Oxygen is an abiotic factor essential for all organisms (except some bacteria) for their survival. Terrestrial organisms get oxygen from the air they breathe. Although oxygen is a gas, it dissolves in water and aquatic organisms such as fishes utilize this dissolved oxygen.
We all know that if the content of oxygen reduces in the environment the organisms will suffocate and die. In an aquarium, the pump producing air bubbles helps to maintain the level of oxygen and saves fish from suffocation. (Please watch the video of the aquarium given in the lesson 2.1)
In the following experiment, we will measure the amount of oxygen dissolved in the water.
Generally, this kind of an experiment requires a sophisticated laboratory. However, we simplified it for you so that you can conduct this experiment in your classroom. The method we are using to measure the oxygen dissolved in the water is called “Winkler’s method”.
Material required
In order to conduct this activity, you need the following Items
BOD bottle SyringeTest tube (1ml) (5ml) Paper cup
Chemicals: Solutions of the following chemicals
Manganese sulphate
Alkaline potassium iodide
Phosphoric acid
Starch
Sodium thiosulphate
Water
2 liter of water collected from any natural water body
2 liter of water cooled after boiling for 15 minutes
Group Exercise
The whole class will be divided into a group of 6 students. Each team will choose the name A or B
Team A will choose the water collected from natural water body
Team B will choose the water cooled after boiling for 15 minutes
This way half of the total number of groups will use the water collected from a natural water body and the other half will choose the water that was cooled after boiling for at least 15 minutes.
Steps for water testing
Step 1
Fill BOD bottle with water sample by dipping the bottle slowly into the water. Please make sure that no air bubble is trapped in the water sample. Presence of air bubbles can cause error. So put the lid on the bottle while it is still under water.
Step 2
Open the lid carefully and add 4 drops of manganese sulphate solution
Step 3
Then add 4 drops of alkaline potassium iodide solution.
Step 4
Close the lid tightly and shake the water very well. You might have noticed that water in the BOD bottle is full of brown colored material, allow it to settle down.
Step 5
Now add 10 drops of phosphoric acid. Close the lid tightly and shake the bottle. Make sure that all the brown materials are dissolved.
Step 6
Using your 5 ml syringe, transfer 5 ml of this solution from the BOD bottle into the test tube.
Step 7
Add 2 drops of starch solution to the test tube. Now your solution will become blue.
Step 8
Take 1 ml of sodium thiosulphate solution in 1 ml syringe.
Step 9
Slowly add the sodium thiosulphate solution drop by drop into the test tube till the blue color just disappears. Then note the amount of sodium thiosulphate solution used for making the solution in test-tube colorless.
Step 10
Put back the sodium thiosulphate solution remaining in the syringe after the experiment.
Step 11
Please watch the videos given below carefully to understand the method.
Calculation
Please use the formula given below to calculate the oxygen present in the water
Oxygen dissolved per one liter of water = Volume of sodium thiosulphate solution used (in ml) X 80.
Measuring an abiotic factor: Oxygen
We all know that if the content of oxygen reduces in the environment the organisms will suffocate and die. In an aquarium, the pump producing air bubbles helps to maintain the level of oxygen and saves fish from suffocation. (Please watch the video of the aquarium given in the lesson 2.1)
Generally, this kind of an experiment requires a sophisticated laboratory. However, we simplified it for you so that you can conduct this experiment in your classroom. The method we are using to measure the oxygen dissolved in the water is called “Winkler’s method”.
Material required
In order to conduct this activity, you need the following Items
(1ml) (5ml) Paper cup
Steps for water testing
Fill BOD bottle with water sample by dipping the bottle slowly into the water. Please make sure that no air bubble is trapped in the water sample. Presence of air bubbles can cause error. So put the lid on the bottle while it is still under water.
Open the lid carefully and add 4 drops of manganese sulphate solution
Then add 4 drops of alkaline potassium iodide solution.
Close the lid tightly and shake the water very well. You might have noticed that water in the BOD bottle is full of brown colored material, allow it to settle down.
Now add 10 drops of phosphoric acid. Close the lid tightly and shake the bottle. Make sure that all the brown materials are dissolved.
Using your 5 ml syringe, transfer 5 ml of this solution from the BOD bottle into the test tube.
Add 2 drops of starch solution to the test tube. Now your solution will become blue.
Take 1 ml of sodium thiosulphate solution in 1 ml syringe.
Slowly add the sodium thiosulphate solution drop by drop into the test tube till the blue color just disappears. Then note the amount of sodium thiosulphate solution used for making the solution in test-tube colorless.
Put back the sodium thiosulphate solution remaining in the syringe after the experiment.
Please watch the videos given below carefully to understand the method.
Calculation