Estimation of dissolved oxygen by redox/Winkler titration

Manganese Sulfate Mn(SO₄)₂ and alkaline potassium iodide when added to water produce what coloured precipitate of manganese hydroxide?

• Brown

• White

• Red brown

Manganese (II) hydroxide reacts with dissolved oxygen in the water producing manganese (III) hydroxide which is coloured?

• Brown

• White

• Red brown

Complete the following statement "the bottles used to collect the samples of water are completely filled under the water to ensure that

• That the individual does not have to return to the location to collect more water

• That no atmospheric oxygen , is added which would lead to an inaccurate level of dissolved oxygen being measured.

• The individual has enough water to carry out the titration.

If the white precipitate of manganese (II)hydroxide remains upon addition of manganese sulfate and alkaline potassium iodide this means

• Further additions of manganese sulfate are required

• There is sufficient oxygen present to complete a titration using sodium thiosulfate.

• The water is heavily polluted and there are no detectable amounts of dissolved oxygen present.

True or false: The manganese (II) hydroxide reacts with dissolved oxygen producing a brown precipitate of manganese (III) hydroxide

• True

• False

True or false: Concentrated sulfuric acid ensures the iodide ions I^- , react with the manganese (III) hydroxide ions liberating iodine, I₂ .

• True

• False

Which of the following options correctly completes the blanks in the sentence?

The bottle is stored in the ___________, at _____________ to _____________ photosynthesis, for __________ days to determine the B.O.D of the water sample.

• light 20 ℃ allow 5

• dark 20 ℃ prevent couple

• light 20 ℃ prevent 5

• Dark 20 ℃ prevent 5

What does B.O.D. stand for when completing the Winkler titration?

When carrying out the titration starch is the indicator used. What is the colour of the solution in the conical flask when it is added

• Pale yellow

• Yellow

• Red brown

When the starch solution is added state the colour change that occurs so that the volume of sodium thiosulfate can be determined by reading the bottom of the meniscus in hte burette.

• Blue black to pale yellow

• Pale yelllow to blue black

• Blue black to colourless