Although most metals are usually electropositive in nature and lose electrons in a chemical reaction they do not react with the same vigour or speed. Metals display different reactions towards different substances. The greater the ease with which an element loses its electrons and acquires a positive charge, the greater is its reactivity. Further, the greater the number of shells and lesser the number of valence electrons, the greater is the reactivity of the metal. The activity series of metals, arranges all metals in order of their decreasing chemical activity. As we go down the activity series from potassium to gold the ease with which a metal loses electrons, and forms positive ions in solutions, decreases.
The most active metal, potassium, is at the top of the list and the least reactive metal, gold, is at the bottom of the list. Although hydrogen is a non-metal it is included in the activity series due to the fact that it behaves like a metal in most chemical reactions i.e., the hydrogen ion has a positive charge [H+] like other metals.
Two non-metals, carbon and hydrogen are important chemical reference points with regard to the method of metal extraction and reactivity towards acids. Metals above carbon cannot be extracted by carbon reduction and are usually extracted by electrolysis. Metals below hydrogen will not displace hydrogen from acids:
Below are the list of various metals and the reactivity and reactions of these metals:
|Metals||Reactivity and reactions|
|Potassium K||Very reactive, very rapid with cold water forming the alkali potassium hydroxide and hydrogen gas(which is ignited).|
2K+2H2O(l) 2KOH(aq) +H2(g)
|Sodium Na||Fast reaction with cold water forming the alkali sodium hydroxide and hydrogen gas.|
2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)
The reaction of sodium with water-the sodium melts to a silvery ball and fizzes as it spins over the water. The rapid exothermic reaction produces a colourless gas that gives a squeaky pop! with a lit splint-hydrogen. Universal indicator will turn from green to purple/violet-the strong alkali sodium hydroxide is formed. The sodium floats because it is less dense than water.
|Calcium Ca||Quite reactive with cold water forming the moderately soluble alkali calcium hydroxide and hydrogen gas.|
Ca(s) +2H2O(l) Ca(OH)2(aq/s) + H2(g)
Very reactive with dilute hydrochloric acid forming the colourless soluble salt calcium chloride and hydrogen gas.
Ca(s) +2HCl(g) CaCl2(aq) +H2(g)
Not very reactive with dilute sulphuric acid because the colourless calcium sulphate formed is not very soluble and coats the metal inhibiting the reaction.
Ca(s) + H2SO4(aq) CaSO4(s) + H2(g)
|Magnesium Mg||Slow reaction with water forming the slightly soluble alkali magnesium hydroxide and hydrogen gas.|
Mg(s) +2H2O(l) Mg(OH)2(aq/s) +H2(g)
With steam, the reaction is faster with heated magnesium and a white powder magnesium oxide is formed along with hydrogen.
|Aluminium Al||Aluminium has no reaction with water or steam due to a protective aluminium oxide layer of Al2O3. Slow reaction with dilute hydrochloric acid to form a colourless soluble salt aluminium chloride and hydrogen gas.|
2Al(s) +6HCl(aq) 2AlCl3(aq) + 3H2(g)
The reaction with dilute sulphuric acid is extremely slow to form colourless aluminium sulphate and hydrogen.
2Al(s +3H2SO4(aq)Al2(SO4)3(aq) + 3H2(g)
|(Carbon C,a non-metal)||Elements higher than carbon i.e aluminium and the more reactive metals must be extracted by electrolysis (or displacing it with an even more reactive metal). Metals below it, i.e., zinc or a less reactive can be extracted by reducing the hot metal oxide with carbon.|
|Zinc Zn||No reaction with cold water. When the metal is heated in steam zinc, oxide and hydrogen are formed.|
Zn(s) + H2O(g) ZnO(s) + H2(g)
Quite reactive with dilute hydrochloric acid forming the colourless soluble salt zinc chloride and hydrogen gas.
Zn(s) +2HCl(aq) ZnCl2(aq) + H2(g)
Quite reactive with dilute sulphuric acid forming the colourless soluble salt zinc sulphate and hydrogen gas.
Zn(s) + H2SO4(g) ZnSO4(s) + H2(g)
(this reaction is catalysed by adding a trace of copper sulphate solution)
|Iron Fe||No reaction with cold water (rusting is a joint reaction with oxygen). When the metal is heated in steam an iron oxide (unusual formula) and hydrogen are formed. This oxide is 'technically' Iron (III, II) oxide!|
3Fe(s) + 4H2O(g) Fe3O4(s) +4H2(g)
Slow reaction with dilute hydrochloric acid forming the soluble pale green salt Iron (II) chloride and hydrogen gas.
Fe(s) + 2HCl(aq) FeCl2(aq) + H2(g)
Slow reaction with dilute sulphuric acid forming the soluble pale green salt Iron (II) sulphate and hydrogen gas.
Fe(s) + 2H2SO4(g) FeSO4(s) + H2(g)
Iron can be extracted by reducing the hot metal oxide on heating with carbon monoxide formed from carbon in the blast furnace e.g.,
Fe2O3(s) +3CO(g) 2Fe(s) +3CO2(g)
Fe3O4(s) +4CO(g) 3Fe(s) +4CO2(g)
|(Hydrogen H non-metal)||None of the metals below hydrogen can react with acids to form hydrogen gas. They are least easily corroded metals and partly accounts for their value and uses in jewellery, electrical contacts etc.|
|Copper Cu||No reaction with cold water or when heated in steam. No reaction with dilute hydrochloric acid or dilute sulphuric acid. Copper can be extracted by reducing the hot black metal oxide on heating with carbon.|
2CuO(s) + C(s) 2Cu(s) +CO2(g)
|Silver Ag||No reaction with cold water or when heated in steam. No reaction with dilute hydrochloric acid or dilute sulphuric acid. Silver can be extracted by reduction but can be found 'native' as the element.|
|Gold Au||No reaction with cold water or when heated in steam. No reaction with dilute hydrochloric acid or dilute sulphuric acid. Gold can be readily extracted from its ores easily by reduction but it is usually found 'native'. Pure gold is 24 carat.|
|Platinum Pt||No reaction with cold water or when heated in steam. No reaction with dilute hydrochloric acid or dilute sulphuric acid. Like gold, it is a very rare metal. It is used in expensive jewellery, laboratory ware (inert crucible container) as a industrial catalyst, and catalytic converters in car exhausts.|