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آفاق علوم 73

كفاءة - سرعة - تطور - خيرية - متعة وإفادة
 
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 C422 Lecture 9

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مُساهمةموضوع: C422 Lecture 9   
الإثنين مايو 01, 2017 7:14 am
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تاريخ التسجيل : 18/01/2016
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الموقع : آفاق علوم 73


References:
1) V.K. Ahluwalia, environmental chemistry, 2nd Edition, Chapter 3, Ane Books pvt. Ltd. 2013
2) E.D. Enger, B.F. Smith , Environmaltal science, 4th edition, chapter 13, Mc Graw HB تقريبا hb



Soil formation:
Soils are formed from rocks by weathering
Weathering:
>> The process of breakdown of massive rock material into smaller aggregates, fine enough to form the soils.
The processes of breakdown and alternation of rocks on the earth's surface by mechanical and chemical process.


The word soild is derived from a latin word "Solum" meaning earthy material in which plants grow.
The study of soild is known as Soil Science or pedology (pedos=earth)
Soil is a natural body called the pedosphere
Soil is the top layer of the earth on which plants and animal grow.

The study of soil is important in many respects:
It produces food materials on which the survival of mankind depends.
It is a vital component of the environmental Biogeochemical cycles.




Soil formation:
Soil are formed from rocks by weathering.

Weathering:
>> The process of breakdown of massive مهمة جداً كلمة ماسيف دي rock material into smaller aggregates, fine enough to form the soils.
>> The process of breakdown and alternation of rock on the earth's surface by mechanical (=physical) and chemical process.



Mechanical (Physical) weathering:
It is the splitting of rocks through the action of heat and extreme temperature changes.

Physical weathering elements originate from climate example: Temperature, ice and wind


موجود في الملزمة بالتفصيل

Sun's heat >> rock becomes warm >> expands >> during night >> rock cools quickly from outside than inside >> cracks in the rock >> cracked layers of the rock >> break into small fragments.

Water run into cracks >> freezes with the change in the temperature >> cracks become deeper.


ex كوباية الشاي بتنفجر بسبب نفس الظاهرة


Google pictures : search for chemical weathering


Chemical Weathering:
Chemical weathering occurs by water, oxygen and carbon dioxide it includes:
1) solution: (dissolving of solid materials by water)
2) Carl ovation: (dissolving of soluble rocks and minerals by weak carbonic acid - formed by the combination of water with atmospheric CO2)
3) Hydration (chemical combination of rock material).
4) Hydrolysis with CO2: silicates weathered rocks are hydrolyzed
K2Al2Si6O16(s) + 2H2O + CO2 >> Al2O3 2SiO2.2H2O + 4 SiO2 + K2CO3
CO2 and H2O combine to form carbonic acid which responsible for the weathering of their rocks.

A rock is formed from K , Al , Si , and Oxygen >> elements and minerals and metals.


K2CO3 >> dissolve in water (ما بقاش روك بقى خلاص)
SiO2 >> الرملة >>
Al2O3 2SiO2.2H2O >> روك جديد أصغر بتجمع بين الألومنيو




note : K salts are soluble


5- Chelation contributes also in chemcial weatehring.
Ligands include onorganic species and the more important ones derived from biological sources, as a result of the decomposition of dead plants and microbial material, like citric acid and humic and fulvic acid.

Ligands : are organic compound containing heteroatoms

Note : O=organic M=metals


What's a citric acid >>
is a carboxylic acid (contain OO in COOH) that can give me OO here




6- Oxidation: (combination of atmospheric oxygen with rock materials).

Oxidation/reduction is important in chemical weathering. Example, the oxidation of iron (II) to iron (III) , is accompanied by loss of potassium:

biotite (ABCFe(II)D) >> Vermiculite (ABCFe(III)D)




Note: Chemical weathering includes hyrdolysis , chelation and redox reactions




From weathered rocks:
* water soluble minerals
>> Like lime stone and gypsum
>> >> increases the presence of CO2

* Decay of animals and plants:
>> increase the presence of organic acids.


Biological weathering:
weathering involves both and chemical processes caused by both plants and animals.



Soils are classified in terms of their structure and texture

Structure of the soil:
It is the way in which individual soil particles are bound together to form aggregates.

Texture of the soil:
The proportion of various particle sizes that it contains.




من ضمن الترمينولوجي
Soil horizons:
A number of distances horizontal layer often seen in a vertical section of soil.


hori >> horizontal
zons >> zones




See page 83 >> picture

There are four horizons common to most soils
Top layer = A horizon = top soil

Contains organic matter and is important for vegetation and agricultural crops.
is lost due to deforestation over the year, takes decades to form a minor thickness of top soil.

Next layer = B horizon = subsoil
Contains little organic matter C horizon
Consisting of weathered rocks from which soil originates.

The lowest layer = hard zone = bed rocks.


Soil composition:

















soil contains a mixture of minerals
- As carbonates , sulfates , chlorides and nitrates.
- Some soils contain clay الطفل mineral, which are hydrated Fe and Al silicates
- These caly minerals bind cations such as Ca2+ , Mg2+ , Na+ , K+ a, NH4+
ده معناه إن الكلاي بيحمل شحنة نيجاتيف لأنه زي ما انت شايف بيمسك في بوسيتيف كاتيون (زي الماجنت)

so these cations are not leached (leak) by water and are available to plants as plant nutrients.

عاملة شبه الماجنيت
بنستفاد ايه؟
بتخلي الكاتيون اللي ماسكة في ما يحصلهاش تسرب (ليكينج) إلى الهوريزونس السفلى عشان يفضل فوق للنبات كعناصر غذائية
غير كده هتنزل تحت في الهوريزونس اللي تحت ما يستفادش مناه لا نبات ولا حيوان




Organic composition in soil:
The fertility of soil depends on the organic matter. The major oranic constituents are:
* Humus: the most important component دبال التربة
- Humic substances are high molecular weight macromolecules.
- These are obtained in the soil as degeneration residues from the decay of plant and dead animals.
- These form complexes with a number of cations, so that there are retained in the soil.

* Lipids: These constitute fats, the physical properties of soil depend on these compounds

* Saccharides: ???????Sakds;ljfsd;klcjm[pfevopk o,igf mo[,k [ k,ok odk, gg p
















Water and air in soil:
- the main source of water in soil is through dew, rain , snow , and irrigation.
Water is essential for the growth of platns.
Water an important medium for transporting plant nutrients from soil into the roots and other parts of the plants.

The Air: in the soil contains O2 , N2 , CO2
The decay of organic matter consumes O and produces CO2
The resut is that soil increases CO2 and dec O2


Macro and micro nutrients:
- plant require carious for their growth
- Macronutrients are needed in larger amounts.
Macronutrients : C H O N P Ca Cu Fe Mg S Na and K
N may be obtained by some plants directly from the air with the help of nitrogen fixin bacteria.


N , P and K are added to soil as fertilizers (like ammonium phosphates , urea , potassium nitrate and superphosphate) the other macronytruents are present in soil.



Miconutrients are needed in trace amounts:
- Micronutrients : Al B Br Zn Co Mn V and Mo . These elemetns >????????????



Liming: لايمينج
Some soild may become deficient in calcium due to up take plant.

Calcium deficient soils are treated with lime to provide calcium to the soil or plant
this process is called liming


From the soil , The nutrients >> find their way into the plant >> when the pants/crops are consumed by human >> these nutrients are used in varios life processes >> most of the micronutrients serve as components of essential enzymes >> when the plants , animals and human being die >> the nutrients return to the soil and in this way most of these elements are recycled.





Soil pollution
>> Soil has been used as dumping ground for most of the waste products:
domestic, human , animal , industrial and agriculture.


Huge amount of a number of hazardous chemicals and several thousand tons of wastes are dumped on the land.

These are leached by municipal and are responsible for pollution of the ground water.

The soil pollution differ from and air pollution in the sense that pollution in soil remain in direct contact with soil for relatively longer periods.


Sources of soil pollution::
1. Industril polution:
The discharge of wastes and by-products generated from various industries like various textile industries , paper and pulp industry , soap and detergent industries, dairy farms and metal processing industry.


2. Urban and domestic wastes( Municipal wastes)
* they constitues grabage, waste materials like plastics, glass , metal containers , fibers, papers and discarded products.
* portion of urban and domestic wastes are not biodegrabable like paints, vvarnishes , oils ,.... they are leached from the dumping sites of sewage along with industrial effluents and pollute even the ground water.
* tHe leaches contain poisonous gases and paritally ....'S.a;skl; kfjdskl jksj;lgk lgsfk


3. Radioactive pollutants: in soil, radioactive pollutants come the following sources:
(A) radioactive fallout: this results from testing a nuclear weapons. Considerable amounts of ????? products e.g c-14 , sr-9- , cs-137 are dispersed in the atmosphere as a result of nuclear weapon testing.

They spread all over the globe , settle on earth's crust as radioactive fallouts and find their way in the food chains


(B) Radioisotopes: used in research , industry , medicine , in nuclear reactors for generation of power and in nuclear fuel ??????????







(D) Accidents in nuclear reactors: these are rare, but if take place, they become major cause of ?????????



4. Agrochemical (Agricultural) : are chemicals used in farming. they include fertilizers and pesticides.
-Fertilizers: used to increase the fertility of soil then better yields.


They are of three typees:
1. Nitrogen based fertilizers like NaNO3, (NH4)2SO4 and urea.
2. Phosphate based fertilizers like super phosphate [Ca2H2(PO4)2.CaSO4.2H2O]
3. Potassium based fertilizers like KCl, K2SO4


Excessive use of fertilizers pollutes the soil.
Example in case of (NH4)2SO4 , NH4 are taken by crops but SO4 2- get accumulated in the soil making it acidic in highly acidic soils. this is unfit for plant growth.

Urea ما فيهاش مشاكل >>> لأن بيستخدمها جيل ورا جيل
يعني لو حطيت زيادة للجيل الحالي >> الجيل اللي بعده هيتسفيد بيه

The acidic soil is improved by liming


equation book page 87


pH is important to analyse in the soil (plants need certain medium to grow)

liming is useful here to neutrlize acidic or basic soil


[Soil] H+ + CaCO3 < -- > [Soil]Ca2+ + CO2 + H2O


Soil is تقريبًا negatively charged.




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C422 Lecture 9
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