Match each aluminium extraction component, compound, or alloy listed on the left with its … — JAMB UTME

Match each aluminium extraction component, compound, or alloy listed on the left with its accurate chemical role, structural behavior, or application on the right.

Molten Cryolite ( $\text{Na}_3\text{AlF}_6$ ) in the Hall-Héroult cellActs as a solvent to lower the melting point of alumina from $2050^\circ\text{C}$ to $\sim 950^\circ\text{C}$ and increases electrical conductivity.
Reaction of bauxite ( $\text{Al}_2\text{O}_3\cdot 2\text{H}_2\text{O}$ ) with concentrated $\text{NaOH}_{(aq)}$ Forms soluble sodium tetrahydroxoaluminate(III), $\text{Na}[\text{Al}(\text{OH})_4]$ , separating alumina from insoluble iron(III) oxide impurities.
Anhydrous aluminium chloride ( $\text{AlCl}_3$ ) below $400^\circ\text{C}$ Exists as a covalent dimer, $\text{Al}_2\text{Cl}_6$ , held together by dative covalent (coordinate) bonds.
Duralumin composition and applicationContains $\text{Al}$ , $\text{Cu}$ , $\text{Mn}$ , and $\text{Mg}$ ; widely used in aircraft construction due to its high strength and low density.

Answer

Molten Cryolite matches with its role as a solvent lowering the melting point of alumina and improving conductivity; reaction of bauxite with concentrated alkali matches with the formation of soluble sodium tetrahydroxoaluminate(III); anhydrous aluminium chloride below 400 °C matches with its existence as a covalent dimer Al2Cl6 with dative bonds; Duralumin matches with the alloy composed of Al, Cu, Mn, Mg used in aircraft structure.

Cryolite serves as a flux and solvent reducing alumina's melting point from

2050^\circ\text{C}

950^\circ\text{C}

. The reaction of bauxite with concentrated sodium hydroxide exploits aluminium's amphoteric property to produce soluble tetrahydroxoaluminate(III). Anhydrous aluminium chloride forms a coordinate-bonded dimer (

\text{Al}_2\text{Cl}_6

) at low temperatures. Duralumin is an aluminium-copper-manganese-magnesium alloy key to aerospace applications due to its high strength-to-weight ratio.

Step-by-Step Solution

Analyze the role of cryolite in industrial extraction

Cryolite lowers the melting temperature of

\text{Al}_2\text{O}_3

from

2050^\circ\text{C}

950^\circ\text{C}

and increases conductivity.

Pure

\text{Al}_2\text{O}_3

has an extremely high melting point and poor conductivity in the solid state; cryolite provides a suitable molten electrolyte mixture.

Examine the Bayer process chemical separation of amphoteric aluminium oxide

Dissolution in concentrated

\text{NaOH}

forms soluble complex ion

\text{Na}[\text{Al}(\text{OH})_4]

Aluminium oxide is amphoteric and reacts with strong base, whereas basic impurities like

\text{Fe}_2\text{O}_3

remain insoluble.

Evaluate the molecular structure of anhydrous aluminium chloride

Forms

\text{Al}_2\text{Cl}_6

dimer via coordinate bonds.

Aluminium in monomeric

\text{AlCl}_3

has only 6 valence electrons; dimerization allows each aluminium atom to complete its octet.

Identify the composition and application of Duralumin

Alloy of

\text{Al}

\text{Cu}

\text{Mn}

\text{Mg}

used in aircraft.

Addition of copper and magnesium to aluminium dramatically increases mechanical strength without significantly compromising low density.

Key Concept

Chemical principles of aluminium extraction (Bayer and Hall-Héroult processes), amphoteric reactivity, dimerization of aluminium chloride, and metallurgical properties of aluminium alloys.

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