Please login with the same password. Encyclopedia of academic concepts Articles and project ideas Expert opinion on doubts Sample papers, board papers and exam tips Latest updates from education sector. Please choose your registered Email Id. Continue the Learning and Knowledge Sharing journey.
Remember me. Login by OTP. Become a member today! Hey , Please provide some more details below to complete sign up. Please enter your name. Please enter your mobile number. Please enter valid Mobile number. Select Class Please select the class. Forgot Password? OTP has been re-sent. OTP has been sent to your mobile. Finding exercises tough?
Install the app to watch our videos and get a crystal clear understanding of concepts Install Now. To produce chlorine, three different electrolysis methods are used. The diaphragm cell-method, which prevents products to mix or react by means of a diaphragm. The electrolysis barrel contains a positive pole, made of titanium and a negative pole, made of steel.
The electrodes are separated by a so-called diaphragm, which is a wall that only lets fluids flow through, causing gasses that form during a reaction to be separated. The application of the countercurrent principle prevents hydroxide ions from reaching the positive pole. However, chlorine ions can pass through the diaphragm, causing the sodium hydroxide to become slightly polluted with chlorine. The mercury cell-methode uses one mercury electrode, causing the reaction products to be purer than those of the diaphragm cell-methode.
With this method an electrolysis barrel is used which contains a positive titanium pole and a negative flowing mercury pole. When the amalgams flow through a second reaction barrel, sodium reacts with water to sodium hydroxide and hydrogen. This causes the hydrogen gas to remain separated from the chlorine gas, which is formed on the positive pole. The membrane-method resembles the diaphragm method. The only difference is that the membrane only allows positive ions to pass, causing a relatively pure form of sodium hydroxide to form.
However, during the membrane and diaphragm processes the solution must be evaporated using steam. Chlorine can also be produced by means of hydrogen chloride oxidation with oxygen from air. Chlorine is a very reactive element, causing it to quickly form compounds with other substances. Chlorine also has the ability to develop a bond between two substances that do not normally react with one another.
When chlorine bonds to a substance that contains carbon atoms, organic substances are formed. Examples are plastic, solvents and oils, but also several human body fluids. When chlorine chemically binds to other elements, it often replaces a hydrogen atom during a so-called substitution reaction.
Multiple hydrogen atoms in the same molecule can be replaced by chlorine atoms, causing new substances to form one after another. Chlorine plays an important role in medical science.
It is not only used as a disinfectant, but it is also a constituent of various medicines. The majority of our medicines contain chlorine or are developed using chlorine-containing byproducts. Medical herbs also contain chlorine. The first anaesthetic used during surgery was chloroform CHCl 3. The chemical industry creates ten thousands of chlorine products using a small number of chlorine containing chemicals. Emaples of products which contain chlorine are glue, paints , solvents, foam rubbers, car bumpers, food additives, pesticides and antifreeze.
One of the most commonly used chlorine-containing substances is PVC poly vinyl chloride. PVC is widely used, for example in drainpipes, insulation wires, floors, windows, bottles and waterproof clothes. Chlorine-based bleach is applied as a disinfectant on a large scale.
The substances are also used to bleach paper. Bleaching occurs as a result of chlorine or hypochlorite oxidation. The remaining chlorine is used to produce inorganic compounds from chlorine and several different elements, such as zinc Zn , iron Fe and titanium Ti. Chlorine as a disinfectant Chlorine is one of the most widely used disinfectants. It is very applicable and very effective for the deactivation of pathogenic microorganisms.
Chlorine can be easily applied, measures and controlled. Is is fairly persistent and relatively cheap. Chlorine has been used for applications, such as the deactivation of pathogens in drinking water , swimming pool water and wastewater , for the disinfection of household areas and for textile bleaching, for more than two hundred years.
When chlorine was discovered we did not now that disease was caused by microorganisms. In the nineteenth century doctors and scientists discovered that many diseases are contagious and that the spread of disease can be prevented by the disinfection of hospital areas. Very soon afterward, we started experimenting with chlorine as a disinfectant.
In doctor and writer Oliver Wendel Holmes advised midwifes to wash their hands in calcium hypochlorite Ca ClO 2 -4H 2 O to prevent a spread of midwifes fever. However, we only started using disinfectants on a wider scale in the nineteenth century, after Louis Pasteur discovered that microorganisms spread certain diseases. Chlorine has played an important role in lenghthening the life-expectancy of humans. For more information about pathogens in aquatic systems, please take a look at pathogens in freshwater ecosystems Chlorine as a bleach Surfaces can be disinfected by bleaching.
Bleach consists of chlorine gas dissolved in an alkali-solution, such as sodium hydroxide NaOH. When chlorine is dissolved in an alkalic solution, hypochlorite ions OCl - are formed during an autoredox reaction.
Chlorine reacts with sodium hydroxide to sodium hypochlorite NaOCl. This is a very good disinfectant with a stable effect. Bleach cannot be combined with acids. When bleach comes in contact with acids the hypochlorite becomes instable, causing poisonous chlorine gas to escape. The accompanying underchloric acid is not very stable.
Bleaching powder CaOCl 2 can also be used. This is produced by directing chlorine through calcium hydroxide CaOH. The benefit of bleaching powder is that it is a solid.
This makes it easier to apply as a disinfectant in medical areas, next to its use as a bleach. When bleaching powder dissolves, it reacts with water to underchloric acid HOCl and hypochlorite ions OCl -. How does chlorine disinfection work? Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules.
Disinfectants that are used for this purpose consist of chlorine compounds which can exchange atoms with other compounds, such as enzymes in bacteria and other cells. When enzymes come in contact with chlorine, one or more of the hydrogen atoms in the molecule are replaced by chlorine.
This causes the entire molecule to change shape or fall apart. When enzymes do not function properly, a cell or bacterium will die. This results in disinfection. Both substances have very distinctive behaviour. Underchloric acid is more reactive and is a stronger disinfectant than hypochlorite. Underchloric acid is split into hydrochloric acid HCl and atomair oxygen O. The oxygen atom is a powerful disinfectant.
The disinfecting properties of chlorine in water are based on the oxidising power of the free oxygen atoms and on chlorine substitution reactions. Figure 5: the neutral underchloric acid can better penetrate cell walls of pathogenic microorganisms that the negatively charged hypochlorite ion.
The cell wall of pathogenic microorganisms is negatively charged by nature. As such, it can be penetrated by the neutral underchloric acid, rather than by the negatively charged hypochlorite ion. Underchloric acid can penetrate slime layers, cell walls and protective layers of microorganisms and effectively kills pathogens as a result. The microorganisms will either die or suffer from reproductive failure.
The effectivity of disinfection is determined by the pH of the water. The level of underchloric acid will decrease when the pH value is higher. When the pH value is 8, this is the other way around. When the pH value is 7,5, concentrations of underchloric acid and hypochlorite ions are equally high.
What is free and bound active chlorine? When chlorine is added to water for disinfection purposes, it usually starts reacting with dissolved organic and inorganic compounds in the water. Chlorine can no longer be used for disinfection after that, because is has formed other products. The amount of chlorine that is used during this process is referred to as the 'chlorine enquiry' of the water.
Chlorine can react with ammonia NH 3 to chloramines, chemical compounds which contain chlorine, nitrogen N and hydrogen H. These compounds are referred to as 'active chlorine compounds' contrary to underchloric acid and hypochlorite, which are referred to as 'free active chlorine' and are responsible for water disinfection.
However, these compounds react much more slowly than free active chlorine. What doses of chlorine does one apply? When dosing chlorine one has to take into acount that chlorine reacts with compounds in the water. The dose has to be high enough for a significant amount of chlorine to remain in the water for disinfection.
Chlorine enquiry is determined by the amount of organic matter in the water, the pH of the water, contact time and temperature. Chlorine reacts with organic matter to disinfection byporducts, such as trihalomethanes THM and halogenated acetic acids HAA. Chlorine can be added for disinfection in several different ways. When ordinary chlorination is apllied, the chlorine is simply added to the water and no prior treatment is necessary.
Pre- and postchlorination means adding chlorine to water prior to and after other treatment steps. Rechlorination means the addition of chlorine to treated water in one or more points of the distribution system in order to preserve disinfection. What is breakpoint chlorination? Breakpoint chlorination consists of a continual addition of chlorine to the water upto the point where the chlorine enquiry is met and all present ammonia is oxidized, so that only free chlorine remains.
This is usually applied for disinfection, but it also has other benefits, such as smell and taste control. In order to reach the breakpoint, a superchlorination is applied. Which chlorine concentration is applied?
Chlorine gas can be obtained as fluid gas in 10 bar pressure vessels.
0コメント