Chemistry_Grade_10-12 (1).pdf

6 dry cells are generally discarded when flat why is

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6. Dry cells are generally discarded when ’flat’. Why is the carbon rod the most useful part of the cell, even when the cell is flat? (DoE Exemplar Paper 2, 2007) 23.6 Summary The growth of South Africa’s chemical industry was largely because of the mines, which needed explosives for their operations. One of South Africa’s major chemical companies is Sasol . Other important chemical industries in the country are the chloralkali and fertiliser industries. All countries need energy resources such as oil and natural gas. Since South Africa doesn’t have either of these resources, Sasol technology has developed to convert coal into liquid fuels. Sasol has three main operation focus areas: Firstly, the conversion of coal to liquid fuel , secondly the production and refinement of crude oil which has been imported, and thirdly the production of liquid fuels from natural gas . The conversion of coal to liquid fuels involves a Sasol/Lurgi gasification process, followed by the conversion of this synthesis gas into a range of hydrocarbons, using the Fischer- Tropsch technology in SAS reactors . Heavy hydrocarbons can be converted into light hydrcarbons through a process called cracking . Common forms of cracking are hydrocracking and steam cracking . With regard to crude oil, Sasol imports crude oil from Gabon and then refines this at the Natref refinery . Gas from Mozambique can be used to produce liquid fuels, through two processes: First, the gas must pass through an autothermal reactor to produce a synthesis gas. Secondly, this synthesis gas is passed through a Sasol Slurry Phase Distillate process to convert the gas to hydrocarbons. All industries have an impact on the environment through the consumption of natural resources such as water, and through the production of pollution gases such as carbon dioxide, hydrogen sulfides, nitrogen oxides and others. The chloralkali industry produces chlorine and sodium hydroxide . The main raw ma- terial is brine (NaCl). 461
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23.6 CHAPTER 23. THE CHEMICAL INDUSTRY - GRADE 12 In industry, electrolytic cells are used to split the sodium chloride into its component ions to produce chlorine and sodium hydroxide. One of the challenges in this process is to keep the products of the electrolytic reaction (i.e. the chlorine and the sodium hydroxide) separate so that they don’t react with each other. Specially designed electrolytic cells are needed to do this. There are three types of electrolytic cells that are used in this process: mercury cell , the diaphragm cell and the membrane cell . The mercury cell consists of two reaction vessels. The first reaction vessel contains a mercury cathode and a carbon anode. An electric current passed through the brine produces Cl and Na + ions. The Cl ions are oxidised to form chlorine gas at the anode.
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