Sustainability and the Environment

What you'll learn

This topic examines how chemistry impacts the environment and explores sustainable approaches to manufacturing, resource use, and energy production. You'll learn to evaluate the environmental, economic, and social factors that influence industrial processes and everyday choices, preparing you to answer extended response questions that require balanced judgements.

Key terms and definitions

Sustainable development — development that meets current needs without compromising the ability of future generations to meet their own needs

Life cycle assessment (LCA) — an evaluation of the environmental impact of a product through all stages: extraction, manufacture, use, and disposal

Carbon footprint — the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service, or event

Green chemistry — the design of chemical products and processes that reduce or eliminate hazardous substances and waste

Finite resources — resources that cannot be replaced once used, such as crude oil, coal, and metal ores

Renewable resources — resources that can be replaced or regenerated, such as timber, crops, and solar energy

Biodegradable — capable of being broken down naturally by microorganisms into harmless substances

Carbon neutral — a process or activity that has no net carbon dioxide emissions, either by producing none or by offsetting emissions through carbon capture or planting trees

Core concepts

Finite resources and sustainable use

The Earth's resources are limited, and chemistry plays a crucial role in how we use them sustainably.

Finite resources include:

• Fossil fuels (coal, crude oil, natural gas)
• Metal ores
• Minerals for construction
• Phosphate rock for fertilisers

Sustainable approaches involve:

• Reducing consumption of raw materials
• Reusing products where possible
• Recycling materials to recover valuable elements
• Finding renewable alternatives

For metals, recycling offers significant advantages:

• Uses less energy than extracting from ores
• Conserves finite ore deposits
• Reduces mining waste and habitat destruction
• Lowers carbon dioxide emissions

For example, recycling aluminium uses only 5% of the energy required to extract it from bauxite ore. However, recycling requires collection systems, sorting facilities, and energy for reprocessing, so a full life cycle assessment must consider all factors.

Life cycle assessments

A life cycle assessment evaluates environmental impact across four key stages:

1. Extraction and processing of raw materials

• Mining ores causes habitat destruction
• Quarrying creates dust and noise pollution
• Processing requires energy, often from fossil fuels
• Transport of materials generates emissions

2. Manufacturing and packaging

• Energy consumption during production
• Waste products and by-products
• Use of water resources
• Chemical emissions to air and water

3. Use and operation

• Energy requirements during use
• Maintenance and repair needs
• Emissions during operation (e.g., vehicle exhaust)
• Durability and lifespan

4. Disposal

• Landfill space requirements
• Potential for recycling or reuse
• Biodegradability
• Incineration and associated emissions

LCAs involve quantitative data (measurable values like energy use or mass of CO₂) and qualitative judgements (subjective assessments like visual pollution). This makes comparing products complex, as different stakeholders may prioritise different factors.

Reducing environmental impact of products

Plastic bags vs paper bags — a classic LCA comparison

Plastic bags (polyethylene):

• Made from crude oil (finite resource)
• Low energy manufacture
• Lightweight, reducing transport emissions
• Non-biodegradable, persist in environment for hundreds of years
• Can be recycled but often end up in landfill or oceans
• Reusable many times if thick enough

Paper bags:

• Made from trees (renewable if replanted)
• Higher energy manufacture, requires more water
• Heavier, increasing transport emissions
• Biodegradable
• Recyclable and often made from recycled paper
• Less durable, typically single-use

Neither option is clearly "better" — the answer depends on weighing multiple factors. Reusable bags (cotton or thick plastic) reduce overall impact if used many times.

Reducing product impact strategies:

• Design for longevity and repairability
• Use recycled or renewable materials
• Minimise packaging
• Reduce energy in manufacture
• Ensure products are recyclable at end of life
• Choose less toxic materials

Alternative fuels and renewable energy

Chemistry provides alternatives to fossil fuels, each with advantages and disadvantages.

Biofuels:

• Produced from plant materials (crops, waste vegetable oil, wood)
• Examples: bioethanol from fermented sugar cane, biodiesel from vegetable oils
• Carbon neutral in theory — CO₂ released when burned was absorbed during plant growth
• However, growing biofuel crops requires land, fertilisers, and energy (tractors, processing)
• May compete with food production
• First-generation biofuels (from food crops) are controversial
• Second-generation biofuels (from waste or non-food crops) are more sustainable

Hydrogen as a fuel:

• Combustion produces only water: 2H₂ + O₂ → 2H₂O
• Can be used in fuel cells for vehicles
• High energy density
• Production methods matter: electrolysis using renewable electricity is clean, but steam reforming of methane (CH₄ + H₂O → CO + 3H₂) produces carbon dioxide
• Storage and transport are challenging (requires high pressure or very low temperatures)

Electric vehicles:

• Zero emissions at point of use
• Electricity generation still may involve fossil fuels
• Battery production requires mining lithium, cobalt, and other metals
• Battery recycling infrastructure is developing
• Overall carbon footprint depends on electricity source

Water resources and potable water

Access to clean drinking water is a sustainability challenge.

Potable water — water safe to drink (low dissolved salts, microbes, and pollutants)

Methods of producing potable water:

In the UK, where rainfall is relatively high:

1. Fresh water collected from rivers, reservoirs, or aquifers
2. Passed through filter beds to remove solid particles
3. Sterilised using chlorine, ozone, or UV light to kill microbes

In areas with water scarcity:

• Desalination of seawater by distillation or reverse osmosis
• Distillation requires heating water to evaporate it, then condensing pure water
• Reverse osmosis forces water through membranes under pressure
• Both methods are energy-intensive and expensive
• Produce waste brine that must be disposed of carefully

Wastewater treatment:

• Sewage and industrial wastewater require treatment before return to environment
• Screening removes large solids
• Sedimentation allows particles to settle
• Biological treatment uses microorganisms to break down organic matter
• Further treatment may include chemical precipitation and sterilisation

Treating wastewater for reuse as drinking water is possible but requires extensive purification and faces public acceptance challenges.

Green chemistry principles

Green chemistry aims to make chemical processes more sustainable by:

• Preventing waste rather than treating it after creation
• Designing safer chemicals that are less toxic
• Using renewable feedstocks where possible
• Increasing energy efficiency
• Using catalysts to reduce energy requirements and waste
• Designing products that degrade after use rather than persisting
• Using safer solvents or avoiding solvents entirely
• Conducting real-time monitoring to prevent pollution

Example: Catalytic converters in vehicles

• Use platinum, palladium, and rhodium catalysts
• Convert harmful emissions to less harmful substances:
  • 2CO + 2NO → 2CO₂ + N₂
  • Unburned hydrocarbons → CO₂ + H₂O
• Reduce air pollution in urban areas
• Catalysts are expensive but can be recycled

Industrial applications:

• Development of biodegradable polymers from plant starches
• Use of supercritical CO₂ as a solvent instead of toxic organic solvents
• Pharmaceutical synthesis with fewer steps and less waste
• Water-based paints replacing solvent-based ones

Worked examples

Example 1: Life cycle assessment comparison (4 marks)

Question: A supermarket is deciding whether to use plastic or glass bottles for milk. Evaluate the environmental impact of each option.

Mark scheme answer:

Plastic bottles:

• Made from crude oil (finite resource) [1 mark]
• Lighter than glass, reducing transport emissions [1 mark]
• Not biodegradable but can be recycled [1 mark]

Glass bottles:

• Made from sand (abundant resource) but requires high energy to melt [1 mark]
• Heavier, increasing fuel use during transport [1 mark]
• Reusable many times if returned and sterilised, reducing overall impact [1 mark]
• Recyclable indefinitely without quality loss [1 mark]

Conclusion: Glass may be better if reused multiple times through a return scheme, but plastic is better for single-use due to lower transport impact. [1 mark for balanced judgement]

[Maximum 4 marks — award for relevant points showing understanding of multiple factors]

Example 2: Carbon footprint calculation (3 marks)

Question: Burning 1 kg of methane (natural gas) produces 2.75 kg of CO₂. A household uses 500 kg of methane per year. Calculate the annual carbon dioxide emissions from their gas use. Show your working.

Mark scheme answer:

CO₂ emissions = mass of methane × CO₂ per kg [1 mark]

CO₂ emissions = 500 kg × 2.75 kg [1 mark]

CO₂ emissions = 1375 kg or 1.375 tonnes [1 mark]

Example 3: Evaluating biofuels (6 marks)

Question: Bioethanol can be produced by fermenting sugar cane and is described as carbon neutral. Evaluate this claim.

Mark scheme answer:

Arguments supporting carbon neutrality:

• Sugar cane absorbs CO₂ from the atmosphere during photosynthesis [1 mark]
• When bioethanol burns, it releases the same amount of CO₂ that was absorbed [1 mark]
• This creates a balanced carbon cycle [1 mark]

Arguments against carbon neutrality in practice:

• Growing sugar cane requires fertilisers produced using energy from fossil fuels [1 mark]
• Tractors and machinery use diesel fuel, producing CO₂ [1 mark]
• Processing sugar cane into bioethanol requires energy, often from fossil fuels [1 mark]
• Transport of fuel produces additional emissions [1 mark]
• May involve deforestation to create farmland, releasing stored carbon [1 mark]

Conclusion: Theoretically carbon neutral, but in practice involves some fossil fuel use, so not fully carbon neutral [1 mark]

[Maximum 6 marks — award for balanced arguments showing understanding of both perspectives]

Common mistakes and how to avoid them

• Confusing renewable and biodegradable: Wood is renewable (can regrow) and biodegradable (decomposes naturally), but these are different properties. Plastic made from plant oils might be renewable but not biodegradable.

• Assuming recycling is always best: Remember to consider the full picture — recycling uses energy and resources. Sometimes reusing products (like glass bottles) or designing for longer life is more sustainable.

• One-sided LCA evaluations: Exam questions ask you to "evaluate" — you must discuss both advantages and disadvantages. Give balanced arguments with specific examples rather than general statements.

• Forgetting that "carbon neutral" doesn't mean "no emissions": Carbon neutral means net-zero emissions through offsetting, not zero emissions. Biofuels release CO₂ when burned but this is balanced by absorption during growth.

• Vague statements in extended answers: Instead of "plastic is bad for the environment," write "plastic is made from crude oil (finite resource) and is non-biodegradable, persisting in landfill for hundreds of years."

• Not justifying conclusions: When asked to evaluate or compare, you must reach a conclusion supported by the evidence you've presented. State which option is better and why, or explain why it depends on specific circumstances.

Exam technique for "Sustainability and the Environment"

• Command words matter: "Evaluate" means present both sides and reach a judgement. "Assess" is similar. "Compare" means identify similarities and differences. "Discuss" requires exploring different aspects. Always address what the question asks.

• Extended response structure: For 6-mark questions, use a clear structure: introduce the topic, present arguments for one side with examples, present counter-arguments, reach a balanced conclusion. Aim for 8-10 developed points across your answer.

• Link to chemistry content: Don't just discuss environmental issues generally — make chemical connections. Mention specific reactions, materials, processes, or chemical principles. Use correct chemical terminology and formulae where appropriate.

• Use data when provided: If the question includes a table, graph, or numerical data, reference specific values in your answer. This demonstrates you're answering the specific question, not writing a generic response.

Quick revision summary

Sustainable development balances current needs with future resource availability. Life cycle assessments evaluate environmental impact from raw material extraction through disposal, considering both quantitative data and qualitative judgements. Reducing impact involves using renewable resources, recycling finite materials, designing durable products, and applying green chemistry principles. Alternative fuels like biofuels and hydrogen offer cleaner energy but involve production trade-offs. Water sustainability requires efficient purification and treatment methods. Exam success requires balanced evaluation of multiple factors with specific chemical examples and clear justification of conclusions.