The chapter ‘general principles and processes of isolation of elements’ is a part of unit 6 of class 12th chemistry as prescribed by the CBSE syllabus. Although, this topic has a relatively low weightage in the final board examination, but this topic is an interesting insight into how elements are extracted from their naturally existing states. Also, the chapter is fairly easy to understand and can be covered in a few hours. The questions asked of this chapter is straightforward and therefore, they become important for entrance examinations as they guarantee easy marks to students who put in efforts to ensure they studied this topic. By studying this chapter, a student is expected to be familiar with the following
- Develop an appreciation of the contribution of various Indian traditions in the realm of metallurgical methods
- Ability to define important terms such as ores, minerals, refining, concentration, roasting, calcinaton etc.
- Appreciate the methodologies used for extraction and describe the role of oxidation and reduction processes.
- Develop a fundamental understanding of thermodynamics, especially concepts such as entropy and Gibbs free energy, and its application for extraction of elements such as iron, zinc, aluminium and copper.
- Describe reducing agents and choice of reducing agents for different temperatures.
Therefore, as one can see that the important sections to be covered in this chapter are not many and covering this chapter should not take a lot of time.
Important topics of the general principles of isolation of the elements
- Ancient traditional processes for extraction of metals: The first important topic that the student should focus on is to develop a fair understanding of ancient traditional processes that were used for extraction of metals. The Indian traditions in science and technology are fairly old, and through the study of various ancient texts, one can decipher that even before chemical processes had become wide-spread, our ancestors had a fair idea of the role of elements (especially metals). They had devised processes in order to extract these metals from the Earth crust and put if for use in applications such as warfare, defence, structures, buildings, ancient machines etc. Historical texts describe that metals such as iron, zinc, copper and mercury were known and our ancestors were also aware of its applications. Ancient Indians knew the use of steel and this steel were of extremely high quality. It was called as a Wonder metal of the orient and it was much sought after, across the world.
- Knowledge of ores and concentration: The next important topic to be studied involves the knowledge of ores and concentration. But before that, one must understand the meaning of the term metallurgy. Metallurgy is defined as a scientific as well as a technical method utilized for the isolation of metals from its ores. Metallurgy is important because only few metals such as sulphur, carbon etc exist in its free state and nature, while the rest of the metals are present in combined form. Minerals are defined as naturally existing substances present in the earth crust. But our focus is on the term ore. Minerals from which metals can be extracted is called as ore. However, the problem lies in the fact that an ore seldom contains only the desired metals. Along with the element of importance, it is contaminated with unwanted materials called as Gangue. The extraction and isolation of metals from ores includes few important steps such as those mentioned below,
- Concentration of the ore
- Segregation of metals from corresponding concentrated ore
- Purification process of the metals obtained after isolation.
Check this important question:
- In the metallurgy of iron, the upper layer obtained in the bottom of blast furnace mainly contains:
- Pig iron
- Cast iron
- Wrought iron
Concentration is defined as the process of removing undesired material from the ore. It is also called as benefaction or dressing. Also, before proceeding, these ores must be crushed to workable size. Important procedures of concentration are hydraulic washing, magnetic separation and froth floatation method. The next step is the extraction of crude metals after the ore has been concentration. More often than not, isolation process requires two steps, namely, transforming the concentrated ore into an oxide followed by reduction of oxide to yield metal. Conversion of ore into an oxide involves the process of calcination first followed by roasting. Later, this is reduced with the help of a reducing agent such as carbon monoxide or coke, to convert oxides into corresponding metals.
After the crude metal has been obtained, then the crude metal must be refined to order to yield a pure metal. Thus, the process of refining is very important. There are many methods used for the purification of the metals and the selection of the purification or refinement technique depends on the properties of the metals and the kind of impurities within. Most common procedures of refining include Distillation, Liquation, Electrolysis, Vapour phase refining, zone refining and other chromatographic methods.
Reducing agents play an important role in reducing metal oxides to corresponding crude metals. Thus, in this chapter, the students should also focus on various reducing agents and its suitability for reactions depending on various properties and conditions.