ALUMINIUM AND ITS COMPOUNDS

1.               Which of the following metals cannot be extracted from its ore by using carbon or carbon (ii) oxide as the reducing agent?    . [w1988 no 39]

• (a) Cu

• (b) Zn

• (c) Al

• (d) Pb

• (e) Fe

Which of the following statements is not correct?

• A. Metals high up in the redox series are usually extracted by electrolysis.

• Leads is less reactive than magnesium therefore it is lower in the redox series.

• Aluminium reduces iron(iii)oxides to iron in the thermitt process

• An amphoteric oxide exhibits both acidic and basic properties

• Metals ionize by electron gain while non-metals form ions by electron loss

The following metals are extracted by the electrolytic method except

• Potassium

• Calcium

• Tin

• Sodium

• Magnesium.

The Complex salt formed when aluminium dissolves in sodium hydroxide solution is

• Na₃Al(OH)₄

• Na₂Al(OH)₃

• NaAl(OH)₃

• Na₄Al(OH)₄

• NaAl(OH)₄

Aluminium is above iron in the electrochemical series, yet iron corrodes easily on exposure to air while aluminium does not. This is because aluminium

• has a lower density than iron

• is a better conductor than iron

• does not corrode spontaneously

• forms a thin layer of inert oxide in moist air

• forms amphoteric oxides while iron does not

Which of the following is an ore of aluminium?

• Haematite,

• Magnetite

• Siderite

• Bauxite

• Cassiterite

Aluminium is extracted from

• magnetite

• cryolite

• duralumin

• bauxite

• cassiterite

In the electrolytic extraction of aluminium from purified alumina; molten cryolite is added in order to

• Lower the melting point of the alumina

• Prevent the aerial oxidation of the molten aluminium

• lower the activation energy of the reaction

• from a protective crust on top of the electrolyte

Which of the following compounds is used for removing impurities from bauxite?

• NaOH

• CaCO₃

• Na₃AlF₆

• H₂SO₄

The process of “seeding” during the extraction of aluminium involves the addition of pure Al(OH)₃ crystals in order to

• lower the temperature

• increase the concentration

• facilitate the precipitation of solid

• reduce the viscosity of the solution