What does the Winkler Method do?

What is the Winkler Method? The Winkler Method is a technique used to measure dissolved oxygen in freshwater systems. Dissolved oxygen is used as an indicator of the health of a water body, where higher dissolved oxygen concentrations are correlated with high productivity and little pollution.

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.

What type of titration is Winkler Method?

The Winkler method is a manual titration method for the determination of dissolved oxygen in a water sample. The analysis is often performed in the field to avoid delays that may result in a change in the oxygen content of the water.

What is Winkler A and Winkler B?

The Winkler test is used to determine the concentration of dissolved oxygen in water samples. In the test, an excess of manganese(II) salt, iodide (I−) and hydroxide (OH−) ions are added to a water sample causing a white precipitate of Mn(OH)2 to form.

What is the end point of Winkler titration method in determination of dissolve oxygen?

The endpoint is determined either by the absorption of ultraviolet light by the tri-iodide ion in the automated method, or using a starch indicator as a visual indicator in the manual method. The amount of oxygen can then be computed from the titer: one mole of O2 reacts with four moles of thiosulfate.

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 is starch added at the end of the reaction and not at the beginning?

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. The release of I2 from the starch-iodine complex is slow at high I2 concentrations.

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.

Why is starch solution added only at the end of titration?

In iodometry the starch is added only after the color due to triiodide has begun to fade, i.e., near the endpoint, because starch can be destroyed in the presence of excess triiodide. iodide in acid solution to yield triiodide, which is subsequently titrated with the standardized thiosulfate solution.

Why is the starch added almost at the end of the titration rather than at the beginning 2 marks?

How do you make 0.025 N sodium thiosulphate?

Standard sodium thiosulfate solution ( 0.025) N Dissolve 6