Topic 7 (Organic Chemistry)

Question 1

What is a hydrocarbon?

Answer 1

A compound made up of only carbon and hydrogen atoms.

Question 2

What are the two types of hydrocarbons?

Answer 2

Alkanes (saturated) and Alkenes (unsaturated).

Question 3

What is the general formula for alkanes?

Answer 3

CₙH₂ₙ₊₂

Question 4

Name the first four alkanes.

Answer 4

Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), Butane (C₄H₁₀).

Question 5

What is the general formula for alkenes?

Answer 5

CₙH₂ₙ

Question 6

How do alkanes differ from alkenes

Answer 6

✅ Single bonds only (C-C)
✅ Saturated – contains maximum hydrogen atoms
✅ General formula: CₙH₂ₙ₊₂
✅ Less reactive – does not react with bromine water

Question 7

how does Alkenes differ from Alkanes

Answer 7

✅ At least one double bond (C=C)
✅ Unsaturated – can react to form more bonds
✅ General formula: CₙH₂ₙ
✅ More reactive – decolorizes bromine water (orange → colourless)

Question 8

Why are alkenes more reactive than alkanes?

Answer 8

✅ The C=C double bond can break open and react with other atoms.
✅ This makes alkenes useful for addition reactions (e.g., polymerization).

Question 9

How does the bromine water test distinguish alkenes from alkanes?

Answer 9

✅ Alkenes react with bromine water, turning it orange → colourless.
❌ Alkanes do not react, so bromine water stays orange.

Question 10

Why do alkenes burn with a smoky flame?

Answer 10

🔥 Alkenes undergo incomplete combustion due to their high carbon content.
🌫️ This produces carbon monoxide (CO) and carbon (soot), leading to a yellow, smoky flame

Question 11

What are the equations for complete and incomplete combustion of alkenes?

Answer 11

✅ Complete combustion:
🔹 Alkene + Oxygen → Carbon Dioxide + Water + Energy (clean blue flame).
✅ Incomplete combustion:
🔹 Alkene + Oxygen → Carbon monoxide (CO) + Carbon (soot) + Water + Energy (smoky flame).

Question 12

What are some important uses of alkenes?

Answer 12

✅ Making plastics (polymerization).
✅ Making ethanol (hydration reaction).
✅ Used in the chemical industry to create useful substances.

Question 13

What is fractional distillation used for?

Answer 13

✅ It is used to separate crude oil into different hydrocarbon fractions based on their boiling points.
✅ The process works because different hydrocarbons evaporate and condense at different temperatures.

Question 14

What are the key steps in fractional distillation?

Answer 14

1️⃣ Crude oil is heated until it evaporates.
2️⃣ The vapors rise up a fractionating column.
3️⃣ The column is hotter at the bottom and cooler at the top.
4️⃣ Fractions condense at different heights based on their boiling points.
5️⃣ The shortest hydrocarbons (low boiling points) leave as gases at the top, while the longest hydrocarbons condense at the bottom.

Question 15

Why do some hydrocarbons condense at the top while others stay at the bottom?

Answer 15

✅ Smaller hydrocarbons (low boiling points) have weak intermolecular forces, so they stay as gases and rise to the top.
✅ Larger hydrocarbons (high boiling points) have stronger intermolecular forces, so they condense and collect at the bottom.

Question 16

What are the main fractions from fractional distillation and their uses?

Answer 16

🔹 Refinery gases → Bottled gas.
🔹 Petrol → Fuel for cars.
🔹 Kerosene → Jet fuel.
🔹 Diesel → Fuel for lorries & trains.
🔹 Bitumen → Road surfacing.

Question 17

How do the properties of hydrocarbons change as you go down the column?

Answer 17

✅ As hydrocarbon molecules get bigger:
🔸 Boiling point increases.
🔸 Viscosity (thickness) increases.
🔸 Flammability decreases (harder to ignite).

Question 18

Why is fractional distillation useful?

Answer 18

✅ It provides useful fuels for transport and industry.
✅ It produces raw materials for making plastics and chemicals.
✅ It allows us to make use of crude oil efficiently.

Question 19

What should you include in a 6-mark question on fractional distillation?

Answer 19

✅ Step 1: Explain that crude oil is a mixture of hydrocarbons.
✅ Step 2: Describe how it is heated to turn into a gas.
✅ Step 3: Explain that the column is hotter at the bottom and cooler at the top.
✅ Step 4: State that different hydrocarbons condense at different levels.
✅ Step 5: Give examples of fractions (e.g., petrol, diesel).
✅ Step 6: Mention how properties change (boiling points, viscosity, flammability).

💡 Tip: Use keywords like boiling points, condense, fractionating column, hydrocarbons for full marks!

Question 20

What is cracking, and why is it important?

Answer 20

✅ Cracking is the process of breaking down long-chain alkanes into shorter, more useful hydrocarbons.
✅ It is important because:
🔹 Shorter hydrocarbons (e.g., petrol) are in high demand.
🔹 It produces alkenes, which are used to make plastics.

Question 21

What are the two types of cracking?

Answer 21

1️⃣ Catalytic Cracking – Uses a catalyst at 550°C to speed up the reaction.
2️⃣ Steam Cracking – Uses high temperatures (850°C) and steam without a catalyst.

Question 22

❓ What is the general equation for cracking?

Answer 22

✅ A long-chain alkane → A shorter alkane + An alkene
🔹 Example: C₁₀H₂₂ → C₈H₁₈ + C₂H₄
✅ One of the products is always an alkene!

Question 23

❓ Why is cracking necessary in the oil industry?

Answer 23

✅ Long hydrocarbons are less useful (e.g., bitumen is thick and not flammable).
✅ Shorter hydrocarbons are in high demand for fuels like petrol and diesel.
✅ Cracking helps balance supply and demand.

Question 24

❓ What are key properties of alkenes?

Answer 24

✅ Contain a C=C double bond (unsaturated).
✅ More reactive than alkanes due to the double bond.
✅ Used to make plastics and chemicals.

Question 25

❓ How can you test for an alkene?

Answer 25

✅ Add bromine water to the sample. 🔹 If it’s an alkene, the solution turns orange → colourless. 🔹 If it’s an alkane, the solution stays orange.

Question 26

❓ What are three important uses of alkenes?

Answer 26

✅ Making plastics (polymerisation). ✅ Producing ethanol (hydration reaction). ✅ Used as chemical feedstocks for making useful substances.

Question 27

❓ What is the key difference between alkanes and alkenes?

Answer 27

✅ Alkanes → Only single bonds (C-C), less reactive. ✅ Alkenes → Contain a C=C double bond, more reactive. ✅ Alkanes do not react with bromine water, but alkenes do.

Question 28

❓ Why are alkenes more reactive than alkanes?

Answer 28

✅ Alkenes contain a C=C double bond, which can open up and form new bonds. ✅ This makes them useful in addition reactions.

Question 29

❓ What happens when alkenes react with hydrogen?

Answer 29

✅ Alkene + Hydrogen → Alkane ✅ Requires a nickel catalyst and 150°C. ✅ This removes the double bond, making a saturated hydrocarbon. 🔹 Example: Ethene + Hydrogen → Ethane C₂H₄ + H₂ → C₂H₆

Question 30

❓ What happens when alkenes react with halogens?

Answer 30

✅ Alkene + Halogen → Dihaloalkane ✅ The double bond opens up, and two halogen atoms add on. 🔹 Example: Ethene + Bromine → Dibromoethane C₂H₄ + Br₂ → C₂H₄Br₂ 💡 Bromine water test is based on this reaction!

Question 31

❓ How can alkenes be converted into alcohols?

Answer 31

✅ Alkene + Steam → Alcohol ✅ Requires a phosphoric acid catalyst and high temperature (300°C). 🔹 Example: Ethene + Steam → Ethanol C₂H₄ + H₂O → C₂H₅OH

Question 32

❓ How do alkenes form polymers?

Answer 32

✅ Many alkene molecules (monomers) join together to form long chains (polymers). ✅ This is called addition polymerisation. 🔹 Example: Ethene → Poly(ethene) (plastic bags, bottles) nC₂H₄ → (C₂H₄)ₙ

Question 33

How do alkenes burn compared to alkanes?

Answer 33

✅ Alkenes burn with a smoky flame due to incomplete combustion. ✅ They release less energy than alkanes when burned. ✅ This is because alkenes contain less hydrogen per carbon atom.

Question 34

❓ What are the four main reactions of alkenes?

Answer 34

1️⃣ Hydrogenation → Alkene + H₂ → Alkane. 2️⃣ Halogenation → Alkene + Br₂/Cl₂/I₂ → Dihaloalkane. 3️⃣ Hydration → Alkene + Steam (H₂O) → Alcohol. 4️⃣ Polymerisation → Alkene monomers → Polymers (plastics).

Question 35

What is an addition polymer?

Answer 35

✅ A long-chain molecule made from many alkene monomers joined together. ✅ Formed through addition polymerisation, where the C=C double bonds open up to connect the monomers.

Question 36

❓ What happens during addition polymerisation?

Answer 36

✅ Monomers (alkenes) join together, forming a long polymer chain. ✅ The C=C double bond breaks to allow bonding with other monomers. 🔹 Example: Ethene → Poly(ethene) nC₂H₄ → (C₂H₄)ₙ

Question 37

❓ How do you name an addition polymer?

Answer 37

✅ Add "poly" in front of the monomer name. ✅ Write the monomer name in brackets. 🔹 Example: Ethene → Poly(ethene) Propene → Poly(propene) Chloroethene → Poly(chloroethene) (PVC)

Question 38

❓ What are the properties of addition polymers?

Answer 38

✅ Strong and durable. ✅ Unreactive (because they are saturated molecules). ✅ Non-biodegradable, causing environmental problems.

Question 39

❓ Why are addition polymers bad for the environment?

Answer 39

❌ Non-biodegradable – they do not break down easily. ❌ Cause plastic pollution in oceans and landfills. ✅ Solutions: Recycling, developing biodegradable plastics.

Question 40

What is the functional group of alcohols?

Answer 40

✅ Alcohols contain the –OH (hydroxyl) functional group. ✅ Their general formula is CₙH₂ₙ₊₁OH. 🔹 Example: Ethanol → C₂H₅OH

Question 41

❓ What are the first four alcohols and their formulas?

Answer 41

1️⃣ Methanol → CH₃OH 2️⃣ Ethanol → C₂H₅OH 3️⃣ Propanol → C₃H₇OH 4️⃣ Butanol → C₄H₉OH

Question 42

❓ What are the key properties of alcohols?

Answer 42

✅ Dissolve in water to form neutral solutions. ✅ Burn in air to produce carbon dioxide and water. ✅ React with sodium to produce hydrogen gas.

Question 43

❓ What happens when alcohols burn?

Answer 43

✅ Alcohol + Oxygen → Carbon dioxide + Water 🔹 Example: Ethanol combustion C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

Question 44

❓ What happens when alcohols react with sodium

Answer 44

✅ Alcohol + Sodium → Sodium Alkoxide + Hydrogen gas 🔹 Example: Ethanol + Sodium C₂H₅OH + Na → C₂H₅ONa + ½H₂ 💡 Slower reaction than sodium with water.

Question 45

❓ What are some common uses of alcohols?

Answer 45

✅ Solvents – In perfumes and cleaning products. ✅ Fuels – Ethanol is used in biofuels. ✅ Drinks – Ethanol is the alcohol in alcoholic beverages.

Question 46

❓ What are the two main ways to make ethanol?

Answer 46

1️⃣ Fermentation – Sugar is converted to ethanol using yeast, at 37°C, in anaerobic conditions. 🔹 Equation: Glucose → Ethanol + CO₂ C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ 2️⃣ Hydration of Ethene – Ethene reacts with steam at 300°C using a phosphoric acid catalyst. 🔹 Equation: C₂H₄ + H₂O → C₂H₅OH

Question 47

❓ What are the two main methods of producing ethanol?

Answer 47

✅ Fermentation of sugars (biological process). ✅ Hydration of ethene (industrial process).

Question 48

❓ How is ethanol produced by fermentation?

Answer 48

✅ Fermentation uses yeast to convert glucose into ethanol and carbon dioxide. ✅ This process occurs in anaerobic conditions at about 37°C. 🔹 Equation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

Question 49

❓ What are the advantages and disadvantages of producing ethanol by fermentation?

Answer 49

✅ Advantages: 🔹 Renewable – Uses sugar from crops like corn and sugarcane. 🔹 Low energy requirements – Fermentation occurs at relatively low temperatures (37°C). ❌ Disadvantages: 🔸 Slow process – Takes time for yeast to ferment the glucose. 🔸 Produces impure ethanol – Requires distillation to purify the ethanol.

Question 50

❓ How is ethanol produced by the hydration of ethene?

Answer 50

✅ Ethene reacts with steam at 300°C in the presence of a phosphoric acid catalyst. ✅ This is a fast industrial process used to produce ethanol on a large scale. 🔹 Equation: C₂H₄ + H₂O → C₂H₅OH

Question 51

❓ What are the advantages and disadvantages of producing ethanol by the hydration of ethene?

Answer 51

✅ Advantages: 🔹 Fast process – Ethene reacts quickly with steam. 🔹 High yield – Produces pure ethanol without the need for distillation. ❌ Disadvantages: 🔸 Non-renewable – Uses ethene, which is derived from crude oil, a non-renewable resource. 🔸 Requires high energy – The process uses high temperatures (300°C) and pressure.

Question 52

❓ What is the functional group of carboxylic acids?

Answer 52

✅ Carboxylic acids contain the –COOH functional group. ✅ The general formula for carboxylic acids is CₙH₂ₙ₊₁COOH. 🔹 Example: Ethanoic acid → CH₃COOH

Question 53

❓ What are the key properties of carboxylic acids?

Answer 53

✅ Weak acids – They only partially dissociate in water. ✅ Soluble in water – Forms acidic solutions. ✅ React with alcohols to form esters. ✅ Have higher boiling points than similar-sized alcohols due to hydrogen bonding.

Question 54

❓ What are the main reactions of carboxylic acids?

Answer 54

1️⃣ Reaction with metals: Carboxylic acid + Metal → Salt + Hydrogen 🔹 Example: Ethanoic acid + Magnesium → Magnesium ethanoate + Hydrogen 2️⃣ Reaction with bases: Carboxylic acid + Base → Salt + Water 🔹 Example: Ethanoic acid + Sodium hydroxide → Sodium ethanoate + Water 3️⃣ Reaction with alcohols (esterification): Carboxylic acid + Alcohol → Ester + Water 🔹 Example: Ethanoic acid + Methanol → Methyl ethanoate + Water

Question 55

❓ How do you name carboxylic acids?

Answer 55

✅ The suffix –oic acid is used. ✅ Remove the ‘e’ from the alkane name and add –oic acid. 🔹 Example: Methane → Methanoic acid Ethane → Ethanoic acid Propane → Propanoic acid

Question 56

❓ What are some common uses of carboxylic acids?

Answer 56

✅ Food additives – Such as acetic acid (vinegar). ✅ Preservatives – Helps preserve food due to its acidic nature. ✅ Making esters – Used in fragrances, flavorings, and plastics. ✅ Manufacturing – Used in the production of soaps and detergents.

Question 57

❓ What are carboxylate salts, and how are they formed?

Answer 57

✅ Carboxylate salts are formed when a carboxylic acid reacts with a base. ✅ The hydrogen from the –COOH group is replaced by a metal ion. 🔹 Example: Ethanoic acid + Sodium hydroxide → Sodium ethanoate + Water CH₃COOH + NaOH → CH₃COONa + H₂O

Question 58

❓ What is an ester?

Answer 58

✅ An ester is a chemical compound formed from an alcohol and a carboxylic acid. ✅ Esters have the general formula RCOOR’. 🔹 Example: Methyl ethanoate (CH₃COOCH₃)

Question 59

❓ How are esters formed?

Answer 59

✅ Esters are formed through a reaction called esterification, which occurs when an alcohol reacts with a carboxylic acid in the presence of a strong acid catalyst (e.g., concentrated sulfuric acid). ✅ The reaction produces an ester and water. 🔹 Example: Ethanol + Ethanoic acid → Ethyl ethanoate + Water C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O

Question 60

❓ How do you name an ester?

Answer 60

✅ The name of an ester is made up of two parts: 1️⃣ The alkyl group from the alcohol (derived from the alcohol’s name). 2️⃣ The carboxylate group from the carboxylic acid (derived from the acid’s name, replacing the “-ic acid” with “-ate”). 🔹 Example: Ethanol + Ethanoic acid → Ethyl ethanoate

Question 61

❓ What are the properties of esters?

Answer 61

✅ Volatile – Evaporate easily, often used in fragrances and flavorings. ✅ Sweet-smelling – Many esters have fruity or sweet smells. ✅ Low boiling points – Due to their small molecular size.

Question 62

❓ What are the common uses of esters?

Answer 62

✅ Flavors and fragrances – Esters give fruits their smells and are used in artificial flavorings. ✅ Solvents – Used in nail polish removers and paint thinners. ✅ Making plastics – Used in the production of certain polyesters.

Question 63

❓ What is hydrolysis of esters?

Answer 63

✅ Hydrolysis is the reverse of esterification, where an ester is broken down by water. ✅ The reaction produces an alcohol and a carboxylic acid. 🔹 Example: Ethyl ethanoate + Water → Ethanol + Ethanoic acid CH₃COOC₂H₅ + H₂O → C₂H₅OH + CH₃COOH

Question 64

❓ What is a condensation polymer?

Answer 64

✅ A condensation polymer is formed when monomers join together with the elimination of a small molecule, often water. ✅ This occurs when two different functional groups react, such as an –OH and –COOH group. 🔹 Example: Nylon and Polyesters

Question 65

❓ What are some examples of condensation polymers?

Answer 65

✅ Polyesters – Made from a dicarboxylic acid and a diol. ✅ Nylon – Made from a dicarboxylic acid and a diamine.

Question 66

❓ How is a polyester formed?

Answer 66

✅ A polyester is formed when a diol (an alcohol with two –OH groups) reacts with a dicarboxylic acid (an acid with two –COOH groups). ✅ Water is eliminated during the reaction, and the ester bonds form. 🔹 Example: Terylene (Polyester) – Formed from ethylene glycol and terephthalic acid.

Question 67

❓ How is Nylon (a polyamide) formed?

Answer 67

✅ Nylon is formed when a diamine (a molecule with two –NH₂ groups) reacts with a dicarboxylic acid. ✅ This reaction also releases water as a by-product. 🔹 Example: Nylon 6,6 – Formed from hexamethylenediamine and adipic acid.

Question 68

❓ What are the properties of condensation polymers?

Answer 68

✅ Stronger and more durable than addition polymers because of stronger intermolecular forces (due to hydrogen bonding). ✅ High melting points – Useful in applications requiring heat resistance. ✅ Can be used to make fibers (e.g., Nylon) and films (e.g., Terylene).

Question 69

❓ What happens during the hydrolysis of condensation polymers?

Answer 69

✅ Hydrolysis of condensation polymers breaks the polymer back down into its monomers by reacting with water. ✅ This process can occur under acidic or basic conditions and can reverse the polymerisation process.

Question 70

❓ What is a naturally occurring polymer?

Answer 70

✅ A naturally occurring polymer is a biopolymer that is found in nature. ✅ They are made up of monomers that are linked together by covalent bonds to form large, complex molecules. 🔹 Example: Starch, Cellulose, Proteins, and DNA.

Question 71

❓ What are some examples of naturally occurring polymers?

Answer 71

✅ Starch – A polymer made from glucose molecules. Found in plants and used for energy storage. ✅ Cellulose – A polymer made from glucose molecules. Found in plant cell walls, providing structure. ✅ Proteins – Polymers made from amino acids. Found in living organisms, important for structure and function. ✅ DNA – A polymer made from nucleotides. Carries genetic information in living organisms.

Question 72

❓ What is starch and how is it used?

Answer 72

✅ Starch is a polysaccharide (a complex carbohydrate) made up of glucose molecules. ✅ It is the main energy store in plants and can be broken down into glucose when needed for energy. 🔹 Example: Found in foods like potatoes, rice, and corn.

Question 73

❓ What is cellulose and what is its role?

Answer 73

✅ Cellulose is a polysaccharide made from glucose. ✅ It provides structural support in plant cell walls, helping plants maintain their shape and integrity. 🔹 Example: Cellulose is used to make paper and cotton fabric.

Question 74

❓ What are proteins and DNA?

Answer 74

✅ Proteins are polymers made of amino acids linked by peptide bonds. They play a crucial role in the structure, function, and regulation of cells in living organisms. ✅ DNA (Deoxyribonucleic Acid) is a polymer made up of nucleotides, which carry genetic information. 🔹 Example: Enzymes and antibodies are proteins, while genetic inheritance is determined by DNA.

Question 75

❓ What are amino acids?

Answer 75

✅ Amino acids are organic compounds that contain both an amino group (–NH₂) and a carboxyl group (–COOH). ✅ They are the building blocks of proteins. 🔹 General formula: NH₂CHRCOOH, where R represents a variable group.

Question 76

❓ What is the basic structure of an amino acid?

Answer 76

✅ An amino acid consists of: 1️⃣ Amino group (–NH₂) 2️⃣ Carboxyl group (–COOH) 3️⃣ A hydrogen atom (–H) 4️⃣ A variable side chain (R), which differs between different amino acids.

Question 77

❓ How do amino acids form proteins?

Answer 77

✅ Amino acids join together via peptide bonds to form polypeptides. ✅ This occurs through a condensation reaction, where a water molecule is released. ✅ A protein is a long chain of amino acids folded into a specific shape. 🔹 Example: Di-peptide formation: Amino acid 1 + Amino acid 2 → Di-peptide + Water

Question 78

❓ What are essential amino acids?

Answer 78

✅ Essential amino acids are amino acids that cannot be synthesized by the body and must be obtained through diet. ✅ There are 9 essential amino acids in humans. 🔹 Example: Leucine, Isoleucine, and Lysine are essential amino acids.

Question 79

❓ What are the uses of carboxylic acids?

Answer 79

✅ Carboxylic acids are used in: 1️⃣ Food and drinks – Citric acid is used as a preservative and tartaric acid in wine. 2️⃣ Manufacturing – Used to make soaps, detergents, and plastics. 3️⃣ Medicines – Some carboxylic acids have medicinal uses, like acetylsalicylic acid (aspirin).