Chapter 16 The Chemical Industry (notes)

Chapter 16: The Chemical Industry

16.1 Fertiliser

• Macronutrients: Essential for plant growth, include:

  • Nitrogen (N)

  • Phosphorus (P)

  • Potassium (K)

• Components of Fertiliser:

  • Ammonium ions (NH4+), Ammonium nitrate (NH4NO3)

  • Phosphate ions (PO3-) and Ammonium phosphate ((NH4)3PO4)

  • Potassium ions (K+) and Potassium chloride (KCl)

Making Fertiliser

• Neutralisation:

  • Formation of ammonium nitrate:

    • NH3 + HNO3 → NH4NO3

  • Formation of ammonium phosphate:

    • 3NH3 + H3PO4 → (NH4)3PO4

  • Potassium chloride (KCl) is mined.

Fertiliser Properties

• Most fertilisers are slightly acidic.

• Soil pH Impact:

  • Excess fertiliser can lead to overly acidic soil.

  • Farmers add lime (CaO) to neutralize.

• Disadvantages of Lime:

  • Reacts with soil water to create slaked lime (Ca(OH)2), which is alkaline.

  • Excess slaked lime can cause ammonia (NH3) gas release from ammonium salts:

    • Ca(OH)2 + 2NH4Cl → CaCl2 + 2H2O + 2NH3

  • Results in nitrogen loss from soil due to gaseous ammonia escape.

16.2 Ammonia (Haber Process)

• Haber Process: The industrial method to synthesize ammonia (NH3).

• Chemical Equation:

  • N2 + 3H2 ⇌ 2NH3

• Sources:

  • Nitrogen (N2): Extracted from air via fractional distillation.

  • Hydrogen (H2): Produced from methane (natural gas) through steam reaction.

Equilibrium Reaction

• Characteristics:

  • Forward reaction is exothermic; reverse reaction is endothermic.

  • Pressure Effects:

    • Increased pressure shifts equilibrium to the right, favoring NH3 production (less gas molecules).

    • High-pressure systems are costly.

  • Temperature Effects:

    • Increased temperature shifts equilibrium left, reducing yield.

    • Optimal temperature: 450°C balances rate and yield.

Industrial Process

• Gases (N2 and H2) mixed in a 1:3 ratio, compressed, and passed over iron catalyst.

• Approximately 15% of gases convert to NH3.

• NH3 is condensed and unreacted gases are recycled to minimize waste.

16.3 Sulfuric Acid (Contact Process)

• Contact Process: Method for producing sulfuric acid (H2SO4).

• Chemical Equations:

  1. Sulfur combustion: S + O2 → SO2

  2. SO2 and O2 reaction: 2SO2 + O2 → 2SO3

  3. SO3 reaction with concentrated H2SO4: SO3 + H2SO4 → H2S2O7 (oleum)

  4. Formation of sulfuric acid: H2S2O7 + H2O → 2H2SO4

• Conditions:

  • Temperature: 450°C

  • Pressure: 2 atm

  • Catalyst: Vanadium (V) oxide (V2O5)

Sulfur, Sulfur Dioxide, and Sulfuric Acid

• Sulfur (S):

  • Properties: Yellow solid, non-metal

  • Sources:

    • Found uncombined in the US, Mexico, Poland, and Italy

    • Extracted from zinc blende (ZnS) and fossil fuels

  • Uses: Production of SO2, H2SO4, and vulcanizing rubber.

• Sulfur Dioxide (SO2):

  • Properties: Colorless gas

  • Sources:

    • Combustion of sulfur and fossil fuels

    • Natural occurrences (volcanos)

  • Uses: Bleaching agents, preservatives for food/drinks.

• Sulfuric Acid (H2SO4):

  • Diprotic acid, reacts to form hydrogen sulfates.

  • Reaction example: H2SO4 + NaOH → NaHSO4 + H2O

16.4 Limestone

• Composition: Primarily made of CaCO3 (calcium carbonate).

• Formation: Derived from ancient marine life remains compressed over time.

Lime Products from Limestone

• Lime Production:

  • Process: Thermal Decomposition of limestone

  • Reaction: CaCO3 → CaO + CO2

  • Lime Kiln: Hot air drives out CO2, preventing reformation of CaCO3.

  • Practical: Indicator tests show slaked lime formation.

• Slaked Lime (Ca(OH)2):

  • Produced by adding water to CaO (very exothermic).

• Lime Water Test:

  • Used to detect CO2 gas presence.

Uses of Limestone Products

• Limestone Uses:

  • Neutralizing soil/lake acidity

  • Manufacture of cement and glass

  • Impurities removal in iron extraction

• Flue Gas Desulfurization:

  • Removal of SO2 from fossil fuel combustion.

  • Process:

    • Reaction with CaCO3, CaO, or Ca(OH)2:

      • CaO + SO2 → CaSO3

      • CaSO3 to Calcium sulfate through oxidation: 2CaSO3 + O2 + 4H2O → 2CaSO4•2H2O

  • Calcium sulfate is commonly used in construction (plaster board) or wasted due to transport costs.