Aluminium - class-X

Sodium aluminate is also formed by the action of sodium hydroxide
on elemental aluminium which is an amphoteric metal. The reaction is
highly exothermic once established and is accompanied by the rapid
evolution of hydrogen gas. The reaction is written as:
$2Al+2NaOH+{ 2H } _{ 2 }O\longrightarrow 2NaAlO _{ 2 }+3{ H }$

$2NaHCO _{ 3 (S) }\longrightarrow N{ a } _{ 2 }CO _{ 3 (S) }+CO _{ 2 (g) }+{ H } _{ 2 }O _{  (l) }$  This statment is correct.

By the reaction of sodium with liquid ammonia sodium ammide can be prepared.Sodium (alkali metal)dissolves in liquid ammoia solution to form a blue solution characteristic of a solvated electron in liquid ammonia, which is conducting in nature, due to ammoniated electrons (solvated electron).
This statment is correct.

Sodium silicate liquid can also be prepared directly by dissolving
silica sand under pressure in a heated aqueous solution of caustic soda
(sodium hydroxide, NaOH):
$2NaOH+{ SiO } _{ 2 }\longrightarrow Na _{ 2 }O.{ SiO } _{ 2 }+{ H } _{ 2 }O$
This statment is correct.

Alane is a hydride of aluminium.

$Al _2(SO _4) _3$ used to make fire proof clothes.

Aluminium hydroxide is insoluble in $H _2O$ but it is soluble in strong acids and strong bases. This is because of $Al(OH) _3$ its amphoteric nature.

• Molten cryolite $(Na _3AlF _6)$ is used as a solvent for aluminium oxide $(Al _2O _3)$ in the Hall–Héroult process, used in the refining of aluminium. 
  
• It decreases the melting point of molten (liquid state) aluminium oxide to 900-1000 °C from 2000-2500 °C. Thus cryolite makes the extraction of aluminium profitable. 
  
• Hence both option B and D are correct .

$Na _{3}AlF _{3}$ is used as a insecticide
So D is false

In aqueous solution, the aluminate ion AlO2- is hydrated and exists as the octahedral complex [Al(OH)4(H2O)2]-.

Solution:- (B) It liberates hydrogen from acid but not from alkalies

Bauxite has a number of impurities in it including iron oxides(hematite and goethite), $Fe _2O _3$ the sand silicon dioxide $SiO _2$ the clay mineral Kaolinite and asmall amount of $TiO _2$ known as Anatase.

Hoop's process for aluminum purification uses a three-layer electrolytic cell. The bottom layer is impure aluminum (anode), the middle is a fused fluoride electrolyte, and the top is pure aluminum (cathode).

In thermite welding, aluminium acts as reducing agent. Aluminium is used in thermite welding of broken iron parts. The reduction of ferric oxide by aluminium is highly exothermic and therefore, the iron formed will be in the molten state. Thermite reaction involving aluminium is also called Goldschmidt alumino thermic reaction.

• If Aluminium foil was used the,the scattering angles would have changed, but the qualitative results would also change: the reason Rutherford chose gold was because it is EXTREMELY malleable. One can stretch gold foil until it is only a few atoms thick in places, which is not possible with aluminum.
  
• Hence option C is correct answer.

${ Al } _{ 2 }{ ({ C } _{ 2 }{ O } _{ 4 }) } _{ 3 }(s)\xrightarrow { \Delta  } { Al } _{ 2 }{ O } _{ 3 }(s)+3CO(g)+3C{ O } _{ 2 }(g)$

$\displaystyle   X _2O _3$ is produced if ratio of element to oxygen is 2:3 in the reaction of element and oxygen, that element is Aluminum (Al). It forms $\displaystyle   Al _2O _3$ . The valence of Al (and X)  is +3 and that of oxygen is -2.
Ca, Li, F and C have valencies +2, +1, -1 and 4 respectively.

1. $[Al(H _2O) _4(OH) _2]^+$

2. $Al(OH) _3$  dissolves in $NaOH$ solution to give $Al(OH)^{-4}$ ion which is supposed to have the octahedral complex species $[Al(OH) _4(H _2O) _2]^-$ in aqueous solution.

3. $Al(OH) _3 + NaOH(aq) \longrightarrow  [Al(OH) _4(H _2O) _2]^-(aq) + NaOH^+(aq)$

When ${ Al } _{ 2 }{ Cl } _{ 6 }$ is dissolved in water, it is ionized to form ${ \left[ Al{ \left( { H } _{ 2 }O \right)  } _{ 6 } \right]  }^{ 3+ }$ and ${ Cl }^{ \left( - \right)  }$ due to large hydration energy of ${ Al }^{ 3+ }$.

There is this rule called as Fajan's rule which states that with increasing size of the anion and with decreasing size of the cation ionic character of the compound decreases while the covalent character increases.

Here, since the cation is same in both the compounds, the size of the anion decides the nature of the compound. Size of chlorine being greater than fluorine, $AlCl _3$ is covalent while $AlF _3$ is ionic.

The properties of aluminium include low density and therefore low weight, high strength, superior malleability, easy machining, excellent corrosion resistance and good thermal and electrical conductivity.
The surface of aluminum metal is covered with a thin layer of oxide that helps protect the metal from attack by air. So, normally, aluminum metal does not react with air. Aluminium hydroxide is amphoteric in nature. Hence, it dissolves in both acidic and basic solution.

Aluminum unlike iron ,does not corrode in moist conditions. Its surface is protected by layer of aluminium oxide. This prevents thealluminium to come in contact with air and oxygen. The layer of aluminium oxide do not vanish, unlike rust which can flake off the surface of iron and steel objects. So $Al$ is covered with a layer by the oxygen

Hence option B is correct.

Solution:-

Anodizing is an electrochemical process that converts the metal surface into a decorative, durable, corrosion-resistant, anodic oxide finish. Aluminum is ideally suited to anodizing, although other nonferrous metals, such as magnesium and titanium, also can be anodized.

Aluminium sulphate is used in producing fire proof textiles.

$ Al _4C _3 + 12H _2O \rightarrow 3CH _4 + 4Al(OH) _3$

Bauxite-$Al _2O _3$

Aluminium, deposited as vapour on a glass, forms good mirrors because it does not tarnish in air. If it tarnishes then the mirror would not be that good. Hence due to the property of it not tarnishing in air the mirror formed are good mirrors.

Aluminium is reactive and reacts spontaneously with water or air to form aluminium oxide $(Al _2O _3)$, forms a stable passive layer which protects aluminium from corrosion or further oxidation.

Duralumin is an alloy of aluminium that has copper and contains small amounts of magnesium, manganese, iron, and silicon: its applications requiring lightness and strength, as in aeroplane construction.So sodium is not present in Duralumin.