 Good morning to one and all, myself Dr. Sanjay Sarsamkar, working as an assistant professor in the Department of Humanities and Sciences, Walshian Institute of Technology, Sulapur. With our today's session, we are going to learn about water, its quality parameters. Starting outcome of today's session, at the end of this session, students will be able to define and describe various types of water quality parameters, content, introduction and parameters. Parameters like pH, alkalinity, acidity, total solids, chlorides, dissolved oxygen, BOD, COD and hardness of water, we are going to learn about these parameters. Introduction. The chemical characteristics of natural water are because of the soil and rocks with which the water is flowing. Water from agricultural operations, municipals and industrial treated wastewater has impact on quality of the water. So quality of water is determined by its physical, chemical and microbiological properties. Microbial and chemical transformations also affect the chemical characteristics of water. Thus, with the study of such parameters, we can decide the quality of water. First parameter that is pH. pH is defined as the negative logarithm of the hydrogen ion concentration. This is the equation to represent this pH. pH is equal to negative log to the base strain of H plus ion concentration. Depending upon the nature of the dissolved salts and the minerals, water found in nature may be acidic or basic. pH value denotes the concentration of hydrogen ions in the water and is the measure of acidity and alkalinity of the water. For public water supply, pH value should be as close to 7. Second water quality parameter that is alkalinity. Alkalinity is a quantitative measurement of the ability of an aqueous solution to neutralize acid. The alkalinity of water is attributed to the presence of hydroxide ions, carbonates and bicarbonate compounds. This can be estimated separately by titration against standard acid solution using phenolphthalein and methyl orange indicators. Third parameter is acidity. Acidity is quantitative measurement of the ability of an aqueous solution to neutralize base. The carbonic acids and mineral acids are imparting acidity to the water. So total acidity of the water is determined by titrating the water sample against sodium hydroxide solution using phenolphthalein as an indicator. Fourth water quality parameter, total solids. Total solid means the combination of dissolved solids and suspended solids. Solids present in water may be suspended form in colloidal form and or in dissolved form. Dissolved solids can be measured by filtration method. Colloidal solids can be measured by coagulation and sedimentation method. And dissolved solids can be measured by either boiling or by chemical treatment method. Next water quality parameter that is chlorides. Total amount of chloride salts present in given sample of water is known as chloride content of that sample. A sample of water containing chlorides gives instant precipitate of silver chloride when it is treated with silver nitrate solution. This process continues as long as chloride ions are present in water. The completion of chloride precipitation can be checked by adding few drops of otashem chromate as an indicator. Sixth dissolved oxygen, it is the amount of oxygen present in water in dissolved condition. The saturated value of dissolved oxygen in water is modest in the order of 8 to 15 ppm or in milligrams per litre depending on temperature and salinity of that particular water. So what are the causes of low levels of dissolved oxygen? Most important cause when water is not in direct contact with atmospheric oxygen. At the same time when organic impurities are present in water the dissolved oxygen level gets reduced as well as when oxidizable impurities are present in water also it reduces the dissolved oxygen level. Next water quality parameter that is BOD also known as biochemical oxygen demand. The amount of oxygen required by aerobic microorganisms to decompose the organic matter in sample of water and used as a measure of degree of water pollution is called as biological oxygen demand. Well in case of this aerobic, aerobic means microorganisms that needs oxygen for their oxidation process for carrying out oxidation of food material that is organic matters. Such organisms are known as aerobic microorganisms. Determination of BOD, the test is based upon determination of dissolved oxygen prior to and following the 5 day period at 20 degree Celsius. The dissolved oxygen content of water sample is predetermined. The water sample is taken in closed bottle and incubated at 20 degree Celsius for 5 days. After this the unconsumed oxygen is determined. The difference between initial oxygen content and final oxygen content of water after 5 days gives BOD. At this juncture pause this video and answer this question. Question is colloidal solids can be measured by dash dash method. Option A, coagulation, option B sedimentation, option C both of these and option D none of these. Well the answer for this question is C both of these. Next eighth one COD that is chemical oxygen demand. It is a measure of oxidizable impurities present in water. COD is a measure of both biologically oxidizable and biologically inert organic matters. It is an index of a total organic content of water. COD is readily measurable parameter for streams and industrial waste water. COD is more scientific than BOD. Generally COD values are higher than BOD. The main advantage of COD is that it takes 2 to 3 hours to complete. Determination of COD. A known volume of water sample is refluxed with known excess of potassium dichromate and dilute sulfuric acid in presence of a little silver sulphate catalyst for one and half hour. The unreacted potassium dichromate is then titrated against more salt solution. The oxygen equivalent of a potassium dichromate is taken as a measure of COD. Next hardness of water. Water which does not produce lather with soap solution readily but forms a white curried precipitate is called as a hard water. Hard water when treated with soap that is sodium or potassium salt of higher fatty acids like oleic acid, palmitic acid, steric acid, etc. does not produce lather but on the other hand forms a white precipitate. This precipitate is formed due to the formation of insoluble soaps with calcium and magnesium. So this is the reaction. Calcium stirrate combines with hardness producing substance from water for example calcium chloride that forms a calcium stirrate which is insoluble and it is having no such ability to produce any type of foam in water. Thus the water which does not produce lather with soap solution readily but forms a white curried precipitate is called as hard water. On the other hand water which lather easily on shaking with soap solution is called as a soft water. Types of hardness. Basically there are two types of hardness in water a temporary and the second one is permanent hardness of water. Temporary or carbonate hardness is caused by the presence of dissolved bicarbonates of calcium, magnesium and other heavy metals and the carbonates of iron. Permanent hardness is due to the presence of chloride, sulphates of calcium, magnesium etc and other heavy metals also. Unlike temporary hardness permanent hardness is not destroyed by boiling. Well for this session I have used a textbook of engineering chemistry by Jane and Jane as a reference. Thank you.