Chapter Notes: Carbon and its Compounds

Introduction

The previous chapter covered important compounds.
This chapter explores more compounds and the significance of carbon in both elemental and combined forms.

Activity 4.1: Categorizing Materials

List ten things used or consumed since morning.
Compile lists with classmates and sort items into categories:
- Things made of metal
- Things made of glass/clay
- Other materials
Many items in the last category contain compounds of carbon.

Testing for Carbon Compounds

When carbon-containing compounds are burnt, they form carbon dioxide (CO₂).
A common test for CO₂:
- Pass the gas through lime water (Ca(OH)₂).
- If CO₂ is present, lime water turns milky due to the formation of calcium carbonate (CaCO₃).

Significance of Carbon

Food, clothes, medicines, books, and most materials contain carbon.
All living organisms are carbon-based.

Carbon Availability in Nature

Earth’s crust: Contains 0.02% carbon in minerals like:
- Carbonates (CaCO₃)
- Hydrogencarbonates (NaHCO₃)
- Coal & petroleum
Atmosphere: Contains 0.03% CO₂.

Importance of Carbon

Despite its small abundance, carbon is highly significant due to its unique properties.
Understanding carbon's properties helps in learning about its wide range of compounds and applications.

4.1 Bonding in Carbon – The Covalent Bond

Comparison of Ionic and Covalent Compounds

Ionic compounds:
- Have high melting and boiling points.
- Conduct electricity in solution or molten state.
- Formed by transfer of electrons, leading to the formation of ions.
Carbon compounds (mostly covalent):
- Have low melting and boiling points.
- Are poor conductors of electricity.
- Do not form ions in solutions.

Electronic Configuration of Carbon

Atomic number of carbon = 6
Electron distribution: K = 2, L = 4
Valence electrons: 4 (needs 4 more electrons to complete its octet).

Why Carbon Does Not Form Ionic Bonds

Forming C⁴⁻ ion (gaining 4 electrons)
- Difficult for the nucleus with 6 protons to hold on to 10 electrons.
Forming C⁴⁺ ion (losing 4 electrons)
- Requires a large amount of energy to remove 4 electrons, leaving behind only 2 electrons.

Formation of Covalent Bonds

Carbon solves this problem by sharing electrons instead of transferring them.
Covalent bonds are formed when atoms share valence electrons to complete their octet.
Covalent bonding occurs in carbon and many other elements.

Examples of Covalent Bonding

1. Hydrogen Molecule (H₂)

Atomic number of hydrogen = 1
Electron distribution: K = 1
Hydrogen needs 1 more electron to complete the K shell.
Two hydrogen atoms share their electrons to form a single covalent bond:

Electron dot structure: H : H or H—H

2. Chlorine Molecule (Cl₂)

Atomic number of chlorine = 17
Electron distribution: K = 2, L = 8, M = 7
Needs 1 more electron to complete the octet.
Two chlorine atoms share one pair of electrons to form a single bond.

Electron dot structure: Cl : Cl or Cl—Cl

3. Oxygen Molecule (O₂)

Atomic number of oxygen = 8
Electron distribution: K = 2, L = 6
Needs 2 more electrons to complete the octet.
Two oxygen atoms share two pairs of electrons forming a double bond.

Electron dot structure: O :: O or O=O

4. Water Molecule (H₂O)

Oxygen (O) has 6 valence electrons, and it needs 2 more to complete its octet.
Hydrogen (H) has 1 valence electron and needs 1 more to complete the K shell.
Each hydrogen shares 1 electron with oxygen, forming two single bonds.
- Electron dot structure:
  - H : O : H
  - or H—O—H

5. Nitrogen Molecule (N₂)

Atomic number of nitrogen = 7
Electron distribution: K = 2, L = 5
Needs 3 more electrons to complete its octet.
Each nitrogen atom shares 3 electrons, forming a triple bond.
- Electron dot structure: N ≡ N

6. Ammonia Molecule (NH₃)

Nitrogen (N) has 5 valence electrons and needs 3 more to complete the octet.
Hydrogen (H) needs 1 more electron to complete the K shell.
Nitrogen shares 3 electrons with three hydrogen atoms, forming three single bonds.
- Electron dot structure:
  - H : N : H
    Ḧ
  - or H—N—H
    |
    H

7. Methane (CH₄) – A Carbon Compound

Carbon has 4 valence electrons and needs 4 more to complete its octet.
Hydrogen has 1 valence electron and needs 1 more to complete the K shell.
Carbon shares 1 electron with each hydrogen, forming four single covalent bonds.
- Electron dot structure:
  H
  |
  H—C—H
  |
  H

Properties of Covalent Compounds

Strong Intramolecular Bonds
- Covalent bonds within the molecules are strong.
Weak Intermolecular Forces
- The forces of attraction between molecules are weak, leading to:
  - Low melting and boiling points.
Poor Conductors of Electricity
- Covalent compounds do not form ions, so they do not conduct electricity.

Table 4.1: Melting and Boiling Points of Some Carbon Compounds

Compound	Melting Point (K)	Boiling Point (K)
Acetic acid (CH₃COOH)	290	391
Chloroform (CHCl₃)	209	334
Ethanol (CH₃CH₂OH)	156	351
Methane (CH₄)	90	111

These compounds have lower melting and boiling points than ionic compounds.
Due to weak intermolecular forces, they exist as liquids or gases at room temperature.

Conclusion

Covalent bonding occurs in carbon and other elements through electron sharing.
Covalently bonded compounds have low melting and boiling points.
They are poor conductors of electricity due to the absence of ions.
The versatility of carbon in forming covalent bonds leads to a large variety of carbon compounds.

Allotropes of Carbon

Carbon exists in different allotropic forms, which have different physical properties but the same chemical properties.

1. Diamond

Structure:
- Each carbon atom is bonded to four other carbon atoms in a tetrahedral structure.
- Forms a rigid three-dimensional network.
Properties:
- Hardest natural substance.
- Transparent and shiny.
- Does not conduct electricity (no free electrons).
- Used in cutting tools, jewelry, and industrial applications.
Synthesis:
- Diamonds can be artificially created by subjecting pure carbon to high pressure and temperature.
- Synthetic diamonds are identical to natural diamonds but smaller.

2. Graphite

Structure:
- Each carbon atom is bonded to three other carbon atoms in a hexagonal arrangement.
- Layers of hexagonal sheets are held together by weak van der Waals forces.
- One of the bonds is a double bond, satisfying carbon’s valency.
Properties:
- Soft and slippery (used as a lubricant).
- Good conductor of electricity (contains free-moving delocalized electrons).
- Used in pencils, lubricants, and electrodes.

3. Fullerenes

Structure:
- Carbon atoms arranged in closed hollow cages.
- The first discovered fullerene, C-60, has a football-like structure.
Properties:
- Named after Buckminster Fuller, who designed similar geodesic domes.
- Used in nanotechnology, medicine, and electronics.

Conclusion

Diamond, graphite, and fullerenes are allotropes of carbon with different physical properties due to different atomic arrangements.
Carbon’s ability to form varied structures makes it one of the most versatile elements.

QUESTIONS

1. What would be the electron dot structure of carbon dioxide (CO₂)?

Answer:

Carbon dioxide (CO₂) consists of one carbon atom and two oxygen atoms.
Carbon has four valence electrons, while oxygen has six valence electrons.
Carbon forms double bonds with both oxygen atoms to complete the octet.

Electron dot structure of CO₂:

Each oxygen shares two electrons with carbon, forming a double bond.

2. What would be the electron dot structure of a molecule of sulphur (S₈)?

Answer:

Sulphur exists as S₈, where eight sulphur atoms form a puckered ring structure.
Each sulphur atom shares two electrons with adjacent sulphur atoms.
The structure resembles a crown shape.

Electron dot structure of S₈ (simplified representation):

(Sulphur atoms are connected in a ring with single covalent bonds.)

Versatile Nature of Carbon

Introduction

Carbon forms a vast number of compounds, outnumbering compounds of all other elements combined.
This ability is due to covalent bonding, allowing carbon to form stable and diverse compounds.
Two key properties of carbon contribute to its versatility:

1. Catenation (Self-Linking Property of Carbon)

Definition: The ability of carbon atoms to form stable bonds with other carbon atoms, creating long chains, branched structures, and rings.
Carbon atoms can be linked by single, double, or triple bonds.
Types of Carbon Compounds Based on Bonding:
- Saturated Compounds: Contain only single bonds between carbon atoms (e.g., alkanes like methane - CH₄).
- Unsaturated Compounds: Contain double or triple bonds between carbon atoms (e.g., alkenes like ethene - C₂H₄ and alkynes like ethyne - C₂H₂).
Uniqueness of Carbon in Catenation:
- No other element shows such extensive catenation as carbon.
- Silicon (Si) can form chains up to 7-8 atoms long, but these compounds are highly reactive and less stable than carbon compounds.
- Reason: Carbon-carbon bonds are strong and stable, enabling the formation of millions of compounds.

2. Tetravalency of Carbon

Definition: Carbon has four valence electrons, meaning it can form four covalent bonds with other atoms.
Bonding Capabilities:
- Carbon can bond with other carbon atoms or with elements like oxygen (O), hydrogen (H), nitrogen (N), sulphur (S), chlorine (Cl), and many others.
- This results in varied chemical properties depending on the atoms bonded to carbon.
Strength of Carbon Bonds:
- The small size of carbon atoms allows its nucleus to strongly hold shared electrons, making its bonds strong and stable.
- Elements with larger atomic sizes (e.g., phosphorus, sulfur) form weaker bonds compared to carbon.

Conclusion

The ability of carbon to catenate and its tetravalency make it an exceptional element for forming a vast variety of stable compounds.
These properties explain why life is carbon-based and why carbon is so important in organic chemistry.

Organic Compounds

Introduction

The tetravalency and catenation of carbon result in the formation of a vast number of compounds.
Many organic compounds have the same functional group attached to different carbon chains.
Initially, organic compounds were believed to be produced only by living organisms.

Vital Force Theory and Its Disproof

Vital Force Theory: Proposed that organic compounds could only be synthesized within a living system, requiring a "vital force".
Friedrich Wöhler (1828) disproved this theory by synthesizing urea (CO(NH₂)₂) artificially from ammonium cyanate (NH₄CNO) in the laboratory.

Classification of Organic and Inorganic Carbon Compounds

Organic Compounds: Carbon compounds that are studied in organic chemistry (e.g., hydrocarbons, alcohols, ketones, proteins, etc.).
Exceptions: Certain carbon compounds are considered inorganic and are not classified under organic chemistry:
- Carbides (e.g., calcium carbide - CaC₂)
- Oxides of Carbon (e.g., carbon dioxide - CO₂, carbon monoxide - CO)
- Carbonates (e.g., calcium carbonate - CaCO₃)
- Hydrogencarbonates (e.g., sodium bicarbonate - NaHCO₃)

Conclusion

The study of organic compounds forms the basis of organic chemistry, which includes millions of carbon-containing compounds.
The artificial synthesis of urea marked the beginning of modern organic chemistry, proving that organic compounds can be synthesized outside living systems.

4.2.1 Saturated and Unsaturated Carbon Compounds

Saturated Hydrocarbons (Alkanes)

Contain only single bonds between carbon atoms.
Example: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), Butane (C₄H₁₀), Pentane (C₅H₁₂), Hexane (C₆H₁₄).
They are less reactive due to stable single bonds.

Unsaturated Hydrocarbons

Contain double or triple bonds between carbon atoms.
Alkenes: Contain at least one double bond. Example: Ethene (C₂H₄), Propene (C₃H₆), Butene (C₄H₈).
Alkynes: Contain at least one triple bond. Example: Ethyne (C₂H₂), Propyne (C₃H₄), Butyne (C₄H₆).
Unsaturated hydrocarbons are more reactive due to the presence of multiple bonds.

Structural Representations

Ethane (C₂H₆):
- Step 1: Link carbon atoms with a single bond → C—C
- Step 2: Attach three hydrogen atoms to each carbon to satisfy valency.
- Electron dot structure: Shows each atom sharing electrons to complete its octet.
Ethene (C₂H₄):
- Step 1: Link carbon atoms with a single bond → C—C
- Step 2: One valency per carbon remains unsatisfied.
- Step 3: A double bond forms between carbons to satisfy valency → C=C.
- Electron dot structure: Represents shared electron pairs including the double bond.
Ethyne (C₂H₂):
- Step 1: Link carbon atoms with a single bond → C—C
- Step 2: Two valencies per carbon remain unsatisfied.
- Step 3: A triple bond forms between carbons to satisfy valency → C≡C.
- Electron dot structure: Represents the triple bond.

4.2.2 Chains, Branches, and Rings

Types of Carbon Skeletons

Straight Chains: Carbon atoms are arranged in a continuous linear sequence.
- Example: Butane (C₄H₁₀) → CH₃-CH₂-CH₂-CH₃.
Branched Chains: Carbon atoms are arranged with side branches.
- Example: Isobutane (C₄H₁₀) → CH₃-CH(CH₃)-CH₃.
Cyclic Structures: Carbon atoms form a closed ring.
- Example: Cyclohexane (C₆H₁₂) → A six-carbon ring structure.

Structural Isomerism

Definition: Compounds with the same molecular formula but different structures.
Example: Butane (C₄H₁₀) exists as:
1. n-Butane (Straight chain).
2. Isobutane (Branched chain).
Structural isomers have different physical and chemical properties.

Aromatic Compounds

Contain ring structures with delocalized π-electrons.
Example: Benzene (C₆H₆)
- Structure: Hexagonal ring with alternating single and double bonds.
- Very stable due to electron delocalization.

4.2.3 Functional Groups in Carbon Compounds

Definition

Functional groups: Specific atoms or groups of atoms that replace hydrogen in a hydrocarbon chain and determine the chemical properties of the compound.

Common Functional Groups

Functional Group	Formula	Example	Name of Compound
Alcohol (-OH)	-OH	CH₃OH	Methanol
Aldehyde (-CHO)	-CHO	CH₃CHO	Ethanal
Ketone (-CO-)	-CO-	CH₃COCH₃	Propanone (Acetone)
Carboxyl (-COOH)	-COOH	CH₃COOH	Ethanoic Acid (Acetic Acid)
Halogen (-X)	-Cl, -Br, -I, -F	CH₃Cl	Chloromethane
Amino (-NH₂)	-NH₂	CH₃NH₂	Methylamine

Functional groups define the reactivity of organic compounds.
They can replace one or more hydrogen atoms in hydrocarbons.
Functional groups remain unchanged in chemical reactions, while the rest of the molecule can undergo transformations.

Summary

Hydrocarbons are classified as:
- Saturated (alkanes - single bonds).
- Unsaturated (alkenes - double bonds, alkynes - triple bonds).
Carbon compounds can exist in:
- Straight chains, branched chains, and rings.
Isomers: Compounds with the same molecular formula but different structures.
Functional groups determine the chemical properties of organic compounds.

4.2.4 Homologous Series

1. Definition

A homologous series is a group of organic compounds with:
1. Same functional group.
2. Similar chemical properties.
3. A difference of –CH₂– unit between successive members.
4. Gradual change in physical properties (melting & boiling points increase with size).

2. Examples of Homologous Series

(a) Alkanes

Formula: CₙH₂ₙ₊₂
Example:
- Methane (CH₄)
- Ethane (C₂H₆)
- Propane (C₃H₈)

(b) Alkenes

Formula: CₙH₂ₙ
Example:
- Ethene (C₂H₄)
- Propene (C₃H₆)
- Butene (C₄H₈)

(c) Alkynes

Formula: CₙH₂ₙ₋₂
Example:
- Ethyne (C₂H₂)
- Propyne (C₃H₄)
- Butyne (C₄H₆)

(d) Alcohols

Formula: CₙH₂ₙ₊₁OH
Example:
- Methanol (CH₃OH)
- Ethanol (C₂H₅OH)
- Propanol (C₃H₇OH)

4.2.5 Nomenclature of Carbon Compounds

IUPAC (International Union of Pure and Applied Chemistry) System is used to name organic compounds.
Naming Steps:
1. Identify the longest carbon chain.
2. Identify the functional group.
3. Identify branches or substituents.
4. Number the chain such that the functional group gets the lowest number.
5. Use proper prefix/suffix.

1. Naming of Alkanes

General name: Alkane (-ane suffix).
Examples:
- CH₄ → Methane.
- C₂H₆ → Ethane.
- C₃H₈ → Propane.

2. Naming of Alkenes

Suffix: "-ene".
Example:
- C₂H₄ → Ethene.
- C₃H₆ → Propene.

3. Naming of Alkynes

Suffix: "-yne".
Example:
- C₂H₂ → Ethyne.
- C₃H₄ → Propyne.

4. Naming of Functional Groups

Functional Group	Prefix/Suffix	Example
Haloalkanes	Prefix: Chloro-, Bromo-	Chloropropane
Alcohols (-OH)	Suffix: -ol	Propanol
Aldehydes (-CHO)	Suffix: -al	Propanal
Ketones (-CO-)	Suffix: -one	Propanone
Carboxylic Acids (-COOH)	Suffix: -oic acid	Propanoic acid

Key Takeaways

Saturated hydrocarbons (alkanes) have single bonds and are less reactive.
Unsaturated hydrocarbons (alkenes & alkynes) have double/triple bonds and are more reactive.
Carbon chains can be straight, branched, or cyclic.
Functional groups determine the chemical properties of a compound.
Homologous series are families of compounds with similar chemical properties but gradual change in physical properties.
Nomenclature follows IUPAC rules, considering the longest chain, functional groups, and position numbers.

QUESTIONS

1. How many structural isomers can you draw for pentane?

Pentane (C₅H₁₂) has three structural isomers:
1. n-Pentane (Straight-chain structure).
2. Iso-Pentane (Branched-chain with one methyl group on the second carbon).
3. Neo-Pentane (Branched-chain with two methyl groups on the second carbon).

2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?

Catenation: The ability of carbon atoms to form long chains, branched chains, and rings by bonding with other carbon atoms.
Tetravalency: Carbon has four valence electrons, allowing it to form stable covalent bonds with other elements (H, O, N, Cl, etc.), leading to a vast variety of compounds.

3. What will be the formula and electron dot structure of cyclopentane?

Formula: C₅H₁₀
Electron dot structure: Cyclopentane forms a ring with single bonds between carbon atoms, and each carbon forms bonds with hydrogen atoms to satisfy tetravalency.

4. Draw the structures for the following compounds:

(i) Ethanoic Acid (Acetic Acid, CH₃COOH)

Functional group: Carboxyl (-COOH).

(ii) Bromopentane (C₅H₁₁Br)

Possible isomers:
1. 1-Bromopentane
2. 2-Bromopentane
3. 3-Bromopentane

(iii) Butanone (C₄H₈O)

Functional group: Ketone (-CO-), positioned on the second carbon (2-Butanone).

(iv) Hexanal (C₆H₁₂O)

Functional group: Aldehyde (-CHO), positioned at the end of the chain.

5. How would you name the following compounds?

(i) CH₃—CH₂—Br

Bromoethane (Haloalkane with bromine attached to an ethane chain).

Here’s the continuation from (ii) and (iii) based on the given structures:

(ii) Methanal (Formaldehyde, CH₂O)

Functional group: Aldehyde (-CHO)
Structure:
```
    H
    |
H — C = O
```

(iii) Pent-2-yne (C₅H₈)

Functional group: Alkyne (Triple bond between Carbon atoms)
Structure:
H H H H| | | |H—C—C—C≡C—H| | | |H H H H

Here are detailed notes on Chemical Properties of Carbon Compounds, covering combustion, types of flames, and the formation of fossil fuels.

CHEMICAL PROPERTIES OF CARBON COMPOUNDS

4.3.1 Combustion

Definition: Combustion is a chemical reaction in which carbon and its compounds burn in the presence of oxygen, producing carbon dioxide, water, heat, and light.
General reaction: $\text{Carbon compound} + O_2 → CO_2 + H_2O + \text{Heat and Light}$

Examples of Combustion Reactions:

Combustion of carbon (graphite, diamond, charcoal): $C + O_2 → CO_2 + \text{heat and light}$
Combustion of methane (a hydrocarbon): $CH_4 + 2O_2 → CO_2 + 2H_2O + \text{heat and light}$
Combustion of ethanol (an alcohol): $C_2H_5OH + 3O_2 → 2CO_2 + 3H_2O + \text{heat and light}$

Observations from Activity 4.3:

Substances like naphthalene, camphor, and alcohol burn with different types of flames.
A metal plate placed over the flame may show soot deposition, indicating incomplete combustion.

4.3.2 Types of Flames

Blue Flame (Complete Combustion):
- Produced when there is sufficient oxygen.
- Hydrocarbons burn completely, producing CO₂ and H₂O.
- Example: LPG, CNG, and well-adjusted gas stove flames.
Yellow Flame (Incomplete Combustion):
- Occurs when oxygen supply is limited.
- Produces carbon particles (soot), CO₂, CO, and unburnt hydrocarbons.
- Example: Burning kerosene, candle flames, or smoky flames.

Observations from Activity 4.4:

Adjusting the air hole of a Bunsen burner changes the flame.
A yellow, sooty flame appears when oxygen is insufficient.
A blue, clean flame appears when there is sufficient oxygen.

Practical Application:

A blue flame in gas stoves ensures complete combustion and prevents soot deposits on utensils.
A yellow flame in gas stoves means air holes are blocked, leading to fuel wastage and blackened utensils.

4.3.3 Why Do Some Substances Burn Without a Flame?

Substances burn with a flame only if they produce vapors when heated.
Solid fuels like coal or wood burn without a flame because they do not vaporize easily.
Coal/charcoal in a traditional stove (angithi) glows red but does not form a flame.
Gaseous fuels like LPG burn with a flame because they readily vaporize.

What Causes the Yellow Colour of a Candle Flame?

The yellow flame is due to glowing carbon particles (soot) formed by incomplete combustion.
The heated soot particles emit yellow light, giving the flame its characteristic color.

4.3.4 Formation of Fossil Fuels

What Are Fossil Fuels?

Fossil fuels are energy-rich substances formed from the remains of ancient plants and animals.
Examples: Coal, Petroleum, and Natural Gas.

Formation of Coal

Formed from the remains of trees, ferns, and plants buried under the earth millions of years ago.
Layers of earth and rock compressed the plant material.
High pressure and heat converted the organic material into coal.

Formation of Petroleum and Natural Gas

Formed from the remains of tiny marine plants and animals.
The dead organisms settled on the seabed and got buried under layers of silt and sand.
Bacteria decomposed the remains, and under high pressure and temperature, they turned into oil and gas.
Oil and gas got trapped in porous rocks, just like water in a sponge.

Why Are Coal and Petroleum Called Fossil Fuels?

They are derived from ancient biological material (fossils).
Formed over millions of years through natural geological processes.
Non-renewable resources—once depleted, they cannot be replenished.

Key Takeaways

Carbon compounds burn in oxygen, releasing heat and light.
Complete combustion (blue flame) produces CO₂ and H₂O, while incomplete combustion (yellow flame) produces soot.
Coal and petroleum are fossil fuels formed from ancient plant and animal remains.
A clean blue flame indicates proper combustion, while a yellow flame indicates incomplete combustion.
Fossil fuels take millions of years to form and are non-renewable.

4.3 CHEMICAL PROPERTIES OF CARBON COMPOUNDS

Carbon compounds exhibit various chemical properties, including combustion, oxidation, addition, and substitution reactions.

4.3.1 Combustion

Definition:

Combustion is a reaction in which carbon or its compounds burn in oxygen to form carbon dioxide and release heat and light.
All forms of carbon (diamond, graphite, coal) undergo combustion.
Carbon compounds like hydrocarbons (methane, ethanol) also burn with the release of a large amount of heat.

Examples of Combustion Reactions

Carbon burning in oxygen: $C + O_2 → CO_2 + \text{heat and light}$
Methane combustion: $CH_4 + 2O_2 → CO_2 + 2H_2O + \text{heat and light}$
Ethanol combustion: $C_2H_5OH + 3O_2 → 2CO_2 + 3H_2O + \text{heat and light}$

Activity 4.3: Observing Combustion

Take naphthalene, camphor, and alcohol on a spatula and burn them.
Observe the flame type and smoke production.
Place a metal plate above the flame and check for deposition of soot.

Activity 4.4: Observing Different Flames

Light a Bunsen burner and adjust the air hole.
Observe different types of flames:
- Yellow, sooty flame: Indicates incomplete combustion (less oxygen).
- Blue flame: Indicates complete combustion (sufficient oxygen).

🔥 Key Concept:

Saturated hydrocarbons burn with a blue, clean flame.
Unsaturated hydrocarbons burn with a yellow, sooty flame.
Blocked air holes in gas stoves cause blackening of vessels due to incomplete combustion.

4.3.2 Oxidation

Definition:

Oxidation is a reaction in which a substance gains oxygen or loses hydrogen.
Carbon compounds can be oxidized either completely (as in combustion) or partially using oxidizing agents.

Oxidizing Agents

Alkaline potassium permanganate (KMnO₄)
Acidified potassium dichromate (K₂Cr₂O₇)
These add oxygen to alcohols and convert them into acids.

Activity 4.5: Oxidation of Ethanol

Take 3 mL ethanol in a test tube and warm it in a water bath.
Add a 5% solution of alkaline potassium permanganate (KMnO₄) drop by drop.
Observe the color change:
- Initially, pink color disappears as ethanol gets oxidized.
- After excess KMnO₄ is added, pink color remains because ethanol is fully oxidized.

Reaction: Oxidation of Ethanol to Ethanoic Acid

$C_2H_5OH + [O] → CH_3COOH$

(Ethanol → Ethanoic Acid)

🔎 Key Concept:

Oxidation helps in the formation of carboxylic acids from alcohols.

4.3.3 Addition Reaction

Definition:

Addition reactions occur when unsaturated hydrocarbons (alkenes, alkynes) react with hydrogen to form saturated hydrocarbons.
A catalyst (Nickel or Palladium) is used to speed up the reaction.

Example: Hydrogenation of Alkenes

(Ethene → Ethane)

Application: Hydrogenation of Vegetable Oils

Vegetable oils (unsaturated fats) remain liquid at room temperature.
Animal fats (saturated fats) are solid at room temperature.
Hydrogenation converts vegetable oils into solid fats (e.g., vanaspati ghee).

🛑 Health Concern:

Saturated fats in animal products can cause heart disease, whereas unsaturated fats are healthier.

4.3.4 Substitution Reaction

Definition:

A substitution reaction occurs when one atom in a molecule is replaced by another atom.
Saturated hydrocarbons (alkanes) undergo substitution reactions in the presence of sunlight.

Example: Chlorination of Methane

(Methane + Chlorine → Chloromethane + Hydrogen Chloride)

The chlorine replaces hydrogen atoms one by one, leading to products like CH₂Cl₂ (Dichloromethane), CHCl₃ (Chloroform), and CCl₄ (Carbon Tetrachloride).

🔎 Key Concept:

Substitution reactions occur only in saturated hydrocarbons.
Requires sunlight to proceed.
Forms multiple chlorinated products when excess chlorine is used.

Summary Table

Reaction Type	Definition	Example
Combustion	Burning of carbon compounds in oxygen, producing CO₂, heat, and light	CH₄ + O₂ → CO₂ + H₂O + heat
Oxidation	Addition of oxygen to alcohols, forming acids	Ethanol → Ethanoic acid
Addition	Addition of hydrogen to unsaturated hydrocarbons using catalysts	Ethene + H₂ → Ethane
Substitution	Replacement of hydrogen by chlorine in alkanes (in sunlight)	Methane + Cl₂ → Chloromethane + HCl

Conclusion

Carbon compounds undergo various reactions due to their versatile bonding.
Combustion produces energy, making hydrocarbons useful fuels.
Oxidation reactions help in converting alcohols into acids.
Addition reactions convert unsaturated hydrocarbons into saturated ones.
Substitution reactions involve replacement of hydrogen in saturated hydrocarbons.

QUESTIONS

Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
- The conversion of ethanol (C₂H₅OH) to ethanoic acid (CH₃COOH) involves the addition of oxygen or the removal of hydrogen.
- In this reaction, an oxidizing agent like alkaline potassium permanganate (KMnO₄) or acidified potassium dichromate (K₂Cr₂O₇) is used to add oxygen to ethanol, converting it into ethanoic acid.
- Since oxidation is defined as the gain of oxygen, this reaction is classified as an oxidation reaction.
- Reaction: $C_2H_5OH + [O] → CH_3COOH$
A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
- Ethyne (C₂H₂) burns with a sooty yellow flame in air due to incomplete combustion, which results in the formation of carbon particles (soot). This type of flame is not hot enough for welding.
- When ethyne is burnt in pure oxygen, complete combustion occurs, producing a very high-temperature blue flame (oxy-acetylene flame).
- This high temperature is necessary to melt and join metals efficiently in welding.
- Reaction: $2C_2H_2 + 5O_2 → 4CO_2 + 2H_2O + \text{heat (very high temperature)}$
- Therefore, a mixture of ethyne and air is not used because air contains only 21% oxygen, which is insufficient for complete combustion and results in a lower temperature flame unsuitable for welding.

Important Carbon Compounds – Ethanol and Ethanoic Acid

4.4 Some Important Carbon Compounds – Ethanol and Ethanoic Acid

Carbon compounds play a crucial role in our daily lives. Two of the most commercially important carbon compounds are ethanol and ethanoic acid.

4.4.1 Properties of Ethanol

Physical Properties

Ethanol (C₂H₅OH) is a liquid at room temperature.
It is soluble in water in all proportions.
Commonly called alcohol, it is the active ingredient in all alcoholic beverages.
Used in medicines like tincture iodine, cough syrups, and tonics due to its solvent properties.
Melting point: 159 K, Boiling point: 351 K.

Effects on Health

Consumption of ethanol in small quantities causes drunkenness.
Excessive intake affects the central nervous system, leading to:
- Lack of coordination
- Mental confusion
- Drowsiness
- Loss of judgement and muscular coordination
Pure ethanol (absolute alcohol) can be lethal.
Methanol (CH₃OH), if consumed, gets oxidized to methanal (formaldehyde) in the liver, which can cause:
- Blindness
- Damage to body cells
- Death

Reactions of Ethanol

(i) Reaction with Sodium

Ethanol reacts with sodium metal to liberate hydrogen gas and form sodium ethoxide.
Reaction: $2Na + 2C_2H_5OH → 2C_2H_5O⁻Na⁺ + H_2$
Observation: Effervescence due to the evolution of hydrogen gas.

(ii) Dehydration to Form Ethene

Ethanol undergoes dehydration (removal of water) when heated at 443 K in the presence of concentrated sulphuric acid (H₂SO₄).
Reaction:

Ethanol (liquid) → Ethene (gas) + Water
Conc. H₂SO₄ acts as a dehydrating agent.

Denatured Alcohol

Industrial ethanol is made unfit for drinking by adding poisonous substances like methanol or adding dyes (blue color).
This is called denatured alcohol.

Ethanol as a Fuel

Ethanol can be obtained from sugarcane juice through fermentation.
It is used as a fuel additive in petrol because:
- It burns completely to produce carbon dioxide (CO₂) and water (H₂O).
- It is a cleaner fuel compared to petrol or diesel.

4.4.2 Properties of Ethanoic Acid

Physical Properties

Chemical formula: CH₃COOH
Commonly called acetic acid.
5-8% solution of ethanoic acid in water is called vinegar (used as a food preservative).
Melting point: 290 K (freezes in cold weather, forming solid "glacial acetic acid").
Weak acid: Unlike HCl, which completely ionizes in water, ethanoic acid ionizes partially.

Reactions of Ethanoic Acid

(i) Esterification Reaction

Esters are sweet-smelling substances used in perfumes and food flavoring.
Ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid (H₂SO₄) to form an ester and water.
Reaction:

Ester formed: Ethyl ethanoate (CH₃COOC₂H₅)
Reverse Reaction (Saponification):
- Esters react with sodium hydroxide (NaOH) to form sodium salt of carboxylic acid and alcohol.
- This reaction is called saponification (used in soap-making).
- Reaction: $CH_3COOC_2H_5 + NaOH → CH_3COONa + C_2H_5OH$

(ii) Reaction with Base (Neutralization)

Ethanoic acid reacts with sodium hydroxide (NaOH) to form sodium ethanoate (CH₃COONa) and water.
Reaction: $CH_3COOH + NaOH → CH_3COONa + H_2O$

(iii) Reaction with Carbonates and Hydrogen Carbonates

Ethanoic acid reacts with carbonates and bicarbonates, releasing carbon dioxide (CO₂) gas.
Reaction with sodium carbonate (Na₂CO₃): $2CH_3COOH + Na_2CO_3 → 2CH_3COONa + H_2O + CO_2$
Reaction with sodium bicarbonate (NaHCO₃): $CH_3COOH + NaHCO_3 → CH_3COONa + H_2O + CO_2$
Observation: The evolved CO₂ gas turns lime water milky (confirming its presence).

Conclusion

Ethanol and ethanoic acid are important carbon compounds used in various applications.
Ethanol is used in medicines, alcoholic drinks, and fuel, while ethanoic acid is used in food preservation and ester production.
Ethanol can react with sodium, concentrated sulphuric acid, and act as a fuel.
Ethanoic acid shows acidic properties, reacting with bases, carbonates, and bicarbonates to form respective salts.
Esterification and saponification are important reactions of ethanoic acid, widely used in perfume and soap industries.

QUESTIONS

How would you distinguish experimentally between an alcohol and a carboxylic acid?
- A simple test using sodium carbonate (Na₂CO₃) or sodium bicarbonate (NaHCO₃) can distinguish between an alcohol and a carboxylic acid.
- Procedure: Add a small amount of the given liquid to a test tube and add a pinch of sodium carbonate or sodium bicarbonate.
- Observation:
  - If effervescence (bubbling) occurs due to the release of carbon dioxide (CO₂) gas, the substance is a carboxylic acid.
  - If no gas is evolved, the substance is likely an alcohol.
- Confirmatory Test: Pass the gas through lime water; if it turns milky, CO₂ is present, confirming a carboxylic acid.
What are oxidising agents?

Oxidising agents are substances that facilitate oxidation by gaining electrons and themselves undergoing reduction.
They help in the addition of oxygen or removal of hydrogen from a substance.
Examples:
- Acidified potassium dichromate (K₂Cr₂O₇)
- Acidified potassium permanganate (KMnO₄)
- Oxygen (O₂)
- Hydrogen peroxide (H₂O₂)
Example Reaction:

Oxidation of ethanol (C₂H₅OH) to ethanoic acid (CH₃COOH) using acidified potassium dichromate:

Here, potassium dichromate (K₂Cr₂O₇) acts as the oxidising agent, converting ethanol into ethanoic acid.

Soaps and Detergents

4.5 SOAPS AND DETERGENTS

What is Soap?

Soap is a sodium or potassium salt of long-chain carboxylic acids (fatty acids).
It is used as a cleansing agent in daily life.

How Does Soap Work?

Soap molecules have two distinct parts:
1. Hydrophobic tail (non-polar, oil-loving) – interacts with grease and oil.
2. Hydrophilic head (polar, water-loving) – interacts with water.
When soap is added to water, it forms micelles that trap dirt and grease in their center, allowing it to be washed away with water.

Micelles – The Cleaning Mechanism of Soap

Structure of Micelle

A micelle is a cluster of soap molecules where:
- Hydrophobic tails of soap molecules face inward (towards the oil/dirt).
- Hydrophilic heads face outward (towards the water).

Working of Micelles

Micelles emulsify oil and dirt so they can be rinsed away with water.
Since micelles scatter light, a soap solution appears cloudy.

Activity 4.10: Demonstration of the Effect of Soap in Cleaning

Procedure:

Take two test tubes (A and B), each containing 10 mL of water.
Add a drop of oil (cooking oil) to both test tubes.
Add soap solution to test tube B.
Shake both test tubes vigorously.
Observe how quickly the oil and water layers separate.

Observations:

In test tube A (without soap), oil and water separate quickly.
In test tube B (with soap), oil forms an emulsion, making it stay mixed longer.
This shows how soap helps in cleaning by emulsifying oil and dirt.

Soap and Hard Water

Hard Water

Water containing calcium (Ca²⁺) and magnesium (Mg²⁺) ions is called hard water.
Hard water reacts with soap to form an insoluble precipitate (scum), making soap less effective.

Activity 4.11: Testing Soap in Hard and Soft Water

Procedure:

Take two test tubes, one with distilled water (soft water) and another with hard water.
Add a few drops of soap solution to both test tubes.
Shake both test tubes vigorously and observe the foam formation.

Observations:

More foam is formed in the test tube with soft water.
In hard water, a white curdy precipitate (scum) forms, reducing the effectiveness of soap.

Detergents – A Solution to Hard Water Problems

What are Detergents?

Detergents are cleansing agents similar to soap but work well in both soft and hard water.
They are sodium salts of sulphonic acids or ammonium salts with chloride/bromide ions.
Unlike soap, detergents do not form scum in hard water.

Uses of Detergents

Used in shampoos, laundry detergents, and household cleaning products.

Activity 4.12: Comparing the Effectiveness of Soap and Detergent in Hard Water

Procedure:

Take two test tubes, each containing 10 mL of hard water.
Add five drops of soap solution to one test tube and five drops of detergent solution to the other.
Shake both test tubes for the same duration.

Observations:

Soap forms a curdy precipitate in hard water, reducing foam.
Detergents produce more foam and do not form a precipitate, making them more effective.

Importance of Agitation in Cleaning Clothes

After applying soap, clothes are:
- Beaten on stones
- Scrubbed with brushes
- Agitated in washing machines
Why is agitation necessary?
- Agitation helps break down grease and dirt, making it easier to rinse away.

Questions & Answers

1. Would you be able to check if water is hard by using a detergent?

No, detergents do not form scum in hard water.

Soap can be used to test for hardness, as it forms an insoluble scum in hard water.

2. Why is agitation necessary to get clean clothes?

Agitation helps in breaking grease and dirt into smaller particles, allowing soap/detergent micelles to trap and remove them.

EXERCISES – SOLUTIONS

1. Ethane, with the molecular formula C₂H₆, has:

(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.

Answer: (b) 7 covalent bonds

Explanation:
Ethane (C₂H₆) consists of two carbon atoms joined by one C–C bond and each carbon atom is bonded to three hydrogen atoms via C–H bonds. Thus, there are 6 C–H bonds + 1 C–C bond = 7 covalent bonds.

2. Butanone is a four-carbon compound with the functional group:

(a) Carboxylic acid
(b) Aldehyde
(c) Ketone
(d) Alcohol

Answer: (c) Ketone

Explanation:
Butanone (also called methyl ethyl ketone) contains a carbonyl group (–CO–) located on an interior carbon, which classifies it as a ketone.

3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that:

(a) The food is not cooked completely.
(b) The fuel is not burning completely.
(c) The fuel is wet.
(d) The fuel is burning completely.

Answer: (b) The fuel is not burning completely.

Explanation:
Incomplete combustion of fuel produces carbon (soot), which deposits on the vessel and causes the blackening.

4. Explain the nature of the covalent bond using the bond formation in CH₃Cl.

Answer:
CH₃Cl (methyl chloride) is formed by the sharing of electrons between atoms. In CH₃Cl:

The carbon atom has 4 valence electrons and forms four bonds: three bonds with hydrogen atoms and one bond with a chlorine atom.
Each hydrogen atom contributes 1 electron, and chlorine (which needs 1 electron to complete its octet) also shares one electron.
The result is the formation of stable covalent bonds where electrons are shared to satisfy the octet (or duet for hydrogen).

Structure (ASCII Representation):

     H
     |
H — C — Cl
     |
     H

5. Draw the electron dot structures for:

(a) Ethanoic acid (CH₃COOH)
(b) H₂S (Hydrogen sulfide)
(c) Propanone (C₃H₆O)
(d) F₂ (Fluorine molecule)

Answer:

(a) Ethanoic acid (CH₃COOH):
- The molecule consists of a CH₃ group attached to a carboxyl group (–COOH). In the carboxyl group, one oxygen is double-bonded to carbon and the other oxygen is single-bonded to carbon and hydrogen.
(b) H₂S (Hydrogen sulfide):
- Sulfur is the central atom with two single bonds to two hydrogen atoms. Sulfur also has lone pairs.
(c) Propanone (C₃H₆O):
- Also known as acetone, its structure is CH₃COCH₃. The central carbon is double-bonded to an oxygen (carbonyl group) and single-bonded to two CH₃ groups.
(d) F₂ (Fluorine molecule):
- Two fluorine atoms share a pair of electrons forming a single bond.

Note: When drawing electron dot structures, depict the shared electron pairs (as lines or dots) and include lone pairs where applicable.

6. What is a homologous series? Explain with an example.

Answer:
A homologous series is a family of organic compounds that have:

The same functional group
Similar chemical properties
A general formula in which each successive member differs by a –CH₂– unit.

Example:
The alkane series (CₙH₂ₙ₊₂) such as:

Methane (CH₄)
Ethane (C₂H₆)
Propane (C₃H₈)
Butane (C₄H₁₀)
Each successive member differs by a –CH₂– group.

7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Answer:

Property	Ethanol (C₂H₅OH)	Ethanoic Acid (CH₃COOH)
Odour	Pleasant, alcoholic smell	Pungent, vinegar-like smell
Taste	Burning sensation, not sour	Sour (acidic taste)
Litmus Test	No effect (neutral)	Turns blue litmus red (acidic)
Reaction with Carbonates	No effervescence	Produces CO₂ (effervescence)
Reaction with Na metal	Produces hydrogen gas and sodium ethoxide	Reacts similarly but the acidic nature is evident

8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Answer:
Micelle formation occurs because soap molecules are amphiphilic; they have:

A hydrophobic tail (repels water, attracts oils)
A hydrophilic head (attracts water)

In water, soap molecules arrange themselves into micelles with the hydrophobic tails clustering inward (to trap grease/dirt) and the hydrophilic heads facing outward toward the water. In less polar solvents such as ethanol, the solvent does not provide the necessary polarity to stabilize the micelle structure, so micelle formation does not occur effectively.

9. Why are carbon and its compounds used as fuels for most applications?

Answer:
Carbon compounds (hydrocarbons) are used as fuels because:

They release a large amount of energy (high calorific value) upon combustion.
They undergo complete combustion to produce carbon dioxide and water, releasing heat.
They are abundant and easily ignited, making them efficient energy sources.

10. Explain the formation of scum when hard water is treated with soap.

Answer:
Hard water contains high concentrations of calcium (Ca²⁺) and magnesium (Mg²⁺) ions. When soap (sodium or potassium salts of fatty acids) is added to hard water, these metal ions react with the soap to form insoluble salts (calcium or magnesium fatty acid salts), which appear as a white, curdy precipitate called scum. This reduces the soap’s ability to clean effectively.

11. What change will you observe if you test soap with litmus paper (red and blue)?

Answer:
Since soap is slightly basic:

Red litmus paper will turn blue.
Blue litmus paper will remain blue.

12. What is hydrogenation? What is its industrial application?

Answer:
Hydrogenation is the process of adding hydrogen (H₂) to unsaturated hydrocarbons (alkenes or alkynes) in the presence of a catalyst (such as nickel, platinum, or palladium) to convert them into saturated hydrocarbons.
Industrial Application:
It is used to convert vegetable oils (unsaturated fats) into solid or semi-solid fats (e.g., margarine, vanaspati ghee).

13. Which of the following hydrocarbons undergo addition reactions: C₂H₆, C₃H₈, C₃H₆, C₂H₂, CH₄?

Answer:
Addition reactions occur in unsaturated hydrocarbons (those containing double or triple bonds).

C₂H₆ (Ethane): Saturated; does not undergo addition reactions.
C₃H₈ (Propane): Saturated; does not undergo addition reactions.
C₃H₆ (Propene): Unsaturated (contains a double bond); undergoes addition reactions.
C₂H₂ (Ethyne): Unsaturated (contains a triple bond); undergoes addition reactions.
CH₄ (Methane): Saturated; does not undergo addition reactions.

Thus, C₃H₆ (propene) and C₂H₂ (ethyne) undergo addition reactions.

14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.

Answer:
The Bromine Water Test is used:

Unsaturated hydrocarbons (alkenes and alkynes) will react with bromine water, decolorizing it from brownish-orange to colorless.
Saturated hydrocarbons (alkanes) do not react with bromine water, so its color remains unchanged.

15. Explain the mechanism of the cleaning action of soaps.

Answer:
Soap molecules are amphiphilic; they have:

A hydrophobic tail that is attracted to oily dirt and grease.
A hydrophilic head that is attracted to water.

When soap is added to water, these molecules arrange themselves into spherical aggregates called micelles. In a micelle:

The hydrophobic tails group together in the center, trapping oily dirt.
The hydrophilic heads face outward, interacting with water.

During washing, agitation helps the micelles encapsulate and lift away the dirt, which is then rinsed off with water.

Chapter 4: Carbon and its Compoundsn

Chapter Notes: Carbon and its Compounds

Introduction

Activity 4.1: Categorizing Materials

Testing for Carbon Compounds

Significance of Carbon

Carbon Availability in Nature

Importance of Carbon

4.1 Bonding in Carbon – The Covalent Bond

Comparison of Ionic and Covalent Compounds

Electronic Configuration of Carbon

Why Carbon Does Not Form Ionic Bonds

Formation of Covalent Bonds

Examples of Covalent Bonding

1. Hydrogen Molecule (H₂)

2. Chlorine Molecule (Cl₂)

3. Oxygen Molecule (O₂)

4. Water Molecule (H₂O)

5. Nitrogen Molecule (N₂)

6. Ammonia Molecule (NH₃)

7. Methane (CH₄) – A Carbon Compound

Properties of Covalent Compounds

Table 4.1: Melting and Boiling Points of Some Carbon Compounds

Conclusion

Allotropes of Carbon

1. Diamond

2. Graphite

3. Fullerenes

Conclusion

QUESTIONS

1. What would be the electron dot structure of carbon dioxide (CO₂)?

2. What would be the electron dot structure of a molecule of sulphur (S₈)?

Versatile Nature of Carbon

Introduction

1. Catenation (Self-Linking Property of Carbon)

2. Tetravalency of Carbon

Conclusion

Organic Compounds

Introduction

Vital Force Theory and Its Disproof

Classification of Organic and Inorganic Carbon Compounds

Conclusion

4.2.1 Saturated and Unsaturated Carbon Compounds

Saturated Hydrocarbons (Alkanes)

Unsaturated Hydrocarbons

Structural Representations

4.2.2 Chains, Branches, and Rings

Types of Carbon Skeletons

Structural Isomerism

Aromatic Compounds

4.2.3 Functional Groups in Carbon Compounds

Definition

Common Functional Groups

Summary

4.2.4 Homologous Series

1. Definition

2. Examples of Homologous Series

(a) Alkanes

(b) Alkenes

(c) Alkynes

(d) Alcohols

4.2.5 Nomenclature of Carbon Compounds

1. Naming of Alkanes

2. Naming of Alkenes

3. Naming of Alkynes

4. Naming of Functional Groups

Key Takeaways

QUESTIONS

1. How many structural isomers can you draw for pentane?

2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?

3. What will be the formula and electron dot structure of cyclopentane?

4. Draw the structures for the following compounds:

(i) Ethanoic Acid (Acetic Acid, CH₃COOH)

(ii) Bromopentane (C₅H₁₁Br)

(iii) Butanone (C₄H₈O)

(iv) Hexanal (C₆H₁₂O)

5. How would you name the following compounds?

(i) CH₃—CH₂—Br

(ii) Methanal (Formaldehyde, CH₂O)

(iii) Pent-2-yne (C₅H₈)

`H H H H| | | |H—C—C—C≡C—H| | | |H H H H`