Objective
Study the composition of exhaled air and confirm the presence of carbon dioxide
Materials required:
- Calcium Hydroxide
- Test tubes
- Dropper
- Test tube holder
- Straw
Procedure:
- Prepare fresh lime water. Pour in 1 teaspoon of slaked lime into a jar filled with water and place a cover on the jar. Shake it thoroughly. At first, shake for a minute or two and then allow the mixture to stand for 24 hours. After the given period, pour the solution into another container. Do not stir the sediments vigorously. The clearer solution must be stored into a clean bottle or jar until its next use. If excess calcium hydroxide is added, the solution has a milky appearance due to suspended calcium hydroxide particles.
- Take two clean test tubes and label them ‘A’ and ‘B’
- Half-fill the test tube ‘A’ with tap water and take the same quantity of freshly prepared lime water in test tube ‘B’.
- Place the glass tube/plastic tube/straw in each test tube, taking care that one end dips properly in the solution
- Blow air (exhale) into test tube ‘A’ for 2-3 minutes. Shake the tube vigorously. Repeat the process 2-3 times and keep it in a test tube stand
- Now, blow air into test tube ‘B’ for 2-3 minutes. Shake the tube vigorously. Repeat the process 2-3 times and keep it by the side of test tube ‘A’
- Observe both the test tubes and compare the colour of solutions in them
Findings:
- The colour of water in test tube ‘A’ remains unchanged whereas the colour of lime water in test tube ‘B’ turns milky.
Conclusions:
- The air which we breathe in and breathe out is not pure oxygen or carbon dioxide respectively. As we all knew that our body and the cells inside it require more oxygen to respire and to perform its regular functions and our environment does not provide us with an exclusive supply of oxygen. In a similar way, while breathing out, we do exclusively give out carbon dioxide.
Theory:
- Exhaled air has much larger quantity of carbon dioxide, which turns lime water milky