what is the role of KOH in the experiment of release of CO2 during respiration
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to absorb the CO2 gas from the air present in glass bottle so that no CO2 is left in air inside the glass bottle
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Real Lab Procedure
Using a spatula, place about 30 germinating bean seeds in a conical flask.Pour 4ml of potassium hydroxide (KOH) solution into a measuring cylinder.Transfer the KOH solution from the measuring cylinder into a small test tube.Tie a cotton thread around the neck of the test tube.Suspend the test tube in the conical flask above the germinating seeds.Close the mouth of the conical flask with a cork.Insert one end of a delivery tube into the conical flask through the cork and dip the other in a beaker containing water.Take some Vaseline with your finger and apply this on the cork to make the apparatus air tight.Keep the apparatus undisturbed for two hours.
Observation
After two hours, you will see that the level of water has risen in the delivery tube at the end dipped in the beaker of water.
Conclusion
The germinating seeds in the conical flask release CO2 during respiration, which is absorbed by the KOH solution kept in the small test tube. This creates a partial vacuum in the flask that forces the water up the delivery tube. Thus, it proves that germinating seeds produce carbon dioxide during respiration.
Precautions:
Germination in seeds can be done by soaking them overnight and then keeping them in moist cotton wool for 1-2 days.Freshly prepared potassium hydroxide should be used.The apparatus should be air tight to prevent escape of CO2.
Respiration in animals
Materials Required:

Real Lab Procedure
Pour freshly prepared lime water into a test tube so that it is 3/4full.Take a cork with two holes and fix it into the mouth of the test tube.Insert the glass tubes, let us name them A and B, into the test tube through the cork, such that end of the glass tube A dips in the lime water.Breathe out air with full force by putting your mouth at the end of tube A.Continue doing this vigorously for at least 1 minute.
Observation
The bubbles of the air breathed out gradually turn the lime water milky.
Conclusion
The only gas that can turn lime water milky is carbon dioxide. When carbon dioxide reacts with lime water, it forms calcium carbonate (CaCO3), thus giving lime water its milky appearance. So, we can conclude that humans and animals give out CO2 during respiration.
Precautions
Use freshly prepared calcium carbonate solution.Breathe out air vigorously for at least 1 minute.
Simulator Procedure (as performed through the Online Labs)
You can select the test - respiration in animals or plants, by clicking on the corresponding icon - ‘Animals’ or ‘Plants’.
Respiration in Plants
You can increase or decrease the number of seeds inside the beaker by moving the ‘Number of seeds’ slider to the right and left respectively.The same way, you can increase or decrease the temperature by moving the ‘Temperature’ slider to the right and left respectively.Click on the ‘Start’ button to start the experiment.You can observe that the level of water in the delivery tube rises at the end dipped in the beaker.A timer is shown and you need to wait till the timer stops.Click on the information icon to see the inference.You can redo the experiment by clicking on the ‘Reset’ button.
Respiration in Animals
To study respiration in a human being or a grasshopper, select your choice from the ‘Select the animal’ drop down list.
Respiration in the Grasshopper:
You can increase or decrease the number of grasshoppers inside the beaker by moving the ‘Number of grasshoppers’ slider to the right and left respectively.The same way, you can increase or decrease the temperature by moving the ‘Temperature’ slider to the right and left respectively.Click on the ‘Start’ button to start the experiment.You can observe that the level of water in the delivery tube rises at the end dipped in the beaker.A timer is shown and you need to wait till the timer stops.Click on the information icon to see the inference.You can redo the experiment by clicking on the ‘Reset’ button.
Respiration in Human Beings:
You can select the indicator - Lime water or BTB (Bromothymol Blue) from the ‘Select the indicator’ drop down listClick on the ‘Start’ button to start the experiment.A timer is shown and you need to wait till the timer stops.Observe the solution (indicator) in the test as the bubbles of air pass through the delivery tube.If the indicator chosen was lime water, it gradually turns milky, and if the chosen indicator was BTB (Bromothymol Blue), it turns green.You can redo the experiment by clicking on the ‘Reset’ button.
Using a spatula, place about 30 germinating bean seeds in a conical flask.Pour 4ml of potassium hydroxide (KOH) solution into a measuring cylinder.Transfer the KOH solution from the measuring cylinder into a small test tube.Tie a cotton thread around the neck of the test tube.Suspend the test tube in the conical flask above the germinating seeds.Close the mouth of the conical flask with a cork.Insert one end of a delivery tube into the conical flask through the cork and dip the other in a beaker containing water.Take some Vaseline with your finger and apply this on the cork to make the apparatus air tight.Keep the apparatus undisturbed for two hours.
Observation
After two hours, you will see that the level of water has risen in the delivery tube at the end dipped in the beaker of water.
Conclusion
The germinating seeds in the conical flask release CO2 during respiration, which is absorbed by the KOH solution kept in the small test tube. This creates a partial vacuum in the flask that forces the water up the delivery tube. Thus, it proves that germinating seeds produce carbon dioxide during respiration.
Precautions:
Germination in seeds can be done by soaking them overnight and then keeping them in moist cotton wool for 1-2 days.Freshly prepared potassium hydroxide should be used.The apparatus should be air tight to prevent escape of CO2.
Respiration in animals
Materials Required:

Real Lab Procedure
Pour freshly prepared lime water into a test tube so that it is 3/4full.Take a cork with two holes and fix it into the mouth of the test tube.Insert the glass tubes, let us name them A and B, into the test tube through the cork, such that end of the glass tube A dips in the lime water.Breathe out air with full force by putting your mouth at the end of tube A.Continue doing this vigorously for at least 1 minute.
Observation
The bubbles of the air breathed out gradually turn the lime water milky.
Conclusion
The only gas that can turn lime water milky is carbon dioxide. When carbon dioxide reacts with lime water, it forms calcium carbonate (CaCO3), thus giving lime water its milky appearance. So, we can conclude that humans and animals give out CO2 during respiration.
Precautions
Use freshly prepared calcium carbonate solution.Breathe out air vigorously for at least 1 minute.
Simulator Procedure (as performed through the Online Labs)
You can select the test - respiration in animals or plants, by clicking on the corresponding icon - ‘Animals’ or ‘Plants’.
Respiration in Plants
You can increase or decrease the number of seeds inside the beaker by moving the ‘Number of seeds’ slider to the right and left respectively.The same way, you can increase or decrease the temperature by moving the ‘Temperature’ slider to the right and left respectively.Click on the ‘Start’ button to start the experiment.You can observe that the level of water in the delivery tube rises at the end dipped in the beaker.A timer is shown and you need to wait till the timer stops.Click on the information icon to see the inference.You can redo the experiment by clicking on the ‘Reset’ button.
Respiration in Animals
To study respiration in a human being or a grasshopper, select your choice from the ‘Select the animal’ drop down list.
Respiration in the Grasshopper:
You can increase or decrease the number of grasshoppers inside the beaker by moving the ‘Number of grasshoppers’ slider to the right and left respectively.The same way, you can increase or decrease the temperature by moving the ‘Temperature’ slider to the right and left respectively.Click on the ‘Start’ button to start the experiment.You can observe that the level of water in the delivery tube rises at the end dipped in the beaker.A timer is shown and you need to wait till the timer stops.Click on the information icon to see the inference.You can redo the experiment by clicking on the ‘Reset’ button.
Respiration in Human Beings:
You can select the indicator - Lime water or BTB (Bromothymol Blue) from the ‘Select the indicator’ drop down listClick on the ‘Start’ button to start the experiment.A timer is shown and you need to wait till the timer stops.Observe the solution (indicator) in the test as the bubbles of air pass through the delivery tube.If the indicator chosen was lime water, it gradually turns milky, and if the chosen indicator was BTB (Bromothymol Blue), it turns green.You can redo the experiment by clicking on the ‘Reset’ button.
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