KPK Board 12th class Chemistry Ch 23 Environmental Chemistry questions answers

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Malakand Board 12th classes short questions Answer

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Abbottabad  Board 12th classes short questions Answer

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Why is acid rain considered as a threat to historical monuments?

Ans. Acid rain also affects the material objects. The acidity of the rain usually increases the rate of decomposition of matter. This results in the accumulation on organic matter in water, which in turn increases the water pollution.


Define Contaminants

Contaminants: Biological, chemical, physical, or radiological substance (normally absent in the environment) which, in sufficient concentration, can adversely affect living organisms through air, water, soil, and or food are called contaminants.

Define Pollutant

Pollutant: A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. A pollutant may cause long or short-term damage by changing the growth rate of plant or animal species, or by interfering with human amenities, comfort, health, or property values. Some pollutants are biodegradable and therefore will not persist in the environment in the long term.

Define Eutrophication

Eutrophication: Eutrophication is defined as an increase in the rate of supply of organic matter in an ecosystem.

The process by which a body of water acquires a high concentration of nutrients, especially phosphates and nitrates. These typically promote excessive growth of algae. As the algae die and decompose, high levels of organic matter and the decomposing organisms deplete the water of available oxygen, causing the death of other organisms, such as fish. Eutrophication is a natural, slow-aging process for a water body, but human activity greatly speeds up the process.

Define Acid rain

Acid Rain: Rain which is unusually atmospheric pollution with sulphur dioxide and nitrogen compounds.

The phenomena of acid rain were first discovered by an English scientist R.A Smith 1851 in the city of Manchester. Initially it was referred as precipitation. This is more acidic then natural rain. The PH of the clean rain is 5.6-62 while PH of acidic rain is ranges from 1.8-5.5.

The greater acidity of acid rain is due to the presence of oxides of Nitrogen and sulphur in the atmosphere, which are emitted from the chimneys of industrial plants. It is due to the varying amounts of the dissolved CO, which is a common constituent (0.036%) of the earth’s atmosphere.

H2O+CO2 à H2CO3

Therefore, any precipitation having a pH of less than 5.6 would be classified as acid rain. To the acidifying effect of CO), must be added the contribution other than acidic constituents of the atmosphere, particularly HNO3 and H2SO4.

Define B.O.D

B.O.D: B.O.D stands for biochemical oxygen demand. Biochemical demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given sample at certain temperature over a specific time period. The term also refers to chemical procedure for determining this amount.

Define Smog

Smog: Smog: Smog is the combination of smoke and fog. The appearance brownish coloration in the atmosphere is due to smog.

Discovery: The smog was first discovered in London in 1940 and the problem of Smog was first observed in Los Angles. This was identified by an American chemist A Heagen. He identifies the role of Industrial effluents and sun light is responsible for photochemical reaction in the atmosphere. This results in the formation of smog. Smog causes a brownish coloration in the atmosphere, and thus reduces the visibility in the area. The situation ultimately leads to increased death rates practically in cities such as Los Angeles, Tokyo, and Chicago etc.

What is importance of dissolved oxygen in water?

Importance of dissolved oxygen: The amount of dissolved oxygen plays a very important role in aquatic life. It also determined the quality of water whether it is fit or unifit for drinking.

What methods are employed for control of SO2 pollution?

Reducing the sulphur contents of the fuel before combustion.

Limestone, Spray dry system

Limestone: This system is relatively simple, crush limestone is mixed with water to form slurry which is then sprayed into the sulphur contain flue gases.

Dry System: With in the spray dry system a slurry of alkali usually slaked lime is injected into the flue gases.

Sea Water Scrubbing Process: Sea water scrubbing process exploit the natural alkalinity of sea water to absorb acid gases.

What are applications of Green Chemistry?
  1. To develop products that are less toxic or which requires less toxic raw materials feed stocks.
  2. To develop products that degrades more readily in environment than the current product. To reduce the requirements for hazardous or environmentally persistent solvents and extractants in chemicals processes.
  3. To improve energy efficiency by developing low temperature and low pressure processes by using new/ improved catalysts To develop efficient and reliable methods to monitor processes (e.g. monitoring reactions and releases) for improved control.
  4. Environmental chemistry is the branch of chemistry which deals with chemical and biochemical occurrence in nature. Pollutant is any substance which contaminate our environment.
  5. Atmosphere is a big tank of gases, surrounding the earth’s surface The term acid rain is referred to all precipitation (rain, snow or dew) which is more acidic than natural water (pH = 7.0).
Name four major green house gases.

The major greenhouse gases are CO2 CH4 H2O (vapours) and CFCs.

Out of CFC's and Co2 which one has higher potential to cause global warming and why?

CFCs has lower potential than CO2 though CFCs longer effect on environment than CO2 but as it is present in fewer amounts so overall effect is less than CO2.

Why does the rain water normally have pH of about 5.6? When does it become acid rain?

Rain water has high pH due to dissolved oxides of Nitrogen and Sulphur is rain water.

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