Solutions-Class 10-Science & Technology-1-Chapter-8-Metallurgy-Maharashtra Board

Sodium amalgam, commonly denoted as Na(Hg), it is an alloy of mercury and sodium.

Al₂O₃.nH₂O.

Aluminium Oxide ( Al₂O₃ ) can react both an acid as well as a base to produce salt and water.

The device used for grinding an ore is grinding mill.

Graphite is a good conductor of electricity.

Aqua regia is 1:3 mixture of concentrated nitric and hydrochloric acids. It dissolves noble metals such as gold, and platinum.

Metallurgy: The process used for extraction of metals in their pure form from its ores and then metals are further purified by various methods of purification. All the process is called metallurgy.
The major steps involved for the extraction of a metal from its ore are:
(i) Concentration of ores (or enrichment of ore)
(ii) Conversion of concentrated ore into metal
(iii) Refining (purification) of impure metal

Ores: Those minerals from which a metals can be extracted conveniently and profitably.

Example : Bauxite (Al₂O₃.H₂O.) Cinnabar (HgS)

Minerals: The Naturally occurring compounds of metals along with other impurities are known as minerals.

Example :Rocks are composed of mixtures of minerals. Talc and granite are minerals.

Gangue is the unwanted impurities like rock material, dust, soil, sand, earthy particles, limestone, mica etc. present in an ore.

• Copper undergoes oxidation in air to form black copper oxide.
• These copper oxide reacts slowly with carbon dioxide in air and copper vessels turned greenish due to the formation of copper carbonate layer.
• The citric acid present in the lemon or tamarind neutralises the basic copper carbonate and dissolves the layer and makes copper vessals shiny again.
• That is why, tarnished copper vessels are cleaned with lemon or tamarind juice.

In an ionic compound there is strong electrostatic force of attraction between opposite charged ions. To overcome these forces a considerable amount of energy is needed. Therefore, ionic compounds have high melting points.

Sodium is a very reactive metal. It vigorously reacts with atmospheric oxygen and catches fire. If it is kept in kerosene it does not react with kerosene and sinks in it. In kerosene, it does not come in contact with oxygen and prevent accidental fire.

Pine oil is added in the froth flotation method to create froth or bubble so that metal can be purify easily because pine oil prevents the ore from gangue for further mixing. Pine oil also acts as best substance for forming froth for the minerals. It also increases the non wettability of mineral particles.

In the electrolysis of alumina, graphite rod is used as anode.

• During the electrolytic reduction of alumina, aluminium is produced at the cathode and oxygen gas is evolved at the anode.
• This gas reacts with the graphite rods (anode) and forms carbon dioxide.
• Thus, the graphite rods are continuously eroded.

Hence, the graphite rods i.e. anodes needs to be replaced from time to time during the electrolysis of fused alumina.

Copper is more reactive than silver. Hence, displacement reaction occurs. When copper coin is dipped in silver nitrate solution, it forms copper nitrate and silver metal. A shining white deposit of silver metal is formed on copper coin. As a result shiny coat of silver is formed on the coin.

Chemical equation:
2AgNO₃(aq) + Cu(s) → Cu(NO₃)₂(aq) + 2Ag(s)

If the number of electrons in the outer most orbit less, then the metal is more reactive.

• The electronic configuration of metal ‘A’ is 2,8,1. This is electronic configuration of sodium metal.
• The electronic configuration of metal ‘B’ is 2,8,2. This is electronic configuration of magnesium metal.
• In the first element of third period, sodium, there is 1 valence electron which it can lose easily to react with other substances, so it is very reactive metal.
• The second element magnesium has 2 valence electrons. It is not easy for an atom to lose 2 electrons,
• so magnesium is less reactive than sodium.

Reaction with dil. hydrochloric acid:

2Na + 2HCl → 2NaCl + H₂

Mg + 2HCl → MgCl₂ + H₂

Magnetic separation method.

Froth floatation method.

Electrolytic reduction of alumina.

Hydraulic separation method.

When Aluminium came in contact with air, it develops a thin layer of aluminium oxide.
Chemical Equation:   
4Al   +   3O₂   \(\underrightarrow{heat}\)   2Al₂O₃

Iron is more reactive than copper. When iron fillings are dropped in copper sulphate solution, iron displaces Copper (Cu) from its salt Copper sulphate (CuSO₄) solution the iron fillings get coated with reddish brown copper metal and the blue color of copper sulphate fades gradually and ferrous sulphate is formed.
Chemical Equation: 

\(Fe +\frac{CuSO_4}{Blue} → \frac{FeSO4}{colorless} +\frac{Cu}{copper}\)

Aluminium is more reactive than iron. Aluminium metal replaces iron from ferric oxide to form aluminium oxide and iron. This reaction is highly exothermic and it is known as thermit reaction
Chemical Equation:
2Al + Fe₂O₃ → Al₂O₃ + 2Fe + Heat

• The electrolysis of alumina is carried out in a steel tank lined inside with graphite.
• The graphite lining serves as cathode. Anode is also made up of graphite rods hanging in the molten mass.
• During electrolysis of alumina, when electric current is passed through this mixture, the aluminum is collected at the cathode.
• Molten aluminium is heavier than electrolyte is sinks and collected at the bottom of the tank.

 Ionization of Alumina: Al₂O₃ → 3O^-2 + 2Al⁺³
Reaction at  Cathode: Al⁺³ + 3e^- → Al +4e^-   (Reduction)
Reaction at Anode: 2O^- + 3e^-→ O₂ + 4e^- (Oxidation), C + O₂ → CO₂

Zinc Oxide is an inorganic compound with formula ZnO. It is insoluble in water. When Zinc oxide reacts with hydrochloric acid it forms zinc chloride and water.
Chemical Equation: 
ZnO_(s) + HCl_(l) → ZnCl_2(aq) + H₂O_(l)

a. Bauxite is the main ore of aluminium. Silica (SiO₂), ferric oxide (Fe₂O₃) and titanium oxide (TiO₂) are the impurities present in bauxite.
Ingredient in bauxite are molten cryolite (Na₃AIF₆), fluorspar (CaF₂).

b. The separation of impurities(silica (SiO₂), ferric oxide (Fe₂O₃) and titanium oxide (TiO₂)) in bauxite ore is done by leaching process using either Bayer’s method or Hall’s method.

c. In the Hall’s process the bauxite is in powdered form and then leached by heating with aqueous sodium carbonate in the digester to form water soluble sodium aluminate. Then the insoluble impurities are filtered out. The filtrate is warmed and neutralised by passing carbon dioxide gas through it. This results in the precipitation of aluminium hydroxide.
Al₂O₃2H₂O_(s)+ Na₂CO_3(aq) →2NaAlO_2(aq) + CO₂ + 2H₂O_(l) 

2NaAlO_2(aq) + 3H₂O + CO_2(g)→ 2Al(OH)₃ + Na₂CO₃  

The precipitate of Al(OH)₃ obtained in both, Bayer’s and Hall’s processes is filtered, washed, dried and then calcined by heating at 1000⁰C to obtain alumina.
2Al(OH)₃ → Al₂O₃ + 3H₂O

d. When aluminium ore is heated with caustic soda  (NaOH) solution under high pressure for 2-8 hours at 1400-1500C, water soluble sodium aluminate is formed.
Al₂O₃+ 2NaOH→ 2NaAlO₂ + H₂O