Obtaining and using metals

• Metal + water -> metal hydroxide + hydrogen
• sodium + water → sodium hydroxide + hydrogen

  2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
• Metal + steam → metal oxide + hydrogen
• Magnesium + steam → magnesium oxide + hydrogen

  Mg(s) + H2O(g) → MgO(s) + H2(g)
• Metal + dilute acid → salt + hydrogen
• Magnesium + hydrochloric acid → magnesium chloride + hydrogen

  Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
• Displacement example:

  magnesium + copper sulfate → magnesium sulfate + copper

  Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s)
• when magnesium displaces copper:

  • magnesium becomes coated with copper
  • the blue colour of the solution fades as blue copper sulfate solution is replaced by colourless magnesium sulfate solution
• A reactivity series can be deduced by carrying out several displacement reactions. A piece of metal is dipped into a saltsolution. Different combinations of metal and salt solution are tested.
• Unreactive metals such as gold are found in the Earth's crust as the uncombined elements. However, most metals are found combined with other elements to form compounds.

  An ore is a rock that contains enough of a metal or a metal compound to make extracting the metal worthwhile:

  • low-grade ores contain a small percentage of the metal or its compound
  • high-grade ores contain a larger percentage
• If a metal is less reactive than carbon, it can be extracted from its compounds by heating with carbon.

  Metal oxide + carbon → metal + carbon dioxide
• • a redox reaction involves the loss and gain of oxygen
• As iron is below carbon in the reactivity series it can be displaced from its compounds by heating with carbon. Iron is extracted from iron ore in a large container called a blast furnace. Iron(III) oxide is reduced to molten iron when it reacts with carbon.

  Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)
• Aluminium ore is treated to produce pure aluminium oxide. The electrolytes used in electrolysis are ionic compounds:

  • in the molten state, or
  • dissolved in water
• • collecting and transporting the used items to a recycling centre
  • breaking up and sorting the different metals
  • removing impurities from the metals
• more economic - less energy is needed to produce a metal

  • less damage to the environment - fewer quarries and mines, less noise and less heavy traffic
  • saves valuable raw materials - reserves of metal ores will last longer
• Disadvantages of recycling arise from the recycling process itself:

  • the collection and transport of used items needs organisation, workers, vehicles and fuel
  • it can be difficult to sort different materials from one another
• A life-cycle assessment or LCA is a 'cradle to grave' analysis of the impact of a manufactured product on the environment. The main stages are:

  1. obtaining the raw materials needed
  2. manufacturing the product
  3. using the product
  4. disposing of the product at the end of its useful life
• All the raw materials we need come from the Earth's crust, atmosphere or oceans, or are due to living organisms. Obtaining these materials has an impact on the environment, including:

  • using up limited resources such as ores and crude oil
  • damaging habitats through quarrying, mining, or felling trees
• The manufacture of products has an impact on the environment, including:

  • using up land for factories
  • the use of machines and people
• The impact of a product on the environment during its use depends on the type of product. For example, a wooden chair has very little impact, unless it needs cleaning or repair. On the other hand, a car will have a significant impact.
• The disposal of old products has an impact on the environment, including:

  • using up land for landfill sites
  • whether any or all of the product can be recycled or reused
• Plants absorb mineral ions through their roots. Phytoextraction makes use of this to extract metals:

  1. plants are grown on a low-grade ore that contains lower amounts of metal
  2. the plants absorb metal ions through their roots and concentrate these ions in their cells
  3. the plants are harvested and burnt
  4. the ash left behind contains a higher concentration of the metal than the original ore
  5. the ash is processed to obtain the metal
• Phytoextraction is slow, but it:

  • reduces the need to obtain new ore by mining
  • conserves limited supplies of more valuable ores with higher metal content
• Certain bacteria can break down low-grade ores to produce an acidic solution containing metal ions. The solution is called a leachate and the process is called bioleaching. Bioleaching can be used to extract copper metal. It does not need high temperatures, but it produces toxic substances, including sulfuric acid, which damage the environment.
• Iron is more reactive than copper. It can displace copper from the leachate. For example:

  Iron + copper sulfate → iron(II) sulfate + copper

  Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

  Since iron is cheaper than copper, the use of scrap iron is a cost-effective way to produce copper from the leachate.