I would recommend to be cautious about prolonged drying which may result in loss of constituents, particularly nitrates and chlorides. Wastewater samples which contains high concentrations, concentrations of calcium, chloride, magnesium or sulfate can rapidly absorb moisture from the air. Such samples may need to be dries for a longer period of time, such as the case in the experiment.
32 | P a g eMAPUA UNIVERSITY School of Civil , Environmental and Geological Engineering ENVIRONMENTAL ENGINEERING EXPERIMENT 5 ALKALINITYDomingo, Nicole Anne M. 2015105288/CESE-3 ESE142P/C1 2QSY17-18 Engr. Martin Jade Duran Instructor
33 | P a g eTHEORETICAL DISCUSSION Alkalinity and pH are two important factors in determining the suitability of water. pH is a measure of the concentration of hydrogen ions in water while alkalinity refers to the capability of water to neutralized acid. Alkalinity is also an expression of buffering capacity. A buffer is a solution to which an acid can be added without changing the concentration of hydrogen ions. It essentially absorbs the excess hydrogens ions and it also protects the water from fluctuations in pH. The most commonly used buffering system is carbonate and bicarbonate. Alkalinity is often associated with the hardness because the main source alkalinity is usually from carbonate rocks which are mostly calcium carbonate. Since hard water contains metal carbonates that is high in alkalinity it less susceptible to fluctuations in pH. Conversely soft water is much more susceptible to fluctuations in pH from acid rains or acid contamination. We measure alkalinity by titrating, titration involves adding a solution in which the concentration of another chemical is unknown in order to measure the concentration of the unknown chemical. The ability of natural water to act as a buffer is controlled in part by the amount of calcium and carbonate ions in solution. The possibility to maintain constant pH is due to the hydroxyl, carbonate and bicarbonate ions present in water. Therefore, water that comes in contact with limestone will contain high levels of both Ca++ and CO3 2- ions and have elevated hardness and alkalinity. Large amount of alkalinity imparts bitter taste in water. Whereas, the environmental importance occurs as following: alkalinity is important for fish and aquatic life because it protects or buffers against rapid pH changes. Higher alkalinity levels in surface waters will buffer acid rain and other acid wastes and prevent pH changes that are harmful to aquatic life.
34 | P a g eMETHODOLOGY 1. Pipette 50ml of sample into a clean Erlenmeyer flask. 2. Add one drop of sodium thiosulfate solution, if residual chlorine is present. 3. Add two drops of phenolphthalein indicator; if the pH is above 8.3, the color of the solution becomes pink. 4. Titrate against standard sulfuric acid in the burette until the color turns yellow.
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