Comprehensive Chemistry Lecture Notes: Higher Secondary Second Year (Volume I)

UNIT 1: METALLURGY

• Introduction to Metallurgy

  • Metallurgy is the science and technology of metals, focusing on their extraction from ores and their conversion into useful forms.
  • Metals occur in two states in nature:
    • Native State: Elements with least chemical reactivity like Gold ($Au$), Silver ($Ag$), and Copper ($Cu$).
    • Combined State: Reactive metals found as oxides, sulphides, or silicates.

• Minerals vs. Ores

  • Mineral: A naturally occurring substance obtained by mining containing metal in free or combined states.
  • Ore: Minerals that contain a high percentage of metal from which it can be extracted economically.
  • Key Quote: "All ores are minerals, but all minerals are not ores."
  • Examples:
    • Aluminum: Bauxite ($Al_2O_3.nH_2O$) is an ore; China clay ($Al_2O_3.2SiO_2.2H_2O$) is a mineral.
    • Iron: Contained in ~800 minerals, but Hematite ($Fe_2O_3$) and Magnetite ($Fe_3O_4$) are its ores.

• Concentration of Ores (Removal of Gangue)

  • Gangue: Non-metallic impurities, rocky materials, and siliceous matter associated with ores.
  • Concentration Methods:
    • Gravity Separation (Hydraulic Wash): Based on specific gravity differences. Lighter gangue is washed away by running water. Used for Gold, Hematite ($Fe_2O_3$), and Tin stone ($SnO_2$).
    • Froth Flotation: Used for sulphide ores (Galena $PbS$, Zinc blende $ZnS$). Uses frothing agents (pine oil) and collectors (sodium ethyl xanthate). Ore particles become water-repellent and rise with froth.
      • Depressing Agents: $NaCN$ is used to separate $ZnS$ from $PbS$ by forming a soluble complex $Na_2[Zn(CN)_4]$ on the $ZnS$ surface.
    • Leaching: Based on solubility in specific solvents.
      • Cyanide Leaching: $4Au (s) + 8CN^-(aq) + O_2(g) + 2H_2O(l) \rightarrow 4[Au(CN)_2]^-(aq) + 4OH^-(aq)$. Gold is recovered via cementation with Zinc.
      • Ammonia Leaching: Used for $Ni$, $Cu$, and $Co$.
      • Alkali Leaching: Bauxite is treated with $NaOH$ at $470-520\,K$ to form sodium meta-aluminate.
      • Acid Leaching: Sulphide ores treated with hot aqueous $H_2SO_4$.
    • Magnetic Separation: Based on magnetic property differences (e.g., separating Tin stone from Wolframite).

• Extraction of Crude Metal

  • Step 1: Conversion to Oxides:
    • Roasting: Heating sulphide ores with excess oxygen below melting point.
      • $2ZnS + 3O_2 \xrightarrow{\Delta} 2ZnO + 2SO_2$
    • Calcination: Heating in absence of air (or limited supply). Expels water of hydration or $CO_2$.
      • $MgCO_3.CaCO_3 \xrightarrow{\Delta} MgO + CaO + 2CO_2$
  • Step 2: Reduction of Metal Oxides:
    • Smelting: Reducing with Carbon/CO in the presence of flux to form slag.
      • Flux: Added to remove gangue (e.g., $CaO$ + $SiO_2 \rightarrow CaSiO_3\text{ (slag)}$).
    • Aluminothermic Process: Use of Al powder for oxides like $Cr_2O_3$.
      • $Cr_2O_3 + 2Al \rightarrow 2Cr + Al_2O_3\,(\Delta H = -852\,kJ\,mol^{-1})$.
    • Auto-reduction: Cinnabar ($HgS$) reduces to Mercury just by roasting.

• Thermodynamic Principles and Ellingham Diagram

  • Standard Gibbs Free Energy: $\Delta G = \Delta H - T\Delta S$. For a spontaneous reaction, $\Delta G$ must be negative.
  • Ellingham Diagram: A plot of $\Delta G^0$ vs Temperature for oxide formation.
    • Positive slope for most metals because $O_2$ gas is consumed (randomness decreases, $\Delta S$ is negative).
    • Negative slope for $C \rightarrow CO$ as gas volume increases.
    • Sudden slope changes indicate phase change (melting/boiling).
  • Applications: Predicts which metal can reduce which oxide. A lower metal in the diagram can reduce the oxide of a metal located above it.

• Electrochemical Principles - Hall-Heroult Process

  • Used for reactive metals (e.g., Aluminum) where carbon reduction is not feasible.
  • $\Delta G^0 = -nFE^0$.
  • Hall-Heroult Process Setup:
    • Cathode: Carbon lined iron tank.
    • Anode: Carbon blocks.
    • Electrolyte: $20\%\,Al_2O_3$ in molten cryolite ($Na_3AlF_6$) + $CaCl_2$ (to lower M.P.).
    • Net Reaction: $4Al^{3+}\text{(melt)} + 6O^{2-}\text{(melt)} + 3C(s) \rightarrow 4Al(l) + 3CO_2(g)$.

• ## Refining Processes

  • Distillation: For low boiling metals ($Zn$, $Hg$).
  • Liquation: For low melting metals ($Sn$, $Pb$).
  • Electrolytic Refining: Anode (impure metal), Cathode (pure metal strip). Example: Silver refining using $AgNO_3$ electrolyte.
  • Zone Refining: Based on fractional crystallization; impurities are more soluble in melt. Used for ultra-pure Semiconductors ($Ge$, $Si$, $Ga$).
  • Vapour Phase Method:
    • Mond Process (Nickel): $Ni + 4CO \xrightarrow{350\,K} [Ni(CO)_4] \xrightarrow{460\,K} Ni + 4CO$.
    • Van-Arkel Method (Ti/Zr): Based on thermal decomposition of volatile iodides ($TiI_4$).

UNIT 2: p-BLOCK ELEMENTS - I

• General Trends

  • Configuration: $ns^2, np^{1-6}$.
  • Metallic Nature: Decreases across a period, increases down a group.
  • Ionization Enthalpy: Generally decreases down a group; however, Group 13 shows deviations ($Al$ to $Tl$) due to poor shielding by d and f electrons.
  • Inert Pair Effect: Reluctance of the valence s-electrons to participate in bonding in heavier p-block elements (e.g., $Tl^{1+}$ is more stable than $Tl^{3+}$).

• Group 13: Boron Group

  • Borax ($Na_2B_4O_7.10H_2O$): Prepared from colemanite. Forms a transparent bead when heated (Borax bead test).
  • Boric Acid ($H_3BO_3$): A weak monobasic acid. It acts as a Lewis acid by accepting $OH^-$ from water rather than donating a proton.
  • Diborane ($B_2H_6$):
    • Structure: Features two 3-center 2-electron (3c-2e) "banana" bonds.
    • sp3 hybridization of Boron.
  • Alum: Double salts like Potash Alum ($K_2SO_4.Al_2(SO_4)3.24H_2O$) used for water purification.

• ## Group 14: Carbon Group

  • Allotropes of Carbon: Graphite (hexagonal sheets, sp2, conductor), Diamond (tetrahedral, sp3, insulator), Fullerenes ($C_{60}$ - buckyballs), Carbon Nanotubes, and Graphene.
  • Catenation: The ability to form long chains. Carbon has the highest catenation property (C >> Si > Ge \approx Sn > Pb).
  • Silicates: Units of $[SiO_4]^{4-}$ linked in patterns (Orthosilicates, Pyrosilicates, Cyclic silicates, etc.).
  • Zeolites: Three-dimensional crystalline solids (microporous aluminosilicates) used as molecular sieves.

UNIT 3: p-BLOCK ELEMENTS - II

• Group 15: Nitrogen Group

  • Ammonia ($NH_3$): Synthesized via Haber's Process. It is pyramidal ($107^\circ$ bond angle, sp3).
  • Nitric Acid ($HNO_3$): Prepared by Ostwald's Process via catalytic oxidation of ammonia. Acts as a strong oxidizing and nitrating agent.
  • Phosphine ($PH_3$): Colorless, poisonous gas with rotten fish smell. Used in Holmes signals.

• Group 16: Oxygen Group

  • Allotropes of Sulphur: Rhombic ($\alpha$ - most stable) and Monoclinic ($\beta$).
  • Sulphuric Acid ($H_2SO_4$): "King of Chemicals." Manufactured by Contact Process (yields Oleum $H_2S_2O_7$).

• Group 17: Halogens

  • Chlorine: Prepared via Deacon’s Process or electrolysis of Brine. Strong bleaching agent (permanent bleaching via oxidation).
  • Inter-halogen Compounds: Formed between two different halogens (e.g., $ClF_3, IF_7$). Usually more reactive than pure halogens (except $F_2$).

• ## Group 18: Noble Gases

  • Xenon Compounds: $XeF_2$, $XeF_4$, $XeF_6$. Xenon is the only noble gas that shows significant chemistry.
  • Uses: Helium (cryogenics, diving mixtures), Neon (advertising signs), Argon (filament bulbs), Radon (radioactive source for cancer treatment).

UNIT 4: TRANSITION AND INNER TRANSITION ELEMENTS

• d-Block Elements (Transition Metals)

  • General Configuration: $(n-1)d^{1-10} ns^{1-2}$.
  • Properties: Metallic behavior, high melting points, variable oxidation states, catalytic properties, and formation of colored complexes.
  • Magnetic Moment: $\mu = \sqrt{n(n+2)}\,BM$ (where n = number of unpaired electrons).

• Potassium Permanganate ($KMnO_4$)

  • Prepared from Pyrolusite ($MnO_2$).
  • Oxidizing Power in different media:
    • Acidic: $MnO_4^- + 8H^+ + 5e^- \rightarrow Mn^{2+} + 4H_2O$ ($Eq. Wt = 31.6$).
    • Neutral: $MnO_4^- + 2H_2O + 3e^- \rightarrow MnO_2 + 4OH^-$ ($Eq. Wt = 52.67$).

• ## f-Block Elements (Inner Transition Metals)

  • Lanthanoid Contraction: The steady decrease in the size of $Ln^{3+}$ ions with increasing atomic number due to poor shielding of 4f electrons.
  • Actinoids: All are radioactive. Stability of +3 oxidation state is common, but show higher states (+4, +5, +6, +7) compared to lanthanoids.

UNIT 5: COORDINATION CHEMISTRY

• Warner's Theory

  • Primary Valence: Ionizable, corresponds to oxidation state.
  • Secondary Valence: Non-ionizable, corresponds to coordination number; directional in nature.

• Valence Bond Theory (VBT)

  • Explains bonding via hybridization (e.g., $d^2sp^3$ or $sp^3d^2$ for Octahedral).
  • High Spin (Outer orbital) vs Low Spin (Inner orbital) complexes.

• Crystal Field Theory (CFT)

  • Treats ligands as point charges causing d-orbital splitting ($t_{2g}$ and $e_g$ in octahedral fields).
  • Crystal Field Splitting Energy ($\Delta_o$): Determines if the complex is high or low spin.
  • Colors: Result from d-d transitions.

• ## Metal Carbonyls

  • Synergic Bonding: Involves $\sigma-donation$ from $CO$ to metal and $\pi-back\,bonding$ from metal to $CO$.