(i) Mention the principle behind the zone refining of metals.

(ii) What is the role of dilute NaCN in the extraction of gold?

(iii) Which form of iron is the purest form of commercial iron?

(i) mention the principle behind the zone refining of metals

Metal extraction generally is faced with the challenge to remove the impurity that comes with it. In general, these impurities are soluble when treated with chemicals or physical processes.

In case of zone refining these impurities are melted along with the rod of impure metal and the impurities move with the melt as the metals crystalizes. The ring shown in the diagram is a hot heater which moves along the axis and the melt of impurity is separated while the metal crystalizes to give high purity.

(ii) What is the role of dilute NaCN in the extraction of gold?

Gold is less reactive as compared to other transition metals; this property makes it difficult to be extracted from its ores. So it is extracted by the process of leaching. The gold ore is leached with NaCN which is basically the oxidation reaction of gold from Au to Au⁺ that forms a complex with the cyanide as ligand.

The gold from this complex xan be obtained with the help og displacement reaction by a more reactive element like Zn or Cu.

Here Zn acts as the reducing agent.

(iii) Which form of iron is the purest form of commercial iron?

In general wrought iron is the purest form of commercial iron available with a purity of 97.5-99.75% with rest being carbon.