Maharashtra Board Class 12 Chemistry Chapter 16 Green and Nanochemistry Solutions

Choose the Most Correct Option

Question i. The development that meets the needs of the present without compromising the ability of future generations to meet their own need is known as
(a) Continuous development
(b) Sustainable development
(c) True development
(d) Irrational development
Answer: (b) Sustainable development
In simple words: Sustainable development means using resources carefully today so that there is enough left for people in the future to live well.

🎯 Exam Tip: Remember this definition as it is a core concept of green chemistry and is frequently asked in board exams.

Question ii. Which of the following is \(\gamma\)-isomer of BHC?
(a) DDT
(b) lindane
(c) Chloroform
(d) Chlorobenzene
Answer: (b) lindane
In simple words: Lindane is just another name for the gamma-isomer of benzene hexachloride, which is used as an insecticide.

🎯 Exam Tip: Memorize the common names of chemical isomers, especially those used as pesticides like BHC and DDT.

Question iii. The prefix ‘nano’ comes from
(a) French word meaning billion
(b) Greek word meaning dwarf
(c) Spanish word meaning particle
(d) Latin word meaning invisible
Answer: (b) Greek word meaning dwarf
In simple words: The word 'nano' comes from a Greek word that means 'dwarf' because nanoscale things are extremely tiny.

🎯 Exam Tip: Knowing the etymology of scientific prefixes like nano, micro, and macro helps in remembering their relative scales easily.

Question iv. Which of the following information is given by FTIR technique?
(a) Absorption of functional groups
(b) Particle size
(c) Confirmation of formation of nanoparticles
(d) Crystal structure
Answer: (a) Absorption of functional groups
In simple words: FTIR is a technique that uses infrared light to find out which chemical groups are present in a substance by seeing how they absorb the light.

🎯 Exam Tip: Remember that FTIR is specifically used for identifying functional groups, while XRD (X-ray diffraction) is used to determine crystal structure.

Question v. The concept of green chemistry was coined by
(a) Born Haber
(b) Nario Taniguchi
(c) Richard Feynman
(d) Paul T. Anastas
Answer: (d) Paul T. Anastas
In simple words: Paul T. Anastas is known as the father of green chemistry because he first introduced this concept to design safer, eco-friendly chemical processes.

🎯 Exam Tip: Memorize the names of key scientists in nanochemistry and green chemistry, as they are frequently asked in multiple-choice questions.

Answer the Following

Question i. Write the formula to calculate % atom economy.
Answer: The formula to calculate the percentage atom economy is:
\[ \% \text{ Atom Economy} = \frac{\text{Formula weight of the desired product}}{\text{Sum of formula weight of all the reactants used in the reaction}} \times 100 \]
This formula helps in determining the efficiency of a chemical reaction by measuring how many reactant atoms end up in the final useful product.
In simple words: Atom economy tells us how much of our starting materials actually turned into the useful product we wanted, rather than going to waste.

🎯 Exam Tip: Always write the complete formula clearly with the multiplication factor of 100 to secure full marks in numerical-based questions.

Question ii. Name the \( \gamma \)-isomer of BHC.
Answer: Lindane. It is also known as Gammexane and is widely used as an effective insecticide.
In simple words: Lindane is a specific form of a chemical called BHC that is very effective at killing insects.

🎯 Exam Tip: Remember that Lindane, Gammexane, and the gamma-isomer of Benzene Hexachloride (BHC) all refer to the same chemical compound.

Question iii. Ridhima wants to detect structure of surface of materials. Name the technique she has to use.
Answer: Scanning Electron Microscopy (SEM). This advanced imaging technique provides high-resolution three-dimensional views of the surface morphology of materials.
In simple words: Ridhima should use SEM, which works like a super-powerful microscope to take detailed 3D pictures of the surface of tiny materials.

🎯 Exam Tip: Clearly distinguish between SEM (used for surface structure/morphology) and TEM (used for internal structure/particle size) in your answers.

Question iv. Which nanomaterial is used for tyres of car to increase the life of tyres?
Answer: Carbon black is the nanomaterial used in car tyres to increase their durability and wear resistance.
In simple words: Carbon black is added to car tyres to make them last much longer and wear out slowly.

🎯 Exam Tip: Remember that carbon black is a key nanomaterial used to improve the durability and life of vehicle tyres.

Question v. Name the scientist who discovered scanning tunneling microscope (STM) in 1980.
Answer: Gerd Binning and Heinrich Rohrer discovered the scanning tunneling microscope (STM) in 1980, for which they received the Nobel Prize in 1986.
In simple words: Gerd Binning and Heinrich Rohrer are the two scientists who invented the STM microscope to see things at the atomic level.

🎯 Exam Tip: Mention both scientists' names and the year of their Nobel Prize (1986) to secure full marks.

Question vi. 1 nm = …..m?
Answer: \( 1\text{ nm} = 10^{-9}\text{ m} \). This represents one-billionth of a meter.
In simple words: One nanometer is extremely tiny, equal to one-billionth of a single meter.

🎯 Exam Tip: Always write the power of 10 correctly as a negative exponent (\( 10^{-9} \)) when converting nanometers to meters.

3. Answer the Following

Question i. Define:
(i) Green chemistry
(ii) Sustainable development.
Answer:
(i) Green chemistry: Green chemistry is the use of chemistry for pollution prevention and it designs the use of chemical products and processes that reduce or eliminate the use or generation of hazardous substances.
(ii) Sustainable development: Sustainable development is the development that meets the needs of the present, without compromising the ability of future generations to meet their own needs.
In simple words: Green chemistry focuses on making chemicals in a safe, eco-friendly way, while sustainable development means using resources carefully so that future generations also have enough.

🎯 Exam Tip: Memorize these standard definitions word-for-word, highlighting keywords like 'pollution prevention' and 'future generations'.

Question ii. Explain the role of green chemistry.
Answer: The role of green chemistry is to design chemical products and processes that reduce or eliminate the use and generation of hazardous substances. It focuses on minimizing waste, utilizing renewable feedstocks, improving energy efficiency, and creating safer chemicals to protect human health and the environment.
In simple words: Green chemistry helps us make products in a clean way that does not pollute nature, saves energy, and keeps people safe from harmful chemicals.

🎯 Exam Tip: Mention key principles like waste minimization, energy efficiency, and the use of non-toxic materials when explaining the role of green chemistry.

Green Chemistry Approach

When the waste and pollution that society generates exceeds the Earth’s natural capacity for dealing with it, the green chemistry approach plays an important role.

• To reduce or eliminate the use or generation of hazardous substances in the design, manufacture and use of chemical products by promoting innovative chemical technologies.
• Capital expenditure required for prevention of pollution is controlled by the use of green chemistry.
• Since green chemistry incorporates and promotes pollution prevention practices in the manufacturing process of chemicals it helps industrial ecology.
• Green chemistry helps to protect the presence of ozone in the stratosphere. Ozone layer is essential for the survival of life on the earth.
• Global warming (Greenhouse effect) is controlled by green chemistry. At present it is the beginning of the green revolution.
• It is an exciting time with the new challenges for chemist involved with the discovery, manufacturing and use of chemicals. Green chemistry helps us to save environment and save earth, which is important for our future.

Question iii. Give the full form (long form) of the names for the following instruments.
a. XRD
b. TEM.
c. STM
d. FTIR
e. SEM
Answer:
a. XRD-X-ray diffraction
b. TEM-Tunneling Electron Microscope
c. STM – Scanning Tunneling Microscope
d. FTIR-Fourier Transform Infrared Spectroscope
e. SEM-Scanning Electron Microscope
These analytical instruments are widely used to characterize nanomaterials and determine their structural properties.
In simple words: These are short names for special high-tech microscopes and machines used by scientists to look at extremely tiny particles.

🎯 Exam Tip: Memorize the exact spelling of these instrument names, as they are frequently asked in one-mark questions.

Question iv. Define the following terms :
a. Nanoscience
b. Nanotechnology
c. Nanomaterial
Answer:
a. Nanoscience: It is the study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales, where properties differ significantly from those at a larger scale.
b. Nanotechnology: It is the design, characterization, production and application of structures, devices and systems by controlling shape and size at nanometer scale.
c. Nanomaterial: It is a material having structural features with at least one dimension in the range of 1 to 100 nm.
Understanding these definitions is fundamental to exploring the field of nanoscience and its modern applications.
In simple words: Nanoscience is studying super small things, nanotechnology is building things with them, and nanomaterials are the tiny materials themselves.

🎯 Exam Tip: Always mention the scale of 1 to 100 nm when defining nanomaterials to secure full marks.

Question. Define the following terms: (a) Nanoscience, (b) Nanotechnology, (c) Nanomaterial, (d) Nanochemistry.
Answer:
(a) Nanoscience: The study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales where properties differ significantly from those at a larger scale is called nanoscience.
(b) Nanotechnology: The design, characterization, production and application of structures, device and system by controlling shape and size at nanometer scale is called nanotechnology.
(c) Nanomaterial: A material having structural components with at least one dimension in the nanometer scale that is \( 1 - 100 \text{ nm} \) is called the nanomaterial. Nanomaterials are larger than single atoms but smaller than bacteria and cells. These unique dimensions give them special physical and chemical properties.
(d) Nanochemistry: It is the combination of chemistry and nanoscience. It deals with designing and synthesis of materials of nanoscale with different size and shape, structure and composition and their organization into functional architectures.
In simple words: Nanoscience and nanotechnology deal with studying and building extremely tiny things at the scale of atoms and molecules. Nanomaterials are these tiny materials, and nanochemistry is the chemistry used to design them.

🎯 Exam Tip: Clearly define each term with its specific scale (1-100 nm) to secure full marks in definition-based questions.

Question v. How nanotechnology plays an important role in water purification techniques?
Answer:
1. Water purification is an important issue as 1.1 billion people do not have access to improved water supply. Water contains waterborne pathogens like viruses and bacteria.
2. Silver nanoparticles are highly effective bacterial disinfectants to remove E. coli from water. Hence, filter materials coated with silver nanoparticles are used to clean water.
3. Silver nanoparticles (AgNps) are a cost-effective alternative technology (for e.g., water purifier). This technology provides a sustainable solution to global drinking water crises.
In simple words: Many people lack clean drinking water, which often contains harmful germs. Using tiny silver particles in water filters helps kill these bacteria and viruses easily and cheaply.

🎯 Exam Tip: Mentioning 'silver nanoparticles' and their role as a 'bacterial disinfectant' are key terms that examiners look for.

Question vi. Which nanomaterial is used in sunscreen lotion? Write its use.
Answer: Zinc oxide (\( \text{ZnO} \)) and Titanium dioxide (\( \text{TiO}_2 \)) nanoparticles are used in sunscreen lotions. They protect the skin by absorbing or reflecting harmful ultraviolet (UV) radiation from the sun. These nanoparticles are transparent on the skin, unlike traditional thick white creams.
In simple words: Zinc oxide and titanium dioxide nanoparticles are put in sunscreens because they block harmful sun rays without leaving a thick white layer on your skin.

🎯 Exam Tip: Remember to write both chemical names and formulas (\( \text{ZnO} \) and \( \text{TiO}_2 \)) to show a complete understanding.

Question vii. How will you illustrate the use of safer solvent and auxiliaries?
Answer:
• Use of safer solvents and auxiliaries is a principle of green chemistry. It states that safer solvents like water or supercritical \( \text{CO}_2 \) should be used in place of volatile halogenated organic solvents, like \( \text{CH}_2\text{Cl}_2 \), \( \text{CHCl}_3 \), and \( \text{CCl}_4 \) for chemical synthesis and other purposes.
• Solvents dissolve solutes and form solutions, facilitating many reactions. Water is a safer, benign solvent, while solvents like dichloromethane (\( \text{CH}_2\text{Cl}_2 \)) and chloroform (\( \text{CHCl}_3 \)) are hazardous.
• The use of toxic solvents affects millions of workers every year and has severe implications for consumers and the environment. A large amount of waste is created by their use, leading to huge environmental and health impacts.
• Finding safer solvents or designing solvent-free processes is the best way to improve both the chemical process and the final product.
In simple words: We should use safe liquids like water instead of harmful chemicals to dissolve substances during reactions. This protects workers and the environment from toxic chemical waste.

🎯 Exam Tip: Always highlight water and supercritical \( \text{CO}_2 \) as excellent examples of green, safer solvents compared to hazardous chlorinated solvents.

Question viii. Define catalyst. Give two examples.
Answer: A substance which speeds up the rate of a reaction without itself being changed chemically in the reaction is called a catalyst. It helps to increase selectivity, minimise waste, and reduce reaction time and energy demands. They work by providing an alternative pathway with lower activation energy. For example: Hydrogenation of oil where the catalysts used are platinum or palladium, and Raney nickel.
In simple words: A catalyst is a helper substance that makes a chemical reaction go much faster without being consumed or changed by the end of the process. Examples include platinum and Raney nickel.

🎯 Exam Tip: Clearly state that a catalyst remains chemically unchanged at the end of the reaction, and memorize at least two specific examples like platinum or Raney nickel.

4. Answer the Following

Question i. Explain any three principles of green chemistry.
Answer:
1. Design for degradation: Environment protection is the prime concern which has led to the need for designing chemicals that degrade and can be discarded easily. These chemicals should break down into harmless substances after use so they do not persist in the environment.
2. Prevention of waste: It is always better to prevent waste generation at the source rather than treating or cleaning up waste after it has been created.
3. Atom economy: Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final desired product, thereby minimizing by-products.
In simple words: Green chemistry focuses on reducing waste, using safer materials, and designing chemicals that break down easily without harming nature.

🎯 Exam Tip: When explaining the principles, use clear headings for each point (like Prevention of Waste or Atom Economy) to make your answer structured and easy to read.

Question ii. Explain atom economy with suitable example.
Answer:
(1) Atom economy is a measure of the amount of atoms from the starting material that are present in the final product at the end of a chemical process. Good atom economy means most of the atoms of the reactants are incorporated in the desired products. Only small amount of waste is produced, hence lesser problem of waste disposal. This concept is fundamental to green chemistry as it maximizes efficiency.
(2) The atom economy of a process can be calculated using the following formula.
In simple words: Atom economy measures how many starting atoms actually end up in our final desired product. A high atom economy means we are using our ingredients very efficiently and creating very little waste.

🎯 Exam Tip: Always define atom economy clearly and state its formula to secure full marks in descriptive questions.

\[ \% \text{ atom economy} = \frac{\text{Formula weight of the desired product}}{\text{Sum of formula weight of all the reactants used in the reaction}} \times 100 \]

Consider the conversion of Butan-1-ol to 1-bromobutane:
\( \text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2\text{OH} + \text{NaBr} + \text{H}_2\text{SO}_4 \longrightarrow \text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{Br} + \text{NaHSO}_4 + \text{H}_2\text{O} \)

\[ \% \text{ atom economy} = \frac{\text{mass of 1-bromobutane}}{\text{sum of mass of 1-butanol} + \text{sodium bromide} + \text{sulfuric acid}} \times 100 \]

\[ = \frac{\text{mass of } (4\text{C} + 9\text{H} + 1\text{Br}) \text{ atoms}}{\text{mass of } (4\text{C} + 12\text{H} + 5\text{O} + 1\text{Br} + 1\text{Na} + 1\text{S}) \text{ atoms}} \times 100 \]

\[ = \frac{137\text{ u}}{275\text{ u}} \times 100 = 49.81\% \]

The atom economy of the above reaction is less than 50% and waste produced is higher.

Question iii. How will you illustrate the principle, minimization of steps?
Answer:
(1) The technique of protecting or blocking group is commonly used in organic synthesis. Finally on completion of reaction deprotection of the group is required. This leads to unnecessary increase in the number of steps and decreased atom economy. Minimizing these steps is crucial for designing an environmentally friendly chemical process.
(2) The green chemistry principle aims to develop processes to avoid unnecessary steps i.e. (minimization of steps). When biocatalyst is used very often there is no need for protection of selective group. For example, conversion of m-hydroxybenzaldehyde to m-hydroxybenzoic acid.
Reaction pathway:

• Step 1 (Protection): m-hydroxybenzaldehyde + \( \text{C}_6\text{H}_5\text{CH}_2\text{Cl} \) \( \rightarrow \) m-benzyloxybenzaldehyde (protecting the \( -\text{OH} \) group)
• Step 2 (Oxidation): m-benzyloxybenzaldehyde + \( [\text{O}] \) \( \rightarrow \) m-benzyloxybenzoic acid
• Step 3 (Deprotection): m-benzyloxybenzoic acid \( \rightarrow \) m-hydroxybenzoic acid (deprotecting the \( -\text{OH} \) group)

🎯 Exam Tip: Use the conversion of m-hydroxybenzaldehyde to m-hydroxybenzoic acid as a classic example to show how biocatalysts eliminate the need for protection/deprotection steps.

Question iv. What do you mean by sol and gel? Describe the sol-gel method of preparation for nanoparticles.
Answer:
(1) Sol: Sols are dispersions of colloidal particles in a liquid. Colloids are solid particles with diameter of 1-100 nm.
(2) Gel: A gel is a rigid, three-dimensional network of polymeric chains containing a liquid within its pores.
(3) Sol-Gel Method: This is a wet-chemical process used to synthesize nanoparticles, primarily metal oxides. This method is highly favored because it allows for excellent control over the chemical composition and particle size. It involves the following key steps:

• Hydrolysis: Metal alkoxide precursors undergo hydrolysis to form a sol.
• Gelation (Condensation): The sol particles condense and polymerize to form a continuous gel network.
• Drying: The liquid is removed from the gel structure (producing xerogel or aerogel).
• Calcination: The dried gel is thermally treated to obtain crystalline nanoparticles.

🎯 Exam Tip: Clearly define both 'sol' and 'gel' separately before explaining the steps of the sol-gel process to secure full marks.

Question 2. Define Gel.
Answer: A gel is an interconnected rigid network with pores of submicrometer dimensions and polymeric chains whose average length is greater than a micrometer. This unique structure gives gels their characteristic semi-solid properties.
In simple words: A gel is a solid-like network with tiny microscopic holes, made of long connected chains.

🎯 Exam Tip: Remember to mention both the submicrometer pore dimensions and the micrometer-length polymeric chains to get full marks.

Question 3. Explain the Sol-gel Process.
Answer: A sol-gel process is an inorganic polymerisation reaction. It is generally carried out at room temperature, and it includes four steps: Hydrolysis, polycondensation, drying and thermal decomposition. This method is widely used to prepare oxide materials.

The reactions involved in the sol-gel process are as follows:
\( \text{MOR} + \text{H}_2\text{O} \rightarrow \text{MOH} + \text{ROH} \) (hydrolysis of metal alkoxide)
\( \text{MOH} + \text{ROM} \rightarrow \text{M-O-M} + \text{ROH} \) (condensation)

Sol-Gel Process Flow:
• Precursor \(\rightarrow\) Sol
• Sol \(\rightarrow\) Thin Film Coating (via spinning and calcination)
• Sol \(\rightarrow\) Powder (via calcination)
• Sol \(\rightarrow\) Gel (via dehydration reaction)
• Gel \(\rightarrow\) Aerogel (via rapid drying)
• Gel \(\rightarrow\) Xerogel \(\rightarrow\) Dense Ceramic (via calcination)

Key Steps:
• Formation of different stable solution of the alkoxide or solvated metal precursor.
• Gelation involves the formation of an oxide or alcohol-bridged network (gel) by a polycondensation reaction.
• Aging of the gel means during that period gel transforms into a solid mass.
• Drying of the gel involves removal of water and other volatile liquids from the gel network.
• Dehydration is achieved when the material is heated at temperatures up to 800°C.
In simple words: The sol-gel method is a chemical process used to make solid materials like ceramics and powders from liquid solutions at room temperature.

🎯 Exam Tip: Clearly list the four main steps (hydrolysis, polycondensation, drying, and thermal decomposition) and write down both chemical equations to secure maximum marks.

Question v. Which flower is an example of self-cleaning?
Answer: Lotus is an example of self-cleaning. Nanostructures on the lotus plant leaves are super hydrophobic, meaning they strongly repel water. This water carries away dirt as it rolls off the surface. This unique property is widely known as the lotus effect. Thus, though the lotus plant (Nelumbonucifera) grows in muddy water, its leaves always appear clean.
In simple words: The lotus leaf has tiny structures that repel water completely. When water droplets roll off the leaf, they carry all the dirt particles with them, keeping the leaf clean.

🎯 Exam Tip: Use the term "super hydrophobic" and mention the scientific name "Nelumbonucifera" to secure full marks.

Activity: Collect Information About the Application of Nanochemistry in Cosmetics and Pharmaceuticals

12th Chemistry Digest Chapter 16 Green Chemistry and Nanochemistry Intext Questions and Answers

Do You Know? (Textbook Page 343)

Question 1. Does plastic packaging impact the food they wrap?
Answer: Yes, plastic packaging impacts the food it wraps. Phthalates and other harmful chemicals leach into food through packaging, so you should avoid microwaving food or drinks in plastic, avoid using plastic cling wrap, and store your food in glass containers whenever possible. These chemical substances can disrupt hormonal balance in the human body over time. Try to avoid prepackaged and processed food so that you will reduce exposure to the harmful effects of plastic.
In simple words: Harmful chemicals from plastic packaging can slowly leak into our food, especially when heated. To stay safe, we should use glass containers instead of plastic ones.

🎯 Exam Tip: Mention "phthalates" and "leaching" as key terms when explaining the hazards of plastic food packaging.

Used Catalyst (Textbook Page 342)

Question 18. Complete the chart:
Answer: The completed chart is as follows:

🎯 Exam Tip: Always specify the physical state or form of the catalyst, such as "finely divided", to show a complete understanding of industrial processes.

Question 1. Complete the following table by matching the chemical reaction with the name of the catalyst used:
1. Hydrogenation of oil (Hardening) : .........................
2. Haber’s process of manufacture of ammonia : .........................
3. Manufacture of HDPE polymer : .........................
4. Manufacture of \( \text{H}_2\text{SO}_4 \) by contact process : .........................
5. Fischer-Tropsch process (synthesis of gasoline) : .........................
Answer: Catalysts play a crucial role in industrial chemistry by lowering the activation energy and accelerating these essential chemical reactions. The completed table is given below:

🎯 Exam Tip: Memorize these specific catalyst-reaction pairs as they are frequently asked in match-the-following or one-mark questions. Pay special attention to the spelling of Zeigler-Natta and the formula of Vanadium oxide (\( \text{V}_2\text{O}_5 \)).