Environmental Chemistry MCQ Quiz - Objective Question with Answer for Environmental Chemistry - Download Free PDF

Concept:

Wet Chemical Synthesis of Nanomaterials

• Wet chemical synthesis of nanomaterials typically involves several key steps, including precursor preparation, hydrolysis, condensation, aging, drying, and sometimes calcination.
• The progression of these steps can be outlined as follows:
  1. Formation of oxide or alcohol-bridged network (Hydrolysis and Condensation)
  2. Aging of the gel
  3. Dehydration
  4. Drying of the gel

Explanation of the Steps:

• Formation of oxide or alcohol-bridged network: This involves the hydrolysis of precursor molecules followed by condensation to form a network of interconnected particles. This is the initial step in the sol-gel process.
• Aging of the gel: After the gel network is formed, it may be allowed to age to strengthen the network and promote further linking within the gel.
• Dehydration: Removal of water or solvent from the gel, often occurring simultaneously with aging as the gel structure consolidates.
• Drying of the gel: The final step involves drying the gel to remove any remaining solvent, resulting in the formation of a dry gel or xerogel. This is the culminating step before any further post-processing such as calcination.

Based on this understanding, the last step in the wet chemical synthesis of nanomaterials is Drying of the gel

CONCEPT:

Green Chemistry in Nanoparticle Synthesis

• Green chemistry aims to design chemical products and processes that reduce or eliminate the use and generation of hazardous substances.
• It emphasizes the use of environmentally benign solvents, renewable feedstocks, and energy efficiency, among other principles.

EXPLANATION:

• Chemical vapor deposition (Option 1) often involves the use of toxic and hazardous gases.
• Sol-gel process (Option 2) can use organic solvents that may be harmful, although some variations use water-based systems.
• Biological methods (Option 3) utilize natural organisms like bacteria, fungi, and plants which act as eco-friendly factories for nanoparticle synthesis, minimizing the need for harmful solvents and reagents.
• Physical vapor deposition (Option 4) typically requires high energy input and may involve hazardous materials.
• Biological methods align best with green chemistry principles by using safe, renewable, and biodegradable resources.

Therefore, the method that primarily benefits from Green Chemistry principles in the synthesis of nanoparticles is option 3, Biological methods.

CONCEPT:

Green Chemistry and Solvent-Free Reactions

• Green chemistry emphasizes the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances.
• A key principle of green chemistry is to conduct reactions under solvent-free conditions whenever possible to minimize the environmental impact.

EXPLANATION:

• Supercritical carbon dioxide is specifically known for enabling reactions under solvent-free conditions.
• Supercritical carbon dioxide (scCO₂) is a state of carbon dioxide where it is held at or above its critical temperature and pressure, making it neither a liquid nor a gas but possessing properties of both.
• scCO₂ is an environmentally friendly solvent that can replace traditional organic solvents, reducing the release of volatile organic compounds (VOCs).
• Reactions conducted in scCO₂ often do not require additional solvents, thus aligning with the principles of green chemistry.

Therefore, the correct answer is option 1, supercritical carbon dioxide.

CONCEPT:

Key Challenges in Large-Scale Implementation of Green Synthesis

• Green Synthesis refers to environmentally friendly chemical processes and methodologies that minimize waste and reduce the use of hazardous substances.
• While Green Synthesis offers numerous benefits, its large-scale implementation faces several challenges.

EXPLANATION:

• Difficulty in minimizing waste by-product formation
• Minimizing waste by-product formation is a challenge, but advancements in process optimization and catalytic methods have provided solutions.
• Lack of understanding of the environmental impact of new materials
• Understanding the environmental impact of new materials is important, but it is not the primary challenge for large-scale implementation.
• High energy requirements for scaling up the processes
• High energy requirements for scaling up the processes is a challenge, but innovations in energy-efficient methods are being developed.
• Difficulty in sourcing renewable feedstocks
• is the key challenge because:
  • Renewable feedstocks are essential for sustainable Green Synthesis processes.
  • Consistent and reliable sourcing of renewable feedstocks can be difficult due to factors like seasonal availability, geographic limitations, and competition with food production.

Therefore, the key challenge in the large-scale implementation of Green Synthesis for industrial processes is the difficulty in sourcing renewable feedstocks.

CONCEPT:

Green Chemistry Principle: Designing Safer Chemicals

• Green Chemistry aims to design chemical products and processes that reduce or eliminate the use and generation of hazardous substances.
• The principle of "Designing Safer Chemicals" focuses on creating chemicals with minimal toxicity, posing less risk to human health and the environment.
• This principle emphasizes the need for chemicals that are effective and safe for use in both industrial and consumer applications, without causing harm to living organisms or ecosystems.

EXPLANATION:

•  "Creating chemicals with minimal toxicity that pose less risk to human health and the environment" is the correct answer. This aligns with the goal of Green Chemistry to ensure the safety of chemicals in their production, use, and disposal.
• While economic viability is important, Green Chemistry prioritizes environmental and health considerations over mere cost-effectiveness.
•  Reducing manufacturing costs at the expense of environmental impact goes against the core principles of Green Chemistry, which advocates for sustainability.
• The aesthetic properties of chemicals are not the primary focus in Green Chemistry, which aims to reduce environmental harm and toxicity, rather than enhancing appearance.

The correct answer is: A) Creating chemicals with minimal toxicity that pose less risk to human health and the environment.

Concept:

In photochemical smog, nitrogen oxides, and hydrocarbons are primary pollutants whereas ozone and acrolein are secondary pollutants.

A chemical reaction between solar ultraviolet radiation and an atmosphere polluted with hydrocarbons and oxides of nitrogen causes photochemical smog. This is especially common from automobile exhaust. Smog can happen both during the day and at night, but photochemical smog only happens in the presence of sunlight.

Photochemical smog is composed of primary and secondary pollutants. Primary pollutants, which include nitrogen oxides and volatile organic compounds, are introduced into the atmosphere via vehicular emissions and industrial processes.

Photochemical smog is a type of smog produced when ultraviolet light from the sun reacts with nitrogen oxides in the atmosphere. It is visible as a brown haze, and is most prominent during the morning and afternoon, especially in densely populated, warm cities.

Correct answer: 1) 

Concept:

• Dinitrogen and dioxygen are the stable forms of nitrogen and oxygen atoms respectively.
• Dinitrogen has a very high bond enthalpy as it has triple bond.
• Due to this reason, it is practically inert at room temperature.
• However, the reactivity of dinitrogen increases as the temperature is increased.
• Dioxygen is a very reactive gas but due to presence of double bond the bond enthalpy of dioxygen is very high.

Explanation:

• Dinitrogen and dioxygen are main constituents of air (N2=78.08%,O2=20.95%" id="MathJax-Element-4-Frame" role="presentation" tabindex="0">N₂=78.08%,O₂=20.95%)
• They do not react with each other to form oxides of nitrogen.
• This is because dinitrogen has a triple bond between the two nitrogen atoms and for dinitrogen and dioxygen to react, this triple bond needs to be broken.
• But the bond dissociation energy that is the energy required to break the bond is very high for dinitrogen.
• This high amount of energy cannot be found in the atmosphere.
• Therefore, for this reaction to take place, it would require very high temperatures to generate enough energy to break the triple bond in dinitrogen.

Conclusion:

Thus, dinitrogen and dioxygen are main constituents of air but these do not react with each other to form oxides of nitrogen because the reaction is endothermic and requires very high temperature.

Additional Information

Correct answer: 1)

Concept:

• Ozone is an important constituent of the stratosphere at altitudes between 15 and 25 km.
• It is formed in the atmosphere by the decomposition of oxygen by ultra-violet radiation from the sun having wavelength shorter than 260 nm. 
• Recently in 1980, scientists have observed a hole in the ozone blanket covering the upper atmosphere around Antarctica.
• Recent observations have also shown that the ozone layer diminishes over the south pole in spring during August-September to a greater extent year after year.
• This depletion of the protective blanket of ozone will cause a damaging effect because harmful ultra-violet rays can reach earth through this hole.
• The increased level of ultra-violet rays will result in damage to plants, animals, human beings and even matter posing great threat to ecosystem over the globe.

Explanation:

• The thick layer of ozone is called ozone blanket because it is very effective in absorbing harmful ultra violet rays given out by the sun.
• Therefore, the ozone layer is also known as protective shield.
• Ozone is also one of the greenhouse gas.
• The contribution of O₃  to the greenhouse effect is about 8 to 10%.
• About 75% of solar energy is absorbed by the surface of the earth, and the rest is radiated back to the atmosphere.
• This heat traps gases like CO₂, CH₄, O₃, CFC’s and H₂O  present in the atmosphere and adds to the heat of the atmosphere, causing global warming.

Conclusion:

Thus, the statement Ozone is not responsible for green house effect is wrong.
 

Correct answer: 3) 

Concept:

• Smog is a mixture of smoke, dust particles and small drops of fog. It is a major air pollutant in big cities.
• Smog is of two types.
• Classical Smog:  This type of smog is formed by the combination of smoke, dust and fog containing sulphur dioxide from polluted air.
• This is also called chemical smog. Chemically, it is a reducing mixture so it is also called reducing smog. 
• Photochemcial Smog :This type of smog is formed by the combination of smoke, dust and fog with an air pollutant in the atmosphere as a result of photochemical reaction. 
• It can cause coughing, wheezing bronchial constriction and Peroxyaetyl nitrates and aldehydes found in smog are eye irritants.
• Materials are also adversely affected by some smog components.

Explanation:

• Photochemical smog occurs in warm, dry and sunny climate.
• The main components of the photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories.
• Photochemical smog has high concentration of oxidising agents and is, therefore, called as oxidising smog.
• This occurs in the months of summer when NO₂ and hydrocarbons are present in large amounts in the atmosphere.
• Concentration of O₃, PAN, aldehydes and ketones increases up in the atmosphere.
• SO₂ is not responsible for photochemical smog.
• NO₂  absorbs u.v. radiations and the entire cycle starts again.
• Both NO₂ and O₃ are strong oxidizing agents and can react with unburnt hydrocarbons (from exhaust of automobiles) to form organic free radicals.
• The formation of organic free radicals results into a number of chain reactions producing many undesirable compounds (such as formaldehyde, acrolein, organic peroxides, organic hydroperoxides, peroxyacyl nitrates etc.) which constitute photochemical smog. 

Conclusion:

Thus, SO₂ is not the components of photochemical smog.

The correct answer is: "It has low concentration of oxidising agent."

Key Points

• Photochemical Smog Characteristics:
  • Photochemical smog, also known as "oxidizing smog," forms when sunlight reacts with pollutants like nitrogen oxides (NO_x) and volatile organic compounds (VOCs).
  • It contains a high concentration of oxidizing agents, such as ozone (O₃), peroxyacetyl nitrate (PAN), and other free radicals, which are harmful to both health and the environment.
  • This high concentration of oxidizing agents leads to respiratory problems, eye irritation, and damage to plants and materials.
• Control Measures for Photochemical Smog:
  • Reducing the release of precursors such as NO₂, hydrocarbons, and ozone is critical in controlling photochemical smog.
  • Improved vehicle emission standards, reduction in industrial emissions, and use of cleaner fuels are effective control measures.
  • Certain plants, such as pinus, neem, and tulsi, can help mitigate smog by absorbing pollutants and improving air quality.
• Incorrect Statement:
  • The statement "It has low concentration of oxidising agent" is incorrect because photochemical smog is characterized by a high concentration of oxidizing agents, which differentiates it from other types of smog, such as reducing smog (London smog).

Additional Information

• Formation of Photochemical Smog:
  • Occurs primarily in urban areas with high vehicular traffic and industrial activity under sunny conditions.
  • The reaction involves nitrogen oxides and hydrocarbons in the presence of sunlight, producing secondary pollutants like ozone and PAN.
• Impact of Photochemical Smog:
  • Adversely affects human health by causing respiratory problems, reduced lung function, and eye irritation.
  • Damages crops, reducing agricultural productivity, and negatively impacts plant health.
  • Causes the deterioration of materials like rubber, plastics, and metals due to the oxidative action of smog.
• Control Methods:
  • Encouraging public transportation and use of alternative fuels like CNG to reduce vehicular emissions.
  • Implementing stricter emission regulations for industries and vehicles.
  • Planting more vegetation in urban areas to naturally filter pollutants.

Concept:

Sun emits UV-radiations, which according to following EM categorisation have the wavelength range from 1 nm to 400 nm.

Concept:

N₂ molecule has minimum role in the formation of photochemical smog. While CH₂ = O, O₃ and NO has major role. When fossil fuels are burnt, a variety of pollutions are emiited.

Two of them are hydrocarbons (unburnt) and NO. When these pollutants build upon high levels, a chain reaction occurs from their interaction with sunlight. The reactions involved in the formation of photochemical smog are as follows;

\({\rm{N}}{{\rm{O}}_2}\left( {\rm{g}} \right)\mathop \to \limits^{{\rm{hv}}} {\rm{NO}}\left( {\rm{g}} \right) + {\rm{O}}\left( {\rm{g}} \right)\)

O (g) + O₂ (g) ⇌ O₃ (g)

NO (g) + O₃ (g) → NO₂ (g) + O₂ (g)

O₃ (g) Reacts with unburnt hydrocarbons to produce chemicals such as formaldehyde, acrolein and PAN.

Concept:

Things float when they are positively buoyant or less dense than the fluid in which they are sitting.

Dichloromethane, DCM (CH₂Cl₂) is heavier (density = 1.3266g cm^-3)) than water (density = 1 g cm^-3).

So, DCM and H₂O will stay as lower and upper layer respectively in the separating funnel (S.F).

Correct answer: 1 and 2)

Concept:

• Gases such as CO₂ , NO₂ , CFCs (chloro fluorocarbons) allow sun rays to pass through them but then absorb and reradiate the heat back towards the earth. These are therefore termed as green house gases.
• Radiations (ultra violet) from the sun penetrate the earth’s atmosphere and reach earth.
• The surface of earth partially absorbs the radiations.
• The rest is re-radiated as infrared radiation from the earth’s surface.
• In polluted air, molecules of CO₂, CH₄, CFCs, N₂O, O₃ and water vapours are present.
• These gases can absorb infrared radiations but cannot absorb the ultra violet radiations.
• Energy of these trapped radiations raise the temperature of earth and its atmosphere.
• Thus if proportion of green house gases increases in the atmosphere heat trapped by them will raise the temperature of the earth and will cause global warming.
• Greenhouse effect leading to global warming shall have severe effects on rainfall, sea level, plant and animal growth. 

Explanation:

• Global warming is the rate at which solar radiation are arriving the earth remain constant but the amount CO₂ in the air increaes.
• The heat radiated back to the earth will increase consequently.
• The temperature of the earth surface will increase.
• This increase in temperature will disturb the thermal balance on the earth and could car glaciers and ice caps to melt.
• About 75% of the solar energy reaching the earth is absorbed by the earth's surface, which increases the temperature.
• The rest of the heat radiates back to the atmosphere.
• The average global temperature will increase to a level which may lead to melting of polar ice caps and flooding of low lying area all over the earth.
• Increase in the global temperature increases the incidence of infectious diseases like dengue, malaria, yellow fever, sleeping sickness etc.

Conclusion:

Thus, the consequences of global warming may be increase in average temperature of the earth and melting of Himalayan Glaciers.

Additional Information

Correct answer: 2,3 and 4)

Concept:

• Acid rain, or acid deposition, is a broad term that includes any form of precipitation with acidic components, such as sulfuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms.  
• This can include rain, snow, fog, hail or even dust that is acidic. 
• Acid Rain or different sorts of precipitation that contain raised hydrogen particle levels, making it acidic, are alluded to as acid rain.
• Raised degrees of hydrogen particles cause the rain to have a low pH, making it harming amphibian animals and plants.
• Acid rain created when sulfur dioxide and nitrogen oxide outflows respond with environmental water atoms and produce acid.

Explanation:

• Acid rain containg H₂SO₄, HNO₃,H₂CO₃ (and small amount of HCl) which are formed from the oxide S and N₂ present in the air is called as acid rain.
• The pH of acid rain is in the range of 4-5.
•  The oxide of nitrogen undergo oxidation reaction.
• The reaction with the water vapour present in the atmosphere to form HNO₃. 
• The SO₃ reacts with water vapour and formed H₂SO₄ .
• The HNO₃ and H₂SO₄ combine with HCl present in the air to produce acidic precipitation which is called as acid rain.
• In acid rain H₂SO₄ = 60 - 70% ; HNO₃ = 30 - 40 % ; HCl = Very small amount.
• The normal rain water has a pH about 5.6 due to dissolution of CO₂ in water. 
• CO₂ react with water to form carbonic acid (H₂CO₃).
• When pH of rain water become less than 5.6 it will be acidic.

Conclusion:

Thus, the acids present in acid rain are H₂SO₄, HNO₃ and H₂CO₃. 

Additional Information