SHREE RAMA JAYAM I PROMISE UNIVERSE

alkanes

methane

Number of carbon atoms	Chemical molecular formula	Molecular mass (g mol⁻¹)	IUPAC chemical name	Full structural formula (text form)	Boiling point (°C)
1	CH₄	16.04	methane	H–C–H	–161.5
2	C₂H₆	30.07	ethane	H–C–C–H (each C has 3 H)	–88.6
3	C₃H₈	44.10	propane	H–C–C–C–H (each C filled with H)	–42.1
4	C₄H₁₀	58.12	butane	CH₃–CH₂–CH₂–CH₃	–0.5
5	C₅H₁₂	72.15	pentane	CH₃–(CH₂)₃–CH₃	36.1
6	C₆H₁₄	86.18	hexane	CH₃–(CH₂)₄–CH₃	68.7
7	C₇H₁₆	100.20	heptane	CH₃–(CH₂)₅–CH₃	98.4
8	C₈H₁₈	114.23	octane	CH₃–(CH₂)₆–CH₃	125.6

b) Identify three alkanes that occur naturally as gases.

The three alkanes that occur naturally as gases at room temperature are:

• Methane (CH₄)

• Ethane (C₂H₆)

• Propane (C₃H₈)

These are the smallest alkanes, with low molecular masses and weak dispersion forces, giving them very low boiling points (below room temperature).
They are found in natural gas and liquefied petroleum gas (LPG) mixtures.

c) Explain why alkanes: i) Do not conduct electricity

Alkanes do not conduct electricity because:

• They are non-polar covalent molecules; all bonds are between carbon and hydrogen atoms with very small differences in electronegativity.

• They contain no free ions or delocalised electrons that can move to carry an electric current.

Therefore, alkanes are electrical insulators.

ii) Are insoluble in water but are soluble in non-polar solvents

Alkanes are non-polar molecules, while water is polar.

• Water molecules are held together by strong hydrogen bonds.

• Alkanes cannot form hydrogen bonds or dipole–dipole interactions with water, so they do not mix (the principle of “like dissolves like”).

• However, alkanes can dissolve in non-polar solvents (e.g. hexane, benzene) because they interact through weak dispersion forces, which are similar to those in other non-polar substances.

In summary:

• Insoluble in water → because they are non-polar and cannot break hydrogen bonds in water.

• Soluble in non-polar solvents → because they share similar types of intermolecular forces (dispersion).

e) In terms of intermolecular bonding, explain why the boiling points of the alkanes increase with increasing molecular mass.

As the molecular mass (and chain length) of the alkanes increases, the number of electrons and surface area of each molecule also increases.
This causes stronger London dispersion forces (a type of intermolecular bonding) between neighbouring alkane molecules.

Because these dispersion forces become stronger with greater molecular size, more energy (heat) is required to overcome them during boiling.
Therefore, the boiling points of alkanes increase as molecular mass increases

alkanes

Alkane	Formula	State at 25 °C	Reason
Methane	CH₄	gas	Very low molecular mass → weak dispersion forces
Ethane	C₂H₆	gas	Weak dispersion forces
Propane	C₃H₈	gas	Still low mass and weak dispersion forces
Butane	C₄H₁₀	gas	Boiling point ≈ –0.5 °C, so just below room temp (gas under normal lab conditions)
Pentane	C₅H₁₂	liquid	Boiling point ≈ 36 °C — higher than room temp
Hexane	C₆H₁₄	liquid	Boiling point ≈ 69 °C
Heptane	C₇H₁₆	liquid	Boiling point ≈ 98 °C
Octane	C₈H₁₈	liquid	Boiling point ≈ 126 °C

need tips for the equations

• C₁–C₄ (methane → butane): gases

• C₅ and higher (pentane → octane): liquids

• Combustion products: CO₂(g) and H₂O(l)

• All are exothermic reactions that release large amounts of energy.

incomplete combustion

3. Both propane and butane are liquid petroleum gases (LPGs) used for heating food and other substances.

Identify ONE risk and how this risk can be managed to safely handle propane and butane

Identify ONE risk and how this risk can be managed to safely handle propane and butane.

Risk:
Propane and butane are highly flammable and volatile gases. If they leak, they can mix with air and form an explosive mixture, easily ignited by heat, sparks or open flames.

Management / Safety control:

• Use and store in well-ventilated areas or in a fume cupboard to prevent gas build-up.

• Keep away from ignition sources such as flames, hot surfaces or electrical sparks.

• Check cylinders, hoses and fittings for leaks before use (using soapy water, never a flame).

• Wear safety glasses and gloves when connecting or disconnecting gas equipment to avoid frost burns from pressurised liquid release.

These controls align with the Safety Data Sheets for propane and butane and the Year 11 Chemistry textbook guidance that flammable and volatile organic compounds such as alkanes must be handled in fume cupboards using protective equipment

Q1. Describe three ways in which hydrocarbons or their products are used daily.

Hydrocarbons and their products are used in a wide range of everyday applications.

1. Fuels: Hydrocarbons such as methane, propane, butane, petrol, and diesel are widely used as fuels in domestic heating, cooking, and transport. When combusted in air, they produce carbon dioxide and water, releasing large amounts of energy, which is essential for powering vehicles, generating electricity, and heating homes.

2. Manufacturing Plastics: Hydrocarbons are used as feedstock in the petrochemical industry to make polymers such as polyethylene and polypropylene, which are used to manufacture plastic bags, bottles, packaging, and clothing fibres.

3. Lubricants and Waxes: Heavier hydrocarbon fractions are used as lubricating oils, paraffin waxes, and greases. These products reduce friction in machinery and are used in candles, cosmetics, and polishes.

Q2(a) Identify the physical property that is considered in this process and explain how it is used.

The physical property used in fractional distillation is the boiling point of each hydrocarbon fraction.

Crude oil is a complex mixture of alkanes with different molecular sizes. During fractional distillation, it is first heated until it vaporises, then passed into a fractionating column with a temperature gradient — hottest at the bottom and coolest at the top. Each hydrocarbon fraction has a different boiling point due to differences in chain length and intermolecular (dispersion) forces.

Hydrocarbons with lower boiling points (shorter chains) condense at the top of the column, while those with higher boiling points (longer chains) condense lower down. This process safely separates alkanes into usable fractions based on their physical property of boiling point.

Q2(b) Predict and explain whether the petrol fraction (average 8 carbons) or kerosene (average 15 carbons) would condense higher in the fractionating tower.

The petrol fraction (C₈H₁₈) would condense higher in the fractionating tower than kerosene (C₁₅H₃₂).

This is because petrol has shorter hydrocarbon chains, which means fewer electrons, weaker dispersion forces, and a lower boiling point. It therefore condenses at a cooler region near the top of the tower.

In contrast, kerosene has longer carbon chains, greater molecular mass, and stronger dispersion forces, resulting in a higher boiling point. It remains as vapour until reaching the hotter lower sections of the tower, where it finally condenses.

Fraction	Approx. No. of Carbons	Boiling Point	Condensation Position	Reason
Petrol	~8	Lower	Higher (cooler region)	Shorter chain → weaker forces
Kerosene	~15	Higher	Lower (hotter region)	Longer chain → stronger forces

3. Outline environmental, economic and social issues involved with the mining and transport of crude oil and natural gas. Use specific examples in your answer.

3. Outline environmental, economic and social issues involved with the mining and transport of crude oil and natural gas.

Mining and transporting crude oil and natural gas present major environmental, economic and social challenges.

Environmental issues

Mining often occurs in ocean-based or remote regions such as the Arctic and Antarctic, where sedimentation over millions of years formed fossil fuels. These regions are ecologically fragile, so extraction disturbs habitats and increases the risk of oil spills. A major example is the Deepwater Horizon oil spill (2010) in the Gulf of Mexico, which released millions of barrels of oil into the ocean and killed 11 workers. The spill led to severe contamination of marine and coastal ecosystems, poisoning fish stocks and disrupting the breeding and feeding of many species.
In addition, the combustion of crude oil and natural gas releases carbon dioxide (CO₂), a greenhouse gas that absorbs infrared radiation, contributing to the enhanced greenhouse effect. According to data from the NOAA Mauna Loa Observatory, atmospheric CO₂ has steadily increased over the past 50 years. This causes global temperature rises, melting of Arctic glaciers, reduction in sea-ice area (from ~7 million km² to just over 4 million km² since 1980), and sea-level rise of nearly 200 mm since 1870. These changes disrupt animal migration, breeding patterns, and plant flowering times.

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Economic issues

Oil spills and gas leaks cause long-term economic losses for local industries and national economies. Following the Deepwater Horizon disaster, it was estimated that 26 000 jobs were lost in tourism and 10 000 jobs were affected in fishing, resulting in US $2.4 billion in lost income. Pollution forced seafood and tourist businesses to close, and many locals abandoned their traditional livelihoods. Cleanup operations also cost billions of dollars. Moreover, economies dependent on fossil fuel exports face price volatility and future decline as reserves deplete and renewable energy becomes more competitive.

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Social issues

Socially, oil and gas disasters lead to psychological stress, unemployment, and financial hardship. Communities affected by spills often experience mortgage stress, prolonged unemployment, and conflict over compensation. The Deepwater Horizon spill caused long-term mental health strain and forced thousands to rely on welfare support systems. In addition, mining in regions such as the Arctic disrupts Indigenous communities, altering traditional ways of life. While fossil fuels provide affordable energy and support modern living, these social costs highlight the need for sustainable management and transition to cleaner energy sources.

examples to be learnt

Environmental Issues

• Oil spills (e.g. Deepwater Horizon spill, 2010) cause long-term damage to marine ecosystems. Over 780,000 m³ of crude oil leaked into the Gulf of Mexico, killing seabirds, fish and affecting coral reefs.

• Gas leaks during extraction release methane (CH₄) — a greenhouse gas 25× more potent than CO₂ — accelerating climate change.

• Land degradation occurs from clearing for drilling sites and pipelines. For instance, the North West Shelf gas project in Western Australia disturbed fragile coastal and marine habitats.

• Water contamination can result from oil and gas drilling fluids seeping into groundwater.

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Economic Issues

• Oil and gas exports are major income sources for countries like Australia and Saudi Arabia, generating billions in government revenue and employment.

• However, clean-up and compensation costs from environmental disasters are enormous — the Deepwater Horizon cleanup exceeded US$60 billion.

• Price volatility in global markets causes economic instability, affecting fuel prices and national budgets.

• Transitioning away from fossil fuels towards renewables could cause job losses in traditional oil sectors but create new employment in sustainable energy.

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Social Issues

• Local communities near mining sites may face health risks from air and water pollution, including respiratory problems and contaminated drinking water.

• Indigenous lands are often disrupted by exploration — e.g., oil and gas projects in the Northern Territory have caused disputes over land rights and cultural heritage destruction.

• Oil and gas projects can provide social benefits like jobs, infrastructure, and education in remote areas, but these are often short-term.

• In cases of spills or leaks, fishing communities and tourism industries suffer loss of livelihood and social displacement.

what is a greenhouse gas—-give an example

A greenhouse gas is a gas in Earth’s atmosphere that traps heat by absorbing and re-emitting infrared radiation from the Earth’s surface.
This process keeps the planet warm — like the glass of a greenhouse — and is known as the greenhouse effect.

✅ Example:

Carbon dioxide (CO₂) is a major greenhouse gas released from burning fossil fuels such as coal, oil, and natural gas.

Q6. Describe three possible consequences of an increase in carbon dioxide emissions

• Global warming: Higher CO₂ levels increase the greenhouse effect, leading to rising average global temperatures and more frequent heatwaves.

• Sea level rise: Melting of polar ice caps and thermal expansion of seawater cause flooding of coastal areas.

• Ecosystem and agricultural impacts: Changes in temperature and rainfall can disrupt ecosystems, reduce crop yields, and cause species extinction.
  ✅ Each consequence is distinct, explained, and linked directly to the question.

alhchols

Number of carbon atoms	Chemical molecular formula	Molecular mass (g mol⁻¹)	IUPAC chemical name	Full structural formula	Boiling point (°C)
1	CH₃OH	32.04	Methanol	H–C–O–H	64.7
2	C₂H₅OH	46.07	Ethanol	CH₃–CH₂–OH	78.4
3	C₃H₇OH	60.10	1-Propanol	CH₃–CH₂–CH₂–OH	97.2
4	C₄H₉OH	74.12	1-Butanol	CH₃–CH₂–CH₂–CH₂–OH	117.7
5	C₅H₁₁OH	88.15	1-Pentanol	CH₃–(CH₂)₄–OH	138
6	C₆H₁₃OH	102.17	1-Hexanol	CH₃–(CH₂)₅–OH	157
7	C₇H₁₅OH	116.20	1-Heptanol	CH₃–(CH₂)₆–OH	176
8	C₈H₁₇OH	130.23	1-Octanol	CH₃–(CH₂)₇–OH	195

basic formula for alcohol

Cn​H2n+1​OH

) Explain why methanol and ethanol are soluble in a polar solvent such as water.

Methanol and ethanol are soluble in water because they contain a polar hydroxyl (–OH) functional group, which allows them to form hydrogen bonds with water molecules.
The oxygen atom in the –OH group is highly electronegative, making both the C–O and O–H bonds strongly polar. As a result, the partially negative oxygen (δ–) in the alcohol can attract the partially positive hydrogen (δ⁺) in water, and vice versa.

This strong hydrogen bonding between alcohol and water molecules overcomes the forces between alcohol molecules themselves, allowing the two substances to mix completely.
Since methanol and ethanol have short hydrocarbon chains, their non-polar regions are small and do not significantly disrupt the hydrogen bonding network in water. Therefore, both are highly soluble (miscible) in water.

As the hydrocarbon chain length increases (e.g., in propanol or butanol), the non-polar carbon chain becomes larger and begins to reduce solubility because it cannot form hydrogen bonds with water.

d i) Describe the trend relating to the molecular mass of the alcohol and its boiling point.

As the molecular mass and the number of carbon atoms in the alcohol increase, the boiling point also increases.
For example, methanol (CH₃OH, 32 g mol⁻¹) boils at 64.7 °C, while 1-octanol (C₈H₁₇OH, 130 g mol⁻¹) boils near 195 °C.
This demonstrates a positive correlation between molecular mass and boiling point — alcohols with longer carbon chains and higher molar masses require higher temperatures to boil.

d ii) Explain the chemical reason for this tren

he boiling point of alcohols depends on the intermolecular forces between their molecules.
All alcohols contain a polar hydroxyl (–OH) group, which enables hydrogen bonding — a strong attraction between the partially positive hydrogen (δ⁺) of one molecule and the partially negative oxygen (δ⁻) of another.

However, as the hydrocarbon chain length and molecular mass increase, the molecule’s surface area becomes larger, strengthening the dispersion (London) forces between molecules.
Although the strength of hydrogen bonding remains roughly constant across the series, these additional dispersion forces make it harder for the molecules to separate during boiling.

Therefore, alcohols with higher molecular masses need more energy (higher temperature) to overcome both hydrogen bonds and dispersion forces.

Integrated textbook references:

Integrated textbook references:

• “The hydroxyl group influences the boiling point of an alcohol compared to the alkanes, alkenes and alkynes, while the size of the hydrocarbon chain influences the properties within the homologous series.”

• “Hydrogen bonding is much stronger than dispersion forces, causing alcohols to have significantly higher boiling points than alkanes, alkenes and alkynes of similar molecular weight.”

• “Comparing butane to 1-butanol shows that the –OH group allows hydrogen bonding between molecules.”

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✅ Summary sentence for your worksheet:

As molecular mass increases in the alcohol series, the boiling point rises because larger molecules have stronger dispersion forces in addition to hydrogen bonding from the polar –OH group.