How does Winkler method calculate BOD?

Procedure:

1. Carefully fill a 300-mL glass Biological Oxygen Demand (BOD) stoppered bottle brim-full with sample water.
2. Immediately add 2mL of manganese sulfate to the collection bottle by inserting the calibrated pipette just below the surface of the liquid.
3. Add 2 mL of alkali-iodide-azide reagent in the same manner.

What is the Winkler titration method used to determine?

The Winkler test is used to determine the concentration of dissolved oxygen in water samples. Dissolved oxygen (D.O.) is widely used in water quality studies and routine operation of water reclamation facilities to analyze its level of oxygen saturation.

Why MnSO4 is adding in Winkler’s method?

In the Winkler method,add MnSO4 and basic KI solution to the water sample. The product,Mn(OH)2 is oxided by the dissolved oxygen to Mn(OH)3, which reacts with KI when add H2SO4 to make the solution acid. The dissolved oxygen can be valued. In order to delete the interference of NO2-, add NaN3 in it.

How much dissolved oxygen do fish need in ppm?

Fish growth and activity usually require 5-6 ppm of dissolved oxygen. Dissolved oxygen levels below 3 ppm are stressful to most aquatic organisms. Levels below 2 ppm will not support fish at all.

Why is BOD done for 5 days?

The standard oxidation (or incubation) test period for BOD is 5 days at 20 degrees Celsius (°C) (BOD5). The BOD5 value has been used and reported for many applications, most commonly to indicate the effects of sewage and other organic wastes on dissolved oxygen in surface waters (see TECHNICAL NOTE).

What is the purpose of adding MnSO4 in Winkler’s method?

In the Winkler method,add MnSO4 and basic KI solution to the water sample. The product,Mn(OH)2 is oxided by the dissolved oxygen to Mn(OH)3, which reacts with KI when add H2SO4 to make the solution acid. The produced I2 is titrated by Na2S2O3 solution. The dissolved oxygen can be valued.

Why sodium thiosulphate is used in titration?

In an iodometric titration, a starch solution is used as an indicator since it can absorb the I2 that is released. This absorption will cause the solution to change its colour from deep blue to light yellow when titrated with standardised thiosulfate solution. This indicates the end point of the titration.

Why starch is added near the end of the titration rather than at the beginning?

Starch is now used as an indicator for the presence of iodine. As to why it is added near the end of the titration rather than at the beginning is because the starch-iodine complex at high I2 concentrations is relatively stable.

Why do we use 0.025 N sodium thiosulphate solution for the titration?

hydroxide forming a mixture of higher, oxides (brown colour compound), which on acidification in the presence of an iodide, release iodine in a quantity chemically equivalent to the oxygen content of the water sample. The liberated iodine is then titrated with a standard solution of sodium thiosulphate.

How to prepare sodium thiosulfate for Winkler titration?

Prepare the starch and sodium thiosulfate solutions within a day of use. Refrigerate until use. To make the starch solution, combine 5 g of starch (soluble, potato) with a few milliliters of distilled or deionized water and mix to a uniform paste.

How is dissolved oxygen determined by the Winkler procedure?

After complete fixation of oxygen and precipitation of the mixed manganese (II) and (III)hydroxides, the sample is acidified to a pH between 2.5 and 1.0. This causes the precipitated hydroxides to dissolve, liberating the Mn (III) ions.

What’s the difference between automated and manual titration?

The fundamental differences between the manual and automated titration methods are the means of endpoint detection (visual versus a UV detector) and the method of thiosulfate delivery. The auto-titrator rapidly dispenses thiosulfate. As the changes in UV absorption are noted, the rate is slowed, and finally the continuous addition is stopped.

What kind of thermometer is used for titration?

4.1.4 Thermometers: one thermometer is used to measure the water temperature at sampling to within 0.5°C. Two platinum resistance temperature sensors are used to monitor the temperatures of the titrating solutions in the laboratory. 4.2.1 Titration box: a three-sided box containing the titration apparatus.