HSC Chemistry Module 7: Organic Chemistry Practice Questions

Question 6 ⭐⭐⭐🔥

Most hydrocarbons are extracted from the Earth are nonrenewable. Assess the impact of extracting and using hydrocarbons on the environment, economy and society. (7 marks)

(L2.6:examine the environmental, economic and sociocultural implications of obtaining and using hydrocarbons from the Earth)

Hydrocarbons

Question 7 ⭐⭐

Draw structural formulas for the following reactions and name their respective products. (3 marks)

1. 3-Hexene and hydrogen gas
2. 2-Butyne and excess bromide gas 
3. 4-octene and water 

(L3.1: investigate, write equations and construct models to represent the reactions of unsaturated hydrocarbons when added to a range of chemicals, including but not limited to:

–  hydrogen (H2)
–  halogens (X2)
–  hydrogen halides (HX)
–  water (H2O))

Question 8 ⭐

Draw structural formulas for the following reactions and name their respective products. (2 marks) 

1. Pentane and chloride gas
2. Decane and hydrogen bromide 

(L3.2: investigate, write equations and construct models to represent the reactions of saturated hydrocarbons when substituted with halogens)

Alcohols

Question 9 ⭐

Rank primary, secondary and tertiary alcohols from lowest to highest boiling point. Explain your ranking system with reference to its structure. (3 marks)

(L4.1: investigate the structural formulae, properties and functional group including:
–  primary
–  secondary
–  tertiary alcohols

Question 10 ⭐⭐⭐🔥

A student performed a first-hand investigation to determine the quantitative relationship between heat of combustion and molar mass of alkanols. The student did this by burning different alkanols to heat water as shown in the diagram below. The calculated heats of combustion for four of the alkanols are given in the table. 

a) On the grid below, graph both the calculated and the theoretical heat of combustion against the molar mass of the alkanols. 

b) Discuss the validity of the student’s investigation.

(L4.3: conduct a practical investigation to measure and reliably compare the enthalpy of combustion for a range of alcohols)

Question 11 ⭐⭐

Write balanced chemical and structural equations for the reactions of the following substances. (4 marks) 

1. Magnesium and oxygen 
2. Dehydration of cellulose 
3. Pentane and hydrogen chloride 
4. Two step oxidation of butane 

(L4.4: write equations, state conditions and predict products to represent the reactions of alcohols, including but not limited to (ACSCH128, ACSCH136):

–  combustion
–  dehydration
–  substitution with HX
–  oxidation)

Question 12 ⭐⭐⭐

Draw and name the products following the oxidation of the listed alcohols (4 marks)

(L4.6: Investigate the products of the oxidation of primary and secondary alcohols)

Question 13 ⭐⭐

Assess the advantages and disadvantages between non-renewable fuels and ethanol. (6 marks) 

(L4.7:  compare and contrast fuels from organic sources to biofuels, including ethanol) 

Reactions of Organic Acids and Bases 

Question 14 ⭐⭐

Explain how the structural difference between amines and amides contribute to their different properties. Include examples with structural formulae. (3 marks)

(L5.1: investigate the structural formulae, properties and functional group including:
–  primary, secondary and tertiary alcohols
–  aldehydes and ketones (ACSCH127)
–  amines and amides
–  carboxylic acids)

Question 15 ⭐⭐⭐

Rank amines, amides and carboxylic acid from lowest to highest boiling point. Account for this trend with reference to its respective intermolecular and intramolecular bonding. ( 5 marks)

(L5.2: explain the properties within and between the homologous series of carboxylic acids amines and amides with reference to the intermolecular and intramolecular bonding present)

Question 16 ⭐

Which organic compounds are characterised as organic acids? Which organic compounds are characterised as organic bases? (3 marks) 

(L5.4: investigate the differences between an organic acid and organic base)

Question 17 ⭐⭐

What is the structural difference between anionic and cationic detergents? Use their structure to account for their unique uses. (4 marks) 

(L5.5: investigate the structure and action of soaps and detergents) 

Question 18 ⭐⭐⭐

Construct a flow chart that depicts the conversion of propane to ethyl propanoate. (3 marks) 

(L5.6: Draft and construct flow charts to show reaction pathways for chemical synthesis, including those that involve more than one step) 

Polymers

Question 19 ⭐⭐⭐

With reference to their structural composition, account for the unique properties and uses of polyethylene (PE), polyvinyl chloride (PVC) and polytetrafluoroethylene (PTFE). (6 marks) 

(L6.1: model and compare the structure, properties and uses of addition polymers of ethylene and related monomers, for example:
–  polyethylene (PE)
–  polyvinyl chloride (PVC)
–  polystyrene (PS)
–  polytetrafluoroethylene (PTFE)) 

Question 20 ⭐⭐

Compare the production of nylon and polyesters through structural diagrams. Account for how the structure of these polymers contribute to its properties and therefore, uses. (5 marks) 

(L6.2: model and compare the structure, properties and uses of condensation polymers, for example: 

– nylon
– polyesters)

Question 1

Each pair has the same molecular formula which is why they are isomers.

Group 1: Functional group isomer as the first molecule is butanal (aldehyde) and the second is butan-2-one (ketone). (C₄H₈O)

Group 2: Chain isomer as the first is butane and the second is 2-methylpropane. (C₄H₁₀)

Group 3: Position isomer as both are alcohols but the first is butanol, whilst the second is butan-2-ol. (C₄H₉OH)

Question 2

Question 3

This statement is not as easily answered as just true or false. When comparing shorter alcohols to other hydrocarbons of similar size they have relatively high boiling points due to strong hydrogen bonds. However, when comparing short alcohols to longer alcohols, longer alcohols have the higher boiling point due to stronger dispersion forces.

Question 4

💡TIP: The main influence on boiling point is the intermolecular forces!

a) The primary trend seen across alkanes, alkanols and alkanoic acids is that as the molecular weight increases, the boiling point increases as well. This is due to stronger dispersion forces as the chain length increases, requiring more energy to separate molecules into the gaseous state. These dispersion forces are present in all organic compounds, however polar molecules will experience additional dipole-dipole interactions or hydrogen bonding, resulting in even stronger intermolecular forces requiring more energy to move to the gaseous state. This is why the polar alkanoic acids and alkanols have higher boiling points compared to the alkanes. Lastly, the hydrogen bonds in alkanoic acids are stronger than those found in alkanols, resulting in higher boiling points for the acids.

 

b) Alkanones would display the same increasing trend in boiling point as the molecular weight increases, due to the presence of greater dispersion forces as the chain length increases. When ranking alkanones compared to the others, alkanones would appear between the alkanes and the alkanols. This is due to both the presence of dipole-dipole interactions that occur in polar molecules, and the lack of an -OH group that prevents hydrogen bonds (compared to the alkanols and alkanoic acids).

Question 5

Carboxylic acids are highly corrosive and reactive, requiring safe disposal procedures. The safest procedure is collection and disposal using a hazardous waste container. They can also be rinsed down the sink once they have been diluted with excess water and neutralised.

Question 6

💡TIP: Think about the mining industry, it’s related to the hydrocarbon industry!

The environmental impacts of hydrocarbons are largely related to pollution and habitat destruction. Extracting hydrocarbons from the earth requires mining which creates issues for the surrounding ecosystems. Furthermore, the use of hydrocarbons results in an increase in greenhouse gases contributing to climate change.

Economically, the hydrocarbon industry provides job and energy security, which can make the industry very appealing. However, oil spills and other environmental damage leads to expensive clean-up and restorative costs. The rising costs of hydrocarbons has resulted in investment into renewable energies.

Indigenous land rights are often dismissed or abused during extraction projects, resulting in societal impacts. Air pollution as a result of hydrocarbon combustion increases health issues such as respiratory diseases. Lastly, there is an increasing societal pressure to transition to cleaner, greener renewable energy alternatives.

Whilst the hydrocarbon industry may have plenty of benefits, the growing impacts on the environment and society outweigh the economic benefits and it’s time to make the switch to renewable energy.

Question 7

Question 8

As these hydrocarbons are completely saturated, they will only react under certain conditions such as UV-light to perform substitution reactions with halogengas (e.g. Br₂).

Question 9

The boiling point of alcohol is determined by the strength of the hydrogen bonding and the level of branching. Primary alcohols have the highest boiling point as they have the strongest hydrogen bonds and no branching, allowing molecules to easily interact with each other. Secondary alcohols still have strong hydrogen bonds, however due to branching the molecules are unable to pack as closely together. Tertiary alcohols have the lowest boiling point as their hydrogen bonding is significantly affected by the level of branching, preventing molecules from interacting closely with each other.

Question 10

a) 

b)

The experiment is valid, as the student is measuring exactly what it was intended to. However the validity could be significantly increased by ensuring no heat is lost to the environment, which would likely increase the calculated heat of combustion and lead to more accurate answers.

Question 11

Question 12

Question 13

Non-renewable fuels such as fossil fuels are high in energy, making them more efficient for industrial uses and more convenient as most of the world’s energy related infrastructure are designed for these non-renewable energies. However, as non-renewable fuels are non-renewable they are being used up at faster rate than they can be replaced. They also have a significant impact on the environment due to the production of greenhouse gases.

Ethanol has a higher production cost and lower energy content compared to non-renewable fuels. However, its advantages benefit the environment as well as the longevity of the infrastructure and systems using ethanol as their energy source.

Whilst both fuel choices have advantages and disadvantages, a blended fuel approach can decrease the reliance on petroleum and slow the use of non-renewable fuels.

Question 14

The largest difference between amines and amides is that amides have a carbonyl group whilst amines do not (both have a NH₂ group). This difference means that amides have significantly stronger hydrogen bondings and dipole-dipole interactions, resulting in higher boiling points, higher solubility with water and being a weaker base.

Question 15

Boiling point is influenced by intermolecular forces, with hydrogen bonding being the strongest, dipole-dipole interactions having moderate influence and dispersion forces the weakest. Carboxylic acids have the strongest hydrogen bonds out of the three groups, meaning they have the highest boiling point. Amides have hydrogen bonding but not as strong as with the carboxylic acid, amides also have strong dipole-dipole interactions. Amines have the lowest boiling point as their hydrogen bonding and dipole-dipole interactions are weaker than the other two due to the lack of a carbonyl group.

Question 16

Organic compounds that are classified as acids are carboxylic acids and alcohol. The basic compounds are amines and amides. Organic acids have hydrogen bonding, whereas organic bases have a lone pair of electrons on nitrogen or oxygen elements for proton acceptance.

Question 17

The structural difference is that anionic detergents have a negatively charged head group which interacts with water, whereas the cationic detergents have positively charged head groups, allowing them to interact with negatively charged surfaces. These key differences mean that anionic detergents allow emulsification and the removal of dirt, resulting in strong cleansing action. Meanwhile, cationic detergents have good antibacterial properties and work well in hard water, but aren’t as strong cleaning agents compared to anionic detergents.

Question 18

💡TIP: If you don’t have a reaction pathways poster to use for your study (and questions like these) make one now and then come back to this question!

Question 19

💡TIP: focus on the constituents and how they will influence interactions

Polyethylene (PE) comes in two forms, high density (HDPE) and low density (LDPE) and its constituent is ethene. HDPE is incredibly linear, allowing long running chains to pack closely together. This and the fact that HDPE is chemically inert makes it incredibly useful for outdoor piping or chemical containers. LDPE has a high degree of chain-branching and is therefore a more flexible and elastic polymer, making it useful for plastic bags, cling film and other soft/flexible plastics. Polyvinyl chloride (PVC) is incredibly similar to HDPE structurally, apart from the chlorine present in its constituent chloroethene. The presence of chlorine makes PVC much heavier and rigid, but also results in its decomposition in sunlight, resulting in applications in underground water and sewerage piping. Polytetrafluoroethylene (PTFE) is made out of the tetrafluoroethylene constituent, with the presence of strong C-F bonds making this polymer incredibly strong, chemically inert and stable, as well as water resistant and non-stick. This makes PTFE incredibly useful in non-stick cookware and electrical insulation.

Question 20

Nylon is produced from amine and carboxylic acid monomers, linking in repeating units. The hydrogen bonds formed between stacked chains of nylon give it a high boiling point and strength. These high strength fibres are used in weight bearing straps such as harnesses and seat belts, as well as in clothing.

Polyester is composed of a dicarboxylic acid and dialcohol monomers. Hydroxides give polyester the ability to degrade, making it more recyclable, and the lack of hydrogen bonding between tight stacks of chains makes polyester more flexible. Polyester is used in plastic bottles and containers as well as fibres in clothing textiles. 

As shown, the main difference is that nylon is a strong fibre, whilst polyester is a flexible polymer.