Organic Functional Groups

This section introduces you to a family of organic compounds derived from carboxylic acids and their natural forms found in living organisms. You will explore alkanoic acid derivatives, including esters, which are sweet-smelling compounds used in perfumes and flavours; amides, which are present in proteins and medicines; and acyl halides, which are very reactive compounds used in synthesis. Additionally, you will study fats and oils (lipids), which are natural compounds found in food and living organisms. By the end of this section, you will understand the structure, preparation, and properties of alkanoic acid derivatives and their everyday uses, such as esters in food flavours and amides in fabrics and drugs. You will also learn to identify the functional groups of these derivatives, explain their synthesis, compare their reactivity, describe the structure and properties of fats and oils, and appreciate their vital roles in everyday life, including food, nutrition, medicine, cosmetics, and industry.

KEY IDEAS

· Acyl halides – Very reactive derivatives of carboxylic acids where the

–OH group is replaced by a halogen (Cl, Br).

C = O Cl · Alkanoic acids – Organic acids containing the –COOH (carboxyl) group.

C = O O – H · Amides – Organic compounds formed when the –OH group of a carboxylic acid is replaced by –NH₂ or substituted amines.

· Derivatives – Compounds obtained from another compound by replacing part of its structure.

· Esters – Sweet-smelling organic compounds formed from a carboxylic acid and an alcohol.

C = O O – R

Alkyl Alkanoates (Esters)

Esters are organic compounds formed when an alcohol (alkanol) reacts with a carboxylic acid (alkanoic acid).

In this reaction, the –H from the acid is replaced by an alkyl group (from the alcohol).

General form: RCOOR′ R – C = O O – R R = hydrogen or an alkyl group R′ = an alkyl group (from the alkanol) Structure and Functional Group Esters contain the –COO– group (called the ester group). It has: C=O (carbonyl group) and C–O single bond attached to the same carbon. The alkyl groups (R and R′) may be the same or different.

Formula General formula: CₙH₂ₙO₂(where n = 2, 3, 4, 5, …). The first ester (n = 2) has formula C₂H₄O₂.

ESTERIFICATION Alkanoic acid reacts directly with the alkanol in an acid-catalysed reversible reaction process.

Reagents: Alkanoic acid and alkanol Catalyst: H₂ SO₄ or dry HCl Condition: heat Formation Reaction Alcohol + Carboxylic acid → Ester + Water R C O O H + OHR' alkanoic acid alkanol conc. H ₂SO₄ D R C O O + H₂O R' alkylalkanoate Examples CH ₃COOH + CH ₃CH ₂OH conc. H ₂SO₄ D CH ₃COOCH ₂CH ₃ + H₂O ethylethanoate Methyl butanoate (apple): C H₃ OH _(Methanol) + C₃ H₇ COOH butanoic acid → C₃ H₇ COOC H₃ methyl butanoate + H₂ O _(water) Ethyl methanoate (rum essence): C₂ H₅ OH ₑₜₕₐₙₒₗ + H COOHmethanoic acid → HCOO C₂ H₅ ethyl methanoate + H₂ O _(water) Ethyl butanoate (pineapple):C₂ H₅ OH ₑₜₕₐₙₒₗ + C₃ H₇ COOH butanoic acid → C₃ H₇ COO C₂ H₅ ethyl butanoate + H₂ O _(water) Everyday Relevance Esters often smell sweet and fruity, so they are used in perfumes and flavourings.

The esterification reaction is analogous to the neutralisation reaction between a mineral acid and a base, which produces a salt and water, but with important differences.

Table 6.1: Everyday relevance and use of esters Esterification reaction Neutralisation reaction An alkanoic acid reacts with an alkanol An acid reacts with a base Products are alkyl alkanoate and water Products are salt and water Does not require an indicator Requires an indicator to show end- point Reaction is reversible Reaction is irreversible It is acid-catalysed It requires no catalyst Esterification reaction Neutralisation reaction Large molecules are reacting, hence very slow Ions are reacting in solution, hence very fast Sources of Alkyl Alkanoates Natural sources

1. Fruits & flowers (aroma compounds): Tiny amounts of esters give many smells/flavours, e.g.,

a. Isoamyl acetate → banana

b. Ethyl butanoate / ethyl hexanoate → apple, pineapple

c. Methyl salicylate → wintergreen/mint

2. Waxes in nature (long-chain alkyl alkanoates): Plant leaf waxes, beeswax, jojoba oil, and some animal waxes (e.g., cetyl palmitate in spermaceti) are mostly long-chain fatty acid + long-chain alcohol esters (R–COO–R′).

3. Fermented foods & drinks: Yeast makes esters such as ethyl ethanoate (ethyl acetate) and isoamyl acetate, contributing fruity notes in bread, beer, wine.

4. Natural signals: Some insect pheromones are acetate esters (help insects communicate).

Human-made (industrial & lab) sources

1. Solvent manufacture: Paints, inks, and glues use ethyl acetate and butyl acetate, produced by reacting the acid with the alcohol (see methods below).

2. Flavour & fragrance industry: “Fruit” esters (banana, pear, pineapple notes) are often synthesised to standard purity for food flavourings and perfumes.

3. Biodiesel (FAME): Fatty Acid Methyl Esters are made by transesterifying vegetable oils or animal fats with methanol (e.g., from palm, soybean, or used cooking oil).

4. Plastics & materials: Many coatings and polymers are esters (e.g., polyacrylates). (Note: big plastics like PET are esters too, though not simple “alkyl alkanoates”.)

IUPAC Naming of Alkyl Alkanoates (Esters)

General Rule

Esters have the form RCOOR′: R comes from the carboxylic acid and R′ comes from the alcohol.

Name = Alkyl (from alcohol) + Alkanoate (from acid) Steps to Name an Ester

1. Identify the alcohol part (R′)

a. This gives the first word in the name.

b. Write it as an alkyl group (methyl, ethyl, propyl, butyl…).

2. Identify the acid part (RCOO)

a. This gives the second word.

b. Change the “-oic acid” ending to “-oate” (methanoic acid → methanoate, ethanoic acid → ethanoate).

3. Combine them Name = [Alkyl group from alcohol] + [Alkanoate from acid].

Examples

1. CH₃COOCH₃→ Methyl ethanoate Alcohol part: CH₃OH → methyl Acid part: CH₃COOH → ethanoate

2. CH₃COOCH₂CH₃→ Ethyl ethanoate Alcohol part: ethanol → ethyl Acid part: ethanoic acid → ethanoate

3. C₂H₅COOCH₃→ Methyl propanoate Alcohol part: methanol → methyl Acid part: propanoic acid → propanoate

4. C₃H₇COOCH₂CH₃→ Ethyl butanoate Alcohol part: ethanol → ethyl Acid part: butanoic acid → butanoate Preparation of Alkyl Alkanoates (Esters)

1. Esterification (Fischer Method)

An acid (alkanoic acid) reacts with an alcohol (alkanol) in the presence of a strong acid catalyst (conc. H₂SO₄or HCl). The reaction is slow at room temperature, so it needs heating. It is a reversible (equilibrium) reaction.

Equation: RCOOH + R′OH ⇌ RCOOR′ + H₂O

Example: CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃+ H₂O (Ethanoic acid + Ethanol ⇌ Ethyl ethanoate + Water)

2. Reaction of Acyl Halides with Alcohols

Acyl halides (like acid chlorides, RCOCl) are very reactive. They react quickly with alcohols at room temperature to form esters. Hydrogen halide (HCl or HBr) is also produced.

Equation: RCOCl + R′OH → RCOOR′ + HCl

Example: CH₃COCl + CH₃CH₂OH → CH₃COOCH₂CH₃+ HCl (Acetyl chloride + Ethanol → Ethyl ethanoate + Hydrogen chloride)

3. Reaction of Acid Anhydrides with Alcohols

Acid anhydrides (RCO–O–COR) are less reactive than acyl halides, but more reactive than acids. They react with alcohols to form an ester and a carboxylic acid. No catalyst is needed.

Equation: (RCO)₂O + R′OH → RCOOR′ + RCOOH

Example: (CH₃CO)₂O + CH₃CH₂OH → CH₃COOCH₂CH₃+ CH₃COOH (Ethanoic anhydride + Ethanol → Ethyl ethanoate + Ethanoic acid)

4. Transesterification One ester reacts with a different alcohol. The alkoxy group (–OR) is exchanged. Needs an acid or base catalyst.

Equation: RCOOR′ + R″OH ⇌ RCOOR″ + R′OH

Example: CH₃COOCH₃+ CH₃CH₂OH ⇌ CH₃COOCH₂CH₃+ CH₃OH (Methyl ethanoate + Ethanol ⇌ Ethyl ethanoate + Methanol) Physical Properties of Alkyl Alkanoates (Esters)

1. State and Appearance: Most low-molecular mass esters are colourless liquids with a sweet, fruity smell. Higher esters (larger molecules) can be waxy solids.

2. Odour: Many esters have pleasant fruity odours (e.g., banana, pineapple, apple). Used in flavourings and perfumes.

3. Boiling Points: Esters have moderate boiling points. Usually lower than carboxylic acids of similar molecular mass (because esters do not form hydrogen bonds as strongly as acids).

4. Solubility in Water: Small esters are slightly soluble in water (due to some hydrogen bonding with water). Larger esters are insoluble in water (non- polar parts dominate). Esters are soluble in organic solvents (e.g., ethanol, ether, chloroform).

5. Density: Esters are usually less dense than water (they float on water).

6. Volatility: Small esters are volatile (evaporate easily), which is why their smell is easily noticed.

Chemical Reactions of Alkyl Alkanoates (Esters)

1. Hydrolysis (Breaking Down with Water): Esters can be broken back into acid + alcohol.

a. Acidic hydrolysis (using dilute HCl or H₂SO₄, with heat):

RCOOR′ + H₂O ⇌ RCOOH + R′OH (Reversible reaction)

b. Alkaline hydrolysis (saponification) (using NaOH):

RCOOR′ + NaOH → RCOONa + R′OH (Forms salt of the acid + alcohol, irreversible)

2. Reaction with Ammonia: Esters react with ammonia (NH₃) to give amides and alcohols.

Equation: RCOOR′ + NH₃→ RCONH₂+ R′OH

3. Reaction with Alcohols (Transesterification): One ester reacts with a different alcohol to form a new ester and an alcohol. Needs an acid or base catalyst.

Equation: RCOOR′ + R″OH ⇌ RCOOR″ + R′OH

4. Reduction of Esters: Esters can be reduced (with strong reducing agents like LiAlH₄) to form primary alcohols.

Equation: RCOOR′ → RCH₂OH + R′OH

5. Combustion: Like other organic compounds, esters burn in oxygen to form carbon dioxide and water.

Equation: RCOOR′ + O₂→ CO₂+ H₂O Amides Structure and Bonding of Amides Amides have the functional group –CONH₂. They come from acids called alkanoic acids.

Amides can be classified as

1. Primary: R–CONH₂(one group attached to nitrogen)

2. Secondary: R–CONHR′ (two groups attached to nitrogen)

3. Tertiary: R–CONR′R″ (three groups attached to nitrogen).

The atoms in an amide lie in the same flat plane. This happens because the nitrogen shares its lone pair with the C=O group (this sharing is called resonance).

Resonance makes amides more stable than expected. In amides, the nitrogen uses sp² orbitals (flat shape), while in amines (NH₃family) nitrogen uses sp³ orbitals (pyramid shape).

Nomenclature of Amides (How to Name Them)

1. Start with the parent acid (alkanoic acid).

Example: ethanoic acid (CH₃COOH).

2. Replace the “–oic acid” ending with “–amide.”

Ethanoic acid → ethanamide (CH₃CONH₂).

Methanoic acid → methanamide (HCONH₂).

3. For secondary and tertiary amides (when there are substituted groups on the nitrogen):

Show these groups using N- to indicate their position in the name.

Example: CH₃CONHCH₃→ N-methyl ethanamide.

Example: CH₃CON(CH₃)₂→ N,N-dimethyl ethanamide.

Preparation Methods of Amides

1. From Alkanoic Acids (via Ammonium Salts)

Step 1: Carboxylic acid reacts with ammonia to form ammonium carboxylate.

RCOOH + NH₃→ RCOONH₄

Step 2: On heating, the ammonium salt dehydrates to form the amide.

RCOONH₄→ RCONH₂+ H₂O

2. From Acid Chlorides (Acyl Chlorides)

Acyl chloride reacts readily with ammonia.

RCOCl + NH₃→ RCONH₂+ HCl

3. From Acid Anhydrides

Acid anhydride reacts with ammonia to give amides.

(RCO)₂O + NH₃→ RCONH₂+ RCOOH

4. From Esters

Ester reacts with ammonia (ammonolysis) to form an amide and alcohol.

RCOOR’ + NH₃→ RCONH₂+ R’OH

5. From Nitriles (Hydrolysis)

Partial hydrolysis of nitriles under controlled conditions forms amides.

RCN + H₂O → RCONH₂ Physical Properties of Amides

1. State and Appearance

Lower aliphatic amides (e.g., methanamide, ethanamide) are colourless liquids. Higher members are crystalline solids with high melting points.

2. Intermolecular Forces

Amides form extensive hydrogen bonding between the –NH₂group and the C=O group. This strong hydrogen bonding is responsible for their high melting and boiling points, higher than comparable hydrocarbons, esters, or ketones.

3. Solubility Low molecular mass amides (up to about 5 carbons) are soluble in water because they can form hydrogen bonds with water molecules. Higher amides become less soluble due to the increasing hydrophobic alkyl chain.

4. Boiling and Melting Points

a. Primary amides (R–CONH₂): Highest boiling points due to two –NH bonds allowing strong hydrogen bonding.

b. Secondary amides (R–CONHR’): Lower boiling points than primary, since only one –NH group is available.

c. Tertiary amides (R–CONR’R”): Lowest boiling points because no –NH group is available for hydrogen bonding, though the carbonyl oxygen can still form weak bonds.

5. Odour and Stability

Lower amides are generally odourless and relatively stable compared to amines. Their planar structure due to resonance makes them less reactive towards bases and nucleophiles.

Chemical Properties of Amides

1. Hydrolysis Amides undergo hydrolysis when heated with acids or bases.

Acidic Hydrolysis: RCONH₂+ H₂O + HCl → RCOOH + NH₄Cl or R CONH2+ H2O dil. HCl heat R COOH + NH4Cl Produces a carboxylic acid and ammonium salt.

Basic Hydrolysis: RCONH₂+ NaOH → RCOONa + NH₃or R CONH2 + H2O R COONa + NH3 dil. NaOH heat Produces a carboxylate salt and ammonia.

2. Dehydration to Nitriles

On heating with phosphorus(V) oxide (P₂O₅) or thionyl chloride (SOCl₂), amides lose water to form nitriles.

RCONH₂→ RC≡N + H₂O

3. Reaction with Nitrous Acid

Primary amides react with nitrous acid (HNO₂) to release nitrogen gas.

RCONH₂+ HNO₂→ RCOOH + N₂+ H₂O

4. Reduction to Amines

Amides can be reduced to amines using lithium aluminium hydride (LiAlH₄).

RCONH₂+ 4[H]+ → RCH₂NH₂

5. Hoffmann Degradation

Heating an amide with bromine and aqueous alkali (NaOH or KOH) gives a primary amine with one carbon atom less.

RCONH₂+ Br₂+ 4NaOH → RNH₂+ Na₂CO₃+ 2NaBr + 2H₂O

6. Resonance and Basicity

Due to resonance between the nitrogen lone pair and the carbonyl group, amides are neutral compounds (very weak bases compared to amines). They resist protonation under normal conditions.

Applications of Amides

1. Pharmaceuticals Many medicines are amide derivatives due to their stability and biological

activity.

Examples:

a. Paracetamol (acetaminophen): Pain reliever and fever reducer.

b. Lidocaine: A local anaesthetic.

c. Penicillin derivatives: Contain amide linkages crucial for antibacterial

activity.

2. Polymers and Synthetic Materials

a. Nylons (polyamides): Produced from diamines and dicarboxylic acids, used in textiles, carpets, and ropes.

b. Kevlar: A high-strength aromatic polyamide used in bulletproof vests, helmets, and aerospace materials.

c. Proteins: Naturally occurring polyamides formed by peptide (amide) bonds between amino acids.

3. Agriculture Amide-based compounds serve as herbicides, pesticides, and fungicides.

Example: Diuron (a urea-derived herbicide).

4. Industrial Uses

Amides are used as solvents and stabilisers in chemical industries. They act as intermediates in the preparation of dyes, rubber chemicals, and resins.

Formamide is a good solvent and plasticizer.

5. Everyday Products

Amides are found in

a. Softeners and detergents (as stabilising agents).

b. Cosmetics and shampoos (conditioning agents).

c. Food industry: Certain amides are used as additives and flavouring agents.

6. Biological Importance

Peptide bonds (amide linkages) form the backbone of proteins, essential for life. Urea (a simple diamide) is the main nitrogen excretion product in mammals.

Structure and Bonding of Acyl Halides

Acyl halides are organic compounds. They have the formula R–COX, where:

R is a carbon group (like a chain or ring).

CO is the carbonyl group (a carbon joined to oxygen with a double bond).

X is a halogen atom (like chlorine, bromine, fluorine, or iodine).

You can think of acyl halides as coming from carboxylic acids. In carboxylic acids, there is an –OH group (like in vinegar). In acyl halides, this –OH is replaced by a halogen atom. The carbon in the C=O group is flat (planar) because of its bonding. The bonds around it spread out at about 120°, like the corners of a triangle.

Nomenclature of Acyl Halides

1. Identify the Parent Carboxylic Acid

a. Look for the carboxylic acid from which the acyl halide is made.

b. Find the carbon chain or ring attached to the –COX group.

c. Count the number of carbon atoms in this chain or identify the ring system.

2. Replace the Ending of the Parent Acid

Change the ending “–oic acid” to “–oyl halide.”

Example: Ethanoic acid → Ethanoyl chloride

3. Specify the Halogen

a. Write the name of the halogen present in the acyl halide.

b. Options: chloride (Cl), bromide (Br), fluoride (F), or iodide (I).

Examples: Ethanoyl chloride (CH₃COCl), Propanoyl bromide (CH₃CH₂COBr)

4. Add Prefixes for Substituents (if any)

a. Start numbering the chain from the carbonyl carbon as position 1.

b. Name and number any groups (like –CH₃, –Cl, –NO₂) as prefixes.

Example: 2-methylpropanoyl chloride Examples of IUPAC Names of some Acyl Halides

1. CH₃COCl: ethanoyl chloride (from ethanoic acid)

2. CH₃CH₂COCl: propanoyl chloride (from propanoic acid)

3. CH₃CH₂COBr: propanoyl bromide (from propanoic acid)

4. CH₂=CHCOCl: propenoyl chloride (from propenoic acid)

5. CH₃CH₂CH₂CH₂COCl: pentanoyl chloride (from pentanoic acid)

6. C₆H₅COCl: benzoyl chloride (from benzoic acid)

7. ClCH₂COCl: chloroethanoyl chloride (from chloroethanoic acid) Examples of Common Names of some Acyl Halides

1. CH₃COCl: acetyl chloride (from acetic acid)

2. HCOCl: formyl chloride (from formic acid, though unstable)

3. CH₃CH₂COCl: propionyl chloride (from propionic acid)

4. C₆H₅COCl: benzoyl chloride (from benzoic acid)

5. CH₃(CH₂) ₁₆COCl: stearoyl chloride (from stearic acid)

6. CH₂=CHCOCl: acryloyl chloride (from acrylic acid) Preparation of Acyl Halides Acyl halides are prepared mainly from carboxylic acids by replacing the –OH group with a halogen atom.

1. From Carboxylic Acids with Halogenating Agents

a. With Thionyl chloride (SOCl₂): R–COOH + SOCl₂→ R–COCl + SO_(2(g)) + HCl_((g)) (Most common laboratory method; gaseous by-products make purification easy.)

b. With Phosphorus trichloride (PCl₃): 3R–COOH + PCl₃→ 3R–COCl + H₃PO₃

c. With Phosphorus pentachloride (PCl₅): R–COOH + PCl₅→ R–COCl + POCl₃+ HCl

2. Interconversion of Acyl Halides

Acid bromides and iodides can be prepared from acid chlorides using NaBr or NaI with a catalyst such as phosphorus:

a. R–COCl + NaBr → R–COBr + NaCl

b. R–COCl + NaI → R–COI + NaCl

3. From Acid Anhydrides

(R–CO) ₂O + HX → R–COX + R–COOH Physical Properties of Acyl Halides

1. Most acyl halides are colourless, fuming liquids with sharp, irritating odours.

2. Aromatic acyl halides such as benzoyl chloride may appear as crystalline solids.

3. They have lower boiling points than carboxylic acids, because they cannot form hydrogen bonds between their own molecules.

4. They are insoluble in water, since they hydrolyse violently, forming the parent carboxylic acid and hydrogen halide (HCl, HBr, etc.).

5. They dissolve well in organic solvents like benzene, ether, and chloroform.

6. Many are denser than water due to the presence of halogen atoms.

7. In moist air, they release dense white fumes of hydrogen halides.

Chemical Properties of Acyl Halides

Acyl halides are very reactive because the carbonyl carbon is strongly electron- deficient, making it easy for nucleophiles to attack.

1. Hydrolysis (reaction with water): R–COX + H₂O → R–COOH + HX

Example: CH₃COCl + H₂O → CH₃COOH + HCl

2. Reaction with Alcohols (Esterification): R–COX + R’–OH → R–COOR’ + HX

Example: CH₃COCl + CH₃OH → CH₃COOCH₃+ HCl

3. Reaction with Ammonia: R–COX + NH₃→ R–CONH₂+ HX

Example: CH₃COCl + NH₃→ CH₃CONH₂+ HCl

4. Reaction with Amines: R–COX + R’–NH₂→ R–CONHR’ + HX

5. Friedel–Crafts Acylation (with Aromatic Compounds):

R–COCl + C₆H₆→ R–CO–C₆H₅+ HCl (in the presence of AlCl₃catalyst) Uses of Acyl Halides

1. Preparation of Esters: Acyl halides react with alcohols to form esters, used in perfumes, flavourings, and solvents.

R–COCl + R’–OH → R–COOR’ + HCl

2. Preparation of Amides: With ammonia or amines, acyl halides form amides, useful in making plastics, fibres, and medicines.

R–COCl + NH₃→ R–CONH₂+ HCl

3. Friedel–Crafts Acylation: In the presence of AlCl₃catalyst, acyl halides react with aromatic compounds to form aromatic ketones.

R–COCl + C₆H₆→ R–CO–C₆H₅+ HCl (Important in making dyes, perfumes, and pharmaceuticals.)

4. Intermediates in Organic Synthesis: Acyl halides serve as starting materials in making anilides, acetyl derivatives, agrochemicals, and pharmaceuticals.

Activity 6.1 Amides and Acyl Halides

1. Observe the representations of amides and acyl halides below

2. Study the flow charts below on the preparation of Amides and Acyl halides

a. Step-by-Step Preparation of Amides Flow Diagrams Two simple routes: make a reactive helper first (acyl chloride) or start from an anhydride.

Flow 1 — Make an Amide (Simple Route A) Idea: Turn the acid into a more reactive form, then add ammonia/amine.

Start Carboxylic acid R-COOH Make it more reactive Use SOCl₂or PCl₅ (gases escape) Now you have Acyl chloride R-COCl Add ammonia 2 NH3 (excess) Or add an amine R'NH 2 + base You get an AMIDE!

NH3 → R-CONH2 + NH4 Cl • R'NH2→ R-CONHR' + (acid captured)

Step 1

Step 2A Step 2B

Safety: These steps give off acidic fumes (HCl, SO₂). Teacher handles chemicals; use goggles & good ventilation.

Flow 1: Carboxylic acid → acyl chloride → amide (add NH₃or R′NH₂+ base).

Flow 2: Acid anhydride → amide (direct with NH₃or amine + base).

a. Step-by-Step Preparation of Acyl Halides — Flow Chart

3. Draw the structures of

a. ethanamide (acetamide) — CH₃CONH₂, Benzamide — C₆H₅CONH₂

b. Ethanoyl chloride (acetyl chloride) — CH₃COCl and Benzoyl chloride — C₆H₅COCl

4. Fill-in-the-Blank Worksheet: Write the correct words or formulas in the blanks. Use standard organic notation (R, R’, X).

a. General Formulas Compound class General formula (fill in the blank) Primary amide R–C O–_____ (write the group) Secondary amide R–CO–_____ (NHR′) Tertiary amide R–CO–_____ (NR′R″) Acyl halide (general) R–CO_____ (X = Cl, Br, I, F) Acyl chloride R–CO_____ Acyl bromide R–CO_____ Benzamide (specific) C₆H₅–_____

b. For acyl halides: change “–oic acid” to “–_____ _____”. (write the two words)

c. For amides: change “–oic acid” to “–_____”.

5. Convert each carboxylic acid below to the named derivative. Write the CORRECT derivative name.

a. Methanoic acid → (acyl chloride) ____________________________

b. Ethanoic acid → (amide) ____________________________

c. Propanoic acid → (acyl bromide) ____________________________

d. Benzoic acid → (amide) ____________________________

e. Butanoic acid → (acyl iodide) ____________________________

f. 2-Methylpropanoic acid → (acyl chloride) ____________________

6. Fill in the missing reactant(s) or product(s). Use HCl/HBr etc. where appropriate.

a. R–COCl + H₂O → __________ + __________

b. R–COCl + CH₃CH₂OH → __________ + __________

c. R–COCl + NH₃→ __________ + __________

d. R–COCl + CH₃NH₂→ __________ + __________

e. R–COOH + PCl₃→ __________ + __________

f. R–COOH + SOCl₂→ __________ + __________ + __________

g. R–COCl + NaBr → __________ + __________

h. C₆H₆+ R–COCl (AlCl₃) → __________ + __________

i. C₆H₅COCl + NH₃→ __________ + __________ j. R–CONH₂(amide) + H₂O (acid) → __________ + __________

Activity 6.2 Structures, Names & Reactions of Amides vs Acyl Halides

1. Draw structural formulae for the following five amides: and five acyl halides:

methanamide, ethanamide, propanamide, Butanamide, benzamide, N-methylacetamide, N, N-dimethylformamide.

2. Draw structural formulae for the following five acyl halides ethanoyl chloride, propanoyl bromide, benzoyl chloride, butanoyl chloride, ethanoyl fluoride, Benzoyl chloride.

3. Assign IUPAC names to the structures from questions 1 and 2; exchange sheets with another group for checking.

4. Create a comparison chart (structure & properties differences). Work in pairs or groups. Use your notes/handouts to complete the table.

Feature Amides Acyl halides Functional group (draw/describe) General formula Element highlight (N vs. halogen) Polarity / resonance (brief) Hydrogen bonding (self / with water) Typical boiling point (relative tendency) Water: solubility vs. reaction Odour / appearance (simple) Common lab preparation (from acids) Key reactivity with NH₃/ amines / alcohols

Example compound (name + formula) Safety note (one line)

5. Record formation reactions from carboxylic acids with reagents/ conditions.

6. Fill in the missing reagents/products/conditions. Keep conditions brief (e.g., ‘dry solvent’, ‘cooling’, ‘reflux’).

a. R–COOH + ______→ R–COCl + ______ + _______ (condition:

______)

b. 3 R–COOH + _____ → 3 R–COCl + _____ (condition: _________)

c. R–COOH + ____ → R–COCl + _____ + _______ (condition:

_________)

d. 3 R–COOH + _____ → 3 R–COBr + ______ (condition: ________)

e. R–COCl + ______ → R–COBr + _______ (condition: __________)

f. R–COCl + ______→ R–COI + __________ (condition: ________)

g. R–COCl + 2 _____ → R–CONH₂+ _______ (condition: ________)

h. R–COCl + ______→ R–CONHR′ + ______ (condition: _______)

i. R–COCl + ________→ R–COOR′ + ______(condition: ________) J. R–COOH + __________ ⇌ R–COO–NH₄ + → (__________) → R–CONH₂+ __________

7. Present one key reaction to your colleagues.

Activity 6.3 Reactions of Amides and Acyl Halides

Formation Reactions — from Carboxylic Acids. Write word and generic symbol equations with reagents and short conditions. Add one safety note.

Route Word

equation Symbol equation Reagents/ conditions Safety

note

Acid → Acyl chloride Acyl chloride → Amide (NH₃) Acyl chloride → N-substituted amide Anhydride → Amide

Activity 6.4 Making Ethyl Ethanoate

Safety rules to observe

1. Wear goggles and gloves; tie back hair; no tasting, only waft smells.

2. Handle concentrated sulphuric acid (H₂SO₄) and hot water with great care.

3. Use a warm water bath (50–60 °C) — no flames.

4. Neutralise spills with sodium bicarbonate, wash hands after.

5. Identify, and collect materials & Equipment to follow the procedure safely

6. Run the Experiment (under supervision)

7. Follow the Basic Procedure step by step.

Basic microscale procedure (per group)

1. In a test tube: add 2 ml ethanol + 2 ml ethanoic acid.

2. Add about 5 drops conc. H₂SO₄(catalyst). Stopper and swirl.

3. Place tube in a 50–60 °C water bath for 10 min, swirling occasionally.

4. Pour into a second tube with 5 ml sodium carbonate solution (~5%). Swirl and vent (CO₂). Check pH with paper; add a little more carbonate if still acidic.

5. Add 5 ml brine (salt water), swirl, and let layers separate.

6. The top layer is ethyl ethanoate. Pipette it into a clean, dry tube.

Observation and calculation

1. Record every observation (colour, bubbles, temperature, smell by wafting, when layers appear)

2. Measure your ester volume (ml).

3. Calculate Percentage Yield using:

Percent yield = your ester volume/3.3 ml × 100%

Note

(3.3 ml is a classroom “ideal max” for 2 mL ethanol + 2 mL acid. Real student yields are often 20–60%.)

Activity 6.5 Reactions of Amides and Acyl Halides

1. Collect your prompt cards with different reagents (such as water, alcohols, or ammonia) from your teacher.

2. Discuss with someone how amides and acyl halides would react with the reagent on your card. (Use words like: “fast,” “slow,” “gives off gas,” “forms a product.)

3. Which reacts faster – amides or acyl halides? Why do you think so?

4. Talk with your partner about where these reactions are useful in everyday life.

5. Join another pair to make a group of four. Share your ideas and listen to theirs.

6. Add new points you had not thought of before.

7. Listen carefully and ask short questions if something is not clear.

Activity 6.6 Presenting Reactions

In small group with your classmates discuss and present on the following.

1. Reaction Mechanisms

a. Define reaction mechanism Key components: reactants, intermediates, transition states and products

b. State the types of reaction mechanisms:

2. Reduction Reactions

a. Define reduction reactions

b. State the types of reduction reactions

3. Chemical Testing Methods

4. Presentation Guidelines

a. Clear and concise language

b. Visual aids (diagrams, charts, spectra)

c. Examples and illustrations

d. Group participation and discussion

5. Present your work to the whole class

Structure, Properties and Uses of Fats and Oils

Fats and Oils

Fats and oils are part of the lipid family. They are made mostly of carbon and hydrogen, with little oxygen. They do not mix with water (they are hydrophobic).

They give us energy and help build parts of living things.

Structure of Fats and Oils

Triglycerides: The Units of Fats and Oils

Fats and oils are made up of triglycerides. A triglyceride = 1 glycerol + 3 fatty acids.

Glycerol Has 3 carbon atoms in a row. Each carbon has a –OH (hydroxyl) group. Because it has 3 –OH groups, glycerol is called a triol.

Formula: C₃H₈O₃.

H2C – OH HC – OH H2C – OH Glycerol Fatty acids Long chains of carbon and hydrogen with a –COOH (carboxyl) group at one end.

Formula: RCOOH (R = long chain).

Chain length usually has 12–20 carbons.

Types of fatty acids

1. Saturated: Only single bonds (C–C). Chains are straight and pack closely.

Usually solid at room temperature.

2. Unsaturated: Have one or more double bonds (C=C). Double bonds create bends (“kinks”). Cannot pack tightly. Usually liquid at room temperature.

Reaction to form triglycerides C₃H₈O₃+ 3RCOOH → (RCOO)₃C₃H₅+ 3H₂O Formation of Triglycerides CH2OH + 3RCOOH → RCOOCH2 + 3 H2O CHOH RCOOCH CH2OH RCOOCH2 Glycerol + Fatty Acid → Triglyceride + water This diagram shows how triglycerides (the building blocks of fats and oils) are formed Sources of Fats and Oils Fats and oils come from both animal and plant sources. Animal sources usually give fats (solid at room temperature), while plant sources usually give oils (liquid at room temperature).

Table 6.2: Some sources of fats and oils Animal Sources (Fats) Plant Sources (Oils) Butter (milk/cream) Olive oil (olives) Lard (pigs) Groundnut/Peanut oil Tallow (cows and sheep) Palm oil (palm fruits) Fish oils (cod liver oil) Coconut oil Soybean oil Sunflower oil Canola oil Summary Animal = Fats (solid at room temperature, saturated fatty acids) Plants = Oils (liquid at room temperature, unsaturated fatty acids) Physical Properties of Fats and Oils Fats and oils are members of the lipid family. Their physical properties help us to tell the difference between them. The Table 6.3 below compares fats and oils:

Table 6.3:Physical properties of fats and oils Fats Oils Solid at room temperature Liquid at room temperature Usually colourless or pale (can be white) Usually colourless, pale yellow or reddish Little or no odour when pure Little or no odour when pure Greasy taste Greasy or mild flavour Insoluble in water, soluble in organic solvents Insoluble in water, soluble in organic solvents Less dense than water (float on water) Less dense than water (float on water) Higher melting point (solid) Lower melting point (liquid) Mostly from animal sources Mostly from plant sources Summary

1. Fats are solid at room temperature, while oils are liquid.

2. Both are insoluble in water but soluble in organic solvents.

3. Both are less dense than water and float on it.

4. Fats mainly come from animals, while oils mainly come from plants.

Chemical Properties of Fats and Oils

1. Hydrolysis (Breaking Down Fats and Oils)

Fats and oils can be broken into glycerol and fatty acids by enzymes (lipases) during digestion. In the small intestine, bile salts first break fats into small droplets (emulsification), giving enzymes more surface area. Pancreatic lipase then hydrolyses the ester bonds in triglycerides.

(RCOO)₃C₃H₅+ 3H₂O → C₃H₈O₃+ 3RCOOH Hydrolysis can also happen in the lab under acidic or basic conditions:

a. Acidic Hydrolysis Uses an acid catalyst (e.g., H₂SO₄). Produces glycerol and fatty acids.

CH₃COOCH₂CH₃+ H₂O/(H₂SO₄) → CH₃CH₂OH + CH₃COOH RCOOCH2 CH2OH RCOOCH + 3H2O/H+→ CHOH + 3RCOOH RCOOCH2 CH2OH Triglyceride + water/acid → Glycerol + Fatty Acid

b. Basic Hydrolysis (Saponification) Uses a strong base (e.g., NaOH). Produces glycerol and soap (salts of fatty acids).

C17H35COOCH2 CH2OH C17H35COOCH + 3NaOH → CHOH + 3 C17H35COONa C17H35COOCH2 CH2OH Tristearin + alkali → Glycerol + Soap

2. Hydrogenation (Hardening of Oils)

Unsaturated oils (liquid) can be changed into saturated fats (solid) by adding hydrogen across the double bonds. This process requires a catalyst such as nickel, palladium, or platinum at high temperature and pressure. It is used in making margarine.

CₙHₘ+ H₂→(Catalyst)→ CₙHₘ₊₂

3. Transesterification Reaction of fats/oils with alcohol to make biodiesel and glycerol. The glycerol backbone is replaced, forming new esters.

(R’COO)₃C₃H₅+ 3R’’OH → C₃H₈O₃+ 3R’COOR’’ R'COOCH2 CH2OH R'COOCH + 3 R''OH → CHOH + 3 R'COO R'' R'COOCH2 CH2OH

4. Rancidity (Spoiling of Fats and Oils)

Fats and oils can spoil when exposed to air, light, moisture, or heat.

This produces unpleasant odour and taste. Oxidative rancidity occurs in unsaturated fats when oxygen attacks double bonds, forming aldehydes, ketones, and short-chain acids.

Unsaturated Fat + O₂→ Hydroperoxides → Aldehydes + Ketones + Short- chain fatty acids Uses of Fats and Oils Fats and oils have many uses in food, industry, medicine, and daily life. The

Table 6.4 below shows how they are applied in different areas:

Table 6.4: Uses of fats and oils Category Uses Food and Nutrition · Rich source of energy · Supply essential fatty acids · Help absorption of fat-soluble vitamins (A, D, E, K) · Add flavour and texture to food (butter, margarine, cooking oil) Industrial Uses · Soap making (saponification) · Cosmetics (creams, lotions, lipsticks) · Candle making · Lubricants for machines · Paints and varnishes (drying oils like linseed oil) · Biodiesel production Medicine and Health · Ointments and medicated creams · Fish oils (omega-3) for heart and brain health Everyday Life · Cooking and frying foods · Polishes (shoe and floor polish) · Provide warmth and energy storage (blubber, body fat) Manufacture of Margarine

1. Start with vegetable oil Margarine is made from liquid vegetable oil (like soybean oil, sunflower oil or palm oil).

2. Clean and prepare the oil The oil is filtered and purified to remove any dirt or unwanted materials.

3. Hydrogenation (hardening the oil) A special process called hydrogenation is used.

Hydrogen gas is bubbled through the oil with a nickel catalyst.

This changes the liquid oil into a semi-solid fat that looks like butter.

4. Blending and mixing The hardened oil is mixed with milk or water, salt (for taste) and vitamins (A and D) Sometimes colouring and flavouring to make it look and taste like butter.

5. Cooling and packaging The mixture is cooled until it becomes smooth and spreadable.

Finally, it is packed into tubs or wrappers and sent to shops.

Refer to Figure 6.1 for the Flowchart diagram of Manufacture of Margarine

Figure 6.1: Flowchart diagram of Manufacture of Margarine Preparation of Soap Soaps are made when oils or fats react with alkalis (bases). This reaction is called saponification, and it also produces glycerol as a by-product. Soap can be made locally or industrially.

Local Production of Soap

Materials

1. Oil (palm oil, coconut oil, shea butter oil, or palm kernel oil)

2. Ashes (from burnt cocoa pods or plantain peels)

3. Water

4. Salt Steps

1. Dissolve ashes in water and filter. The liquid is the alkali solution.

2. Heat the oil in a pot (don’t overheat).

3. Slowly add the alkali solution to the hot oil and stir well.

4. Keep stirring for about 20–30 minutes until the mixture thickens (soap forms).

5. Add salt solution and allow to cool.

6. The soap formed is shaped into bars and packaged.

Industrial Production of Soap

Materials

1. Fats or oils (palm oil, coconut oil, olive oil)

2. Sodium hydroxide or potassium hydroxide

3. Brine (salt solution)

4. Water Steps

1. Heat the oils in large tanks.

2. Add the alkali (base) carefully and stir. Soap and glycerol are formed.

3. Boil for 1–2 hours while stirring until the mixture thickens.

4. Add brine (salt solution) – soap floats to the top, glycerol stays below.

5. Skim off the soap, remove and purify the glycerol.

6. Wash and bleach the soap to remove colour, smell, and impurities.

7. Add fragrance, preservatives, and colouring for better quality.

8. Mould the soap into shapes and allow it to dry and harden.

Activity 6.7 Exploring Fats and Oils

Work in a group with your classmates for this activity.

1. Write the general molecular formula of a fat (triglyceride) molecule:

2. Use model kits or cutouts to build saturated and unsaturated fats.

3. List the differences in structure and physical properties

a. Structure differences

b. Physical property differences

4. List common sources of fats and oils. Classify them as animal or plant- based.

5. (a) Explain why fats and oils are classified as triglycerides

(b) Write the balanced equation for the formation of a triglyceride

6. Research and presents one reaction of fats and oils

a. Hydrolysis in alkaline/acidic conditions → formation of glycerol and soap/fatty acids.

b. Enzymatic hydrolysis → action of lipase enzyme in digestion.

c. Catalytic hydrogenation → conversion of oils to margarine.

d. Rancidity → why fats spoil and how to prevent it.

Activity 6.8 Making and Understanding Soap

Work in a group with your classmates for this activity.

Materials Palm oil or coconut oil, Wood ash (alkali) or caustic soda (NaOH), Procedure

1. Prepare a small sample of soap by mixing the oil and alkali, following the procedure from the “local production of salt method”.

2. Observe the outcomes (texture, hardness, lathering, scent).

3. Discuss and make suggestions to improve quality (e.g., adding perfume, colour, herbs, or improving smoothness).

4. Draw the general structure of a soap molecule. A soap molecule has:

a. A long tail (hydrocarbon chain) that loves oil and grease( hydrophobic).

b. A head (–COONa or –COOK) that loves water (hydrophilic).

5. Label the oil-loving part and the water-loving part.

6. Outline the main stages of soap manufacture:

a. Hydrolysis of fat/oil (Saponification): Fat + Alkali → Glycerol + Soap.

b. Separation: Soap is separated from glycerol and impurities.

c. Purification: Soap is washed, dried, and sometimes mixed with additives (perfume, colouring).

7. Give a short oral presentation on observations and improvements.

Activity 6.9 Soap versus Soapless Detergents

1. Observe examples of soapy detergents (traditional soap) and soapless detergents (synthetic detergents) in Figure 6.2.

a. Discuss how their structures are different.

b. Discuss how each one removes grease and dirt.

Figure 6.2: Soapy detergents (traditional soap) and soap - less detergents

2. Make a list of advantages of soapless detergents compared to soaps.

a. Which one works better in hard water?

b. Which one leaves less residue on clothes and surfaces?

3. Share your ideas with the class.

1. a. State the functional group present in

i. Esters

ii. Amides

iii. acyl halides.

b.

i. Write the general formula of an ester.

ii. Give two everyday uses of esters.

2. Write a balanced chemical equation to show the reaction between:

a. ethanoic acid and ethanol in the presence of concentrated H₂SO₄.

b. ethanoyl chloride and ammonia.

c. Explain briefly why acyl halides are more reactive than amides.

3. a. Describe how ethyl ethanoate can be prepared in the laboratory.

b. State two methods by which amides can be prepared from carboxylic acids.

c. Compare the solubility of esters and amides in water. Explain your answer in terms of hydrogen bonding.

4. A student prepared an ester in the lab but obtained a very low yield.

a. Suggest three possible reasons for the low yield.

b. Propose modifications to improve the yield.

c. Discuss the importance of alkanoic acid derivatives in everyday life, with at least one example each from the categories below.

· food and flavours · medicine · industrial processes.

5. a. State the general molecular formula of a triglyceride.

b. Name the type of chemical bond that joins glycerol to fatty acids in fats and oils.

c. Mention two physical properties that distinguish fats from oils.

6. a. Write a balanced chemical equation for the formation of a triglyceride from glycerol and three fatty acids.

b. Explain briefly why fats are solid at room temperature while most oils are liquid.

7. a. Describe the structure of glycerol and fatty acids that make up fats and oils.

b. Distinguish between saturated and unsaturated fatty acids using their structural features.

c. Compare the solubility of fats and oils in water and in organic solvents. Explain your answer.

8. a. Discuss three everyday uses of fats and oils, giving one example for each use.

b. A nutritionist wants to compare the health effects of saturated and unsaturated fats in the human diet.

i. Explain why excess consumption of saturated fats may be harmful.

ii. Suggest two benefits of including unsaturated oils in the diet.

Soap and Soapless Detergents

1. a. State the functional group present in a soap molecule.

b. Write the general formula of the hydrophilic head in soap.

c. List two examples each of

i. Soapy detergents

ii. Soapless detergents.

2. a. Explain why soaps do not lather well in hard water.

b. State two differences in the structure of soap and soapless detergents.

3. a. Describe how soap can be prepared locally from vegetable oil.

b. Write a balanced chemical equation for the saponification of a fat.

c. Compare the cleansing action of soap and soapless detergents, explaining the role of the hydrophilic and hydrophobic parts.

4. a. Discuss three everyday uses of soaps and three uses of soapless detergents.

b. A chemist wants to reduce the environmental problems caused by soapless detergents.

i. Identify one major environmental problem caused by some synthetic detergents.

ii. Suggest two solutions to reduce this problem.

Polymers are very large molecules that can be natural or man-made. Natural polymers include proteins (from amino acids) and carbohydrates (from glucose), which are important for life. Synthetic polymers, such as polythene, PVC, nylon, and terylene, are made by humans and are widely used in everyday materials.

KEY IDEAS

· Amino acid: the small building block (monomer) that makes up proteins.

· Carbohydrates: natural polymers made of glucose molecules, providing energy.

· Glucose: a simple sugar molecule, the monomer of carbohydrates.

· Natural polymers: polymers that occur in living things, such as proteins and carbohydrates.

· Polymers: very large molecules made of many repeating units (monomers).

· Proteins: natural polymers made of amino acids, important for growth and repair.

· Synthetic polymers: man-made polymers like nylon, PVC, and polythene.

Natural Polymers

Polymers are very big molecules made up of many small, repeating units called monomers. Think of them like a chain made of many identical links. The word polymer comes from Greek: “poly” means many and “mer” means parts So, polymers are “many parts joined together.”

How are polymers made?

The making of polymers is called polymerisation. In this process, monomers join together by forming strong bonds, just like beads being joined on a string.

Types of Polymerisations

1. Addition Polymerisation (Chain-Growth)

In this process, monomers join one after another to make a long chain. No small molecule is released – everything stays in the chain. Usually happens with monomers that have double bonds (C=C) or triple bonds (C≡C).

Key Features

a. The chain grows very fast once it starts.

b. The polymer has the same atoms as the monomer (nothing lost).

c. Needs careful control of temperature because it gives out heat.

Example: Making polythene from ethene.

2. Condensation Polymerisation (Step-Growth)

Here, monomers join together but at the same time, a small molecule like water (H₂O), hydrogen chloride (HCl), or ammonia (NH₃) is released. The monomers must have two or more special reactive groups to link up.

Key Features

a. The chain grows step by step (slowly).

b. Small molecules are given off during the reaction.

c. The final polymer is different from the monomer, because something was lost.

Example: Making nylon (water is released).

Types of Polymers by Source

1. Natural Polymers: Found in living things, e.g., proteins, carbohydrates, nucleic acids (DNA).

2. Synthetic Polymers: Man-made, e.g., plastics, nylon, polyester, rubber.

Properties of Polymers

The properties of polymers depend on the following

1. The type of monomer used.

2. The arrangement of the monomers.

3. The length of the chains.

4. The interactions between chains.

These factors determine whether a polymer is strong, flexible, soluble, or resistant to heat.

Addition vs. Condensation Polymerisation

Table 7.1: Comparison of addition and condensation polymerisation Addition Polymerisation Condensation Polymerisation What happens Monomers add one by one to form a chain.

Monomers join, but a small molecule (like water or HCl) is released.

Speed Fast once it starts. Slow, step-by-step growth.

Monomer type Needs monomers with double (C=C) or triple bonds (C≡C).

Needs monomers with two or more special groups (functional groups).

Atoms lost? No atoms lost – polymer has same atoms as monomer.

Atoms lost – small molecules (e.g., H₂O) are removed.

Polymer composition Same as the monomer. Different from the monomer.

Example Polythene (from ethene). Nylon (water is released when formed).

Proteins Proteins are natural polymers. They are made from small building blocks called amino acids. Many amino acids join together in a chain to form a protein.

Functions of Proteins in the Body

1. Help with growth and repair of body tissues (muscles, skin, hair).

2. Make important enzymes and hormones.

3. Provide some energy when needed.

Example foods rich in protein: eggs, beans, fish, meat, milk, nuts.

Structure of an Amino Acid

Every amino acid has the same basic structure

1. Central Carbon Atom (C) – also called the alpha carbon.

2. Amino Group (–NH₂) – this makes the molecule a base.

3. Carboxyl Group (–COOH) – this makes the molecule an acid.

4. Hydrogen Atom (–H) – attached to the central carbon.

5. Side Chain (–R group) – this part is different for each amino acid and gives it special properties.

Special Features

Each amino acid has two important parts

1. Amino group (–NH₂)

2. Carboxyl group (–COOH) They link together like beads on a string to make proteins.

Protein Formation (Peptide Bonds)

When two amino acids join together, the acid part (–COOH) of one reacts with the amino part (–NH₂) of the other. In this process, a water molecule (H₂O) is removed, and a peptide bond is formed.

H₂N − CHR − COOH + H₂N − CHR′− COOH → H₂N − CHR − CO − NH − CHR′− COOH + H₂O This process keeps repeating, so many amino acids link together in a long chain.

The chain always grows in one direction from the amino end (N-end) to the acid end (C-end). The order of amino acids in the chain (called the primary structure) is controlled by the genetic code (DNA).

Because there are 20 different amino acids, proteins can be made in almost endless ways. This is why proteins can do many different jobs in living things.

1. Keratin makes your hair and nails strong.

2. Enzymes help break down food in your body.

So, proteins show us how simple building blocks can combine to make complex, useful materials for life.

Carbohydrates Carbohydrates are food molecules made of carbon, hydrogen, and oxygen.

Their name means “carbon with water.” They are one of the main groups of substances living things need, along with proteins, fats (lipids), and nucleic acids.

Carbohydrates give the body energy. Examples include sugar, bread, rice, and potatoes.

Sugar bread Classification of Carbohydrates Carbohydrates are grouped by how many sugar units they have.

1. Monosaccharides (One sugar unit): The simplest sugars.

Examples: Glucose (in fruits), Fructose (in honey), Galactose (in milk).

2. Disaccharides (Two sugar units): Made when two simple sugars join together.

Examples

a. Sucrose = Glucose + Fructose (table sugar)

b. Lactose = Glucose + Galactose (milk sugar)

c. Maltose = Glucose + Glucose (malt sugar)

3. Oligosaccharides (A few sugar units): Chains of 3–10 sugars. Often found on cell surfaces and help cells “recognize” each other.

4. Polysaccharides (Many sugar units): Very long chains of sugars. Used for energy storage (e.g., starch in plants, glycogen in animals) or for structure (e.g., cellulose in plants, chitin in insects).

Glucose – The Main Building Block of Carbohydrates Glucose (C₆H₁₂O₆) is a simple sugar (monosaccharide). It is the main source of energy for living things, like plants, animals, and humans.

Structure of Glucose

It has 6 carbon atoms usually arranged in a ring.

It has several –OH groups (hydroxyl groups) that make it dissolve easily in water.

In one form, it has a special –CHO group (aldehyde group).

Glucose can exist in two slightly different ring forms: α-glucose and β-glucose.

This difference is important because it affects how glucose units join to form bigger carbohydrates like starch and cellulose.

α-glucose β-glucose

Figure 7.1: Structures of α and β glucose Glycosidic Bonds – How Glucose Units Join Glucose molecules can join together to make bigger carbohydrates. They do this through a condensation reaction, where a water molecule (H₂O) is removed. The link that holds two glucose units together is called a glycosidic bond.

Example of reaction: C₆H₁₂O₆+ C₆H₁₂O₆→ C₁₂H₂₂O₁₁+ H₂O The type of glycosidic bond formed (α or β) depends on how the glucose units are joined. This difference (α or β) decides whether the larger carbohydrate will be used for energy storage (like starch or glycogen) or for structure (like cellulose).

Major Glucose Polymers and Their Functions

When many glucose units join together, they form glucose polymers. These are very important for living things.

Table 7.2: Glucose polymers and their functions Polymer Where found Function Examples Starch Plants (rice, yam, potatoes, maize) Stores energy for plants; source of energy for humans Rice, bread, maize Glycogen Animals (liver, muscles) Stores energy in animals; quickly broken down to glucose Human liver and muscles Cellulose Plant cell walls Provides strength and structure;

dietary fibre in humans Wood, cotton, vegetables Chitin Exoskeletons of insects, crabs, lobsters Provides hard protective covering and support Insects, crabs, lobsters Structural Diversity from One Building Block All these polymers are made from the same sugar unit – glucose. But the way glucose units are joined together makes a big difference!

Table 7.3: Structural differences in different glucose polymers Polymer Properties Function Starch & Glycogen Easy to break down Energy storage in plants and animals Cellulose Strong, indigestible fibres Strength and support in plant cell walls Chitin Tough, flexible covering Protective shells in insects, crabs, lobsters The properties of a big molecule (polymer) depend not only on the building block (glucose), but also on how the blocks are joined together.

Activity 7.1 Testing Carbohydrates

1. Wear goggles and gloves. Always handle test solutions carefully and listen to your teacher’s instructions.

2. Test the following solutions · Glucose solution · Sucrose solution · Starch solution

3. Test for Reducing Sugars (Benedict’s Test)

a. Add Benedict’s solution to each test tube.

b. Heat gently in a warm water bath.

c. Watch the colour changes · Blue = No sugar · Green/Yellow/Red = Sugar present

4. Test for Starch (Iodine Test)

a. Add a few drops of iodine solution to the starch sample.

b. Watch the colour change: Blue-black = Starch present

5. Record Results

Fill in the table below with your observations Food Sample Test Used Observation (Colour Change) Glucose solution Benedict’s Test Sucrose solution Benedict’s Test Starch solution Iodine Test

6. Answer these questions

a. Which samples had sugar?

b. Which sample had starch?

c. Why do we need carbohydrates?

Activity 7.2 Carbohydrate Classification

1. Observe the list foods items in Figure 7.2, list 5 foods that contain carbohydrates.

Figure 7.2: List of food items

2. Compare your list with a partner.

3. On your paper, draw three columns and title them

a. Monosaccharides (e.g., glucose, fructose)

b. Disaccharides (e.g., sucrose, maltose, lactose)

c. Polysaccharides (e.g., starch, cellulose, glycogen)

4. From the food samples, place or draw each food under the most likely group.

5. Write one sentence under each column: “These usually have 1, 2, or many sugar units.”

Test for starch

6. Put a tiny piece or smear of the sample (bread/pasta) on a white tile/paper towel.

7. Ask for one drop of iodine from your teacher. Place it on the sample.

8. Observe: If it turns blue-black, starch is present.

9. Record in your notebook: Food → Iodine colour → Starch present? (Yes/ No).

10. In one sentence, explain: “Polysaccharides → Disaccharides → Monosaccharides.”

11. Your group will receive one carbohydrate to represent

a. Starch

b. Sucrose

c. Lactose

d. Cellulose

12. Explain Where your assigned carbohydrate is found.

Can humans digest it easily?

Why or why not?

13. Present your explanation to the class.

A synthetic polymer is a very large molecule made from many smaller, repeating parts called monomers. These are not found naturally – they are made by scientists in factories through chemical reactions. Most synthetic polymers come from oil or natural gas. Some newer ones are made from plants. Scientists can control how polymers are made by choosing the following

1. The type of monomer

2. How the monomers join

3. How long the chains are

4. Whether the chains are straight, branched, or linked together.

Because of this, polymers can be designed to have the following features.

a. Hard or soft

b. Bendable or stiff

c. Clear or not see-through

d. Waterproof or able to absorb water.

One problem: most synthetic polymers (like plastics) do not break down easily in nature. This leads to plastic pollution.

Classification of Synthetic Polymers

1. By Structure

a. Linear: one straight chain

b. Branched: main chain with side chains

c. Cross-linked: chains joined together

d. Network: lots of cross-links forming a 3D web.

2. By Heat Behaviour

a. Thermoplastics: soften when heated and can be reshaped.(They have weak intermolecular forces that break down under heat)

b. Thermosets: set hard when heated and cannot be reshaped. (Due to its three-dimensional cross-linked structure, they are rigid and cannot be remelted or reshaped)

c. Elastomers: rubber-like; can stretch and go back to their original shape when released. (They have weak intermolecular forces allowing them to stretch. They are also lightly cross-linked and cannot be remelted)

3. By Reaction Type

a. Addition Polymers: monomers join without making other small molecules.

b. Condensation Polymers: monomers join while giving off small molecules (like water).

Addition Polymerisation (Chain Growth)

In addition-polymerisation, monomers with double bonds join to form long chains.

Steps

1. Initiation – a starter (like a free radical) attacks a monomer.

2. Propagation – the chain grows quickly as more monomers join.

3. Termination – the chain stops growing when active ends combine.

Example: Polyethene (Polythene)

Made from ethene (C₂H₄). Reaction: n CH₂=CH₂→ [–CH₂–CH₂–]ₙ Properties

1. Resists acids, bases, and most chemicals.

2. Does not absorb water.

3. Not biodegradable.

Uses

1. Plastic bags, bottles, food containers.

2. Pipes, water tanks, insulation.

3. Car parts, wire coatings.

Example: Polyvinyl Chloride (PVC)

Made from vinyl chloride (CH₂=CHCl).

Reaction: n CH₂=CHCl → [–CH₂–CHCl–]ₙ Properties

1. Resists many chemicals.

2. Damaged by heat and sunlight (needs stabilisers).

3. Flame-resistant (self-extinguishing).

4. Not biodegradable.

Uses

1. Pipes, gutters, window frames, doors.

2. Credit cards, bottles, packaging.

Example: Polytetrafluoroethene (PTFE / Teflon) Made from tetrafluoroethene (CF₂=CF₂). Reaction: n CF₂=CF₂→ [–CF₂–CF₂–]ₙ Properties

1. Resists almost all chemicals.

2. Waterproof and non-sticky.

3. Does not break down in sunlight or weather.

4. Not biodegradable.

Uses

1. Non-stick frying pans.

2. Wire and cable coatings.

3. Medical implants and devices.

4. Chemical storage linings.

5. Dental floss coating.

Condensation Polymerisation (Step Growth)

In condensation polymerisation, monomers with special groups react and release a small molecule (like water or HCl). Two different monomers often join together.

Molecules get bigger step by step.

General Idea: A–A + B–B → A–B–A–B–A–B + small molecule (like water).

This process makes important materials such as nylon and polyesters.

Types of Condensation Polymers

Polyesters What are they?

Polyesters are man-made plastics made when two special chemicals (a dicarboxylic acid and a diol) join together. When this happens, water is released, and long chains called polymers are formed.

Properties of Polyesters

1. They do not wear out easily.

2. They resist acids, oils, and many chemicals.

3. They can handle medium heat.

4. They are light in weight.

5. They do not rot away in nature (non-biodegradable).

Uses of Polyesters (where we use them)

1. For clothing, sportswear, and other fabrics.

2. For packaging, like PET bottles and food wraps.

3. In cars, for seat belts, airbags, and inside parts.

4. In buildings, for strong roofs and insulation.

5. In hospitals, for stitches and artificial heart valves.

6. In electronics, for tapes and light casings.

Polyamides What are they?

Polyamides (like nylon) are made when two types of chemicals (dicarboxylic acids and diamines) join together. Water is released, and strong chains with special amide bonds are formed. These bonds allow hydrogen bonds between chains, making them strong.

Properties of Polyamides

1. They are very light materials.

2. They are strong but can also bend easily.

3. They stay flexible even in heat.

4. They are very strong and hard to break.

5. They can handle high temperatures before melting.

6. They resist wearing out, even with rubbing.

7. They do not rust or get damaged by strong chemicals.

Uses of Polyamides

1. In clothing, stockings, sportswear, and swimsuits.

2. In homes, for carpets, curtains, and furniture covers.

3. Outdoors, for parachutes, tents, and climbing ropes.

4. In cars, for tyres, airbags, and engine parts.

5. In machines, for gears, bearings, and cable ties.

6. In wires, for insulation and coverings.

7. In sports, for fishing lines, tennis racquet strings, and bike wheels.

8. In personal care, for toothbrush and hairbrush bristles.

Pollution Problems Caused by Non-Biodegradable

Plastics Plastics that do not rot away (non-biodegradable) cause big problems

1. They stay in the environment for hundreds of years.

2. They fill up landfills and may leak harmful chemicals into the ground.

3. Millions of tons end up in the sea each year.

4. Animals get trapped in plastic waste.

5. Animals eat plastics, which can block their stomachs and cause death.

6. Making plastics uses up lots of oil and produces greenhouse gases.

7. Burning plastics in open air releases dangerous gases.

8. Plastics can block drains and cause floods in cities.

9. When plastics hold water, they can become homes for mosquitoes that spread diseases.

Activity 7.3 Exploring Polymers

Step 1: Group Work (research groups) Group A: Types of Polymerisations (Addition vs. Condensation).

Group B: Synthetic vs. Natural Polymers.

Group C: Addition Polymers made from Alkenes (e.g., Polyethene).

Group D: Condensation Polymers (e.g., Nylon and Terylene).

Step 2: Research Time

Go to the computer lab and research your group topic using the websites, videos, and templates provided.

You may use the websites below or any relevant textbooks for your research.

a. https://byjus.com/chemistry/difference-between-addition-and- condensation-polymerization/?utm_source=chatgpt.com

b. +https://en.wikipedia.org/wiki/Polymer?utm_source=chatgpt.

com

c. https://en.wikipedia.org/wiki/Addition_polymer?utm_ source=chatgpt.com

d. https://en.wikipedia.org/wiki/Condensation_polymer?utm_ source=chatgpt.com

Step 3: PowerPoint Training

1. Open Microsoft PowerPoint.

2. Create a new slide for your group topic.

3. Show chemical structures and reactions clearly.

Example: show ethene changing into polyethene.

4. Use colours, arrows, and labels to make your slides easy to understand.

Step 4: Finish your group slides

1. Show them to the teacher before the final presentation.

2. The teacher will check for scientific accuracy (make sure the reactions and properties are correct).

Step 5: Class Presentations

1. Each group will present their work to the class.

2. Use drawings, molecular models, or animations to make the presentation interesting.

3. Be ready to answer simple questions from classmates.

Step 6

Make one big comparison chart on the board or wall.

The chart should include the following.

a. Addition vs. Condensation polymers.

b. Properties (strength, flexibility, biodegradability).

c. Uses in Ghana (e.g., packaging, clothes, building materials).

Activity 7.4 Plastics and the Environment

Step 1: Observe the different plastic items your teacher shows you (bags, bottles, cups, pipes, rubber bands).

1. Based on your observation what are plastics?

2. What do we already know about them?

3. Write your ideas together on the board.

Step 2: Group Investigation

1. Working in small groups study one type of plastic.

a. Thermoplastics – soften when heated, can be reshaped.

b. Thermosets – hard plastics that cannot be reshaped after heating.

c. Elastomers – rubber-like, can stretch and return to shape.

2. Create an informational poster showing

a. What your plastic type is.

b. Its properties.

c. Examples of everyday use.

Step 3

1. Use the link to watch a short video showing plastic waste in Ghana’s rivers and cities. https://youtu.be/uFlKQdf6Klo

2. Alternatively, if no video is available, look at newspaper articles and photographs about plastic pollution.

Step 4: Take a minute to think about plastic pollution you have seen in your community.

1. Share your thoughts with a partner.

2. Together, tell the class what you noticed.

Step 5

1. As a class, make one big list of environmental problems caused by non- biodegradable plastics in Ghana.

2. Examples: dirty streets, blocked drains, flooding, dead animals, mosquito breeding, etc.

Step 6

1. In your groups, discuss and debate on the questions below.

a. What are the advantages of plastic?

b. What are the disadvantages?

c. What are possible solutions to plastic pollution?

2. Think about technology (like recycling) and laws/policies (like plastic bans).

Step 7: Design a short pamphlet (one page) with pictures and messages about

1. How to use plastics responsibly.

2. How to dispose of plastics properly.

1. a. Define monomer.

b. Define polymer.

2. State two differences between natural and synthetic polymers, giving one

example of each.

3. Name the linkage that

a) joins amino acids in proteins,

(b) joins glucose units in starch/cellulose.

4. Classify each item as mono-, di-, or polysaccharide: glucose, sucrose, cellulose, glycogen.

5. State whether protein formation is addition or condensation polymerisation.

Give a reason.

6. State whether starch formation from glucose is addition or condensation polymerisation. Give a reason.

7. Write a balanced condensation equation for forming the dipeptide Gly– Ala from glycine and alanine.

8. A hexapeptide is formed from 6 amino acids.

a. How many peptide bonds are present?

b. How many molecules of water are eliminated during its formation?

9. Write the overall formula equation for forming maltose from two glucose molecules.

10. Complete the table (each row) Polymer Linkages (major) Branching? Main function Starch Glycogen Cellulose

11. Indicate the expected test outcome (Positive/Negative and observed colour/change) for these samples

a. Egg white with biuret test

b. Gari/cooked rice with iodine test

c. Ripe banana juice with Benedict’s test.

12. Explain briefly why proteins can show different shapes/functions even though they are all polymers of amino acids.

13. Explain why humans digest starch but not cellulose, although both are polymers of glucose.

14. Show, using symbols, how glucose units form the repeating unit of starch.

Hence write the general formula of starch as a polymer of glucose and state how many water molecules are eliminated per n glucose units (use the conventional polymer formula).

15. Compare primary structure of proteins with that of polysaccharides. How does sequence relate to function in proteins versus carbohydrates?

16. A learner claims, “All polymers made from glucose are soluble and sweet.”

Evaluate this claim with two examples and structural reasons.

17. State two laboratory conditions for hydrolysis of

a. a dipeptide to amino acids

b. maltose to glucose.

18. Investigation design: Test three local foods (e.g., beans, kenkey, groundnuts/ rice) for protein and starch. Provide the following · Aim and hypothesis · Reagents & safety (biuret, iodine; goggles/gloves) · Procedure + control · Results table template (food | biuret result | iodine result | inference) · Conclusion linking results to macromolecules.

19. Quantitative reasoning: When glucose polymerises to starch, each glucose unit (Mᵣ180) becomes a repeating unit (C₆H₁₀O₅, Mᵣ162).

a. What mass fraction of the original glucose is lost as water per unit formed?

b. If 5.40 g of glucose are converted completely to starch repeating units, calculate the mass of water evolved.

c. State one assumption/limitation of this calculation for real starch.

20. Case analysis: A cereal label per 100 g shows: Protein 9 g; Carbohydrate 74 g (Sugars 12 g); Fibre 5 g.

a. Classify the carbohydrate portion into likely mono-/di- (sugars) and poly- (starch + non-starch fibre).

b. Predict results for iodine, Benedict’s, and biuret tests on an aqueous extract. Justify briefly.

c. Suggest one dietary implication of the polysaccharide fraction.

21. a. Define the term synthetic polymer.

b. Give two examples of synthetic polymers and their monomers.

22. Explain briefly how addition polymerisation and condensation polymerisation differ. Illustrate your answer with one example each.

23. a. Describe the formation of polyethene from ethene. Write the chemical equation.

b. State three properties of polyethene.

c. Mention three uses of polyethene.

24. Nylon is an important synthetic polymer produced by condensation polymerisation.

a. Name the two types of monomers used in making nylon-6,6.

b. Write a simple equation to represent the formation of nylon.

c. State three properties of nylon.

d. Mention three uses of nylon.

25. Plastics are very useful but have created major environmental problems in Ghana.

a. State four environmental problems caused by non-biodegradable plastics.

b. Suggest three practical solutions that can reduce plastic pollution in Ghana.