(Unit 4)Chemistry in industry and environmental pollution

• Aluminium reacts with oxygen to form a thin film of aluminium oxide on its surface, inhibiting further reaction with oxygen
• The thin film of oxide can be removed by rubbing with mercury or mercury (II) chloride solution
• Aluminium reacts with dilute acids like HCl and H2SO4, forming salts and liberating hydrogen gas
• Aluminium does not react with dilute or concentrated HNO3 due to the formation of a protective oxide layer on its surface
• Aluminium burns in chlorine gas to form aluminium chloride
• Aluminium reacts with sodium hydroxide solution to form sodium aluminate and hydrogen gas
• Uses of aluminium include making light alloys like duralumin, used in the transport industry for aircraft, ships, and cars, household cooking utensils, door and window frames, roofing for buildings, packaging material in food industries, and electrical transmission lines
• In the thermite welding process, powdered aluminium mixed with iron (III) oxide and ignited produces a temperature of about 3000°C, sufficient for welding metals
• Iron is the second-most abundant metal next to aluminium in the earth's crust
• Iron is generally extracted from hematite, magnetite, and siderite ores in a blast furnace
• The extraction of iron from its ores involves a series of reactions in the blast furnace, including oxidation of coke to carbon dioxide, reduction of carbon dioxide to carbon monoxide, reduction of iron oxides to metallic iron by carbon monoxide, decomposition of limestone to remove impurities, and formation of slag
• The iron obtained directly from the blast furnace is called pig iron, which is impure and contains silicon, phosphorus, manganese, and traces of sulphur
• Pig iron can be re-melted with scrap iron to form cast iron
• Wrought iron is the purest form of commercial iron, obtained by removing impurities from pig iron
• Conversion of pig iron to steel involves a purification process where impurities are removed by oxidation using methods like the Bessemer Converter, Open-hearth Furnace, and Basic Oxygen Process
• Physical Properties of Iron:

  • Grey, lustrous, malleable, and ductile metal
  • Good conductor of heat and electricity
  • High melting point (1580°C) and high density (7.87 g/cm3)
  • Ferromagnetic metal, can be permanently magnetized
• Chemical Properties of Iron:

  • Reactive metal, rusts in the presence of air and moisture to form hydrated iron (III) oxide
  • Reacts with dilute acids like HCl and H2SO4 to form iron (II) salts and liberate hydrogen gas
  • Exhibits different oxidation states as ferrous (Fe2+) and ferric (Fe+3) ions
  • Compounds of iron (II) are pale-green, and iron (III) compounds are yellowish brown
• Iron has the ability to displace less active metals from solutions of their salts

  • For example, when placed in a solution of CuSO4, iron is oxidized to Fe2+ and copper metal forms on the surface
• Uses of Iron:

  • Widely used metal, used in construction, domestic boilers, railings, water pipes, castings, and more
  • Used to make alloys like carbon steels and alloy steels
  • Carbon steels classified as mild steel, medium steel, and high-carbon steel based on carbon content
• Physical Properties of Copper:

  • Soft, ductile, malleable, reddish-brown metal with a density of 8.96 g/cm3
  • Second to silver in electrical conductivity, melts at 1086°C and boils at 2310°C
• Chemical Properties of Copper:

  • Less reactive metal, forms copper (II) oxide when heated in air
  • Does not react with dilute acids, but can be oxidized by oxidizing acids like nitric acid and hot concentrated sulphuric acid
  • Corrodes in moist air forming verdigris, a basic copper carbonate
• Uses of Copper:

  • Used to manufacture alloys like bronze and brass
  • Widely used in the electrical industry for electric wires and cables
  • Copper compounds used as pesticides
• Nitrogen molecule structure:

  • Nitrogen molecule is represented as N≡N
  • It forms a triple bond due to the high energy required to break the bond
• Green plants absorb nitrogen in the form of nitrate (NO3-) or ammonium (NH4+)
• In the industrial production of nitrogen:

  • Air is compressed under high pressure and low temperature to remove impurities like dust and other particles
  • The air is then fractionally distilled to separate nitrogen and oxygen
  • Nitrogen is collected and stored in steel cylinders under pressure
• Physical properties of nitrogen:

  • Colourless, odourless, and tasteless gas
  • Inert under ordinary conditions
  • Found in atmospheric air as N2
• Chemical properties of nitrogen:

  • Nitrogen is relatively unreactive under ordinary conditions
  • Reacts with metals of group IA and IIA, as well as oxygen at higher temperatures
  • Forms compounds like nitrides with reactive metals
  • Combines with oxygen to form oxides
• Uses of nitrogen:

  • Used in food packaging to prevent oxidation
  • Creates an inert atmosphere in semiconductor production
  • Liquid nitrogen is used as a refrigerant
  • Major use in the production of ammonia
• Oxygen:

  • Most abundant element on earth
  • Exists in nature in the elemental state in atmospheric air
  • Manufactured industrially by fractional distillation of liquid air
• Chemical properties of oxygen:

  • Combines with most elements to form oxides
  • Combines with metals to form basic oxides and with non-metals to form acidic oxides
  • Supports combustion and burning of substances
• Sulphur:

  • Found in nature and in compounds like galena, pyrites, cinnabar, etc.
  • Extracted from underground deposits using the Frasch process
  • Uses include chemical industries and obtained as a waste product
• Sulphur can be obtained as a waste product of other industrial processes, such as from natural gas, during the purification of crude oil, and from the roasting of sulphide ores during the manufacture of metals
• The use of sulphur obtained from waste products of other industries reduces the demand for the element from natural deposits and reduces pollution of atmospheric air and the formation of acid rain
• Sulphur exhibits allotropy with the most important allotropes being rhombic and monoclinic sulphur, with rhombic sulphur being the most stable form consisting of S8 molecules
• Chemical properties of sulphur:

  • Relatively stable and unreactive at room temperature
  • Reacts with metals and non-metals when heated
  • Combines with metals when heated to form sulphides
  • Burns in oxygen to form oxides
  • Used as raw material for the production of sulphuric acid by the Contact Process
• Contact Process for sulphuric acid production involves:

  1. Oxidizing sulphur to produce sulphur dioxide

  2. Converting sulphur dioxide to sulphur trioxide at high temperatures in the presence of a catalyst

  3. Absorbing sulphur trioxide into concentrated sulphuric acid to produce oleum

  4. Diluting oleum with water to produce concentrated sulphuric acid
• Chlorine is the most abundant element among the halogens and is found in nature chiefly in the form of chlorides of sodium, potassium, calcium, and magnesium
• Commercially, chlorine is manufactured by the electrolysis of a concentrated aqueous solution of sodium chloride, where chlorine is formed at the anode and reduction of water occurs at the cathode, producing hydrogen gas and hydroxide ions
• Physical properties of chlorine:

  • Greenish-yellow gas at room temperature
  • Melts at -102°C and boils at -34°C
  • Fairly soluble in water
  • Extremely poisonous if inhaled, causing inflammation of the lungs and mucous membranes
• Chemical properties of chlorine:

  • Highly reactive non-metal
  • Reacts directly with almost all elements except noble gases, carbon, and nitrogen
  • Powerful oxidizing agent
  • Reacts with metals to form chloride salts
  • Reacts with hydrogen to form hydrogen chloride
  • Displaces less reactive halogens from their compounds
  • Dissolves in water to form an acidic solution containing hydrochloric acid and hypochlorous acid