General Principles of Isolation of Elements Test - 5

Both the given statements are correct as all ores are minerals, but all minerals are not ores, and metals are extracted from minerals, but every mineral is not suitable for the extraction of metals. In fact, the mineral from which a metal is conveniently and economically extracted is called an ore.

The froth flotation process is based on the difference in the wetting properties of the ore (oil soluble) and the gangue (water soluble).

Impurities that can be oxidised to volatile products can be removed by oxidation. For example, the impurity of lead from silver is removed when lead is oxidised and led away by a current of air. Shining silver is left behind. Molten pig iron is also purified by this technique in a Bessemer converter. The impurities in the form of volatile oxides escape out.

In Van Arkel method, impure metal is first converted into one of its unstable compounds. Heating the unstable compound of the metal at higher temperatures decomposes it to give pure metal. For example, pure titanium can be obtained from impure titanium by converting it into tetraiodide and then decomposing this tetraiodide to pure Ti.

Aluminium cannot be extracted by reducing its oxide by carbon. Hence, this option is correct. Aluminium can be extracted by electrolytic reduction of Aluminium oxide in iron tank.

Iron in Fe₂O₃ or haematite is present as Fe(III) and is reduced by smelting. The temperature in the upper parts of the blast furnace is around 700°C, and carbon monoxide is a better reducing agent at this temperature.

Fe₂O₃ + 3CO → 2Fe + 3CO₂

Gold forms water-soluble complexes with reagents used for its extraction, and thus, is separated from its ore as given below:
2K[Au(CN)₂] + Zn → K₂[Zn(CN)₄] + 2Au

This option is correct because in extraction of zinc, when ZnO is reduced to Zn, the blue flame is due to formation of CO.

The mixture of lead sulphide and zinc sulphide ores is concentrated by the method of electrostatic concentration. The powdered ore is fed upon a roller in a thin layer and subjected to the influence of an electrostatic field. Lead sulphide, being a good conductor, gets charged immediately and is thrown away from the roller. Zinc sulphide, being a poor conductor, falls vertically from the roller.

NOTE: Ore containing both PbS as well as ZnS can be concentrated by froth floatation in which PbS is obtained by adding a depressant like NaCN, which converts ZnS into a water soluble complex. However, the option (1) does not mention the use of a depressant,

When metals are required in an ultra-pure state, the zone refining method is used. The principle employed states that the impurities which lower the melting point of a metal remain preferentially dissolved in the liquid phase and pure metal will emerge in the solid phase.