remain separate and distinct at the macroscopic level within the finished structure. Types: Fiber-reinforced (e.g., Fiberglass, Carbon fiber). Particle-reinforced (e.g., Concrete, Metal matrix composites). 5. Green Chemistry 5.1 Principles of Green Chemistry 1. Prevention: Prevent waste rather than treat it. 2. Atom Economy: Maximize incorporation of all materials used into the final product. $$\% \text{ Atom Economy} = \frac{\text{Molecular weight of desired product}}{\text{Molecular weight of all reactants}} \times 100$$ 3. Less Hazardous Chemical Syntheses: Design syntheses to use and generate substances with little or no toxicity. 4. Designing Safer Chemicals: Design chemical products that are fully effective yet have minimum toxicity. 5. Safer Solvents and Auxiliaries: Avoid using auxiliary substances (solvents, separating agents) or make them innocuous. 6. Design for Energy Efficiency: Minimize energy requirements. 7. Use of Renewable Feedstocks: Use renewable raw materials whenever practicable. 8. Reduce Derivatives: Avoid unnecessary derivatization (blocking groups, protection/deprotection). 9. Catalysis: Catalytic reagents are superior to stoichiometric reagents. 10. Design for Degradation: Design chemical products to degrade into innocuous products after use. 11. Real-time Analysis for Pollution Prevention: Develop analytical methodologies to allow for real-time monitoring. 12. Inherently Safer Chemistry for Accident Prevention: Choose substances and forms that minimize potential for chemical accidents. 6. Fuels and Combustion 6.1 Calorific Value Gross Calorific Value (GCV) / Higher Calorific Value (HCV): Heat liberated when a unit mass of fuel is completely burnt and products of combustion are cooled to room temperature. Net Calorific Value (NCV) / Lower Calorific Value (LCV): GCV minus latent heat of water vapor formed. $$NCV = GCV - m_w \times L_v$$ where $m_w$ is mass of water formed, $L_v$ is latent heat of steam ($~2442 \text{ kJ/kg}$). Bomb Calorimeter: Measures GCV of solid and liquid fuels. 6.2 Fuels Solid Fuels: Coal (Peat, Lignite, Bituminous, Anthracite), Wood. Liquid Fuels: Petroleum (Petrol, Diesel, Kerosene), Biofuels (Ethanol, Biodiesel). Octane Number: Measures knocking tendency of petrol. Isomers of octane (iso-octane = 100, n-heptane = 0). Cetane Number: Measures ignition delay of diesel. n-Cetane = 100, $\alpha$-methyl naphthalene = 0. Gaseous Fuels: Natural Gas, LPG, CNG, Biogas, Producer Gas, Water Gas. LPG (Liquefied Petroleum Gas): Propane, Butane. CNG (Compressed Natural Gas): Methane. Biogas: Methane + CO$_2$.