Friday, 19 September 2014
LESSON TRANSCRIPT
INDUCTIVE THINKING MODEL(Arun)
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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
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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
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Salt solution
|
Starch
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Sugar solution
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Rock
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Milk
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Muddy water
|
Air
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Soil
|
Steel
|
Sand
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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(Arun)
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 (Arun)
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.
- 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 (Arun)
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:
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)
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.
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