Environmental Chemistry MCQ Quiz in বাংলা - Objective Question with Answer for Environmental Chemistry - বিনামূল্যে ডাউনলোড করুন [PDF]

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.

Key Points

• The ozone layer in the stratosphere is affected by the increase in the atmospheric concentration of CFC(chlorofluorocarbons).
• In the atmosphere, CFCs drift slowly upward to the stratosphere, where they are broken up by ultraviolet radiation, releasing chlorine atoms, which can destroy ozone molecules.
• CFCs are the main reason for the Ozone hole.
• The other reasons for ozone depletion are a wide range of industrial and consumer applications, mainly refrigerators, air conditioners (hydrochlorofluorocarbons (HCFCs), and fire extinguishers.

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).

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:

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 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:

Photochemical Smog

• Photochemical smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes. These pollutants react in the atmosphere in the presence of sunlight to form secondary pollutants that contribute to the smog.
• It typically contains a mixture of pollutants including:
  • Nitrogen oxides (NO and NO₂)
  • Ozone (O₃)
  • Volatile organic compounds (VOCs) such as aldehydes (e.g., formaldehyde, HCHO)

EXPLANATION:

• The components of photochemical smog are primarily formed through the reaction of sunlight with pollutants like nitrogen oxides and VOCs. Specifically:
  • NO (Nitric oxide): Emitted directly from vehicles and industrial processes.
  • NO₂ (Nitrogen dioxide): Formed by the oxidation of NO in the atmosphere.
  • HCHO (Formaldehyde): A type of VOC formed from various hydrocarbon emissions.
• SO₂ (Sulfur dioxide) is generally not a component of photochemical smog, as it is more associated with industrial processes and the combustion of sulfur-containing fuels. While SO₂ can contribute to air pollution, it does not play a significant role in the formation of photochemical smog.

Therefore, the photochemical smog does not generally contain SO₂.