Physical and chemical properties of metals
Physical properties of metals:Metals can be easily identified by their physical properties,metals are generally hard and lustrous substances, some of the metals can be beaten into thin sheets. This property of metals is known as malleability.The metals can be drawn into wire,such a property is known as ductility of metals.Metals are used for manufacturing vessels for cooking due to their properties of high melting point and high conductivity of heat.Metallic wires are used for electric wiring and coated with polyvinylchloride(PVC) a rubber like material because of their property of conductance of electricity.Metals are used to make musical instruments because of their property of being sonorous.
Metals are regrouped on the basis of their reactivity, metals that are at the top of the series are (K, Na, Ca, Mg, and Al) , these are so reactive that are never found in nature as free elements. The metals in the middle of the reactivity series (Zn, Fe, Pb, etc) are moderately reactive. The metals at the bottom of the reactivity series are least reactive. They are often found in a free state. For example, gold, silver, platinum, and copper are found in a free state, copper and silver are also found in the earth’s crust in the form of their oxide or sulfide ores.
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Chemical Properties of Metals
Reaction with oxygen:Almost all metals reacts with oxygen to form metal oxides.
Metal + Oxygen → Metal oxide
Examples: When copper and aluminium are heated to air,it combines with oxygen to form copper(I)oxide(black in colour) and aluminium oxide(white in colour).
2Cu + O2 → 2CuO
4Al + 3O2 → 2Al2O3
Sodium and potassium are highly reactive metals they combine with oxygen and get fire, it is that’s why they are kept inside the kerosene that keeps them away from oxygen.
4Na + O2 → 2Na2O
4K + O2 → 2K2O
Most of the metalic oxides are insoluble in water but some of them like Na2O and K2O dissolves in water and forms alkalis as follows.
Na2O(s) + H2O(l) → 2NaOH(aq)
K2O(s) + H2O(l) → 2KOH(aq)
Oxides of metals are basic in nature but oxides of a few of the metals Al, Zn, Sn,Pb, Cu,Be show the properties of acids as well as base, such type of oxides which behaves like acid and base known as amphoteric oxides. Aluminum oxides react with acid and base in the following manner, which means it neutralizes both acid and base-forming salts and water.
Al2O3 + 6HCl → 2AlCl3 + 2H2O
Al2O3 + 2NaOH → 2NaAlO3 + H2O
Aluminum oxides reacting with hydrochloric acid form aluminum chloride and reacting with sodium hydroxide forms sodium aluminate.
The reaction of metals with water: Metal reacts with water and produces metal oxide and hydrogen gas, metal oxides that are dissolved in water to further form a metal oxide and a metal hydroxide.
Metal + Water → Metal oxide + Hydrogen
Metal + Water → Metal hydroxide
Metals like pottasium and sodium reacts with water violently with cold water,the reaction releases heat in such an extent that evolved hydrogen gas catch fire.
2K(s) + H2O(l) → 2KOH(aq) + H2(g) + heat energy
2Na(s) + H2O(l) → 2NaOH(aq) + H2(g) + heat energy
The reaction of calcium with water is less violent with cold water. The heat evolved is not sufficient for the hydrogen to catch fire.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2 + heat energy
Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.
Magnesium does not react with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen. It also starts floating due to the bubbles of hydrogen gas sticking to its surface.
Metals like aluminum, iron and zinc do not react either with cold or hot water. But they react with steam to form a metal oxide and hydrogen.
2Al(s) + 3H2O(g) → Al2O3(s) + 3H2(g)
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
Metals such as lead, copper, silver and gold do not react with water at all.
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The reaction of metal with acids: Metals react with acids to give a salt and hydrogen gas.
Metals + Dilute acid → Salt + Hydrogen
Mg + 2HCl → MgCl2 + H2
Al + HCl → AlCl3 + H2
Magnesium and aluminium react with hydrochloric acid gives magnesium chloride and aluminum chloride respectively,all metals react with HCl gives hydrogen gas and their corresponding chlorides.
Hydrogen gas is not evolved when a metal reacts with nitric acid.It is because HNO3 is a strong oxidising agent.It oxidises the H2 produced to water and itself gets reduced to any of the nitrogen oxides (N2O,NO, NO2), but magnesium(Mg) and manganese(Mn) react with very dilute HNO3 to evolve H2 gas.
Example: Al +6HNO3 → Al(NO3)3 + 3NO2 + 3H2O
3Cu + 8HNO3 → 3Cu(NO3)2 + 2NO + 4H2O
Aluminum and copper reacts with nitric acid produces aluminum nitrate and copper nitrate with oxides of nitrogen and water.
The reaction of metals with the solutions of other salts: All metals are not equally reactive.The comparison in the reactivity of the metals can be identified through the displacement reaction. When more reactive metal reacts with the salt solution of less reactive metal,then more reactive metal displaces the less reactive metal and substitutes it to form its own salt as following.
Metal A + Salt solution of metal B → Salts solution of A + Metal B