Background

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The effect of air pollution in the form of photochemical smog, acid deposition, greenhouse effects and the destruction of ozone shield are major concerns to all. In Sarawak, among the major sources of air pollution are those originating from burning of fossil fuels, wood and automobile exhaust. The concern of the effects of air pollutants, like sulphur dioxide and carbon dioxide on plants is usually stressed to students; but it is usually difficult for them to visualize such effects.

Objectives

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1. This activity provides a means of linking the presence of air pollutants, particularly sulphur dioxide and carbon dioxide, and their impact on growth of plants.  

2. The effects of laboratory engineered ‘acid rain’ on plants can be studied.  

Benefits for teaching and learning process

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This activity is an example of active teaching and learning of science where students conduct an experiment on acidic gases rather than just discussing the effects of ‘acid rain’ on their environment. This experiment allows students to see for themselves the effects of ‘acid rain’.  The following are some of the benefits in this activity:

• Students can see the effect of acidic gases on plants.

• Students should be able to differentiate between quantitative and qualitative results

• Students are able to relate production of sulphur dioxide and carbon dioxide to sources like burning of wood and fossil fuels.

• Environment and economic implications : student will be aware of the potential harm of continuous deforestation and burning on a long-term basis. Trees are no longer available to act as a ‘sink’ to take up carbon dioxide during photosynthesis.

• Cost effective – this experiment/demonstration cost little and can be conducted within a few days.

• Safety :  
  (1) Students need not leave the school compound.  
  (2) Students’ health and well being will not be jeopardized.

• Moral values – cooperativeness, cleanliness, responsibility, willingness to be involved, curiosity.  

• Thinking skills – identifying, comparing and contrasting, relating, predicting.  

Apparatus/ materials

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1. 3 plastic bottles with covers (1.5 litre capacity)

2. a splinter  

3. matches  

4. duckweeds/vegetable seedlings/moss  

5. water

Construction of teaching aids

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Preparation of bottles.

1. Each group of students is required to bring 3 empty mineral water bottle of size 1.5 litre.  Each of the bottle is cut into two with the bottom half of about 5 – 8 cm in height. [Refer 4-D1] The bottom halves are filled with soil and students are asked to plant vegetable seedlings of their choice, collect pond duckweeds or moss. They are encouraged to use plants that are familiar to them and can easily be grown.  
   

2. If seedlings are used, the seedlings need to reach a height of about 3 cm before they can be used. [Refer 4-P1]
   

3. One bottle will be used as the control while the other will be used as the tested experiment.  
   

4. To the inside of the upper half of the experimental bottle, students will fix 3 matches with craft glue. [Refer 4-P2]    
   

5. The matches are then lighted [Refer 4-P3]. Immediately, the upper half of the bottle is joined with the lower half and the two halves are sealed together with cello tape. Burning of the matchsticks within the containers releases both gaseous sulphur dioxide and carbon dioxide.   
   

6. Water is sprayed through the mouth of both bottles. Spraying of    water droplets simulate rain drops. The gases dissolved in  the water will produce ‘acid rain’. [Refer 4-P4]  
   

7. The two bottles are left for 2- 3 days to observe the difference of the plants in both experimental and control groups.  
   

8. Students are required to find out the pH of the ‘acid rain’ produced in the experimental and control bottles. A piece of pH paper is placed at the bottom half. The matches are lighted in the experimental bottle and the upper and lower sections of the bottles are sealed. Water is sprayed in the two bottles. Students then checked the pH of the water in both bottles.

Implementation of the teaching

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A. First lesson: Briefing and discussion on the procedures to conduct the experiment

This activity can be an investigation, a group experiment or a demonstration by the teacher. Students can also change the independent variable by using different number of matchsticks or different types of matchsticks for experimental sets.

Testing of the pH of water after burning will indicate that the water in the experimental bottle is acidic. Students are asked to give alternative ways of testing the acidity of the water in the bottle. They should discuss the advantages and disadvantages of each method. They are also encouraged to make improvement on the experiment.

B. Subsequent days: Students record observations and draw     conclusion

Observation :

Most terrestrial plants in the experimental set turned yellow on the second day and died on the third day. [Refer 4-P5]

Dramatic results are obtained from moss plants mainly because they don’t have any protective surface. Pond duckweeds need about 10 days before any qualitative observations can be made. [Refer 4-P6]

Conclusion :

Students are able to link the burning of wood and fossil fuels to acid rain and its effect on various types of plants.

Suggestion for modification

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Food for thought for the students:

• Besides pH is there any other factors introduced during the process of carrying out the above experiment that may also affect the growth of plants in the experiment? If so how does it affect the growth of plants?
• Suggest ways to improve the above experiment.