Metals in the Earth's Crust

• Composition of the Earth's Crust

  • Metals primarily come from the Earth's crust.

  • The crust is composed of a mixture of many compounds and elements, including:

    • Native (Uncombined) Elements: Sulfur, Copper, Silver, Platinum, and Gold (unreactive).

    • Major Components:

      • Oxygen: ~45% (almost half)

      • Silicon: ~27% (over one quarter)

      • Iron: 6%

      • Aluminum: 8%

      • Calcium: 5%

      • Sodium: 2.5%

      • Magnesium: 3%

      • Potassium: 1.5%

  • Nearly three-quarters of the Earth's crust is made up of just oxygen and silicon, found in compounds like silicon dioxide (silica).

  • Reactive metals (like iron and aluminum), do not occur uncombined.

• Scarcity of Metals

  • Only six metals are abundant, while other metals make up less than 2% of the Earth's crust. Scarce metals include:

    • Copper, Zinc, Lead, Tin, Mercury, Silver, Gold, Platinum.

  • Scarce metals are generally more expensive and are used up quickly due to high demand.

Metal Ores

• Definition of Ores

  • Ores are rocks that contain a high amount of a particular metal compound, worth mining for metal extraction.

  • Examples of ores include:

    • Rock Salt (Sodium Chloride)

    • Bauxite (Aluminum Ore, mainly aluminum oxide)

    • Native Gold (occur unreactively)

• Mining Considerations

  • Economic viability of mining an ore is determined by answers to key questions:

    1. How much ore is available?

    2. How much metal can be extracted?

    3. Are there challenges in extracting the ore?

    4. What are the costs (infrastructure, labor, etc.)?

    5. What is the potential selling price of the metal?

    6. Will mining be profitable?

  • Local communities may welcome job creation but express concern over environmental impacts.

Extracting Metals from Their Ores

• Initial Steps in Extraction

  • Extracting metals mainly involves separating them from their ores after mining.

  • Less reactive metals (gold, silver) can be found as elements and require no chemical reactions for extraction. More reactive metals must go through extraction processes.

• Methods of Extraction

  • Reduction: Removal of oxygen from metal oxides to obtain pure metals.

    • Carbon (as a reducing agent) is commonly used.

    • Example: Iron (III) Oxide with carbon monoxide yields iron and carbon dioxide.

  • Electrolysis: Used for obtaining metals like aluminum that are difficult to extract other ways. This involves splitting the compound with electricity.

    • Example: Electrolysis of aluminum oxide yields aluminum and oxygen.

Summary of Extraction Methods

• Extraction Methods Overview:

  • Potassium, Sodium, Calcium: Extracted by electrolysis.

  • Magnesium, Aluminium: Also through electrolysis.

  • Zinc, Iron, Lead: Extracted through heating with carbon or carbon monoxide.

  • Silver and Gold: Usually occur as natural elements.

Pure Metals and Alloys

• Properties and Uses

  • The utility of metals often depends on their properties; for instance:

    • Pure Aluminium: Lightweight, rolled into sheets; used for foils and containers.

    • Copper: Excellent conductor; used in electrical wiring.

    • Iron: Formed into alloys for increased strength, like mild steel for construction.

• Alloys: Mixtures of metals or non-metals that often enhance certain properties:

  • Examples: Stainless steel (iron, nickel, chromium), brass (copper, zinc).

Extracting Iron

• Blast Furnace: A fundamental component of iron extraction:

  • Hot air burned coke creating carbon dioxide and carbon monoxide.

  • Further reactions reduce iron(III) oxide to molten iron.

Electrolysis of Compounds

• Electrolysis: Key method for breaking down ionic compounds into elements, usually requires:

  • Compounds to be molten or dissolved for ion mobility.

• Practical Examples: For instance,

  • Electrolysis of lead bromide results in lead and bromine.

Environmental and Economic Factors in Mining

• Companies must consider ecological impacts and community concerns alongside the economic factors of mining and extraction processes.

Properties of Metals and Their Applications

• Metals have unique characteristics that make them suitable for specific uses based on their physical and chemical properties.

Chloralkali Industry

Overview

The chloralkali industry involves the production of chlorine (Cl2), hydrogen (H2), and sodium hydroxide (NaOH) through the electrolysis of sodium chloride (NaCl) solutions.

Key Products

1. Chlorine (Cl2)

   • A greenish-yellow gas

   • Uses:

     • Water treatment and disinfection

     • Production of various chemicals including PVC and other plastics.

2. Sodium Hydroxide (NaOH)

   • Also known as caustic soda

   • Uses:

     • Used in soap making

     • Paper production

     • Cleaning agent and within various chemical processes.

3. Hydrogen (H2)

   • A flammable gas used as a fuel, in chemical processes, and in the production of ammonia for fertilizers.

   • Uses:

     • Fuel cells and as a clean energy source

     • Hydrogen Peroxide

     • Chemical reduction processes.

Production Process

1. Electrolysis of Brine

   • Brine (concentrated sodium chloride solution) is subjected to electrolysis in an electrolytic cell.

   • Chemical Reaction:

     • 2NaCl(aq) + 2H2O(l) → Cl2(g) + H2(g) + 2NaOH(aq)

   • The process yields chlorine gas at the anode and hydrogen gas at the cathode, with sodium hydroxide formed in the solution.

2. Methods of Electrolysis

   • Membrane Cell Process: Uses a selective membrane to separate products, improving efficiency.

   • Diaphragm Cell Process: Utilizes a porous diaphragm to separate chlorine from hydroxide and hydrogen.

   • Mercury Cell Process: Involves mercury as a cathode; less commonly used due to environmental concerns.

Environmental Considerations

• The chloralkali process generates hazardous chemicals; thus, proper management is required to minimize environmental impact.

• Effluent treatment and emission control are vital to prevent pollutants from entering the ecosystem.

Economic Importance

• The chloralkali industry is essential for producing raw materials for various downstream chemical processes, making it a key component of the chemical manufacturing sector.

Reactions of the Halogens

Overview of Halogens

• Halogens are elements found in Group 17 of the periodic table, notable for their high reactivity. They include:

  • Fluorine (F): The most reactive and electronegative element.

  • Chlorine (Cl): Widely used in disinfectants and bleach.

  • Bromine (Br): A liquid at room temperature, used in flame retardants.

  • Iodine (I): Essential for thyroid hormones and used in antiseptics.

  • Astatine (At): Rare and radioactive, with limited applications.

General Properties of Halogens

• Physical State: Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid at room temperature.

• Color: Fluorine is a pale yellow gas, chlorine is greenish-yellow, bromine is reddish-brown, and iodine appears as dark purple.

• Reactivity: Halogens are highly reactive nonmetals, especially with alkali and alkaline earth metals, due to their tendency to gain an electron to achieve a stable octet.

• Molecular Form: They commonly exist as diatomic molecules (e.g., F₂, Cl₂, Br₂, I₂) in nature.

Reactivity

• Trends in Reactivity:

  • Reactivity decreases down the group due to increasing atomic size and decreased electronegativity.

  • Fluorine is the most reactive due to its high electronegativity, while iodine is the least reactive.

Types of Reactions

1. Displacement Reactions:

   • A more reactive halogen can displace a less reactive halogen from its compound.

   • Example:

     • Cl₂ + 2KBr → 2KCl + Br₂

   • In this reaction, chlorine displaces bromine from potassium bromide.

2. Formation of Halides:

   • Halogens react with metals to form ionic compounds known as halides.

   • Example:

     • 2Na + Cl₂ → 2NaCl

   • Here, sodium reacts with chlorine gas to form sodium chloride.

3. Organic Reactions:

   • Halogens can react with hydrocarbons through substitution or addition reactions:

     • Substitution: Chlorination of methane (CH₄) in the presence of UV light.

     • Example:

       • CH₄ + Cl₂ → CH₃Cl + HCl

     • This indicates a one-to-one substitution of hydrogen for chlorine.

   • Addition: Halogens add across double bonds in alkenes.

     • Example:

       • C₂H₄ + Br₂ → C₂H₄Br₂

     • This shows the addition of bromine to ethylene to form a dibromide.

4. Reactions with Elements:

   • Halogens can react with hydrogen to produce hydrogen halides, which are strong acids.

   • Example:

     • H₂ + Cl₂ → 2HCl

     • This illustrates the combination of hydrogen and chlorine to form hydrochloric acid.

Oxidation States

• Common Oxidation States: Halogens usually exhibit -1 in halides but can show positive oxidation states when reacting with more electronegative elements, like oxygen or fluorine.

• Examples of Compounds:

  • Interhalogen Compounds (e.g., ClF, BrCl) display unique reactivities and properties.

  • Oxidation states can vary, for instance, in compounds like ClO⁻ where chlorine is in a +1 state.

Environmental Impact

• Despite their usefulness (e.g., chlorine in water treatment), halogens can generate hazardous byproducts and pose ecological risks.

• Chlorofluorocarbons (CFCs), once used in refrigeration and aerosol propellants, have significantly contributed to ozone layer depletion.

• Safety: When handling halogens, appropriate safety measures should be observed due to their corrosive nature and potential to emit toxic gases.

Summary

• The halogens possess distinct characteristics and undergo a variety of reactions that emphasize their reactivity and significant roles in both industrial applications and organic synthesis. Understanding their reactions is crucial for advancements in chemical processes and environmental protection.