Chapter 16 Green Chemistry & Nanochemistry - Mock Test & Solutions | Chemca.in

Maharashtra HSC Board Pattern

Chapter 16: Green Chemistry & Nanochemistry Mock Test

Time: 1 Hour | Maximum Marks: 25

General Instructions:

All questions are compulsory.
Section A contains Q1 (Multiple Choice) and Q2 (Very Short Answer).
Section B contains Short Answer Type I questions (2 marks each). Attempt any 4.
Section C contains Short Answer Type II questions (3 marks each). Attempt any 2.
Section D contains Long Answer questions (4 marks each). Attempt any 1.
Calculators are not allowed.

SECTION A

Q1. Select and write the most appropriate answer from the given alternatives: [4 Marks]

The size range of nanomaterials is:

(A) 1 mm to 100 mm
(B) 1 cm to 100 cm
(C) 1 nm to 100 nm
(D) 1 pm to 100 pm
Which of the following is an example of a One-Dimensional (1D) nanomaterial?

(A) Carbon nanotube
(B) Thin film
(C) Quantum dot
(D) Graphene
The principle of Green Chemistry that focuses on maximizing the incorporation of all reactants into the final product is:

(A) Prevention of waste
(B) Atom Economy
(C) Design for degradation
(D) Catalysis
In the Sol-Gel process, the solid particles suspended in a liquid are known as:

(A) Gel
(B) Emulsion
(C) Sol
(D) Precursor

Q2. Answer the following questions in one sentence: [3 Marks]

Write the formula for calculating Percentage Atom Economy.
Define: Nanochemistry.
What is meant by the 'Top-down' approach in the synthesis of nanomaterials?

SECTION B

Attempt any FOUR of the following: [8 Marks]

Define Green Chemistry. Why is it important in modern industries?
Distinguish between Top-down and Bottom-up approaches in nanotechnology.
Explain the principle of "Use of safer solvents and auxiliaries" in Green Chemistry.
Give two applications of silver nanoparticles.
What is meant by 'Nanotoxicology'? Give one reason why nanoparticles can be hazardous to human health.

SECTION C

Attempt any TWO of the following: [6 Marks]

Calculate the percentage atom economy for the synthesis of Butyl bromide from the following reaction:
$C_4H_9OH + NaBr + H_2SO_4 \rightarrow C_4H_9Br + NaHSO_4 + H_2O$
(Given atomic masses: C=12, H=1, O=16, Na=23, Br=80, S=32).
Explain the Sol-Gel process for the synthesis of nanomaterials.
Describe the optical and catalytic properties of nanomaterials.

SECTION D

Attempt any ONE of the following: [4 Marks]

(a) Classify nanomaterials on the basis of their dimensions (0D, 1D, 2D) with one example of each. [3 Marks]
(b) What is meant by 'Design for Degradation' in Green Chemistry? [1 Mark]
(a) State any three principles of Green Chemistry. [3 Marks]
(b) State one disadvantage of nanotechnology in the environment. [1 Mark]

Self-Evaluation Guide

Solutions & Marking Scheme

SECTION A [7 Marks]

Q1. Multiple Choice Answers:

1. (C) 1 nm to 100 nm [1 Mark for correct option]

2. (A) Carbon nanotube [1 Mark. Thin films/Graphene are 2D, Quantum dots are 0D]

3. (B) Atom Economy [1 Mark for correct option]

4. (C) Sol [1 Mark for correct option]

Q2. Very Short Answers:

1. Percentage Atom Economy Formula:

$\% \text{ Atom Economy} = \frac{\text{Formula weight of the desired product}}{\text{Sum of formula weights of all reactants}} \times 100$ [1 Mark]

2. Nanochemistry Definition:

It is the combination of chemistry and nanoscience which deals with designing and synthesizing materials at the nanoscale with different sizes, shapes, and highly distinct properties. [1 Mark]

3. Top-down approach:

It involves breaking down a large, macroscopic (bulk) material into progressively smaller pieces until they reach the nanoscale (usually using physical methods). [1 Mark]

SECTION B [8 Marks]

Q3. Green Chemistry:

Definition: Green Chemistry is the design of chemical products and processes that reduce or completely eliminate the use and generation of hazardous substances. [1 Mark]

Importance: It promotes pollution prevention at the molecular level, saves energy, prevents toxic waste accumulation, and makes industrial manufacturing sustainable and economical. [1 Mark]

Q4. Top-down vs Bottom-up Approach:

Top-down Approach	Bottom-up Approach
Bulk material is broken down into nanoscale particles.	Individual atoms or molecules are assembled to build up nanomaterials.
Mainly uses physical methods (e.g., ball milling).	Mainly uses chemical/biological methods (e.g., Sol-Gel).

[1 Mark for each point of distinction. Total 2 Marks]

Q5. Safer Solvents and Auxiliaries:

This principle states that the use of auxiliary substances (like toxic solvents, separating agents) should be avoided wherever possible. If they must be used, they should be innocuous (harmless). [1 Mark]

Instead of toxic volatile organic compounds (VOCs) like dichloromethane or chloroform, green chemistry promotes the use of safer alternatives like water, supercritical $CO_2$, or performing reactions in solvent-free conditions. [1 Mark]

Q6. Applications of Silver Nanoparticles:

Used in water purifiers due to their highly effective antibacterial and antimicrobial properties. [1 Mark]
Used in medical wound dressings, bandages, and antibacterial coatings on surgical instruments. [1 Mark]

Q7. Nanotoxicology:

Definition: It is the study of the adverse toxicity and health effects caused by nanomaterials on living organisms and the environment. [1 Mark]

Hazard: Due to their extremely small size, nanoparticles can easily be inhaled deep into the lungs, penetrate cell membranes, and cross the blood-brain barrier, potentially causing DNA damage or cellular toxicity. [1 Mark]

SECTION C [6 Marks]

Q8. Atom Economy Numerical:

Reaction: $C_4H_9OH + NaBr + H_2SO_4 \rightarrow C_4H_9Br + NaHSO_4 + H_2O$

Step 1: Formula weight of desired product ($C_4H_9Br$)
$= (4 \times 12) + (9 \times 1) + 80 = 48 + 9 + 80 = 137 \text{ u}$ [1 Mark]

Step 2: Sum of formula weights of ALL reactants
$C_4H_9OH = 48 + 10 + 16 = 74 \text{ u}$
$NaBr = 23 + 80 = 103 \text{ u}$
$H_2SO_4 = 2 + 32 + 64 = 98 \text{ u}$
Total $= 74 + 103 + 98 = 275 \text{ u}$ [1 Mark]

Step 3: Calculation
$\% AE = \frac{137}{275} \times 100 = 0.4981 \times 100$ [1/2 Mark]

$\% \text{ Atom Economy} = 49.81\%$ [1/2 Mark for correct answer]

Q9. Sol-Gel Process:

It is a wet-chemical, bottom-up approach used primarily for the fabrication of metal oxides.

Hydrolysis: Metal alkoxide precursors are dissolved in water/alcohol and hydrolyzed to form a colloidal suspension of solid particles called a Sol. [1 Mark]
Polycondensation: The particles connect to form a continuous 3D network enclosing the liquid, creating a semi-solid Gel. [1 Mark]
Drying & Calcination: The gel is dried to remove the liquid. It is then calcined (heated at high temperatures) to remove organic residues and form the final solid nanoparticles (e.g., $TiO_2$). [1 Mark]

Q10. Optical and Catalytic Properties:

Optical Properties: Unlike bulk materials, nanoparticles (like Gold) change color depending on their exact size and shape due to Surface Plasmon Resonance (SPR), where surface electrons resonate with specific wavelengths of visible light. [1.5 Marks]

Catalytic Properties: Nanomaterials have a massively high surface-area-to-volume ratio. This provides an enormous number of surface atoms with free valencies, making them highly efficient, active, and selective catalysts compared to bulk metals. [1.5 Marks]

SECTION D [4 Marks]

Q11. (a) Classification of Nanomaterials [3 Marks] (b) Design for Degradation [1 Mark]

(a) Classification based on dimensions:

Zero-Dimensional (0D): All three dimensions are at the nanoscale (<100 nm). Example: Quantum dots, Fullerenes, Spherical Nanoparticles. [1 Mark]
One-Dimensional (1D): Two dimensions are at the nanoscale, but one dimension is macroscopic (larger). Example: Carbon nanotubes (CNTs), Nanowires. [1 Mark]
Two-Dimensional (2D): Only one dimension is at the nanoscale, while two dimensions are macroscopic. Example: Graphene, Thin films. [1 Mark]

(b) Design for Degradation:

Chemical products (like plastics/pesticides) should be designed so that at the end of their functional life, they break down into innocuous (harmless) degradation products and do not persist in the environment. [1 Mark]

Q12. (a) Principles of Green Chemistry [3 Marks] (b) Nanotechnology Disadvantage [1 Mark]

(a) Principles of Green Chemistry (Any 3): [1 Mark each. Accept any 3 of the 12 principles]

Prevention of Waste: Better to prevent waste formation than to treat it after it is formed.
Atom Economy: Maximize incorporation of all starting materials into the final product.
Less Hazardous Chemical Syntheses: Design syntheses to use and generate substances with little or no toxicity to humans and the environment.
Catalysis: Use catalytic reagents instead of stoichiometric reagents to save energy and reduce waste.

(b) Disadvantage of Nanotechnology (Environment):

Nanopollution: Because nanoparticles are so small and lightweight, they can easily become airborne or wash into water systems, leading to unknown toxic effects on ecosystems, aquatic life, and soil microorganisms. [1 Mark]

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