Sulphideore is converted into oxide by the process of roasting. In this process, ZnS isheated in a regular supply of air in a furnace at a temperature, which is belowthe melting point of Zn.

(iii) Extraction of zinc from zinc oxide (Reduction)

Zinc isextracted from zinc oxide by the process of reduction. The reduction of zincoxide is carried out by mixing it with powdered coke and then, heating it at673 K.

(iv) Electrolytic Refining

Zinc canbe refined by the process of electrolytic refining. In this process, impurezinc is made the anode while a pure copper strip is made the cathode. Theelectrolyte used is an acidified solution of zinc sulphate (ZnSO₄). Electrolysis resultsin the transfer of zinc in pure from the anode to the cathode.

Question - 12 : -
State the role of silica in themetallurgy of copper.

Answer - 12 : -

During the roasting of pyriteore, a mixture of FeO and Cu₂Ois obtained.

The role of silica in themetallurgy of copper is to remove the iron oxide obtained during the process ofroasting as ‘slag’. If the sulphide ore of copper contains iron, then silica (SiO₂) is added as flux beforeroasting. Then, FeO combines with silica to form iron silicate, FeSiO₃ (slag).

Question - 13 : -
What is meant by the term“chromatography”?

Answer - 13 : -

Chromatography is a collectiveterm used for a family of laboratory techniques for the separation of mixtures.The term is derived from Greek words ‘chroma’ meaning ‘colour’ and ‘graphein’meaning ‘to write’. Chromatographic techniques are based on the principle thatdifferent components are absorbed differently on an absorbent. There areseveral chromatographic techniques such as paper chromatography, columnchromatography, gas chromatography, etc.

Question - 14 : -
What criterion is followed forthe selection of the stationary phase in chromatography?

Answer - 14 : -

The stationary phase is selectedin such a way that the components of the sample have different solubility’s inthe phase. Hence, different components have different rates of movement throughthe stationary phase and as a result, can be separated from each other.

Question - 15 : -
Describe a method for refiningnickel.

Answer - 15 : -

Nickel is refined by Mond’sprocess. In this process, nickel is heated in the presence of carbon monoxideto form nickel tetracarbonyl, which is a volatile complex.

Then, the obtained nickeltetracarbonyl is decomposed by subjecting it to a higher temperature (450 − 470K) to obtain pure nickel metal.

Question - 16 : -
How can you separate alumina fromsilica in bauxite ore associated with silica?Give equations, if any.

Answer - 16 : -

To separate alumina from silicain bauxite ore associated with silica, first the powdered ore is digested witha concentrated NaOH solution at 473 − 523 K and 35 − 36 bar pressure. Thisresults in the leaching out of alumina (Al₂O₃)as sodium aluminate and silica (SiO₂) as sodium silicate leaving the impurities behind.

Then, CO₂ gas is passed through the resulting solution toneutralize the aluminate in the solution, which results in the precipitation ofhydrated alumina. To induce precipitation, the solution is seeded with freshlyprepared samples of hydrated alumina.

During this process, sodiumsilicate remains in the solution. The obtained hydrated alumina is filtered,dried, and heated to get back pure alumina.

Question - 17 : -
Giving examples, differentiatebetween ‘roasting’ and ‘calcination’.

Answer - 17 : -

Roasting is the process ofconverting sulphide ores to oxides by heating the ores in a regular supply ofair at a temperature below the melting point of the metal. For example,sulphide ores of Zn, Pb, and Cu are converted to their respective oxides bythis process.

On the other hand, calcination isthe process of converting hydroxide and carbonate ores to oxides by heating theores either in the absence or in a limited supply of air at a temperature belowthe melting point of the metal. This process causes the escaping of volatilematter leaving behind the metal oxide. For example, hydroxide of Fe, carbonatesof Zn, Ca, Mg are converted to their respective oxides by this process.

Question - 18 : -
How is ‘cast iron’ different from‘pig iron”?

Answer - 18 : -

The iron obtained from blastfurnaces is known as pig iron. It contains around 4% carbon and many impuritiessuch as S, P, Si, Mn in smaller amounts.

Cast ironis obtained by melting pig iron and coke using a hot air blast. It contains alower amount of carbon (3%) than pig iron. Unlike pig iron, cast iron isextremely hard and brittle.

Question - 19 : -
Differentiate between “minerals”and “ores”.

Answer - 19 : -

Minerals are naturally occurringchemical substances containing metals. They are found in the Earth’s crust andare obtained by mining.

Ores arerocks and minerals viable to be used as a source of metal.

Forexample, there are many minerals containing zinc, but zinc cannot be extractedprofitably (conveniently and economically) from all these minerals.

Zinc canbe obtained from zinc blende (ZnS), calamine (ZnCO₃), Zincite (ZnO) etc.

Thus,these minerals are called ores of zinc.

Question - 20 : -
Why copper matte is put in silica lined converter?

Answer - 20 : -

Copper matte containsCu₂S and FeS. Copper matte is put in a silica-linedconverter to remove the remaining FeO and FeS present in the matte as slag (FeSiO₃). Also, some silica isadded to the silica-lined converter. Then, a hot air blast is blown. As aresult, the remaining FeS and FeO are converted to iron silicate (FeSiO₃) and Cu₂S is converted intometallic copper.

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Chapter 6 General Principles and Processes of Isolation of Elements Solutions

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