Extracting Metals and Equilibria

Obtaining and Using Metals

The reactivity series of metals will be given in any exam question involving it

• The Reactivity Series is a list of metals in order of reactivity, with the most reactive at the top. The relative reactivity of a metal with water and acids can be used to determine their place in the series.
• The reactivity series can be used to predict whether reactions will occur. Each metal will displace any metal below it in a compound during a reaction as it is more reactive, during as a displacement reaction. These reactions are redox reactions, as the less reactive metal is oxidised to lose electrons and become a part of the solution while the more reactive metal is reduced to form a solid.

Metal	Reactivity
	Water	Acid		Extraction
Potassium	Cold Water to form H2 & M-OH(aq)	Violent reaction		Electrolysis of a molten compound to decompose it into its elements. Aluminium is produced by the electrolysis of aluminium oxide, found in its ore bauxite. Molten Al2O3 is dissolved in cryolite at 1000°C and the aluminium is attracted to the cathode which surrounds the cell, where it is formed as a liquid. Electrolysis is very expensive and is therefore only used to extract very reactive metals that are more reactive than carbon.
Sodium
Calcium
Magnesium	React with steam to form H2 and M-O(s)	React with less vigour
Aluminium
(Carbon)
Zinc	Some metals do not corrode e.g. Al because tarnish (protective oxide layer) prevents further reaction			Heat the ore with carbon. Carbon is more reactive than iron so it displaces it in its compound of iron oxide from the ore of haematite. This method of extraction is only used for metals less reactive than carbon.IronRusts with O2 and H2
Iron Rusts with O2 and H2O in air
Copper	Unreactive with water, acid and O2. Therefore they do not corrode at all and are used in jewellery
(Hydrogen)
Silver				Very unreactive metals are found in the earth’s crust in theirnatural state, as uncombined elements.
Gold
Platinum
Bioleaching: grow bacteria on low grade ore. Microorganisms produce solution containing ions called leachate. Purify metal by displacement using scrap metal then electrolysis. Used for copper, nickel, cobalt and zinc. No high temperatures required, and no gases produced. Less harmful than mining and conserved high grade ores. However, toxic substances and H2SO4 produced and these damage the environment
Phytomining: grow plants on low grade ore. Plants absorb metal compounds. Plants are burnt to form ash from which metal is extracted. It is useful as metals can be recovered from contaminated soil, but it can be very expensive and the growth of plants is dependent on weather conditions

• Most reactive metals react with other elements to form compounds in rocks. An ore is a rock that contains enough of a compound to extract a metal for profit. Ores are reduced to extract metals.

Many metals can be recycled by melting them down and using them in new products.

• Natural reserves of metal ores last longer as demand for mining, which damages landscape and creates noise and dust pollution, decreases
• Less pollution produced e.g. SO2 from metals extracted from sulfide ores
• Less energy needed for recycling than extracting new metals from ore, saving money and resources and less metal ends up in landfill sites
• However, recycling is expensive and requires large amounts of energy in collection and sorting

A life cycle assessment works out the environmental impact of a product in disposal, using raw materials, manufacturing and packaging the product and using the product, helping people to decide whether it is worthwhile to manufacture or recycle a product, and to compare the effect of using different materials for the same product. Data from an LCA can be evaluated to show whether it is more viable to recycle and the extract in terms of energy used to generate an amount of metal

Dynamic Equilibrium

Some chemical reactions are reversible, as the products react to reform the reactants. A double arrow ⇌ is used to show that the forward and backward reactions are occurring simultaneously.

During a reaction, the forward reaction starts fast and slows over time. At a certain point, the forward and backward reactions are still occurring, but the percentage of the reactants and products are no longer changing – dynamic equilibrium. This can only happen in closed systems

Ammonia is manufactured by the Haber Process involving a reversible reaction between nitrogen from the air and hydrogen from natural gas. The equilibrium positions are changed to increase the yield and the rate of reaction for maximum profit. The conditions are a temperature of 450°C, a pressure of 200atm and the use of an iron catalyst.