6.1 Flashcards
(135 cards)
1
Q
What are alkanes?
A
A: Alkanes are a group of saturated hydrocarbons, meaning they contain only single carbon-carbon bonds.
2
Q
What does the term “saturated” mean in the context of alkanes?
A
A: In the context of alkanes, “saturated” means that they contain only single carbon-carbon bonds; there are no double bonds present.
3
Q
What is the general formula of alkanes?
A
A: The general formula of alkanes is CnH2n+2, where “n” represents the number of carbon atoms in the molecule.
4
Q
: Describe the physical properties of alkanes.
A
A: Alkanes are generally colorless compounds with a gradual change in their physical properties as the number of carbon atoms in the chain increases.
5
Q
Q: Are alkanes reactive compounds?
A
A: Generally, alkanes are unreactive compounds. However, they do undergo combustion reactions and can be cracked into smaller, more useful molecules.
6
Q
Q: What is methane and its significance?
A
A: Methane is an alkane and is the major component of natural gas, making it important both as a fuel source and as a greenhouse gas.
7
Q
Q: List the first five members of the alkane homologous series.
A
A: Methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), and pentane (C5H12).
8
Q
Q: Explain the combustion reactions of alkanes.
A
A: Alkanes undergo combustion in the presence of air. Complete combustion results in the formation of water and carbon dioxide gas. For example, methane burns as follows: CH4 + 2O2 → CO2 + 2H2O.
9
Q
Q: What is the composition of gasoline, and what happens during its combustion?
A
A: Gasoline is largely composed of isomers of octane (C8H18). During combustion, it requires large amounts of oxygen to combust fully, forming carbon dioxide and water. For example: 2C8H18 + 25O2 → 16CO2 + 18H2O.
10
Q
What environmental problems are associated with the combustion of hydrocarbons?
A
A: Car exhaust contains small amounts of unburnt hydrocarbons, carbon monoxide, and soot, all of which contribute to environmental problems. Additionally, carbon dioxide, a product of combustion, is a major contributor to global warming.
11
Q
Q: What are alkenes?
A
A: Alkenes are unsaturated hydrocarbons containing a double carbon-carbon bond (C=C
12
Q
Q: How is the double carbon-carbon bond represented in alkenes?
A
A: The double carbon-carbon bond in alkenes is represented as two lines between two carbon atoms, denoted as C=C.
13
Q
Q: What is the functional group in alkenes, and why is it important?
A
A: The functional group in alkenes is the double carbon-carbon bond (C=C). It is significant because it allows alkenes to react in ways that alkanes cannot, imparting unique chemical properties.
14
Q
Can you provide examples of the first four alkenes in the homologous series?
A
A: The first four alkenes in the homologous series are ethene (C2H4), propene (C3H6), but-1-ene (C4H8), and pent-1-ene (C5H10).
15
Q
Q: What does it mean for a compound to be unsaturated?
A
A: A compound is considered unsaturated if it contains one or more double or triple bonds between carbon atoms. In the context of alkenes, the presence of the C=C double bond makes them unsaturated.
16
Q
How does the presence of a double bond affect the reactivity of alkenes compared to alkanes?
A
A: Alkenes are more reactive than alkanes due to the presence of the double bond. This double bond can be opened up, allowing incoming atoms to form additional single bonds with each carbon atom of the functional group.
17
Q
Q: What happens when the double bond in alkenes is opened up?
A
A: Opening up the double bond in alkenes allows each carbon atom to form four single bonds instead of one double bond and two single bonds. This makes alkenes more reactive and capable of forming additional bonds with other atoms or molecules.
18
Q
Q: What term is used to describe compounds with a C=C double bond?
A
A: Compounds containing a C=C double bond are referred to as unsaturated compounds due to their ability to form additional bonds with other atoms or molecules.
19
Q
How do alkenes compare to alkanes in terms of reactivity?
A
A: Alkenes are generally more reactive than alkanes due to the presence of the double bond, which allows for a wider range of chemical reactions, including addition reactions. Alkanes, being saturated hydrocarbons, are relatively inert and undergo limited reactions compared to alkenes.
20
Q
Q: What type of combustion do alkenes undergo, and why is incomplete combustion more common for alkenes?
A
A: Alkenes undergo both complete and incomplete combustion, but incomplete combustion is more common due to their higher carbon to hydrogen ratio. This results in a smoky flame in air.
21
Q
Q: What happens during incomplete combustion of butene when there is insufficient oxygen?
A
A: Incomplete combustion of butene in insufficient oxygen produces a mixture of carbon monoxide and water: C4H8 + 4O2 → 4CO + 4H2O.
22
Q
Q: How is soot produced during the combustion of alkenes?
A
A: Soot, consisting of carbon particles, is produced when alkenes undergo incomplete combustion in conditions of limited oxygen. For example: C4H8 + 2O2 → 4C + 4H2O.
23
Q
What type of reaction do alkenes mainly undergo, and what allows them to react in this manner?
A
A: Alkenes mainly undergo addition reactions, facilitated by the presence of the C=C double bond functional group, which allows for the opening of the double bond and the addition of atoms across it.
24
Q
Q: What is the process of hydrogenation, and what catalyst is used?
A
A: Hydrogenation is an addition reaction in which alkenes react with hydrogen to form alkanes. It occurs at 150ºC using a nickel catalyst.
25
Q: How is hydrogenation used in the food industry?
A: Hydrogenation is used in the food industry to manufacture margarine from vegetable oils. It involves partially hydrogenating polyunsaturated vegetable oils to increase their molecular weight and convert them into solid fats.
26
Q: Describe the process of halogenation with alkenes.
A: Halogenation involves halogens participating in addition reactions with alkenes, where the halogen atoms add across the C=C double bond. This reaction occurs readily at room temperature
27
Q: What is the bromine water test, and how does it differentiate between alkanes and alkenes?
A: The bromine water test is a chemical test used to differentiate between alkanes and alkenes. Bromine water, which is orange in color, will remain orange when added to an alkane but will lose its color when added to an alkene due to the addition of bromine across the C=C double bond.
28
Q: What are polymers, and how are they formed?
A: Polymers are large molecules with high relative molecular mass, formed by linking together numerous smaller molecules known as monomers. Each monomer serves as a repeat unit and is connected to adjacent units via covalent bonds.
29
Q: What is the role of polymerisation reactions in the formation of polymers?
A: Polymerisation reactions involve the linking of monomers to form polymers. These reactions typically require high pressures and often involve the use of catalysts to facilitate the bonding of monomers into long polymer chains.
30
Q: Give examples of everyday materials that are polymers.
A: Many everyday materials, such as resins, plastics, polystyrene cups, and nylon, are examples of polymers. These are often manufactured and are known as synthetic polymers.
31
Q: How do synthetic polymers differ from natural or biological polymers?
A: Synthetic polymers are manufactured by humans through industrial processes, while natural or biological polymers are produced by living organisms or found in nature. Examples of natural polymers include proteins, cellulose, and DNA
32
Q: How are addition polymers formed, and what type of monomers are involved?
A: Addition polymers are formed by the joining of many monomers, typically those containing carbon-carbon double (C=C) bonds. During polymerization, one of the bonds in each C=C bond breaks, and a bond is formed with the adjacent monomer, resulting in a polymer with only single bonds.
33
Q: What are some examples of monomers used in the formation of addition polymers?
A: Addition polymers can be made from various alkene monomers, including ethene, propene, and others. Additionally, some polymers are formed from alkene monomers with different atoms attached, such as chlorine or hydroxyl groups.
34
Q: How are addition polymers named?
A: The name of an addition polymer is determined by placing the name of the monomer in brackets and adding "poly-" as the prefix. For example, if propene is the alkene monomer used, the polymer is named polypropene. Similarly, polyethene is formed by the addition polymerization of ethene monomers.
35
Q: How can you deduce the monomer from the polymer structure?
A: To deduce the monomer from the polymer structure, you can reverse the process of polymerization. Start by identifying the repeat unit within the polymer structure, which involves changing the double bond in the monomer to a single bond in the repeat unit and adding bonds to each end of the repeat unit to indicate continuation. Then, add the rest of the groups in the same order they surrounded the double bond in the monomer. Finally, add a subscript "n" to indicate a large number of repeat units.
36
Q: How are condensation polymers formed, and what distinguishes them from addition polymers?
A: Condensation polymers are formed when two different monomers are linked together with the removal of a small molecule, typically water. This removal of a small molecule distinguishes condensation polymers from addition polymers, where no small molecule is eliminated during polymerization
37
Q: What types of functional groups do monomers in condensation polymers typically have, and how do they react during polymerization?
A: The monomers in condensation polymers typically have two functional groups present, one on each end. Examples include diols (alcohol at each end) or dicarboxylic acids (carboxylic acid at each end). During polymerization, the functional groups at the ends of one monomer react with the functional group on the end of the other monomer, resulting in the formation of long chains with an A-B-A-B pattern
38
Q: What is the significance of the A-B-A-B pattern in condensation polymers?
A: The A-B-A-B pattern in condensation polymers arises from the alternating arrangement of monomers along the polymer chain. This pattern reflects the repeating sequence of functional groups from the monomers and contributes to the overall structure and properties of the polymer.
39
Q: Can monomers with different functional groups react to form condensation polymers?
A: Yes, monomers with different functional groups can react to form condensation polymers. For example, polyesters are often formed from two different monomers, such as diols and dicarboxylic acids, resulting in the elimination of water during polymerization
40
Q: What are the two main types of synthetic condensation polymers, and how do they differ?
A: The two main types of synthetic condensation polymers are polyesters and polyamides. Polyesters are formed from diols and dicarboxylic acids, while polyamides are formed from diamines and dicarboxylic acids. These polymers differ in their chemical composition and properties.
41
Q: How are polyesters formed, and what are the typical monomers involved in their synthesis?
A: Polyesters are formed from dicarboxylic acid monomers (containing a carboxylic acid group, -COOH, at each end) and diols (containing an alcohol group, -OH, at each end). During polymerization, each -COOH group reacts with the -OH group on a diol from another monomer, forming an ester link (-COO-) and releasing one water molecule per linkage.
42
Q: What is the chemical process involved in forming ester links during polyester synthesis?
A: The formation of ester links during polyester synthesis involves a condensation reaction, where the -COOH group of a dicarboxylic acid reacts with the -OH group of a diol. This reaction results in the loss of one water molecule (H2O), formed from the combination of a hydrogen ion (H+) from the -COOH group and a hydroxide ion (OH-) from the -OH group.
43
Q: Can you provide an example of a polyester, and what are some of its properties or applications?
A: Terylene is an example of a polyester. It is a synthetic polymer known for its durability, wrinkle resistance, and resistance to stretching and shrinking. Terylene is commonly used in clothing, upholstery, and packaging materials due to its excellent mechanical properties and resistance to environmental factors such as moisture and sunlight.
44
Question: What are the health and safety aspects to consider when working with the solutions used in the formation of condensation polymers?
Answer:
Solutions used are hazardous and contain toxic materials and solvents.
Handle and dispose of them with care.
Use small quantities to minimize risks.
45
Question: Describe the procedure for making nylon in the lab.
Answer:
Prepare two solutions: one containing 1,6-diaminohexane in water, and the other containing decanedioyl dichloride in cyclohexane.
Pour 5 cm³ of aqueous 1,6-diaminohexane solution into a 25 cm³ beaker.
Carefully add 5 cm³ of decanedioyl dichloride solution on top to minimize mixing.
The dichloride solution floats on top without mixing, and a white nylon film forms at the interface.
Pick up a little of the film with tweezers and wrap it around a glass rod.
Rotate the glass rod to extract a "rope" of nylon from the beaker.
46
Question: What is the principle behind the formation of nylon in the lab?
Nylon formation involves two monomers, each containing reactive groups at their ends.
These groups react, joining together to form long chains, akin to a bead necklace with alternating colored beads.
The resulting nylon is named after New York and London, where it was first discovered.
47
Question: What is the significance of the term "nylon 6,10" in the context of nylon formation?
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Answer:
"Nylon 6,10" indicates the lengths of the monomer pieces: 6 carbons long from the diamine and 10 carbons long from the diacyl chloride.
It refers to the specific composition of the monomers used in the polymerization process
48
Question: How does the nylon rope trick demonstrate the polymerization process?
Answer:
The nylon rope trick showcases the formation of long chains of nylon from the reaction of two monomers.
By rotating the glass rod, a continuous "rope" of nylon is extracted, demonstrating the polymerization process visually.
49
Question: What is DNA, and what is its primary function?
Answer:
DNA stands for Deoxyribonucleic acid and is a large molecule essential to all life.
Its primary function is to store genetic information and encode instructions necessary for the development and functioning of organisms.
50
Question: Describe the composition of DNA.
Answer:
DNA consists of nucleotides, which are made up of three components: a phosphate group, a sugar molecule (deoxyribose), and a nitrogenous base (adenine, thymine, cytosine, or guanine)
51
Question: What are the four different bases in DNA, and how are they abbreviated?
Answer:
The four bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G).
52
Question: Explain the structure of DNA.
Answer:
DNA consists of two strands that intertwine to form a double helix.
The strands are held together by hydrogen bonds between complementary base pairs: A with T, and C with
53
Question: How is genetic information stored in DNA?
Answer:
Genetic information is stored in the sequence of the bases along the DNA strands.
The order of the bases serves as a code for the organism's genes, determining its traits and functions.
54
Question: What is the significance of the double helix structure of DNA?
Answer:
The double helix structure of DNA provides stability and protection for the genetic information stored within.
It allows for the efficient packaging of DNA within cells and facilitates processes such as replication and transcription
55
Question: What are carbohydrates, and what is their general formula?
Answer:
Carbohydrates are compounds composed of carbon, hydrogen, and oxygen.
Their general formula is Cx(H2O)y.
56
Question: Differentiate between simple and complex carbohydrates.
Answer:
Simple carbohydrates are monosaccharides, such as fructose and glucose.
Complex carbohydrates are polysaccharides, like starch and cellulose.
57
Question: What are monosaccharides, and give examples.
Answer:
Monosaccharides are simple sugars and the building blocks of carbohydrates.
Examples include fructose and glucose.
58
Question: Define polysaccharides and provide examples.
Answer:
Polysaccharides are complex carbohydrates formed from the polymerization of simple sugar monomers.
Examples include starch (used for energy storage) and cellulose (used in plant cell walls for support).
59
Question: Describe the process of polymerization for complex carbohydrates.
Answer:
Complex carbohydrates are formed through condensation polymerization from simple sugar monomers.
An H2O molecule is eliminated as the sugars polymerize, forming glycosidic linkages (-O- linkages) between the monomers.
60
Question: What is the function of starch and cellulose in living organisms?
Answer:
Starch is used for energy storage in plants and some animals.
Cellulose serves as a stiff polymer used in plant cell walls to provide structural support.
61
Question: What are proteins, and what are some of their biological functions?
Answer:
Proteins are important natural polymers with specific biological functions.
Examples of protein functions include transporting oxygen in the blood (haemoglobin), protecting the body from viruses and bacteria (antibodies), and acting as biological catalysts (enzymes).
62
Question: Describe the function of haemoglobin in the body.
Answer:
Haemoglobin is a protein that transports oxygen in the blood.
It binds to oxygen in the lungs and carries it to tissues and organs throughout the body, facilitating cellular respiration.
63
Question: What role do antibodies play in the immune system?
Answer:
Antibodies are proteins produced by the immune system to help protect the body from viruses, bacteria, and other pathogens.
They recognize and bind to specific antigens, marking them for destruction by other immune cells or neutralizing their harmful effects.
64
Question: What are enzymes, and what is their function in biological systems?
Answer:
Enzymes are biological catalysts, typically proteins, that facilitate chemical reactions in living organisms.
They speed up the rate of reactions by lowering the activation energy required for the reaction to occur, without being consumed or permanently altered in the process.
65
Question: How do proteins exhibit specificity in their biological functions?
Answer:
Proteins have unique three-dimensional structures that allow them to interact selectively with specific molecules, such as substrates, antigens, or other proteins.
This specificity is crucial for their diverse biological functions, ensuring that they perform their roles effectively and accurately
66
Question: What functional groups are present in amino acids?
Answer:
Amino acids contain the amino group (NH2) and the carboxylic acid group (COOH).
67
Question: Describe the properties of the amino group in amino acids.
Answer:
The amino group (NH2) is basic and behaves similarly to ammonia.
It can accept protons (H+) in solution, making it capable of acting as a base.
68
Question: Explain the properties of the carboxylic acid group in amino acids.
.
Answer:
The carboxylic acid group (COOH) is acidic and is also known as the carboxyl group.
It can donate protons (H+) in solution, making it capable of acting as an acid
69
Question: How many naturally occurring amino acids are there, and what is their general structure?
Answer:
There are twenty naturally occurring amino acids, all sharing the same general structure.
This structure includes a central carbon atom (the alpha carbon) bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group).
70
Question: What is the significance of amino acids in the formation of proteins?
Answer:
Amino acids serve as the monomers that join together to form very long protein molecules through peptide bond formation.
Different combinations and sequences of amino acids determine the unique structure and function of each protein.
71
Question: What functional group is present in all alcohols, and what is its chemical symbol?
Answer:
All alcohols contain the hydroxyl functional group (-OH), which is responsible for their characteristic reactions.
72
Question: What is the general formula for alcohols, and what does it represent?
Answer:
The general formula for alcohols is CnH2n+1OH.
This formula represents a homologous series of compounds where each member differs by one -CH2 unit from the next.
73
Question: How are alcohols named, and what is the naming convention?
Answer:
Alcohols are named using the same system as alkanes and alkenes.
The final 'e' in the corresponding alkane or alkene name is replaced with 'ol' to indicate the presence of the hydroxyl group
74
Question: Describe the structure of the hydroxyl group in alcohols.
Answer:
The hydroxyl group (-OH) consists of an oxygen atom bonded to a hydrogen atom.
This group is attached to a carbon atom, which can be part of a larger carbon chain or ring structure in the alcohol molecule
75
Question: Provide the names and molecular structures of the first four alcohols.
Methanol (CH3OH), ethanol (C2H5OH), propanol (C3H7OH), and butanol (C4H9OH).
Each alcohol has an additional -CH2 unit compared to the previous one in the series.
76
Question: What distinguishes one alcohol from another within the homologous series?
Answer:
The length of the carbon chain and the arrangement of atoms within the molecule, particularly around the hydroxyl group, distinguish one alcohol from another within the homologous series.
77
Question: Describe the solubility of alcohols in water.
Answer:
Alcohols are colorless liquids that dissolve in water to form neutral solutions.
They can dissolve substances that water cannot, such as fats and oils, while also dissolving most substances that water can
78
What are some common uses of the first four alcohols?
Answer:
The first four alcohols (methanol, ethanol, propanol, and butanol) are commonly used as fuels.
Ethanol is often used in spirit burners in school laboratories due to its clean burning properties and lack of strong odors.
Methanol and ethanol are also extensively used as solvents due to their ability to dissolve a wide range of substances.
79
Flashcard:
Question: Write the balanced equation for the complete combustion of ethanol.
Answer:
CH3CH2OH + 3O2 → 2CO2 + 3H2O
Ethanol reacts with oxygen to produce carbon dioxide and water in a combustion reaction.
80
Question: Describe the oxidation reaction of alcohols to produce carboxylic acids.
Answer:
Alcohols undergo oxidation reactions to produce carboxylic acids, which are organic acids.
This reaction can be achieved by heating the alcohols with acidified potassium manganate(VII) as an oxidizing agent.
For example, ethanol can be oxidized to produce ethanoic acid:
CH3CH2OH + 2[O] → CH3COOH + H2O
81
Question: What does the symbol [O] represent in the oxidation reaction of alcohols?
Answer:
The symbol [O] represents an oxidizing agent, which facilitates the oxidation reaction by providing oxygen atoms to react with the alcohol.
It is a symbolic representation used to simplify the equation.
82
Question: What is the general formula for carboxylic acids, and what does it represent?
Answer:
The general formula for carboxylic acids is CnH2n+1COOH.
This formula represents a homologous series of compounds where each member differs by one -CH2 unit from the next
83
Question: Describe the physical properties of carboxylic acids.
Answer:
Carboxylic acids show a gradation in physical properties:
Boiling points increase with increased carbon chain length.
Viscosity increases with increased carbon chain length.
They have similar chemical properties, but their reactivity may vary depending on the structure and functional groups present.
84
Question: What functional group is present in all carboxylic acids, and what is its chemical symbol?
Answer:
All carboxylic acids contain the carboxyl functional group (-COOH).
The chemical symbol for this group is COOH.
85
Question: How are carboxylic acids named, and what is the naming convention?
Answer:
Carboxylic acids are named using the same system as alkanes and alkenes.
The final 'e' in the corresponding alkane or alkene name is replaced with 'oic', followed by the word "acid" to indicate the presence of the carboxyl group.
86
Question: Provide the names and molecular structures of the first four carboxylic acids.
Answer:
Methanoic acid (formic acid) - HCOOH
Ethanoic acid (acetic acid) - CH3COOH
Propanoic acid - CH3CH2COOH
Butanoic acid - CH3CH2CH2COOH
Each acid has an additional -CH2 unit compared to the previous one in the series.
87
What is crude oil, and what is another name for it?
Answer:
Crude oil is a complex mixture of hydrocarbons found in the Earth's crust.
It is also known as petroleum.
88
Question: Define hydrocarbons and describe their composition.
Answer:
Hydrocarbons are compounds composed of carbon and hydrogen atoms only.
In crude oil, hydrocarbon molecules consist of a carbon backbone, which can be in the form of rings or chains, with hydrogen atoms attached to the carbon atoms.
89
Question: How is crude oil formed, and over what period of time does this process occur?
Answer:
Crude oil forms over millions of years from the effects of high pressures and temperatures on the remains of plants and animals.
This process involves the decomposition and transformation of organic matter buried deep within the Earth's crust.
90
Question: Describe the physical properties of crude oil.
Answer:
Crude oil is a thick, sticky, black liquid found in porous rock formations underground or beneath the sea.
It is a complex mixture containing molecules with varying ring sizes and chain lengths.
91
Question: Why is crude oil considered a finite resource?
Answer:
Crude oil is being used up much faster than it is being formed, making it a finite resource.
Its extraction and consumption rates exceed the rate of natural replenishment, leading to concerns about its depletion over time.
92
Question: What is fractional distillation, and why is it used?
Answer:
Fractional distillation is a process used to separate the various fractions of crude oil based on differences in their boiling points.
It is used to obtain valuable hydrocarbon fractions from crude oil, as each fraction has different applications and properties
93
Question: Describe the composition of crude oil fractions.
Answer:
Each fraction consists of groups of hydrocarbons with similar chain lengths.
The molecules in each fraction have similar properties and boiling points, which depend on the number of carbon atoms in the chain
94
Question: How are the fractions in petroleum separated during fractional distillation?
Answer:
During fractional distillation, crude oil is heated to high temperatures in a fractionating column.
The different fractions are separated as they vaporize at different temperatures based on the size and length of the hydrocarbon molecules.
95
Question: What determines in which fraction a hydrocarbon molecule will be separated during fractional distillation?
Answer:
The size and length of each hydrocarbon molecule determine which fraction it will be separated into.
Larger molecules with more carbon atoms typically have higher boiling points and are separated into higher boiling fractions
96
Question: What types of compounds are found in most fractions obtained from fractional distillation?
Answer:
Most fractions obtained from fractional distillation contain mainly alkanes.
Alkanes are compounds of carbon and hydrogen with only single bonds between them, and they are the primary constituents of crude oil fractions.
97
Question: How is fractional distillation carried out in terms of temperature variations in the fractionating column?
Answer:
Fractional distillation is conducted in a fractionating column that is very hot at the bottom and cool at the top.
This temperature gradient allows for the separation of hydrocarbons based on their boiling points.
98
Question: Describe the process of fractional distillation in the fractionating column.
Answer:
Crude oil enters the fractionating column and is heated, causing vapors to rise.
Hydrocarbons with very high boiling points immediately condense into liquid at the higher temperatures lower down the column and are collected at the bottom.
Hydrocarbons with lower boiling points rise up the column and condense at the top to be collected.
The different fractions are tapped off at various heights according to their boiling points.
99
Question: How are the fractions collected in fractional distillation?
Answer:
Fractions containing smaller hydrocarbons are collected at the top of the fractionating column as gases.
Fractions containing larger hydrocarbons are collected at the lower sections of the column as liquids
100
Question: What determines the position of a fraction in the fractionating column during fractional distillation?
Answer:
The boiling point of a hydrocarbon determines its position in the fractionating column.
Hydrocarbons with higher boiling points condense and collect at lower levels of the column, while those with lower boiling points condense and collect at higher levels.
101
Question: How does the boiling point of hydrocarbons change as the size of the hydrocarbon molecule increases?
Answer:
As the size of the hydrocarbon molecule increases, the boiling point also increases.
This is because larger molecules have stronger intermolecular forces, such as van der Waals forces, which require more energy to break, resulting in higher boiling points.
102
Question: Define cracking and its purpose.
Answer:
Cracking is a process used to convert long-chain hydrocarbons into shorter-chain hydrocarbons.
Its purpose is to produce more useful products, such as smaller hydrocarbons like alkenes, which are in higher demand.
103
Question: Differentiate between saturated and unsaturated molecules.
Answer:
Saturated molecules contain single bonds only between carbon atoms.
Unsaturated molecules contain double bonds between their carbon atoms.
104
Question: Provide examples of saturated and unsaturated compounds.
Answer:
Alkanes, such as methane and ethane, are saturated compounds.
Alkenes, like ethene and propene, are unsaturated compounds due to the presence of double bonds between carbon atoms
105
Question: Explain why cracking is necessary in the petroleum industry.
Answer:
Cracking is necessary to break down long-chain hydrocarbons into smaller, more valuable molecules.
It allows for the production of high-demand products like petrol, as well as other useful compounds such as alkenes and hydrogen
106
Question: Describe the products obtained from the cracking process.
Answer:
Cracking produces smaller hydrocarbons, including small alkenes and hydrogen gas.
For example, kerosene and diesel oil can be cracked to produce petrol, other alkenes, and hydrogen gas, which are all valuable products.
107
Question: What are some examples of hydrocarbons commonly cracked in industrial processes?
Answer:
Decane is an example of a long-chain alkane that can be cracked to produce smaller hydrocarbons, including alkenes and hydrogen gas.
108
Question: Describe the conditions under which cracking occurs.
Answer:
Cracking involves heating hydrocarbon molecules to around 600 – 700°C to vaporize them.
The process typically occurs in the presence of a powdered catalyst such as alumina or silica.
109
Question: Explain the role of catalysts in the cracking process.
Answer:
Catalysts, such as alumina or silica, facilitate cracking by providing a surface for the hydrocarbon molecules to interact with.
They break covalent bonds in the molecules as they come into contact with the catalyst surface, leading to thermal decomposition reactions.
110
Question: How does cracking break down hydrocarbon molecules?
Answer:
Cracking breaks down hydrocarbon molecules in a random manner, resulting in the formation of a mixture of smaller alkanes and alkenes.
Covalent bonds within the hydrocarbon molecules are broken as they interact with the catalyst surface.
111
Question: What products are typically formed during the cracking process?
Answer:
Cracking produces a mixture of smaller alkanes and alkenes, as well as hydrogen gas.
The exact composition of the product mixture depends on factors such as temperature and pressure.
112
Question: How do temperature and pressure affect the products formed in cracking?
Answer:
At higher temperatures and pressures, cracking tends to produce a higher proportion of alkenes and hydrogen gas.
This is because higher temperatures and pressures favor the breaking of covalent bonds, leading to more extensive decomposition of the hydrocarbon molecules.
113
Question: What is the purpose of cracking in the petroleum industry?
Answer:
Cracking is used to break down long-chain hydrocarbons into smaller, more useful molecules.
114
Question: Provide an example of a cracking reaction.
Answer:
An example of a cracking reaction is the conversion of hexane (C6H14) into butane (C4H10) and ethene (C2H4):
C6H14 ⟶ C4H10 + C2H4
115
Question: How is the equation for a cracking reaction balanced?
Answer:
The equation is balanced by ensuring that the number of carbon and hydrogen atoms is the same on both sides of the reaction.
116
Question: What are the general formulas for alkanes and alkenes?
Answer:
The general formula for alkanes is CnH2n+2.
The general formula for alkenes is CnH2n.
117
Question: How can you verify if a cracking reaction is balanced?
Answer:
Check that the number of carbon and hydrogen atoms is the same on both sides of the equation.
Ensure that the reactants are long-chain hydrocarbons (alkanes) and the products include smaller hydrocarbons (alkanes and alkenes)
118
Question: What are some examples of products obtained from cracking?
Answer:
Products of cracking include smaller alkanes, smaller alkenes, and hydrogen gas, all of which are valuable in various industrial processes.
119
Question: What is a simple cell, and what is its purpose?
Answer:
A simple cell is a source of electrical energy.
It consists of two electrodes made from metals of different reactivity immersed in an electrolyte, connected to an external voltmeter by wire to create a complete circuit.
120
Question: Describe the components of a simple cell.
Answer:
A simple cell consists of two electrodes made from metals of different reactivity, an electrolyte, and an external voltmeter connected by wire.
121
Question: How does the difference in reactivity between metals affect the function of a simple cell?
Answer:
The more reactive metal releases electrons more readily, giving its electrode a negative charge.
This sets up a charge difference between the electrodes, causing electrons to flow around the circuit to the less reactive electrode, which becomes more positive.
122
Question: What factors affect the voltage produced by a simple cell?
Answer:
The difference in reactivity between the metals used in the electrodes affects the voltage produced.
Additionally, the choice of electrolyte influences the voltage, as different ions react with the electrodes in different ways
123
Question: How long does a simple cell produce voltage?
Answer:
A simple cell produces voltage until one of the reactants is used up, at which point the cell will stop functioning.
124
Question: What is the relationship between the difference in metals' reactivity and the voltage produced by a cell?
Answer:
The greater the difference in the metals' reactivity, the greater the voltage produced by the cell.
125
Question: What is a simple cell, and how does it function?
Answer:
A simple cell is a source of electrical energy.
It consists of two electrodes made from metals of different reactivity immersed in an electrolyte.
The more reactive metal releases electrons more readily, setting up a charge difference between the electrodes and producing voltage.
126
Question: How does the difference in reactivity between metals affect the voltage produced by a simple cell?
Answer:
The greater the difference in reactivity between the metals used in the electrodes, the greater the voltage produced by the cell.
127
Question: What is a common example of a simple cell, and why is it used?
Answer:
A common example of a simple cell is the zinc-copper cell.
It is used to demonstrate the principle of electrochemical cells and to generate small amounts of electrical energy.
128
Question: Describe the process that occurs in a hydrogen-oxygen fuel cell.
Answer:
At the anode, hydrogen molecules lose electrons to form hydrogen ions (2H2 → 4H+ + 4e-).
Electrons flow through the external circuit to the cathode.
Hydrogen ions migrate through a special membrane to the cathode.
At the cathode, hydrogen ions gain electrons and react with oxygen to form water (4H+ + O2 + 4e- → 2H2O).
The overall reaction is 2H2 + O2 → 2H2O, releasing energy and water.
129
Question: What is the purpose of a hydrogen-oxygen fuel cell, and how is it advantageous?
Answer:
A hydrogen-oxygen fuel cell is used to generate electrical energy.
It is advantageous because it produces electricity without generating pollution, as its only byproduct is water
130
Question: What are some advantages of hydrogen fuel cells?
Answer:
Hydrogen fuel cells do not produce any pollution.
They produce more energy per kilogram than either petrol or diesel.
No power is lost in transmission as there are no moving parts, unlike an internal combustion engine.
131
Question: What are some environmental benefits of hydrogen fuel cells?
Answer:
Hydrogen fuel cells do not produce pollution, contributing to cleaner air.
They do not require batteries, reducing the environmental impact associated with battery disposal.
132
Question: What are some disadvantages of hydrogen fuel cells?
Answer:
Materials used in producing fuel cells are expensive.
High-pressure tanks are needed to store the oxygen and hydrogen, which are dangerous and difficult to handle.
Fuel cells are affected by low temperatures, becoming less efficient.
133
Question: What challenges are associated with the storage of hydrogen in fuel cells?
Answer:
High-pressure tanks are required to store sufficient amounts of oxygen and hydrogen, presenting safety concerns.
Hydrogen is expensive to produce and store, limiting its widespread adoption.
134
Question: What is a notable advantage of hydrogen fuel cells regarding energy production?
Answer:
Hydrogen fuel cells operate as a continuous process, continuously producing energy as long as fuel is supplied.
135
Question: Can you state three advantages and three disadvantages of hydrogen fuel cells?
Answer:
Advantages: (1) No pollution, (2) Higher energy density than petrol or diesel, (3) No power loss in transmission.
Disadvantages: (1) Expensive materials, (2) High-pressure storage requirements, (3) Reduced efficiency at low temperatures.
