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State Board · Class 12 · Chemistry

Lesson 16: Green Chemistry and Nanochemistry

7 concepts · 56 practice questions with answers · Free to read

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Green chemistry and sustainable development

From daily life

Rather than throwing out waste daily, why not make less of it? That is green chemistry.

Simple definition

Green chemistry designs products and processes to reduce or remove hazardous substances; principle 1: prevent waste instead of cleaning it up.

12 principlesThe 12 principles of green chemistry1Prevent waste2Atom economy3Less hazardous synthesis4Safer chemicals5Safer solvents6Energy efficiency7Renewable feedstock8Avoid derivatives9Catalysis10Design for degradation11Real-time analysis12Accident preventionPrevention beats clean-up — the core ideaPollution Prevention Act 1990; framed by Anastas and Warner

In the figure : The 12 principles.

Rule 1: What is green chemistry? — Preventing pollution at the source; Anastas and Warner set out 12 principles in the 1990s; aim: health + environment + economy.

  • Easy : Prevention, not clean-up.
  • Medium : Goal: fewer hazardous substances.
  • Exam-type : 1990: Pollution Prevention Act.

Rule 2: Sustainable development — Meeting today's needs without harming future generations; green chemistry uses fewer resources and makes less waste.

  • Easy : Renewable sources.
  • Medium : Recycling.
  • Exam-type : Lower CO₂.

Rule 3: The 12 in groups — 1 waste, 2 atom economy, 3 less hazardous synthesis, 4 safer chemicals, 5 safer solvents, 6 energy, 7 renewable feedstock, 8 avoid derivatives, 9 catalysis, 10 degradation, 11 monitoring, 12 accident prevention.

  • Easy : 1–6: process.
  • Medium : 7–9: inputs and tools.
  • Exam-type : 10–12: outcome and safety.

Reasoning: why prevention beats clean-up

  • Step 1: Once waste exists, treating it costs money and carries risk.
  • Step 2: A process that makes no waste costs less.
  • Step 3: Health and environment are both protected.

CET level (MCQ)

  • CET 1) Principle 1? 1) prevent waste 2) catalysis 3) safer solvents 4) energy — Answer: 1).
  • CET 2) Core idea of green chemistry? 1) prevention 2) treatment 3) burning 4) storage — Answer: 1).

Real-life use: Pharma, textile, paper and farming.

Remember

12 principles; principle 1 = prevent waste; prevention > cure.

Common mistake

Thinking green chemistry is only recycling.

CET trap

Recycling is one part; prevention is the core.

Shortcut

Memory clue: "stop it first, clean later".

Spot the difference

EarlierGreen
clean-upprevention
much wastelittle waste

Practice questions

Easy
  1. 1Define green chemistry.
  2. 2Principle 1.
  3. 3What is sustainable development?
Medium
  1. 4Four of the 12.
  2. 5Why is prevention better?
  3. 6Green chemistry and economics.
Challenging
  1. 7One example.
  2. 8Groups of principles.
Show answers (try them yourself first)
  1. 1Cut hazards.
  2. 2Prevent waste.
  3. 3Future generations.
  4. 4Any 4.
  5. 5Less cost and risk.
  6. 6Less waste ⇒ lower cost.
  7. 7A reaction in water.
  8. 81–6, 7–9, 10–12.

Principles 2 to 6: atom economy, safer synthesis, solvents and energy

From daily life

Like using all the dough for chapatis, all reactant atoms should end up in the product.

Simple definition

Atom economy % = M(desired product) ÷ ΣM(reactants) × 100.

Principles 2–6Principles 2–6: atom economy, solvents, energyAtom economy % = M(desired product) ÷ ΣM(reactants) × 100CH₃COOH (60) + C₂H₅OH (46) → CH₃COOC₂H₅ (88) + H₂O (18)88 / (60 + 46) × 100 = 83.0 %Addition / Diels–Alder: 100 %ChoicePrinciplewater, scCO₂, ionic liquidssafer solventsambient T, P; microwave, ultrasoundless energyavoid toxic reagentsless hazardousPrinciple 4: effective yet less toxic products (e.g. safer pesticides)

In the figure : Atom economy and solvents.

Rule 1: Principle 2: atom economy — Addition reactions are 100 %; substitution/elimination less; esterification: 88/106 = 83.0 %.

  • Easy : CH₂=CH₂ + H₂ ⇒ 100 %.
  • Medium : Ethyl acetate 83.0 %.
  • Exam-type : More by-products ⇒ lower %.

Rule 2: Principles 3 and 4 — 3: avoid toxic reagents and by-products; 4: effective but less toxic products (safer pesticides).

  • Easy : A safer route instead of phosgene.
  • Medium : Biodegradable pesticides.
  • Exam-type : Less toxic = safer.

Rule 3: Principles 5 and 6 — 5: water, supercritical CO₂, ionic liquids instead of benzene or CCl₄; 6: ambient T and P, microwaves, ultrasound.

  • Easy : scCO₂: dry cleaning.
  • Medium : Microwaves heat fast.
  • Exam-type : Less energy = less CO₂.

Calculation: atom economy of CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O

  • Step 1: Reactants M = 60 + 46 = 106.
  • Step 2: Desired product M = 88.
  • Step 3: 88/106 × 100 = 83.0 %.

CET level (MCQ)

  • CET 1) Highest atom economy? 1) addition 2) elimination 3) substitution 4) condensation — Answer: 1).
  • CET 2) A safer solvent? 1) water 2) benzene 3) CCl₄ 4) chloroform — Answer: 1).

Real-life use: Drug synthesis, dry cleaning, dyes.

Remember

AE % = desired M ÷ reactant M × 100; addition 100 %; water/scCO₂ are safe.

Common mistake

Confusing percentage yield with atom economy.

CET trap

AE is theoretical (design); yield is experimental.

Shortcut

Memory clue: "more atoms wasted, lower AE".

Spot the difference

ReactionAE
Addition100 %
Esterification83.0 %

Practice questions

Easy
  1. 1Define atom economy.
  2. 2AE of esterification.
  3. 3AE of addition.
Medium
  1. 4Principle 3.
  2. 5Principle 5 examples.
  3. 6Principle 6 examples.
Challenging
  1. 7What is scCO₂?
  2. 8AE vs yield.
Show answers (try them yourself first)
  1. 1Desired M / reactant M × 100.
  2. 283.0 %.
  3. 3100 %.
  4. 4Less hazardous synthesis.
  5. 5Water, scCO₂.
  6. 6Microwave, ultrasound.
  7. 7Supercritical CO₂.
  8. 8Theoretical vs experimental.

Principles 7 to 12: feedstocks, catalysis, degradation and safety

From daily life

Coconut shells as fuel — farm waste becomes a new feedstock.

Simple definition

Catalysts are reusable and cut waste; renewable feedstocks do not run out.

Principles 7–12Principles 7–12#Principle7renewable feedstock (biomass, farm waste)8avoid needless derivatisation/protecting groups9catalysts, not stoichiometric reagents10products degrade to harmless substances11real-time monitoring to prevent pollution12inherently safer chemistrye.g. ibuprofen: 6 steps ⇒ 3 catalytic steps, far less wasteFewer steps ⇒ higher atom economy

In the figure : Principles 7–12.

Rule 1: Principles 7 and 8 — 7: use biomass and farm waste; 8: avoid protecting groups and extra steps (waste).

  • Easy : Wood and sugarcane.
  • Medium : Fewer steps ⇒ less waste.
  • Exam-type : Petroleum is finite.

Rule 2: Principle 9: catalysis — A small amount of catalyst is reusable and selective; e.g. ibuprofen: old 6 steps ⇒ new 3 steps.

  • Easy : Not stoichiometric.
  • Medium : Enzymes.
  • Exam-type : Higher AE.

Rule 3: Principles 10, 11, 12 — 10: degrade to harmless products; 11: real-time monitoring inside the process; 12: chemistry safe from explosion, fire and leaks.

  • Easy : PHBV degrades.
  • Medium : Sensors.
  • Exam-type : Avoid volatile solvents.

Reasoning: why the new ibuprofen route is greener

  • Step 1: Steps fall from 6 to 3.
  • Step 2: Catalysts are reusable.
  • Step 3: Higher atom economy, less waste.

CET level (MCQ)

  • CET 1) Catalysis is principle number? 1) 9 2) 7 3) 10 4) 12 — Answer: 1).
  • CET 2) A renewable feedstock? 1) biomass 2) coal 3) petrol 4) natural gas — Answer: 1).

Real-life use: Medicines, biofuels, plastics.

Remember

7 renewable; 9 catalysts; 10 degradation; 12 accident prevention.

Common mistake

Counting a catalyst as a reactant.

CET trap

A catalyst is not consumed, so it is not in AE.

Shortcut

Memory clue: "7 renewable, 9 catalyst, 10 degrade".

Spot the difference

No.Principle
7renewable
9catalysis
10degradation

Practice questions

Easy
  1. 1State principle 7.
  2. 2Why principle 8?
  3. 3Benefits of catalysis.
Medium
  1. 4The ibuprofen example.
  2. 5Principle 10.
  3. 6Principle 11.
Challenging
  1. 7Principle 12.
  2. 8What is renewable?
Show answers (try them yourself first)
  1. 1Renewable feedstock.
  2. 2Less waste.
  3. 3Reusable, selective.
  4. 46 ⇒ 3 steps.
  5. 5Degradation.
  6. 6Real-time monitoring.
  7. 7Accident prevention.
  8. 8Does not run out.

Nanoscience: nanoscale, nanomaterials and dimensions

From daily life

A hair is about 80 000 nm thick; DNA is about 2 nm wide — nano is far finer than hair.

Simple definition

The nanoscale is 1–100 nm (1 nm = 10⁻⁹ m); a nanomaterial has at least one dimension in that range.

NanoscaleThe nanoscale: 1–100 nmnano: 1–100 nm0.111010010³10⁴10⁵nm (log scale)H atom (0.1 nm)DNA width (2 nm)virus (100 nm)red blood cell (7000 nm)hair (80000 nm)1 nm = 10⁻⁹ m; 10⁷ nm = 1 cm0Dall 3 dims nano: particles, quantum dots1D2 dims nano: wires, tubes2D1 dim nano: graphene, thin films3Dbulk nanostructured

In the figure : Sizes and dimensions.

Rule 1: Nanoscale — 1 nm = 10⁻⁹ m = 10⁻⁷ cm ⇒ 10⁷ nm = 1 cm; a virus ≈ 100 nm; a red cell ≈ 7000 nm.

  • Easy : 100 nm = 10⁻⁷ m.
  • Medium : 1 µm = 1000 nm.
  • Exam-type : Atoms ≈ 0.1 nm.

Rule 2: Dimensions 0D, 1D, 2D — 0D: all dimensions nano (particles, quantum dots); 1D: two nano dimensions (wires, tubes); 2D: one nano dimension (graphene, thin films); 3D: bulk nanostructured.

  • Easy : C₆₀: 0D.
  • Medium : Carbon nanotube: 1D.
  • Exam-type : Graphene: 2D.

Rule 3: Examples — Fullerene C₆₀, carbon nanotubes, graphene, Au/Ag nanoparticles, quantum dots; nanoscience studies properties, nanotechnology applies them.

  • Easy : C₆₀: football shape.
  • Medium : Graphene: one atom thick.
  • Exam-type : Ag particles: antibacterial.

Calculation: 50 nm = ? m and ? cm

  • Step 1: 1 nm = 10⁻⁹ m.
  • Step 2: 50 nm = 5 × 10⁻⁸ m.
  • Step 3: = 5 × 10⁻⁶ cm.

CET level (MCQ)

  • CET 1) The nanoscale is? 1) 1–100 nm 2) 1–100 µm 3) 1–100 pm 4) 1–100 mm — Answer: 1).
  • CET 2) Graphene is? 1) 2D 2) 0D 3) 1D 4) 3D — Answer: 1).

Real-life use: Medicine, chips, coatings, sunscreen.

Remember

1 nm = 10⁻⁹ m; 1–100 nm; 0D particle, 1D wire, 2D layer.

Common mistake

Calling graphene 3D.

CET trap

Graphene: one nano dimension (thickness) ⇒ 2D.

Shortcut

Memory clue: "0D = all small; 2D = only thickness small".

Spot the difference

Dim.Example
0Dparticle
1Dnanowire
2Dgraphene

Practice questions

Easy
  1. 1What is the nanoscale?
  2. 21 nm in m?
  3. 3What is a nanomaterial?
Medium
  1. 40D, 1D, 2D examples.
  2. 5Nanoscience vs nanotechnology.
  3. 650 nm = ? m.
Challenging
  1. 7Shape of C₆₀.
  2. 8Hair thickness (nm).
Show answers (try them yourself first)
  1. 11–100 nm.
  2. 210⁻⁹ m.
  3. 3One nano dimension.
  4. 4Particle, wire, layer.
  5. 5Study vs use.
  6. 65 × 10⁻⁸ m.
  7. 7Hollow sphere.
  8. 8≈ 80 000 nm.

Characteristic features of nanoparticles

From daily life

Gold is yellow, but as nanoparticles it looks red — size changes colour.

Simple definition

Main reasons: very large surface-area-to-volume (6/a) and quantum confinement.

FeaturesFeatures of nanoparticlesSurface area ÷ volume = 6/a (cube of side a), in m⁻¹600 m⁻¹1 cm6×10⁷ m⁻¹100 nm6×10⁸ m⁻¹10 nm6×10⁹ m⁻¹1 nm1 cm cube cut into 1 nm cubes ⇒ area ×10⁷ (6 cm² ⇒ 6×10⁷ cm²)quantum confinement ⇒ size-dependent colour (Au: red)lower m.p., higher reactivity and catalysissuperparamagnetism; distinct electrical/optical behaviour

In the figure : Surface area ÷ volume.

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Characteristic features of nanoparticles

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Rule 1: Surface-to-volume — Cube of side a: 6a²/a³ = 6/a; a small ⇒ huge ratio; a 1 cm cube cut into 1 nm cubes ⇒ area ×10⁷.

  • Easy : 1 cm: 600 m⁻¹.
  • Medium : 100 nm: 6 × 10⁷ m⁻¹.
  • Exam-type : 1 nm: 6 × 10⁹ m⁻¹.

Rule 2: Changed properties — Lower melting point; more reactive and catalytic; Au changes colour with size; Fe₃O₄ becomes superparamagnetic.

  • Easy : More atoms at the surface.
  • Medium : Catalysis rises.
  • Exam-type : Transparent ZnO.

Rule 3: Quantum confinement — Tiny particles have discrete electron levels so the band gap depends on size ⇒ colour changes (quantum dots).

  • Easy : Smaller particle ⇒ bluer.
  • Medium : Larger ⇒ redder.
  • Exam-type : Display screens.

Calculation: surface ÷ volume of a 10 nm cube

  • Step 1: a = 10 nm = 10⁻⁸ m.
  • Step 2: 6/a = 6/10⁻⁸.
  • Step 3: = 6 × 10⁸ m⁻¹.

CET level (MCQ)

  • CET 1) As size falls, surface/volume? 1) rises 2) falls 3) same 4) zero — Answer: 1).
  • CET 2) Colour of nano-gold? 1) red 2) yellow 3) black 4) green — Answer: 1).

Real-life use: Catalysts, sunscreens, displays.

Remember

6/a; smaller ⇒ larger; quantum confinement ⇒ size-dependent colour.

Common mistake

Thinking surface/volume rises with size.

CET trap

Large a ⇒ small 6/a; it is large for small particles.

Shortcut

Memory clue: "smaller particle, more surface".

Spot the difference

Side a6/a (m⁻¹)
1 cm600
100 nm6×10⁷
1 nm6×10⁹

Practice questions

Easy
  1. 1Surface ÷ volume formula.
  2. 2A 100 nm cube.
  3. 3Quantum confinement.
Medium
  1. 4Why does Au change colour?
  2. 5Melting point change.
  3. 6Why more catalysis?
Challenging
  1. 76/a for a 10 nm cube.
  2. 8Magnetic feature.
Show answers (try them yourself first)
  1. 16/a.
  2. 26 × 10⁷ m⁻¹.
  3. 3Discrete electron levels.
  4. 4Size ⇒ band gap.
  5. 5Decreases.
  6. 6More surface.
  7. 76 × 10⁸ m⁻¹.
  8. 8Superparamagnetism.

Synthesis and characterisation of nanomaterials

From daily life

Carving a statue (top-down) versus stacking bricks (bottom-up) — the same for nano.

Simple definition

Top-down: bulk ⇒ small (ball milling, lithography); bottom-up: atoms ⇒ larger (sol–gel, CVD, reduction).

SynthesisMaking and characterising nanomaterialsTop-downbulk ⇒ smallball milling, lithographyetching, cuttingBottom-upatoms ⇒ largersol–gel, CVDself-assembly, reductione.g. HAuCl₄ + citrate ⇒ red gold nanoparticles (reduction)TechniqueTells youTEM / SEMsize, shape (images)AFM / STM3-D surface mapXRDcrystal structure, grain sizeUV–Vissize ⇒ absorption (plasmon)

In the figure : Synthesis and tests.

Rule 1: Top-down — Ball milling grinds with spinning balls; lithography etches patterns with light; simple but weaker size control.

  • Easy : Chips: lithography.
  • Medium : Less pure.
  • Exam-type : More energy.

Rule 2: Bottom-up — Reduction: HAuCl₄ + citrate ⇒ Au nanoparticles; sol–gel; CVD; self-assembly; better size control.

  • Easy : Citrate reduces and stabilises.
  • Medium : CVD makes graphene.
  • Exam-type : Biomolecules self-assemble.

Rule 3: Characterisation — TEM/SEM: size and shape; AFM/STM: surface; XRD: crystal structure and grain size; UV–Vis: plasmon absorption ⇒ size.

  • Easy : TEM: electron beam.
  • Medium : STM: sees atoms.
  • Exam-type : XRD: Scherrer.

Reasoning: what citrate does in gold nanoparticle synthesis

  • Step 1: It reduces Au³⁺ to Au atoms.
  • Step 2: Atoms cluster into nanoparticles.
  • Step 3: It coats the particles, preventing clumping.

CET level (MCQ)

  • CET 1) A top-down method? 1) ball milling 2) CVD 3) sol–gel 4) self-assembly — Answer: 1).
  • CET 2) To see particle size and shape? 1) TEM 2) UV 3) IR 4) NMR — Answer: 1).

Real-life use: Chips, catalysts, medicine.

Remember

Top-down = milling; bottom-up = sol–gel, CVD; TEM size; XRD structure.

Common mistake

Calling CVD top-down.

CET trap

CVD builds up atoms from gas ⇒ bottom-up.

Shortcut

Memory clue: "milling breaks big; CVD builds from atoms".

Spot the difference

MethodType
Ball millingtop-down
CVDbottom-up
Sol–gelbottom-up

Practice questions

Easy
  1. 1Two approaches.
  2. 2Ball milling.
  3. 3Sol–gel.
Medium
  1. 4Making Au nanoparticles.
  2. 5Use of TEM.
  3. 6Use of XRD.
Challenging
  1. 7What is STM?
  2. 8Difference between the two.
Show answers (try them yourself first)
  1. 1Top-down / bottom-up.
  2. 2Grinding bulk.
  3. 3Gel from solution.
  4. 4Reduction, citrate.
  5. 5Size, shape.
  6. 6Crystal structure.
  7. 7Sees atoms.
  8. 8Control vs simplicity.

History, examples, applications and risks of nanotechnology

From daily life

Sunscreens do not leave white marks because TiO₂ and ZnO particles are nano-sized.

Simple definition

History: 1959 Feynman, 1974 Taniguchi, 1981 STM, 1985 C₆₀, 1986 Drexler, 1991 CNT; risks: toxicity and bioaccumulation.

HistoryNanotechnology: history, uses, risks1959Feynman: ‘plenty of room at the bottom’1974Taniguchi coins ‘nanotechnology’1981STM: Binnig, Rohrer (textbook: 1980)1985Fullerene C₆₀: Kroto, Curl, Smalley (textbook: 1986)1986Drexler: ‘Engines of Creation’1991Carbon nanotubes: IijimaUsestargeted drug deliverysunscreen TiO₂/ZnOAg antibacterial fabricwater purification, chipsRisksenter body via lungs/skinbioaccumulation, toxicitypersist in environmentregulation needed

In the figure : History, uses, risks.

Rule 1: History — 1959: Feynman's ‘plenty of room at the bottom’; 1974: Taniguchi coins ‘nanotechnology’; 1981: STM (Binnig, Rohrer; textbook: 1980); 1985: C₆₀ (Kroto, Curl, Smalley; textbook: 1986); 1986: Drexler's ‘Engines of Creation’; 1991: carbon nanotubes (Iijima).

  • Easy : STM ⇒ seeing atoms.
  • Medium : C₆₀: 1996 Nobel.
  • Exam-type : CNT: strong, light.

Rule 2: Applications — Medicine: targeted delivery; sunscreens: TiO₂/ZnO; clothes: antibacterial Ag; water purification; computer chips; catalysts; batteries.

  • Easy : Cancer-drug delivery.
  • Medium : Self-cleaning glass: TiO₂.
  • Exam-type : Tennis rackets: CNT.

Rule 3: Risks — Particles can enter via lungs or skin, bioaccumulate and persist in the environment; long-term effects unknown ⇒ regulation and testing needed.

  • Easy : Ag particles in water bodies.
  • Medium : CNT can harm lungs.
  • Exam-type : Safety testing.

Reasoning: why nano sunscreen looks transparent

  • Step 1: Particles are far smaller than visible wavelengths (400–700 nm).
  • Step 2: Visible light is not scattered.
  • Step 3: UV is absorbed ⇒ transparent yet protective.

CET level (MCQ)

  • CET 1) Who coined ‘nanotechnology’? 1) Taniguchi 2) Feynman 3) Iijima 4) Kroto — Answer: 1).
  • CET 2) Who discovered carbon nanotubes? 1) Iijima 2) Smalley 3) Curl 4) Binnig — Answer: 1).

Real-life use: Medicine, water, textiles, electronics.

Remember

1959, 1974, 1981, 1985, 1991; many uses, but risks need testing.

Common mistake

Assuming nano is always safe.

CET trap

Small size ⇒ easy entry into the body ⇒ testing needed.

Shortcut

Memory clue: "59-74-81-85-91".

Spot the difference

YearEvent
1959Feynman
1981STM
1985C₆₀
1991CNT

Practice questions

Easy
  1. 1History of nanotechnology.
  2. 2Feynman's contribution.
  3. 3What is STM?
Medium
  1. 4Three applications.
  2. 5Sunscreen and nano.
  3. 6Three risks.
Challenging
  1. 7Properties of CNT.
  2. 8Discoverers of C₆₀.
Show answers (try them yourself first)
  1. 1Events 1959–1991.
  2. 2Presented the idea.
  3. 3Scanning tunnelling microscope.
  4. 4Drugs, clothes, water.
  5. 5Transparent, absorbs UV.
  6. 6Toxicity, bioaccumulation, environment.
  7. 7Strong and light.
  8. 8Kroto, Curl, Smalley.

Quick revision of the whole lesson

ConceptKey formula / fact
Atom economyM(product)/ΣM(reactants) × 100
Esterification AE88/106 × 100 = 83.0 %
Nanoscale1–100 nm
1 nm10⁻⁹ m
Surface ÷ volume6/a
0Dparticles, quantum dots
2Dgraphene
Top-downball milling, lithography
Live figure

🚀 Quick revision of the whole lesson

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🎯 Most important points for the exam

  • 12 principles.
  • Principles 2–6.
  • Principles 7–12.
  • Nanoscale, dimensions.
  • Nanoparticle properties.
  • Synthesis, characterisation.
  • History, uses, risks.
Study mantra

understand the idea → remember the formula → solve the example → solve problems yourself.