Chemistry topic 4

• The chemistry of the metals is seen by comparing their characteristic reactions.
• A reactivity series of metals can be produced based on these reactions.
• The series can be used to place a group of metals in order of reactivity based on the observations of their reactions with water, acids and salts.
• When a metal reacts with water it produces a metal hydroxide and hydrogen gas.
• The reactions of potassium and sodium are covered in more detail in another section, but the reaction with calcium and water is given here for reference: Ca (s) + 2H O (l) ⟶ Ca(OH) (aq) + H (g) calcium + water ⟶ calcium hydroxide + hydrogen.
• Only metals above hydrogen in the reactivity series will react with dilute acids.
• The more reactive the metal then the more vigorous the reaction will be.
• Metals that are placed high on the reactivity series such as potassium and sodium are very dangerous and react explosively with acids.
• When acids react with metals they form a salt and hydrogen gas: metal + acid ⟶ salt + hydrogen.
• Some examples of metal-acid reactions and their equations are given below: Mg + 2HCl ⟶ MgCl2 + H2.
• A metal ore is a rock that contains enough of the metal to make it worthwhile extracting.
• After writing half equations, you can check if they are correct by checking that the number of electrons on either side is the same, which should combine to give 0 charge.
• Metals higher up on the reactivity series, such as silver and gold, have to be extracted using electrolysis as they are too reactive and cannot be reduced by carbon.
• The Earth’s crust contains metals and metal compounds such as gold, copper, iron oxide and aluminium oxide.
• Metal displacement reactions involve the principles of electron loss and gain to identify which species undergo oxidation and reduction.
• Useful metals are often chemically combined with other substances forming ores.
• Deducing redox changes in displacement reactions involves determining which species undergoes oxidation and which species undergoes reduction.
• Metals lower on the reactivity series, such as iron and aluminium, can be extracted by heating with carbon which reduces them.
• Using the reaction between zinc and copper(II) sulfate as an example, zinc displaces copper from a solution of copper(II) sulfate.
• The more reactive metals displace the less reactive metals, and this principle can be used to identify redox changes in metal displacement reactions.
• The extraction method depends on the position of a metal in the reactivity series.
• The reactivity between two metals can be compared using displacement reactions in salt solutions of one of the metals.
• Magnesium is a reactive metal and can displace copper from a copper sulfate solution: Mg + CuSO4 ⟶ MgSO4 + Cu2+.
• The blue color of the CuSO4 solution fades as colourless magnesium sulfate solution is formed.
• Copper coats the surface of the magnesium and also forms solid metal which falls to the bottom of the beaker.
• By combining different metals and metal salts solutions it is possible to come up with a relative reactivity order.
• In all these reactions the more reactive metals lose electrons to become cations.
• The more reactive the metal the more easily it becomes a cation: M ⟶ M+.
• The loss of electrons is oxidation.
• Unreactive metals are more resistant to oxidation.
• The plants are grown in areas known to contain metals of interest in the soil.
• Bioleaching does not require high temperatures, but it does produce toxic substances which need to be treated so they don’t contaminate the environment.
• Both phytomining and bioleaching are used to extract metals from mining wastes, which may contain small quantities of metals or toxic metals that need to be removed from that environment.
• These parts of the plant are harvested, dried and burned, resulting in ash containing metal compounds from which the useful metals can be extracted by displacement reactions or electrolysis.
• Phytoextraction and bioleaching are principally used for copper extraction due to the high global demand for copper, but these methods can be applied to other metals.
• Bioleaching is often used to extract metals from suldes such as CuS or Fe S.
• Biological methods are slow and also require either displacement or electrolysis to purify the extracted metal.
• Extraction of metal ores from the ground is only economically viable when the ore contains sufficiently high proportions of the useful metal, such as iron ores and aluminium ores.
• As the plants grow, the metals are taken up through the plants vascular system and become concentrated in specific parts such as their shoots and leaves.
• The ions can then be reduced to the solid metal form and extracted by displacement reactions or electrolysis.