Chapter 6 Chemistry Notes – General Principles and Processes of Isolation of Elements Chemistry Notes
6.1 Which of the ores mentioned in Table 6.1 can be concentrated by magnetic separation method?
Ans: Ores which contains some magnetic particles or they can attract by the magnetic field only they can be concentrated by magnetic separation method.
Among the ores mentioned in table 6.1, the ores of iron such as haematite(Fe2O3), magnetite(Fe3O4), siderite(FeCO3), and iron pyrites(FeS2) can be separated by the process of magnetic separation
6.2 What is the significance of leaching in the extraction of aluminium?
Ans: Leaching or chemical separation is quite effective to purify bauxite an ore of aluminium associated with the impurities of iron oxide.
The ore is leached with concentrated solution of NaOH to form a soluble complex leaving behind the impurities.
6.3 The reaction, Cr2O3+2Al → Al2O3+2Cr (∆rG 0 = –421kJ) is thermodynamically feasible as is apparent from the Gibbs energy value. Why does it not take place at room temperature?
Ans: This is explained on the basis of Keq, the equilibrium constant. In the given redox reaction, all reactants and products are solids at room temperature, so, there is no equilibrium between the reactants and products and hence the reactions does not occur at RT. At high temperature, Cr melts and values of TAS increases. As a result, the value of:
Gibbs energy becomes more negative and hence the reaction proceeds rapidly.
6.4 Is it true that under certain conditions, Mg can reduce Al2O3 and Al can reduce MgO? What are those conditions?
Ans: Yes, below 1350°C, Mg can reduce Al2O3 and above 1350°C, Al can reduce MgO. This can be inferred from ∆G° vs T plots.