Tag: chemistry

Questions Related to chemistry

Which of the following water pollutants encourage the formation of algae?

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  1. Insecticides

  2. Heavy metals

  3. Plant nutrients

  4. Sediments

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Correct Option: C
Explanation:

Explosive growth of plants and algae is a response to the addition of excess nutrients, mainly phosphates, which induces, the decaying of which consumes oxygen from the water causing water pollution. Phosphates are among the major nutrients that is required by plants for growth. 

Measurement of rate of oxygen utilisation by the unit volume of polluted water over a period of time is referred to as:

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  1. fermentation

  2. chemical oxygen demand

  3. oxidation potential

  4. biological oxygen demand

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Correct Option: D
Explanation:

Biochemical oxygen demand is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period. The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at $20^{\circ}C$ and is often used as a surrogate of the degree of organic pollution of water.

BOD is similar in function to chemical oxygen demand (COD), in that both measure the amount of organic compounds in water. However, COD is less specific, since it measures everything that can be chemically oxidized, rather than just levels of biodegradable organic matter

Sewage water is purified by

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  1. microorganisms

  2. light

  3. fish

  4. aquatic plant

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Correct Option: A
Explanation:

In general, all common methods of sewage purification use sedimentation processes by which solids (sludge) sink to the bottom – in some cases this primary sludge is removed for further treatment.

After this comes the secondary or biological treatment of sewage purification, this involves biological processes and the use of microorganisms that “eats” away a lot of the hazardous contaminants. Use of oxygen by various implementation techniques is very important.

After the secondary stage of sewage purification comes final settlement of biological solids and then a tertiary treatment that removes even better the rest of the biological and organic materials in the water. 

Potassium permanganate is used for purifying drinking water, because:

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  1. it is a sterilising agent

  2. it dissolves the impurities of water

  3. it is a reducing agent

  4. it is an oxidising agent

Show answer
Correct Option: D
Explanation:

Potassium permanganate is an inorganic chemical compound and it is a strong oxidizing agent. Potassium permanganate is used in water treatment to remove odor-causing compounds and is also used to remove iron and manganese in water.

Permanent hardness of water may be removed by the addition of:

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  1. sodium carbonate

  2. alum

  3. potassium permanganate

  4. lime

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Correct Option: A
Explanation:

Sodium carbonate, $Na _2CO _3$, is also known as washing soda. It can remove temporary and permanent hardness from water. Sodium carbonate is soluble but calcium carbonate and magnesium carbonate are insoluble. The water is softened because it no longer contains dissolved calcium ions and magnesium ions.

Which of the following activity causes water depletion?

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  1. Increasing population

  2. Increasing industries

  3. Agricultural activities

  4. All of the above

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Correct Option: D
Explanation:

Factors responsible for the depletion of water table-

(i) Population- due to the increase in population, the open area decreases in order to fulfill the demands such as the house, shops, roads, pavements, office, etc, thereby cutting trees resulting in deforestation which decreases the open area for the seepage of water into the ground.
(ii) Agriculture- for agricultural process water is needed for irrigation for which ground water is used which in turn decreases the water table.
(iii) Most of the people keep the taps open though water is not in use, this is how wastage of water resources occur.
Many industrial practices cause water pollution, for eg-mining, drilling. Oil spills also cause water pollution. These type of pollution leads to depletion of water.

Which of the following is/are correct statement(s) regarding increasing population as a reason for water scarcity?

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  1. Increasing population creates demand for construction of houses, shops, offices, roads and pavements.

  2. This decreases the open areas like parks, and playgrounds.

  3. This in turn decreases the seepage of rainwater into ground.

  4. A pukka floor does not allow water to seep in easily, while in a grass lawn water seeps through in no time.

Show answer
Correct Option: A,B,C,D
Explanation:

All of the following are correct statements regarding increasing population as a reason for water scarcity.
Increasing population creates demand for construction of houses, shops, offices, roads and pavements.
This decreases the open areas like parks, and playgrounds.
This in turn decreases the seepage of rainwater into ground.
A pukka floor does not allow water to seep in easily, while in a grass lawn water seeps through in no time.

Which of the following is a measurement of water pollution ?

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  1. PSC

  2. PCB

  3. BOD

  4. COD

Show answer
Correct Option: C
Explanation:

  1. Polar stratospheric clouds (PSCs) are the medium on which reservoir chlorine compounds are converted into ozone-destroying chlorine radicals, they are essentially two types of  PSC known as type 1 and type 2.
  2. Polychlorinated biphenyl (PCBs) is a group of organic compounds used in the manufacture of plastics, as lubricants, in transformers, adhesives and so forth. They are highly toxic to aquatic life and persist in the environment for long periods of time. They can accumulate in food chains and may produce harmful side-effects at high concentrations.
  3. Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed (i.e demanded ) by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.
  4. Chemical oxygen demand (COD) is defined as a  measure of the oxygen equivalent of the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant. Therefore, BOD is a measurement of water pollution.

Option (C) is correct.

Which of the following statement is false?

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  1. Lower the concentration of D.O., the more polluted is the water sample

  2. The tolerable limit of lead in drinking water is $50\ ppm$

  3. Water is considered pure if it has BOD less than $5\ ppm$

  4. In COD determination, the pollutants resistant to microbial oxidation are not oxidized by an oxidizing agent like $K _{2}Cr _{2}O _{7}$

Show answer
Correct Option: D
Explanation:

In COD, the degradation is affected by an oxidizing agent, $K _2 Cr _2 O _7.$ COD  is a measure of amount of oxygen , required to degrade or breakdown the organic matter. 

Biochemical Oxygen Demand (BOD) is a measure of organic material present in water. BOD value less than 5 ppm indicates a water to be ________.

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  1. rich in dissolved oxygen

  2. poor in dissolved oxygen

  3. highly polluted

  4. not suitable for aquatic life

Show answer
Correct Option: A
Explanation:

Clean water has BOD which is less than 5 ppm. If it is equal to or more than 12 ppm, then the water is considered as polluted. So this indicates water be rich in dissolved oxygen, that helps the microorganisms to oxidize inorganic and organic materials.