Top10,10th,Sci.I, Metallurgy 2

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Today we are going to learn about ionic compounds.

Definition :- The compounds formed by two units namely cations ( positively charged ions) and anions (negatively charged ions) are called ionic compounds. 

Ionic compounds are electrically neutral. Ionic compounds are crystalline in nature. Crystalline means the atoms or molecules form a three-dimensional arrangement.

The melting point of ionic compounds are high because strong electrostatic attraction between ions.

🎷General properties of ionic compounds

1. Ionic compounds are in solid state and are hard because the attraction between positively and negatively charged iron is strong.

2. Ionic compounds are brittle and can be broken into pieces when applied pressure.

3. The melting point MP and boiling point BP of ionic compounds are high.

4. Ionic compounds are water soluble.

5. Ionic compounds in the fused / molton state can conduct electricity. ( Because free ions are available in this state.)

Metallurgy

 Definition :- metallurgy is the science and technology regarding the extraction of metals from ores and their purification for further use.

Occurrence of metals

In nature silver , gold , platinum these metals occur in a free state. Because these metals are not affected by air , water and other natural factors therefore they are called as most unreactive metals.

But in nature most of the metal elements are reactive , therefore they occur in nature in a combined state as their salts such as oxides, carbonate, sulphide and nitrites.

🎷 Definitions

Ores :- The minerals from which the metals can be easily separated economically are called ores.

Gangue. :- Ores contain many types of impurities such as soil, sand , Rocky substances , humus. along with the metal compounds, these impurities are called gangue. Ex. Silica, ferric oxide , titanium dioxide etc.

 🎷 Pure metal is obtained from the ore by the following stages

1. Concentration of ores.

2. Separation based on gravitation

A) Wilfley table method.

B. Hydraulic separation meter.

3. Magnetic separation method.

4.froth flotation method.

5. Leaching.

🎻 Write note on leaching.

In the leaching process ore is soaked in a certain solution for a long time. Ore dissolves in that solution due to a specific chemical reaction. The gangue which does not dissolve , it is separated by filtration. This process is used in the extraction of metals like aluminum(Al), silver (Ag), gold (Au).

🥁 Extraction of metal Aluminium Al

Symbol :- Al

color :- silver white 

atomic number :- 13

electronic configuration :- 2,8,3

valency :- 3

group :- 13

ore :- Bauxite

Aluminum is a reactive element so aluminum does not occur in nature in free state. After oxygen and silicon aluminum is the third highly abundant element in the earth crust. Aluminum is extracted from ore Bauxite. Bauxite contains 30% to 70% of aluminum oxide Al2O3 and remaining part is gangue. The extraction of aluminum takes place in two steps.

1. Concentration of Bauxite ore by Bayer's method :-

Bauxite Al2O3.nH2O is the main ore of aluminium. Silica SiO2 , ferric oxide (Iron(III) oxide) Fe2O3 and titanium dioxide TiO2 these are the impurities present in Bauxite.  Impurities present in bauxite are separated by Bayer's process using the leaching method.

Ore is first ground in a ball mill. Fine powder is leached by heating with a concentrated solution of caustic soda (sodium hydroxide NaOH). In a digester this mixture is heated at 140°C to 150°C under high pressure for 2 to 8 hours.

Aluminium oxide is amphoteric in nature, it reacts with an aqueous solution of caustic soda to form water soluble sodium aluminate.

The iron oxide in the gangue does not dissolve in aqueous sodium hydroxide , NaOH it is separated by filtration. Silica in the gangue dissolves in aqueous sodium hydroxide to form water soluble sodium silicate.

Aqueous sodium aluminate NaAlO2 is diluted by putting in water H2O and is cooled to 50°C.

The precipitate of aluminium hydroxide obtained is filtered , washed , dried and then calcinated by heating at 1000°C to obtain pure alumina.

2. Aluminium is extracted by electrolytic reduction of alumina.

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