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chemical properties of metal, extraction of metal

In this lesson we are going to learn:

Metals are the elements that have 1, 2, or 3 electrons in the valence/outer shell.


 

Valency of metals
Metals have valencies +1, +2 or +3.
Metals lose electrons and form cations like, Na - 1e- ⇒ Na1+ (valency +1)

Reducing nature of metals: Metals lose valence electrons and are hence good reducing agents.

Activity Series Of Metals

Activity series is a series of arrangements of metals in decreasing order of their reactivity. The most active metal is at the top of the series and the least active metal is at the bottom of the series. It is used to determine the products of single displacement reactions, whereby metal A will replace another metal B in a solution if A is higher in the series.

Reaction With

 Metals

Water




 

 
  • K and Na react violently to cold water

2K + 2H2O ⇒ 2 KOH + H2

  • Ca react less vigorously with cold water

Ca + 2H2O ⇒ Ca(OH)2 + H2

  • Mg to Fe react smoothly with hot water/steam

3 Fe + 4H2O ⇔ Fe3O4 + 4H2

  • Metals in the activity series below Hydrogen, do not react with water to displace Hydrogen.
Acid
  • K and Na react explosively with dilute HCL or dilute H2SO4  

2K + 2HCL ⇒ 2KCl + H2

  • Ca to Fe react with decreasing vigor with dil. HCL and dil. H2SO4

Fe + H2SO4⇒ FeSO4 + H2   

  • Metals in the activity series below Hydrogen, do not react with dilute acids to displace hydrogen.
Oxygen
  • K to Ag reacts with oxygen to form metallic oxides. 

4K + O2 ⇒ 2K2O

  • Pt and Au do not form oxides

Extraction of Metals

The extraction process depends on the physical and chemical properties of the constituents of an ore. There are three steps involved in the extraction of metals from ore: The large-scale processes involved in the extraction of pure metals from their respective ores are called metallurgy.

Step 1: The concentration of Ore

Ores are common oxides, for example, bauxite(Al2O3), haematite (Fe2O3), rutile (TiO2), or sulfides, for example, pyrite (FeS2), chalcopyrite(CuFeS2)

This step involves the separation of impurities from the ore. Methods involved are: 

a) Electromagnetic Process:

The magnetic ore is attracted by a magnet and non-magnetic impurities move away from the magnet. 

b) Froth Floatation Process:

Ore wetted by oil floats on top and impurities wetted by water settles down. The principle of froth floatation is that sulfide ores are preferentially wetted by pine oil, whereas the gangue particles are wetted by water.

c) Gravity Separation Process:

Dense ore particles settle in grooves and light impurities washed away by water. 

Step 2: Extraction of Metal from concentrated Ore
Metals Extraction By  Procedure
K, Na, Ca, Mg, Al Electrolysis

Electrolysis of fused metallic salts. Pure metals formed at the cathode.

KBr ⇔ K+ + Br-
K+ + 1 e- ⇒ K (deposited at the cathode)
Zn, Fe, Pb, Cu

Reducing Agents
[CO, H2, C]

- Ores are first converted to oxides (as oxides are easy to reduce) 
ZnCO3  ⇒  ZnO + CO2
- Metallic oxides are then reduced to metals by reducing agent
ZnO + C ⇒ Zn + CO
Hg, Ag Thermal Decomposition

Metallic oxides reduced to metals by heat alone

2HgO ∆⇒ 2 Hg + O2

 

Step 3: Refining of Impure Metal

Separation of impurities from the above-extracted metals.

Electrolytic Refining During electrolysis, electrons are being added directly to the metal ions at the cathode (the negative electrode). The pure metal is deposited at the cathode and impurities are settled down as anode mud. For example Cu, Pb, Al
Oxidation Refining For refining metals by oxidation of their impurities, for example, iron. On oxidation pure metal remains behind in molten form and impurities example P, S, C are oxidized by air to respective oxides. 
Distillation refining For refining volatile metals like zinc, mercury. On heating pure metals vaporizes and is condensed and collected and the non-volatile impurities remain behind

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