Environmental Chemistry Notes by umair khan academy


Environmental Chemistry is the last chapter from Class 12 FS.c. Umair Khan Academy provides Short question handouts for students. For more notes and video-lectures visit Umair Khan Academy and its YouTube Channel.

Important Short Questions for ENVIRONMENTAL CHEMISTRY are given below with Video discussion for your easy understanding.

Q.1 What are the components of the environment?

The environment consists of the following components:

  • Atmosphere
  • Hydrosphere
  • Lithosphere
  • Biosphere

Q.2 What is the composition of the environment and its thickness?

Atmosphere is composed of 78% N2, 21% O2, 0.9% Ar, 0.03% CO2 and some traces amount of H2, O3, CH4, CO and noble gases. The concentration of water vapours changes with time.

Q.3 What is lithosphere?

The lithosphere is the component of the environment which consist of a rigid rooky crust of the earth.99.5% of the lithosphere has a composition of 46.6% oxygen, 27.72% silicon 8.13% aluminium. 5% Fe and the rest are some other metals.

Q.4 What is Biosphere?

The component of the environment includes the region of the earth where life is possible, called the biosphere. It consists of a lower atmosphere, oceans, lakes, soils and solid sediments.

Q.5 What are environmental pollutants?

Any substance in the environment which has adverse effects on human health, quality of life and the natural functioning of the ecosystem is called an environmental pollutant.

Q.6 What are primary pollutants?

The primary pollutants are waste products which are given out from the chimneys of industries and exhaust of vehicles and are directly mixed in the atmosphere are called primary pollutants. Examples: CO, NH3, NO2, SO2, radioactive materials etc.

Q.7 What are secondary pollutants?

The pollutants which are produced from primary pollutants through various chemical reactions are called secondary pollutants. Examples: H2SO4, HNO3, HF, peroxyacetyl nitrate (P.A.N), ozone etc.

Q.8 How do you discuss the poisoning of CO? What are the effects of CO on human health?

CO is a highly poisonous gas. It is named Silent Killer because it combines with haemoglobin and blocks the site. As a result of which oxygen-carrying capability is decreased. High concentration of CO in the blood causes fatigue, headache, and unconsciousness which may cause death.

Q.9 What are the conditions for the formation of smog?

There should be a sufficient amount of NO (nitric oxide), hydrocarbons and volatile organic compounds (VOC). The movement of air must be little so that the reactions are not disturbed. There must be the presence of sunlight to speed up the reactions.

Q.10 What is reducing smog? Give its effects and resources.

Smog is the combination of smoke and fog. It contains high contents of SO2 then it has the reducing property called reducing smog. Combustion of coal and chemical reactions taking place in the air are the sources of smog.

Q.11 What is photochemical smog? Give its properties.

Photochemical smog consists of high concentrations of oxidants like ozone. It is yellowish brown, grey, hazy having an unpleasant odour

Q.12 What is acid rain?

The rainwater having a PH less than 5 is termed as acid rain or acid deposition. It is formed due to the dissolution of CO2, SO2 and NO₂ which produce acid with rainwater.
SO2 + ½ O2 + H2SO4 → HSO4
3NO2 + H2O → 2HNO3 + NO

Q.13 What are the effects of Acid rain on the environment?

  1. It makes the soil, rivers and lakes slightly acidic.
  2. Acid rain corrodes steel, marbles, limestones, plants, plastics etc.
  3. By acidification of soil with acid rain. some nutrients of the soil leach out and the growth of plants are affected.

Q.14 What is the thickness of the ozone layer? Also, give its purpose.

The ozone layer is present in the stratosphere region and it is 15 km above the surface of the earth. The thickness of the ozone layer is 25 to 28 km. It filters most of the harmful rays present in the sunlight such as ultraviolet (UV) radiation.

Q.15 How ozone is produced?

Ozone is produced in tropical regions by the photochemical reactions of oxygen. Then it is transported to the polar regions. The concentration of ozone in the stratosphere is 350 DU.

Q.16 What is an ozone hole?

The decrease in the thickness of the ozone layer in the stratosphere is termed as ozone hole. The thickness of the ozone layer has been decreasing over the Antarctic region during the springtime since the mid-1970s

Q.17 How thickness of the ozone layer is reduced by chlorofluorocarbons?

Chlorofluorocarbons are used as a refrigerant in air conditioning. They slowly diffuse into the stratosphere and reacts with ozone. Chlorine radical is generated when ultraviolet radiations fall at CFCs. They decompose ozone due to the following reactions.
CFCl3 → CFCI₂°+ Cl°
Cl° + O3 →CIO°+ O2CIO° +O→ CI°+ O₂

Q.18 What are pesticides?

The substances which are used to kill pests are called pesticides. Pests harm crops. Pesticides are classified as:

  1. Insecticides which kill insects
  2. Herbicides, which kill unwanted plants
  3. Fungicides which control the growth of fungus

Q.19 Which is the main pollutant of leather tanneries and how wastewater can be treated to remove it?

The main pollutant of leather tanneries is chromium (VI) which is highly toxic and carcinogenic. The wastewater can be treated with a reducing agent to change chromium (VI) to chromium (III). Trivalent chromium (III) is treated with alkali to form Cr(OH)3 which is precipitated out.

Q.20 How the quality of water is determined? Write the names of the methods.

The quality of water can be determined by the following methods:

  1. Dissolved oxygen (DO)
  2. Chemical oxygen demand (COD)
  3. Biochemical oxygen demand (BOD)

Q.21 What is dissolved oxygen?

Dissolved oxygen is the most important oxidizing agent. Its concentration varies from 4-8 ppm. The organic matter which is present in polluted water is oxidized by this oxygen. Its value of less than 4 means water is polluted.

Q.22 What is biochemical oxygen demand?

The value of BOD is the amount of oxygen consumed as a result of the biological oxidation of dissolved organic matter in the sample. It is the capacity of organic matter in natural water to consume O2 within five days. The normal values range from 4-8 ppm.

Q.23 What is chemical oxygen demand?

The organic content of water which consumes oxygen during chemical oxidation is the chemical oxygen demand of water. The COD of water is determined directly by treating it with dichromate ion Cr2O7 -­2, which is a powerful oxidizing agent.

Q. 24 Name the processes by which the quality of water can be improved.

  1. Aeration
  2. Coagulation
  3. Removal of the hardness of water
  4. Chlorination

Q.25 What is the effect of aeration on water?

The aeration has the following advantages:

  1. It improves the oxygen demand in water.
  2. It removes the foul smell.
  3. Oxidizes water soluble Fe+2 ions to Fe+³ ions.

Q.26 What is coagulation? Which coagulants are used for the purification of water?

The process in which colloidal particles will join together to make larger groups which separate in the form of precipitates is called coagulation. The coagulants are; alum, aluminium sulphate and ferric salts. This process is used to remove the impurities which are in the form of colloids.

Q.27 What is solid waste management? What methods are usually used for the disposal of solid waste?

The disposal of domestic, commercial, and agricultural solid waste is called solid-waste management. The following methods are usually used for the disposal of solid waste.

  1. Dumping of waste in sea or river
  2. Landfill
  3. Incineration
  4. Recycling

Q.28 What is a Landfill?

Municipal solid waste is mainly disposed of by dumping it in a landfill. The landfill is a big hole in the ground. When the landfill becomes full of waste, then it is covered by soil and clay.

Q.29 What is leachate?

 The groundwater, which seeps into the landfill and liquid from waste percolates through the refuse (waste material) is called leachate.

Q.30 What is incineration?

The waste treatment process in which a solid is burnt at a high temperature ranging from 900-1000°C is called incineration.

Q.31 Explain the disposal of solid waste by incineration is better than other methods.

The incineration method has the following advantages:

  1. This method reduces the volume of solid waste.
  2. Combustible components i.e., paper and plastic provide fuel for the fire.
  3. In incineration, the heat of combustion may be used for producing steam which can run the turbine and electricity can be created.

Q.32 Name different methods for recycling plastics.

  1. Reprocessing
  2. Depolymerization
  3. Transformation

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