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Isolation of Elements

Section: Chemistry

Question : 3 of 22

Marks: +1, -0

the reaction of $\mathrm{Al}_2 \mathrm{O}_3$ with coke
at a temperature $>2500^{\circ} \mathrm{C}$ .
the neutralization of aluminate solution by passing $\mathrm{CO}_2$ gas to precipitate hydrated alumina $(\mathrm{Al}_2 \mathrm{O}_3 \cdot 3 \mathrm{H}_2 \mathrm{O})$
(C) the dissolution of $\mathrm{Al}_2 \mathrm{O}_3$ in hot aqueous $\mathrm{NaOH}$ .
the electrolysis of $\mathrm{Al}_2 \mathrm{O}_3$ mixed with $\mathrm{Na}_3 \mathrm{AlF}_6$ to give $\mathrm{Al}$ and $\mathrm{CO}_2$ .

Solution:

(A) Electrochemical extraction of Aluminum from bauxite done below

2500^{\circ} \mathrm{C}

(B)

2 \mathrm{Na}[\mathrm{Al}(\mathrm{OH})_4]_{\text{aq.}} + 2 \mathrm{CO}_{2(g)} \rightarrow \mathrm{Al}_2 \mathrm{O}_3 \cdot 3 \mathrm{H}_2 \mathrm{O}_{(s)} \downarrow + 2 \mathrm{NaHCO}_{3(\text{aq.})}

The sodium aluminate present in solution is neutralised by passing

\mathrm{CO}_2

gas and hydrated

\mathrm{Al}_2 \mathrm{O}_3

is precipitated.

(C)

\mathrm{Al}_2 \mathrm{O}_{3(s)} + 2 \mathrm{NaOH}_{(\text{aq.})} + 3 \mathrm{H}_2 \mathrm{O}_{(l)} \rightarrow 2 \mathrm{Na}[\mathrm{Al}(\mathrm{OH})_4]_{\text{aq.}}

Concentration of bauxite is carried out by heating the powdered ore with hot concentrated solution of

\mathrm{NaOH}

(D) In metallurgy of aluminum,

\mathrm{Al}_2 \mathrm{O}_3

is mixed with

\mathrm{Na}_3 \mathrm{AlF}_6

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