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Determination of Flourid 12-04-2014

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1. Determination of Fluoride: Fluorides occur in varying amounts in land waters. They are responsible for dental problems. Dental caries are caused by low fluoride waters, whereas mottled enamel and endemic Fluoride by Excess amount of fluorides. In public water supplies a regulated amount ranging between 0.5 and 1.0 is necessary. Fluorides can not be supplemented by tooth pastes. The most common method recommended for measuring fluorides is the colorimetric method. This method is based
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  1. Determination of Fluoride: Fluorides occur in varying amounts in land waters. They are responsible for dental problems. Dental caries are caused by low fluoride waters, whereas mottled enamel and endemic Fluoride by Excess amount of fluorides. In public water supplies a regulated amount ranging between 0.5 and 1.0 is necessary. Fluorides can not be supplemented by tooth pastes. The most common method recommended for measuring fluorides is the colorimetric method. This method is based on the reaction of fluoride and zirconium - Dye Lake the fluoride decolorizes the dye by complexation Zr F 62   . As fluoride concentration increases the color produces becomes lighter. Direct measurement is made when the fluoride range is between 0.005  –  1.4 mg/l. Distillation method is practiced to avoid interferences. Reagents: 1. Sulfuric acid (conc.) 2. Silver Sulfate (Ag 2 SO 4 ) Crystals 3. Standard Fluoride Solution 4. SPANDNS solution 5. Zirconyl acid reagent 6. Acid Zirconyl- SPADNS reagent Procedure: Distillation Step Place 400 ml distilled water in the distillation flask and carefully add 200 ml conc. H 2 SO 4 . Swirl until homogenous. Add glass beads. Connect the flask as shown in figure. Begin heating slowly until the temp. Reaches 180 c. discard the distillate. Cool the mixture to about 100 c. Add 300ml sample and distilled. Add Ag 2 SO 4  to the distillation flask at the rate of 5 mg/mg CL when high chloride sample are distilled. Collect the distillate. Preparation of Standard Curve: Prepare fluoride standards in the range 0  –  1.4 mg/l by diluting appropriate quantities of standard fluoride solution to 50 ml. sample with distilled water. Add 5.0 ml each of SPANDS solution and zirconyl acid reagent or 10.0 ml of mixed acid zirconyl SPANDS reagent to each standard and mix well. Measure absorbance and plot fluoride absorbance curve. The dye lake follows an inverse Beer’s law . Take the sample or distilled portion diluted to 50 ml. add 10.0 ml. acid zirconyl SPADNS reagent. Mix well and read the absorbance. Calculation : Mg/L, F = A/ml sample*B/C Where,  A = µg F determined photometrically B/C = only when sample is distilled, B/C applies to a   Volume B and a portion C taken from it for color development 1. Determination of Sulfates (SO 4   ) The sulfate ion is one of the major anions occurring in natural waters. It is one of important anion imparting hardness. The sulfates are responsible for forming scates in boilers and heat exchangers. In waste under reducing environment. Sulfates are converted to H 2 S and are responsible for corrosion and bad odor: SO 4    + Organic  –  matter anaerobic/bacteria    + H 2 O + CO 2      + H ⁺   ↔      HS ⁺  + H ↔  H 2 S Method of determination of sulfates There are four methods of determining sulfates Gravimetric Turbid metric  Automated methyl thymol blue Ion chromatography Thought the most sensitive method is ion chromatography but turbid metric method is most common in determining sulfates The sulfate ion is precipitated in a HCL medium with barium chloride ( BaCl 2 ) to form barium sulfate. The absorbance of barium sulfate suspension is measured by a nephlometer or photometer by comparison with a standard curve. Reagent: (i) Conditioning reagent (ii) Barium chloride. Crystals 20-30 mesh (iii) Standard sulfate Solution Procedure: Take 100 ml sample in a conical flask. Filter the sample if turbid. Add 5.0 ml conditioning reagent and mix on a magnetic stirrer. Add a spoonful of BaCl 2  crystals. Stir for one minute at constant speed. Take a portion of the sample in the Nephlometer curette and measure the turbidity at 30 sec. intervals for 4 min. Preparation of calibration curve: Prepare standards at 5 mg/l increment in the 0-40 mg/l sulfate range. Proceed with standards as for sample note the turbidity reading draw a calibration curve of sulfate concentration in standard and turbidity reading run blank of sample for any correction Calculation : Mg/l SO 4    = mg SO 4  *1000/ml sample

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