Solved Exercise, Chem-12, Ch-16


Q.01: Fill in the blanks:

(i) Only _______ of the total earth’s water resources are available as fresh water. (1%)

(ii) ________ is a smaller unit of biosphere which consists of community of organisms and their interaction with environment. (ecosystem)

(iii) Carbon monoxide is highly poisonous gas and causes suffocation if inhaled, it binds blood _________ more strongly than oxygen thus excluding oxygen from normal respiration. (haemoglobin)

(iv) The elevated concentration of _______ is harmful for fish as it clogs the gills thus causing suffocation. (aluminium)

(v) The ozone layer in the _______ surrounds the globe and filters most of the harmful UV rays in the sunlight before they could reach the earth. (stratosphere)

(vi) The presence of _______ in livestock waste can contaminate surface and ground water causing various infectious diseases. (chemical and bacterial content)

(vii) The substances which can directly kill the unwanted organisms are called _______. (pesticides)

(viii) _______ is frequently used to disinfect water. (chlorine)

(ix) Incineration is not a clean process because it produces air pollution and toxic ______. (ash)

(x) A process in which some of the used or waste materials are not discarded after their initial use but are processed so that it can be used again is called ______. (recycling)

Q.02: Indicate True or False:

(i) Half of the mass of the atmosphere is concentrated in lower 10 km. (FALSE)

CORRECT: Half of the mass of the atmosphere is concentrated in lower 5.6 km.

(ii) The oceans cover approximately 71 percent of the earth. (TRUE)

(iii) The volcanoes produce 55% of SO2. (FALSE)

CORRECT: The volcanoes produce 67% of SO2.

(iv) The reducing smog is due to the presence of sulphur dioxide. (FALSE)

CORRECT: The reducing smog is due to the presence of nitric oxide.

(v) Ozone is produced in the polar regions by the photochemical reaction of oxygen. (TRUE)

(vi) The temperature in the troposphere decreases with the increasing altitude from 15 to -56° C. (TRUE)

(vii) Incineration is a waste treatment process in which solid waste is dumped in a land fill. (FALSE)

CORRECT: Incineration is a waste treatment process in which solid waste is burnt at high temperature, ranging from 900oC to 1000oC.

(viii) Acid rain is due to the presence of oxides of sulphur and nitrogen which get mixed with the rain water. (TRUE)

(ix) The heavy metals have a safe limit where they are not toxic. (FALSE)

CORRECT: The heavy metals are highly toxic and don’t have any safe limits.

(x) The reprocessing of the plastics is to convert back to their components by a chemical or thermal process so that these can be used again. (TRUE)

Q.03: Multiple choice questions.

(i) The pH range of the acid rain is:

(a)   7 — 6.5

(b)   6.5 — 6

(c)   6 — 5.6

(d)   Less than 5

EXPLANATION: Normal rain water is slightly acidic with pH 5.6, due the presence of CO2 in atmosphere. But when acidic pollutant gases such as SO2, SO3, NO2 etc., are present in air, the rain water becomes more acidic. Its pH decreases below 5. Such a rain is said to be truly acidic.

(ii) Peroxyacetyl nitrate (PAN) is an irritant to human beings and it affects:    

(a)   Eyes

(b)   Ears

(c)   Stomach

(d)   Nose

EXPLANATION: Peroxyacetyl nitrate (PAN) is a secondary pollutant which causes irritation in eyes.

(iii) To avoid the formation of toxic compounds with chlorine, which substance is used for disinfecting water?

(a)   KMnO4

(b)   O3

(c)   Alums

(d)   Chloramines

EXPLANATION: To avoid the formation of toxic compounds (such as chloroform, chlorinated phenols etc.) with chlorine, ozone or chlorine dioxide is used for the disinfection of water.

(iv) A single chloride free radical can destroy how many ozone molecules?

(a)   100

(b)   100000

(c)   10000

(d)   10

EXPLANATION: Chlorofluorocarbons when subjected to ultraviolet radiations in stratosphere, generate Clo free radicals. These radicals react with O3 and convert it into O2 molecules through photochemical reactions. Thus, they play a role in decreasing the concentration of atmospheric ozone. A single chloride free radical can destroy upto 100,000 ozone molecules.

(v) Fungicides are the pesticides which:

(a)   Control the growth of fungus

(b)   Kill insects

(c)   Kill plants

(d)   Kill herbs

EXPLANATION: Fungicides are the pesticides which control the growth of fungus and thus protect crops from fungal diseases and stored food from fungal attack.

(vi) Ecosystem is a smaller unit of:

(a)   Lithosphere

(b)   Hydrosphere

(c)   Atmosphere

(d)   Biosphere

EXPLANATION: Ecosystem is a smaller unit of biosphere which includes community of living organisms living at a place along with several abiotic factors.

(vii) The main pollutant of leather tanneries in the waste water is due to the salt of:

(a)   Lead

(b)   Chromium (VI)

(c)   Copper

(d)   Chromium (III)

EXPLANATION: Chromium is used in the tanning process to convert raw hides and skins into leather, a process known as chrome tanning. However, the hexavalent chromium is a toxic and carcinogenic compound. If not managed properly, the discharge of chromium-containing wastewater from tanneries can contaminate water sources, soil, and aquatic ecosystems, leading to harmful ecological impacts.

(viii) In purification of potable water, the coagulant used is: 

(a)   Nickel sulphate

(b)   Copper sulphate

(c)   Barium sulphate

(d)   Alum

EXPLANATION: During the purification of water, many suspended particles are separated by means of coagulants such as alum, aluminium sulphate or ferric salts etc. When alum is used in alkaline medium, it forms gelatinous aluminium hydroxide which adsorbs and separates the suspended particles from raw water.

(ix) The temperature in the non-rotating chamber in the incineration of industrial and hazardous waste process has a range:

(a)   900 to 1000oC

(b)   250 to 500oC

(c)   950 to 1300oC

(d)   500 to 900oC

EXPLANATION: In non-rotating chamber, the temperature from 950°C to 1300°C is maintained. At this temperature, organic molecules are completely destroyed.

(x) Newspaper can be recycled again and again by how many times?

(a)   2

(b)   3

(c)   4

(d)   5

EXPLANATION: In recycling process, the fibres of the newspaper become shorter, so it can be recycled again and again maximum for five times.

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