B.O.D Past Exam Questions Flashcards
Why was it important to avoid trapping air bubbles each time the stopper was inserted into the sample bottle?
It is important to avoid trapping air bubbles in order to prevent more oxygen dissolving in the water as this would increase the concentration of oxygen in the water
A small amount of compound A was the first substance added to the bottle filled with river water.
Name this substance
Manganese (II) Sulphate, MnSO4
What was observed on the addition of the concentrated sulfuric acid followed by the mixing of the contents of the bottle?
The brown precipitate dissolves and a red-brown solution of iodine is formed after adding the concentrated sulfuric acid and mixing the contents of the bottle
Describe how the burette was rinsed and filled for use in the titrations
(6)
The burette was rinsed with deionised water
The burette was rinsed with the sodium thiosulfate solution
Clamp the burette vertically
Using a funnel add the sodium thiosulfate solution to the burette
Adjust the liquid to ensure that the bottom of the meniscus is on the zero mark of the burette
Read the bottom of the meniscus at eye level
What conclusion should have been reached had a white precipitate been observed instead of the brown precipitate after the first two additions of reagents to the bottle filled with river water?
If the white precipitate does not turn brown, this indicates that there is no dissolved oxygen in the water
Kits, designed for use in the field, allow the dissolved oxygen concentration to be measured immediately on collection of the sample.
Why is the immediate determination of dissolved oxygen considered best practice?
The measurement of dissolved oxygen is carried out immediately so that the oxygen content does not increase due to photosynthesis by plant material in the water or decrease due to the respiration by microorganisms in the water
Name the indicator used
Starch
