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Chemistry 2 Marks Questions

Environmental Chemistry · Gujarat Board (GSEB) STD 11 Science (GSEB - English Medium). 36 questions.

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Question 12 Marks
What are pesticides and herbicides? Explain giving examples.
Answer
  1. Pesticides : They are chemicals that are used to kill pests. They act by blocking the neurotransmission in the pest. e.g., DDT, BHC, etc.
  2. Herbicides : They are chemicals such as $\mathrm{NaClO}_3, \mathrm{Na}_3 \mathrm{AsO}_3$ which are used to control the population of weeds in the fields.
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Question 22 Marks
What do you mean by Biochemical Oxygen Demand (BOD)?
Answer
Organic matter in water is biodegradable, i.e., it can be decomposed by the action of bacteria. Now, these bacteria need oxygen to decompose the organic waste. Thus, the amount of oxygen required by bacteria to breakdown the organic matter in a certain volume of a sample of water is called Biological Oxygen Demand (BOD) for that sample.
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Question 32 Marks
Why is CO more toxic than $\mathrm{CO}_2$?
Answer
Carbon monoxide reacts with haemoglobin to form carboxy -haemoglobin which does not act as oxygen carrier, therefore, it is more harmful than $\mathrm{CO}_2$.
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Question 42 Marks
What are viable and non-viable particulates?
Answer
Viable particulates are small size living organisms such as bacteria, fungi, moulds, algae, etc. Non-viable particulates are formed by disintegration of large size materials or condensation of small size particles or droplets, e.g. mist, smoke, fume and dust.
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Question 52 Marks
Acid rain is known to contain some acids. Name these acids and where from they come in rain?
Answer
The acids commonly present in acid rain are nitric acid, sulphuric acid and carbonic acid. Nitric acid is formed by oxidation of nitric oxide present in air to $\mathrm{NO}_2$ & $\mathrm{NO}_3$, which dissolve in water also present in air. Sulphuric acid is formed by the oxidation of $\mathrm{SO}_2$ result in air to $\mathrm{SO}_3$ followed by dissolution in water. $\mathrm{CO}_2$ present in the acid dissolves in water to give carbonic acid.
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Question 62 Marks
What are polar stratospheric clouds (PSCs)?
Answer
Polar Stratospheric Clouds: PSC's are formed over Antarctica. They are of two types:
Type I clouds contain some solidified nitric acid trihydrate $\left(\mathrm{HNO}_3 3 \mathrm{H}_2 \mathrm{O}\right)$ formed at - $77^{\circ} \mathrm{C}$.
Type II clouds contain some ice, formed at $-85^{\circ} \mathrm{C}$.
These clouds play an important role in ozone depletion.
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Question 72 Marks
Why does rain water normally have a pH of 5.6? When does it become acid rain?
Answer
Rain has pH of about 5.6 due to dissolution of $\mathrm{CO}_2$, gas in water.
$\text{CO}_2+\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ \ \ \ \ }\text{H}_2\text{CO}_3$
$\text{H}_2\text{CO}_3\rightleftharpoons\text{2H}^++\text{CO}^{2-}_3$
When pH of rain falls below 5.6 it becomes acid rain.
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Question 82 Marks
A factory was started near a village. Suddenly villagers started feeling the presence of irritating vapours in the village and cases of headache, chest pain, cough, dryness of throat and breathing problems increased.
  1. Explain what could have happened?
  2. Give chemical reactions for the support of your explanation.
Answer
  1. The gases evolved from the factory caused headache, chest pain cough, dryness of throat and breathing problems.
  2. $2\text{C(s)}+\text{O}2\text{(g)}\xrightarrow{\ \ \ \ \ \ \ \ } 2\text{CO(g)}$
Carbon monoxide causes headache, nervousness, muscular weakness and weak eye sight.

$\text{S}+\text{O}_2\xrightarrow{\ \ \ \ \ }\text{SO}_2$

$2\text{SO}_2+\text{O}_2\xrightarrow{\ \ \ \ \ \ }\text{SO}_3$

Oxides of sulphur are irritating and can cause cough, dryness of throat and breathing problems.
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Question 92 Marks
Why 'photochemical smog' is called so?
Answer
It is because it is formed as a result of photochemical reaction (i.e. in the presence of sunlight) between oxides of nitrogen and hydrocarbons.
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Question 102 Marks
Why is hand pump water not considered as drinking water in these days? Explain.
Answer
Hand pump water is ground water. It is getting contaminated by fertilizers, pesticides, herbicides which are soluble in rain water and pass through the soil and enter underground water and make it unfit for drinking. Presence of Arsenic, excess of fluoride ions, heavy metals also make it unfit for drinking.
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Question 112 Marks
What is the role of $\mathrm{CO}_2$ in the 'green house effect'?
Answer
Heat from the sun after being absorbed by the earth is re-emitted by the earth and absorbed by $\mathrm{CO}_2$ which then radiate it back to the earth, thus, maintaining the constant temperature of the earth.
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Question 122 Marks
What is the importance of measuring BOD of a water body?
Answer
BOD is a measure of level of pollution caused by organic biodegradable material present in the sample of given water. Low value of BOD indicates that water contains less organic matter.
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Question 132 Marks
What are biodegradable and non biodegradable pollutants? Give are example of each.
Answer
Those pollutants which are decomposed by micro organism are called biodegradable pollutants. e.g. detergents with linear alkyl chain are biodegradable water pollutants. Soaps are also biodegradable.
Non-biodegradable pollutants: Those pollutants which are not decomposed by micro-organisms are called non-biodegradable pollutants, e.g. Detergents with branched alkyl chain, DDT (insectide) are non-biodegradable.
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Question 142 Marks
Every year some people die by being in room containing a faulty heater that uses coal, or oil? How might the death occur?
Answer
The death occurs due to carbon monoxide which reacts with haemoglobin to form carboxy haemoglobin which does not act as oxygen carrier.
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Question 152 Marks
In winter, Sonia's parent burn coal in Angithi to keep the room warm. One late right, they wanted to keep angithi with burning coal inside the room. Sonia stopped them for doing so. She explained about the incomplete combustion of coal and harmful effects of burning coal in deficiency of oxygen.
Name the gas formed by incomplete combustion of coal. Also write the chemical reaction involved.
Suggest a reason as to why this gas is poisonous.
Answer
  1. Carbon monoxide is formed by incomplete combustion of coal.
$2\text{C(s)}+\text{O}_2\text{(g)}\xrightarrow{\ \ \ \ \ \ \ }2\text{CO(g)}$
  1. Carbon monoxide reacts with haemoglobin to form carboxy haemoglobin due to which delivery of oxygen to the organs and tissues is blocked. It results in headache, breathlessness, asphyxia (cardio vascular disorder) and even death in high concentration.
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Question 162 Marks
What is pneumoconiosis?
Answer
It is lung disease such a lung cancer, bronchital asthma, chronic brochities, etc caused by small sized particulates which enter into lung through nose and provide large surface area for adsorption of carcinogenic substances.
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Question 172 Marks
Ozone gas is heavier than air. Why does ozone layer not settle down near the earth?
Answer
Ozone layer is formed at an altitude of 25-30km from earth's surface by action of U.V. light on oxygen.
At this altitude force of gravitation is negligible that is why ozone does not settle near the earth.
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Question 182 Marks
Why are aquatic species more comfortable in cold water than warm water?
Answer
It is because dissolved oxygen is more in cold water than warm water.
Solubility of gas in liquid decreases with increase in temperature.
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Question 192 Marks
Photochemical smog occurs in warm, dry and sunny climate. Among $\mathrm{SO}_2$, $\mathrm{NO}_2$, $\mathrm{O}_3$ and hydrocarbons which one is not amongst the components of photochemical smog and why?
Answer
$\mathrm{SO}_2$ is reducing in nature and not obtained in sunny and dry climate. So, it is not a component of photochemical smog. It is a component of classical smog.
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Question 202 Marks
Why is ozone depletion mainly over Antartica?
Answer
This is because in other parts of stratosphere, chlorine free radicals combine away to form harmless products.
It Antarctica, compounds formed are converted into chlorine free radical again which cause ozone depletion.
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Question 212 Marks
A trainee pilot was flying his plane in stratosphere. His senior advised him not to fly the aeroplane in the stratosphere.
Answer the following:
  1. In your opinion, why the senior pilot advised his trainee pilot not to fly his plane in the stratosphere.
  2. Write the possible reaction affecting stratosphere.
Answer
  1. It is because No (nitric oxide) released by aeroplane will deplete ozone layer that is why aeroplane should not be flying in stratosphere.
  2. $\text{N}_2+\text{O}_2\xrightarrow{\ \ \ \ }2\text{NO}$ [nitric oxide]
$2\text{NO}+\text{O}_3\xrightarrow{\ \ \ \ \ }2\text{NO}_2+\text{O}_2$ [ozone depletion]
No reacts with ozone to form $\mathrm{NO}_2$ and $\mathrm{O}_2$.
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Question 222 Marks
  1. Name the two greenhouse gases.
  2. What is global warming?
Answer
  1. Carbon dioxide and methane are green house gases.
  2. Global warming when concentration of green house gases like $\mathrm{CO}_2$ increases, these gases trap infrared radiations of sun and increase the temperature of the earth i.e. increase green house effect causing global warming. Global warming leads to abnormal changes in climate.
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Question 232 Marks
How can you apply green chemistry for the following:To control photochemical smog.
Answer
The most straight forward way to reduce or prevent the formation of photochemical smog is to minimise the release of oxides of nitrogen and hydrocarbons to the atmosphere. The following methods can be applied to minimise the oxides of nitrogen and hydrocarbons.
  1. By fitting efficient catalytic converters in automobiles, the harmful gases are converted catalytically into harmless gases.
  2. By spraying certain compounds into the atmosphere which generate free radicals that readily combine with the free radicals that initiate the reactions forming toxic compounds of the photochemical smog. The compound diethyl hydroxylamine has been found to possess smog inhibiting property.
  3. Certain plants such as pinus, jiniparus, pyrus, vitis, etc., can metabolise oxides of nitrogen.
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Question 242 Marks
What is greenhouse effect?
Answer
The increase in temperature of atmosphere due to presence of gases like $\mathrm{CH}_4$, $\mathrm{CO}_2$ and water vapours which absorb infrared radiation is called greenhouse effect.
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Question 252 Marks
How can you apply green chemistry for the following:To reduce the consumption of petrol and diesel.
Answer
Instead of petrol and diesel, the use of CNG (Condensed Natural Gas) and LNG (Liquefied Natural Gas) has been preferred as they are pollution free fuels. The other sources such as hydrogen, ethyl alcohol, etc., can be tried in place of petrol and diesel.
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Question 262 Marks
  1. What do you mean by sink? Give one example.
  2. What is the sink for hydrocarbons and why?
Answer
  1. Medium present in the environment that take up some amount of certain pollutants is called sink e.g. oceans act as sink for $\mathrm{SO}_2$, $\mathrm{CO}_2$ and $\mathrm{NO}_x$.
  2. Chemical and photochemical reactions act as sink for hydrocarbons as these get decomposed in these reactions.
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Question 272 Marks
$\mathrm{CO}_2$ is inert and harmless gas, yet it is thought to be a serious pollutant. Explain.
Answer
$\mathrm{CO}_2$ absorbs infrared radiations from atmosphere which lead to global warming. If $\mathrm{CO}_2$​​​​​​​ level increases beyond 0.03%, the natural greenhouse balance may get disturbed. $\mathrm{CO}_2$​​​​​​​ is a major contributor to global warming, therefore, it is considered as serious pollutant.
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Question 282 Marks
A person was using water supplied by Municipality. Due to shortage of water he started using underground water. He felt laxative effect. What could be the cause?
Answer
The laxative effect is observed only when the sulphates present in water have concentration greater than 500ppm. Otherwise at moderate levels it is harmless.
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Question 292 Marks
What are primary and secondary pollutants of air?
Answer
Primary pollutants are those which remain as such in atmosphere e.g., NO.
Secondary pollutants are formed by reaction between primary pollutants e.g., PAN (peroxy acetyl nitrate).
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Question 302 Marks
Explain giving reasons "The presence of CO reduces the amount of haemoglobin available in the blood for carrying oxygen to the body cells."
Answer
Co combines with haemoglobin (Hb) of the red blood corpuscles (RBCs) about 300 times more readily than oxygen to form carboxyhaemoglobin complex, as follows
$\text{Hb}+\text{CO}\rightleftharpoons\text{HbCO}$
Thus, Hb is not able to combine with oxygen to form oxyhaemoglobin complex and hence, transport of oxygen to different body cells does not occur.
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Question 312 Marks
Dissolved oxygen in water is very important for aquatic life. What processes are responsible for the reduction of dissolved oxygen in water?
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Question 322 Marks
How can you apply green chemistry for the following:To reduce use of synthetic detergents.
Answer
To reduce the use of synthetic detergents as cleaning agent, emphasis should be made on the use of soaps prepared of vegetable oils. The vegetable oils are biodegradable while detergents do not undergo biodegradation.
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Question 332 Marks
What is meant by polar vortex?
Answer
Polar Vortex: When polar stratospheric clouds are formed over Antarctica during winters, stable wind patterns, in the stratosphere are called polar vortex which encircle the continent.
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Question 342 Marks
Why is $\mathrm{SO}_2$ considered air pollutant?
Answer
$\mathrm{SO}_2$ reacts with $\mathrm{O}_2$ and $\mathrm{H}_2\mathrm{O}$ to produce acid rain. $\mathrm{SO}_2$ also causes problem in breathing and irritation in eyes.
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Question 352 Marks
Why there is ozone depletion mainly over Antarctica?
Answer
This is because in other parts of the stratosphere, chlorine free radicals combine away with NO or $\mathrm{CH}_4$ but in Antarctica, the compounds formed are converted back into chlorine free radicals which deplete the ozone layer.
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Question 362 Marks
How can you apply green chemistry for the following:To avoid use of halogenated solvents in drycleaning and that of chlorine in bleaching.
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