LESSON TRANSCRIPT

INDUCTIVE THINKING MODEL

Name of school        : Model Boys H.S.S                                                              Standard        : VIII Name of teacher       : ArunBose. A                                                                       Strength         : Subject                       : Chemistry                                                                            Date                : Unit                            : Molecule, Atom                                                                 Duration        : Topic                          :  Homogeneous and heterogeneous mixtures

                                                                               

Name of the concept: Homogeneous and heterogeneous mixtures

OBJECTIVES:

Ø  Pupils develop observation skill.

Ø  Identification of different types of homogeneous and heterogeneous mixtures.

Ø  Generalization about the properties of homogeneous and heterogeneous mixtures.

Ø  Pupils develop hypothesing predicts results.

PHASE 1: DATA CATEGORISATION

T: What is the common property of salt solution, sugar solution, muddy water, lemon            juice etc.? 

S: They all are solutions.      

T: Ok. If I add soil and air to the above list, then can you find any other common property?   

S: They all are mixtures.

T: Can you name some more mixtures?

S: Starch, gold, steel etc.

T: Can you group them on the basis of their similarities?

A	B
Salt solution	Starch
Sugar solution	Rock
Milk	Muddy water
Air	Soil
Steel	Sand

PHASE 2: INTERPRETATION OF DATA

T: Now let us analyze the above mentioned examples. How did you classified them/

S: Items in group A are mainly liquid solution.

T: Then what about air and steel?

S: The components of group A mixtures are not visible.

T: What about group B mixtures?

S: The different components of group B mixtures are not easily visible.

T: Right. Anything more?

S: The components in group A mixtures are uniformly distributed whereas the components in group B mixtures are localized.

T: Absolutely right. Can you name them?

T: They are homogeneous and heterogeneous mixtures.

Homogeneous mixtures are mixtures where the components that make up the mixture are uniformly distributed. Heterogeneous mixtures are the mixtures in which components can be seen as if there were three or more phases are present.

PHASE 3: APPLICATION OF GENERALISATION

T: Now I will give you some examples. Identify them?

    Dust

S: Heterogeneous mixture.

T: Right. Why it is heterogeneous?

S: Because dust particles are easily visible.

T: Yes, then clay.

S: Heterogeneous.

T: Milk.

S: Homogeneous.

T: Gravel.

S: heterogeneous.

T: All right. So heterogeneous mixtures are mixtures where the properties are not uniform        throughout, whereas in homogeneous mixtures the properties are uniform throughout.

SCIENCE LIBRARY

A library is the storehouse of knowledge, the flowing stream of living thoughts and an educational apparatus of considerable value. It is one of the most stimulating and potent instruments of dynamic developmental education in the school. It is the richest source of experience from which the teacher can choose at will, any number of learning task appropriate to the student initiated and activity centered style of pedagogy. Work and play go side by side in a typical progressive school library. Now a day we are emphasizing ‘education for democracy’ which, in turn warrants ‘democracy in education’. Library is the agency for experimentation in this ‘education for democracy’ and ‘education in democracy’.

From the beginning children need an environment enriched by attractive books and it is one of the duties of the school to see that this environment is provided. One of the important recommendations made by Secondary Education Commission was that every school has subject libraries, which are under the charge of subject teachers .It was felt that subject teachers could enrich their teaching, making use of small collections of books on their own subjects. Science being one of the most important areas of school curriculum, the content of which rapidly goes on changing, both teachers and pupils have to constantly go on reading books in the subject. This warrants provision of a rich and updated science library in every school. This is essentially needed to help the teachers and pupils keep abreast of the explosion of scientific knowledge. First of all let the teachers find out the latest books and update their knowledge. Then they can recommend some books to their students and encourage them to acquire the habit of extending and supplementing their knowledge by making proper use of science library. Science library thus can be a wonderful teaching-aid for realizing the demands of developmental education.

a)     The main objectives of organizing a Science Library

The following are the main objectives of organizing a science library in the school:

1.      To help teachers and pupils alike update scientific knowledge

2.      To facilitates ‘self studies’ and ‘learning to learn’

3.      To enrich curricular experiences

4.      To enable pupils participate in discussion and project works meaningfully

5.      To make co-curricular activities such as participation in science club activities more meaningful and dynamic..

6.      To create interest in science as a subject of study

7.      To develop the habit of concentrated reading of knowledgeable books with a purpose

8.      To develop in the students critical attitude and capacity for independent judgment

9.      To develop the habit of reading as a useful leisure time activity

b)    Important library resources for Science

1.      Book resource

A variety of books are essential for presenting different points of view and for providing adequate experiences for the learning of concepts, principles, and processes. In book resources we can include:

a)      Text books

b)      Booklets

c)      Library materials

d)     Reference materials

2.      Non- book resources

The field of science is connected with everyday life. The following non-book resources should be available in the library.

a)      Periodicals

b)      Pamphlets

c)      News papers

d)    Making Science Library popular

In order to attract students to the science library and to train them to properly use facility with a liking and will, the science teacher should seriously consider the following guidelines:

1.      One of the most important objectives is to develop in the children  interest in science

2.      The teacher should set an example to pupils in using the library

3.      Many opportunities should be provided to  the children to have a free and frank discussions with teacher about science books

4.      The pupils may be encouraged to start science magazines.

5.      A bulletin board should be placed in the science library.

6.      Pupils can be given assignments that require them to borrow books from science library

7.      Reading groups can be organized under the science club

Science library is a very important agency of a dynamic programmeof science education. Let us hope and trust that in the progressive schools of modern India, the significance and worth of science library service will be realized and practical steps taken for its implementation.

DEFORESTATION

        

             Deforestation, clearance or clearing is the removal of a forest or stand of trees where the land is thereafter converted to a non-forest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use.

        The term deforestation is often misused to describe any activity where all trees in an area are removed. However in temperate climates, the removal of all trees in an area in conformance with sustainable forestry practices is correctly described as regeneration harvest. In temperate mesic climates, natural regeneration of forest stands often will not occur in the absence of disturbance, whether natural or anthropogenic. Furthermore, biodiversity after regeneration harvest often mimics that found after natural disturbance, including biodiversity loss after naturally occurring rainforest destruction.

    Deforestation occurs for many reasons: trees are cut down to be used or sold as fuel (sometimes in the form of charcoal) or timber, while cleared land is used as pasture for livestock, plantations of commodities and settlements. The removal of trees without sufficient reforestation has resulted in damage to habitat, biodiversity loss and aridity. It has adverse impacts on biosequestration of atmospheric carbon dioxide.

Environmental problems

1.Atmospheric

         Deforestation is a contributor to global warming, and is often cited as one of the major causes of the enhanced greenhouse effect. Tropical deforestation is responsible for approximately 20% of world greenhouse gas emissions. According to the Intergovernmental Panel on Climate Change deforestation, mainly in tropical areas, could account for up to one-third of total anthropogenic carbon dioxide emissions. But recent calculations suggest that carbon dioxide emissions from deforestation and forest degradation (excluding peat land emissions) contribute about 12% of total anthropogenic carbon dioxide emissions with a range from 6 to 17%. Deforestation causes carbon dioxide to linger in the atmosphere. As carbon dioxide accrues, it produces a layer in the atmosphere that traps radiation from the sun. The radiation converts to heat which causes global warming, which is better known as the greenhouse effect. Plants remove carbon in the form of carbon dioxide from the atmosphere during the process of photosynthesis, but release some carbon dioxide back into the atmosphere during normal respiration. Only when actively growing can a tree or forest remove carbon, by storing it in plant tissues. Both the decay and burning of wood releases much of this stored carbon back to the atmosphere. In order for forests to take up carbon, there must be a net accumulation of wood. One way is for the wood to be harvested and turned into long-lived products, with new young trees replacing them. Deforestation may also cause carbon stores held in soil to be released. Forests can be either sinks or sources depending upon environmental circumstances. Mature forests alternate between being net sinks and net sources of carbon dioxide (see carbon dioxide sink and carbon cycle).

2.Hydrological

       The water cycle is also affected by deforestation. Trees extract groundwater through their roots and release it into the atmosphere. When part of a forest is removed, the trees no longer transpire this water, resulting in a much drier climate. Deforestation reduces the content of water in the soil and groundwater as well as atmospheric moisture. The dry soil leads to lower water intake for the trees to extract. Deforestation reduces soil cohesion, so that erosion, flooding and landslides ensue.

Tree , and plants in general, affect the water cycle significantly:

• their canopies intercept a proportion of precipitation, which is then evaporated back to the atmosphere (canopy interception);
• their litter, stems and trunks slow down surface runoff;
• their roots create macro pores – large conduits – in the soil that increase infiltration of water;
• they contribute to terrestrial evaporation and reduce soil moisture via transpiration;
• their litter and other organic residue change soil properties that affect the capacity of soil to store water.
• their leaves control the humidity of the atmosphere by transpiring. 99% of the water absorbed by the roots moves up to the leaves and is transpired.

       As a result, the presence or absence of trees can change the quantity of water on the surface, in the soil or groundwater, or in the atmosphere. This in turn changes erosion rates and the availability of water for either ecosystem functions or human services. The forest may have little impact on flooding in the case of large rainfall events, which overwhelm the storage capacity of forest soil if the soils are at or close to saturation. Tropical rainforests produce about 30% of our planet's fresh water.

3.Soil

         Undisturbed forests have a very low rate of soil loss, approximately 2 metric tons per square kilometer (6 short tons per square mile). Deforestation generally increases rates of soil erosion, by increasing the amount of runoff and reducing the protection of the soil from tree litter. This can be an advantage in excessively leached tropical rain forest soils. Forestry operations themselves also increase erosion through the development of roads and the use of mechanized equipment.

4.Biodiversity

         Deforestation on a human scale results in decline in biodiversity, and on a natural global scale is known to cause the extinction of many species. The removal or destruction of areas of forest cover has resulted in a degraded environment with reduced biodiversity. Forests support biodiversity, providing habitat for wildlife; moreover, forests foster medicinal conservation. With forest biotopes being irreplaceable source of new drugs, deforestation can destroy genetic variations (such as crop resistance) irretrievably.

ACID RAIN

        Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals and infrastructure. Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. Governments have made efforts since the 1970s to reduce the release of sulfur dioxide into the atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes and sulfur dioxide is produced by volcanic eruptions. The chemicals in acid rain can cause paint to peel, corrosion of steel structures such as bridges, and erosion of stone statues.

Definition

"Acid rain" is a popular term referring to the deposition of wet (rain, snow, sleet, fog, cloudwater, and dew) and dry (acidifying particles and gases) acidic components. Distilled water, once carbon dioxide is removed, has a neutral pH of 7. Liquids with a pH less than 7 are acidic, and those with a pH greater than 7 are alkaline. "Clean" or unpolluted rain has an acidic pH, but usually no lower than 5.7, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid according to the following reaction:

H₂O (l) + CO₂ (g) H₂CO₃ (aq)

Carbonic acid then can ionize in water forming low concentrations of hydronium and carbonate ions:

H₂O (l) + H₂CO₃ (aq) HCO₃⁻ (aq) + H₃O⁺ (aq)

However, unpolluted rain can also contain other chemicals which affect its pH (acidity level). A common example is nitric acid produced by electric discharge in the atmosphere such as lightning. Acid deposition as an environmental issue (discussed later in the article) would include additional acids to H₂CO₃.

Emissions of chemicals leading to acidification

       The most important gas which leads to acidification is sulfur dioxide. Emissions of nitrogen oxides which are oxidized to form nitric acid are of increasing importance due to stricter controls on emissions of sulfur containing compounds.

1.Natural phenomena

     The principal natural phenomena that contribute acid-producing gases to the atmosphere are emissions from volcanoes. Thus, for example, fumaroles from the Laguna Caliente crater of Poás Volcano create extremely high amounts of acid rain and fog, with acidity as high as a pH of 2, clearing an area of any vegetation and frequently causing irritation to the eyes and lungs of inhabitants in nearby settlements. Acid-producing gasses are also created by biological processes that occur on the land, in wetlands, and in the oceans. The major biological source of sulfur containing compounds is dimethyl sulfide.

Nitric acid in rainwater is an important source of fixed nitrogen for plant life, and is also produced by electrical activity in the atmosphere such as lightning.

Acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe.

Soils of coniferous forests are naturally very acidic due to the shedding of needles, and the results of this phenomenon should not be confused with acid rain.

2.Human activity

       The principal cause of acid rain is sulfur and nitrogen compounds from human sources, such as electricity generation, factories, and motor vehicles. Electrical power complexes utilising coal are among the greatest contributors to gaseous pollutions that are responsible for acidic rain. The gases can be carried hundreds of kilometers in the atmosphere before they are converted to acids and deposited. In the past, factories had short funnels to let out smoke but this caused many problems locally; thus, factories now have taller smoke funnels. However, dispersal from these taller stacks causes pollutants to be carried farther, causing widespread ecological damage.

Adverse effects

      Acid rain has been shown to have adverse impacts on forests, freshwaters and soils, killing insect and aquatic life-forms as well as causing damage to buildings and having impacts on human health.

1.Surface waters and aquatic animals

      Both the lower pH and higher aluminium concentrations in surface water that occur as a result of acid rain can cause damage to fish and other aquatic animals. At pHs lower than 5 most fish eggs will not hatch and lower pHs can kill adult fish. As lakes and rivers become more acidic biodiversity is reduced. Acid rain has eliminated insect life and some fish species, including the brook trout in some lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains of the United States. However, the extent to which acid rain contributes directly or indirectly via runoff from the catchment to lake and river acidity (i.e., depending on characteristics of the surrounding watershed) is variable. The United States Environmental Protection Agency's (EPA) website states: "Of the lakes and streams surveyed, acid rain caused acidity in 75% of the acidic lakes and about 50% of the acidic streams".

2.Soils

      Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are unable to tolerate changes to low pH and are killed. The enzymes of these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins such as aluminium, and leach away essential nutrients and minerals such as magnesium.

2 H⁺ (aq) + Mg²⁺ (clay) 2 H⁺ (clay) + Mg²⁺ (aq)

Soil chemistry can be dramatically changed when base cations, such as calcium and magnesium, are leached by acid rain thereby affecting sensitive species, such as sugar maple (Acer saccharum).

3.Forests and other vegetation

        Adverse effects may be indirectly related to acid rain, like the acid's effects on soil (see above) or high concentration of gaseous precursors to acid rain. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain.

       Other plants can also be damaged by acid rain, but the effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands. When calcium is leached from the needles of red spruce, these trees become less cold tolerant and exhibit winter injury and even death.