Using resources: finite and renewable resources and sustainability

What you'll learn

This topic examines how Earth's resources are used, processed and replaced, and the environmental impact of these activities. You'll explore the difference between finite and renewable resources, understand sustainable development principles, and evaluate methods of resource extraction and processing. This knowledge is essential for the Chemistry Paper 2 examination and represents approximately 10% of your final marks.

Key terms and definitions

Finite resources — materials that are being used up faster than they can be replaced, including fossil fuels and metal ores; they will eventually run out

Renewable resources — materials that can be replaced at the same rate or faster than they are being used, such as timber from managed forests or crops for biofuels

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

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

Potable water — water that is safe to drink because it contains low levels of dissolved salts and microbes

Desalination — the process of removing dissolved salts from seawater to produce fresh water

Phytomining — the use of plants to absorb metal compounds from soil; the plants are then harvested and burned to produce ash containing metal compounds

Bioleaching — the use of bacteria to extract metals from low-grade ores by producing solutions containing metal compounds

Core concepts

Finite and renewable resources

Earth's natural resources provide materials and energy for human activities. Understanding the distinction between finite and renewable resources is crucial for sustainable planning.

Finite resources from the Earth's crust:

• Metal ores (iron, copper, aluminium, gold)
• Limestone and marble
• Crude oil and natural gas
• Coal
• Minerals including gemstones and phosphate rock

These resources form over millions of years through geological processes. Once extracted and used, they cannot be replaced within human timescales.

Renewable resources:

• Timber from managed forests
• Fresh water from the water cycle
• Crops for food, biofuels and materials
• Energy from wind, waves, tides and sunlight

Agricultural products can be supplemented or replaced by synthetic alternatives. For example, natural rubber can be replaced by synthetic rubber made from crude oil fractions, though this creates dependency on another finite resource.

The challenge of resource management: Chemistry plays a vital role in developing processes to:

• Extract resources more efficiently
• Reduce waste during manufacturing
• Recycle materials to extend resource availability
• Develop sustainable alternatives

The global population continues to grow, increasing demand for resources. This makes sustainable development essential to ensure future generations have access to necessary materials.

Sustainable development principles

Sustainable development requires balancing economic, social and environmental factors. This involves making decisions that:

• Meet current needs without depleting resources for future use
• Minimise environmental damage
• Consider long-term consequences of resource extraction and use

Key considerations for sustainability:

1. Resource depletion: Using finite resources at current rates means they will run out. For example, at present consumption rates, known copper reserves may last only 50-60 years.

2. Environmental impact: Extraction and processing damage ecosystems through habitat destruction, pollution and energy consumption.

3. Waste generation: Manufacturing produces waste that requires disposal. Reducing, reusing and recycling extends resource availability.

4. Energy requirements: Processing raw materials requires significant energy, often from fossil fuels, contributing to climate change.

Practical applications:

• Recycling metals reduces the need for mining and uses less energy than extracting metals from ores
• Using renewable energy sources for manufacturing decreases fossil fuel consumption
• Developing biodegradable plastics reduces long-term waste accumulation
• Water treatment and recycling conserves fresh water supplies

Life cycle assessments

A life cycle assessment (LCA) evaluates the total environmental impact of a product from "cradle to grave." This systematic analysis helps identify opportunities to reduce environmental harm.

The four stages of an LCA:

1. Extraction and processing of raw materials:

   • Mining ores or drilling for oil
   • Energy consumption during extraction
   • Habitat destruction and pollution
   • Transportation of raw materials

2. Manufacturing and packaging:

   • Energy use in factories
   • Waste products generated
   • Emissions to air and water
   • Production of packaging materials

3. Use and operation:

   • Energy consumption during product lifetime
   • Maintenance requirements
   • Consumables needed
   • Emissions produced during use

4. Disposal:

   • Landfill space required
   • Potential for recycling
   • Energy recovered through incineration
   • Pollution from decomposition or degradation

Limitations of LCAs:

• Quantifying some impacts is difficult (e.g., visual pollution, habitat loss)
• Values assigned to different impacts can be subjective
• Selective or abbreviated LCAs may ignore important factors
• Different methods may produce different conclusions
• Data may be incomplete or biased

Example comparison — plastic vs paper bags:

Plastic bags:

• Made from crude oil (finite resource)
• Require less energy to manufacture
• Can be reused multiple times
• Take hundreds of years to decompose
• Recyclable but often not recycled

Paper bags:

• Made from trees (renewable if forests managed sustainably)
• Require more energy and water to produce
• Less durable, typically single-use
• Decompose relatively quickly
• Recyclable and biodegradable

The "better" choice depends on which environmental factors are prioritised and actual usage patterns.

Potable water production

Potable water contains sufficiently low levels of dissolved salts and microbes to be safe for drinking. In the UK, rain provides abundant water that requires only simple treatment. In other regions, different methods are necessary.

UK water treatment process:

1. Screening: Removes large objects (leaves, twigs)
2. Sedimentation: Allows suspended particles to settle
3. Filtration: Water passes through sand and gravel beds to remove remaining particles
4. Chlorination: Chlorine gas kills bacteria and other microorganisms

Alternative methods in water-scarce regions:

Desalination: Removes dissolved salts from seawater through:

• Distillation: Heating seawater to evaporate pure water, leaving salts behind; requires significant energy
• Reverse osmosis: Forcing seawater through membranes that trap salt ions; uses high pressure

Desalination is expensive due to high energy requirements, making it suitable only where fresh water is extremely scarce (e.g., Middle Eastern countries, Caribbean islands).

Treating waste water: Sewage and agricultural/industrial waste water can be treated to produce potable water:

1. Screening and sedimentation remove solid waste
2. Aerobic bacteria break down organic matter
3. Additional treatment with chemicals and UV light kills microbes
4. Further processing may be needed to remove persistent pollutants

This is more expensive than treating fresh water but necessary in water-stressed regions.

Alternative metal extraction methods

As high-grade metal ores become depleted, chemists have developed methods to extract metals from low-grade ores that would otherwise be uneconomical to process.

Phytomining:

1. Plants are grown on soil containing low concentrations of metal compounds
2. Plants absorb metal ions through their roots
3. Plants are harvested and burned
4. Ash contains metal compounds in higher concentrations
5. Metal compounds are processed to extract pure metal

Advantages:

• Extracts metals from contaminated soil, cleaning it in the process
• Works on low-grade ores
• Less environmental damage than traditional mining

Disadvantages:

• Slow process (plants take months to grow)
• Produces relatively small quantities of metal
• Still requires processing the ash

Bioleaching:

1. Bacteria are added to low-grade ore
2. Bacteria obtain energy by breaking down minerals in the ore
3. This produces solutions (leachates) containing metal compounds
4. Metal compounds are extracted from the solution
5. Methods like electrolysis or displacement reactions extract pure metal

Advantages:

• Works on ores with very low metal content
• Less disruptive than traditional mining
• Lower energy requirements than conventional extraction

Disadvantages:

• Very slow process
• Produces toxic leachate that must be contained
• Limited to certain metals (mainly copper)

Both methods are examples of biometallurgy — using biological organisms to extract metals. These techniques become economically viable as traditional ore reserves decline.

Recycling and resource conservation

Recycling conserves finite resources and reduces environmental impact. Metals are particularly suitable for recycling because they can be melted and reshaped without losing their properties.

Benefits of metal recycling:

• Conserves metal ores (finite resources)
• Reduces energy consumption (recycling aluminium uses only 5% of the energy needed to extract it from ore)
• Decreases landfill waste
• Reduces mining activities and associated environmental damage
• Economic savings for manufacturers

The recycling process:

1. Collection and sorting of metal waste
2. Shredding or cutting into small pieces
3. Melting in furnaces
4. Purifying the molten metal
5. Casting into blocks for manufacturing

Challenges:

• Collection and sorting requires infrastructure and public participation
• Some products contain mixed materials that are difficult to separate
• Contamination can reduce quality of recycled material
• Energy still required for melting and processing
• Not economically viable for all materials in all locations

Glass, plastics and paper can also be recycled, though some plastics degrade during reprocessing, limiting the number of times they can be recycled.

Worked examples

Example 1: Evaluating resource sustainability (4 marks)

Question: A company manufactures furniture from either hardwood timber or plastic made from crude oil. Evaluate which material is more sustainable. In your answer, consider both environmental and resource availability factors.

Mark scheme approach:

Point 1 (1 mark): Timber is from a renewable resource if forests are replanted / managed sustainably, whereas crude oil is a finite resource.

Point 2 (1 mark): Plastic furniture may last longer than wooden furniture, reducing the need for replacement.

Point 3 (1 mark): Hardwood trees take many years/decades to grow, so even with replanting, supply may be limited.

Point 4 (1 mark): Plastic production and disposal create pollution, whereas timber is biodegradable.

Model answer: "Hardwood timber comes from a renewable resource, provided forests are managed sustainably and trees are replanted after harvesting. In contrast, plastic is made from crude oil, which is a finite resource that will eventually run out. However, hardwood trees can take 50-100 years to mature, meaning replacement is very slow even with good management. Plastic furniture typically lasts longer than wooden furniture, reducing the frequency of replacement. When considering disposal, timber is biodegradable and will decompose naturally, whereas plastic persists in the environment for hundreds of years and can cause pollution. Overall, sustainably sourced timber is more sustainable if properly managed, but durability and disposal methods must also be considered."

Example 2: Life cycle assessment comparison (6 marks)

Question: Compare the life cycle of ceramic mugs and disposable paper cups. Include at least three stages in your answer and make a reasoned judgement about which has less environmental impact.

Mark scheme approach:

Stage 1 — Extraction (2 marks):

• Ceramic: Clay extracted by mining, which damages habitats
• Paper cups: Trees are renewable but logging affects ecosystems; cups have plastic lining from crude oil (finite)

Stage 2 — Manufacturing (2 marks):

• Ceramic: Fired at very high temperatures (over 1000°C), requiring significant energy
• Paper cups: Require less energy to produce but also need energy and chemicals

Stage 3 — Use and disposal (2 marks):

• Ceramic: Used thousands of times, no waste generated during use; lasts many years
• Paper cups: Single use, generate waste after each drink; millions disposed daily

Judgement: Ceramic mugs have lower impact over their lifetime despite higher initial manufacturing energy.

Model answer: "During extraction, ceramic mugs require clay obtained through mining, which destroys habitats and creates waste rock. Paper cups use timber, which is renewable if forests are replanted, but they also require a plastic lining made from crude oil, a finite resource. In manufacturing, ceramic mugs must be fired at temperatures exceeding 1000°C, consuming large amounts of energy. Paper cups require less energy per unit but are manufactured in vastly larger quantities. During use, a ceramic mug can be washed and reused thousands of times over many years, whereas each paper cup is used once for a few minutes before disposal, generating constant waste. When disposed of, ceramic mugs rarely break and last decades, while paper cups create ongoing landfill waste or require energy for recycling. Overall, ceramic mugs have significantly less environmental impact when their full lifetime is considered, despite higher initial manufacturing energy."

Example 3: Calculating water treatment costs (3 marks)

Question: A coastal town needs 10 million litres of potable water per day. Fresh water treatment costs £0.15 per 1000 litres. Desalination costs £1.80 per 1000 litres. Calculate the additional annual cost if the town uses desalination instead of fresh water treatment.

Working:

• Daily volume: 10,000,000 litres = 10,000 × 1000 litres (1 mark)
• Fresh water cost per day: 10,000 × £0.15 = £1,500
• Desalination cost per day: 10,000 × £1.80 = £18,000 (1 mark)
• Additional cost per day: £18,000 - £1,500 = £16,500
• Annual additional cost: £16,500 × 365 = £6,022,500 (1 mark)

Answer: The additional annual cost of using desalination is £6,022,500 (or approximately £6 million).

Common mistakes and how to avoid them

• Confusing "renewable" with "unlimited": Renewable resources can be depleted if used faster than they're replaced. Timber is only renewable if forests are replanted and managed sustainably. Always mention management or replacement rates when discussing renewable resources.

• Stating "recycling has no environmental impact": Recycling still requires energy for collection, transport, sorting and reprocessing. The benefit is that recycling typically uses less energy and resources than producing materials from raw resources. Always acknowledge both advantages and disadvantages.

• Incomplete life cycle assessments: Students often describe only one or two stages. Ensure you cover all four stages: extraction, manufacture, use, and disposal. Marks are often allocated for each stage discussed.

• Making subjective claims without evidence: Statements like "plastic bags are worse for the environment" need specific justification. Explain which aspects you're considering (energy use, disposal, resource type, longevity) and why they lead to your conclusion.

• Misunderstanding potable water: Potable water is not the same as pure water. It contains some dissolved substances but at safe levels. Distilled water (pure H₂O) is not the same as potable water.

• Overlooking economic factors in sustainability: Sustainability isn't purely environmental. Sustainable solutions must be economically viable and socially acceptable. Desalination produces potable water but may not be sustainable due to high costs and energy requirements.

Exam technique for "Using resources: finite and renewable resources and sustainability"

• Identify command words precisely: "Evaluate" requires you to give advantages and disadvantages then reach a justified conclusion. "Compare" needs you to describe both items, highlighting similarities and differences. "Suggest" means apply your knowledge to an unfamiliar situation — several reasonable answers may exist.

• Use specific scientific terminology: Replace vague language with precise terms. Instead of "digging up," use "extraction" or "mining." Rather than "getting rid of," use "disposal" or "recycling." This demonstrates scientific understanding and secures marks.

• Structure LCA questions systematically: Use the four stages as paragraph headings or clear sections. This ensures you cover all required content and makes your answer easy for examiners to mark. Allocate your time based on the marks available — a 6-mark question needs substantially more detail than a 2-mark question.

• Support judgements with data when possible: In evaluation questions, referencing specific information strengthens your answer. State that "recycling aluminium uses 95% less energy than extraction from ore" rather than just "recycling uses less energy." Numbers provided in questions should typically be used in your answer.

Quick revision summary

Earth's resources divide into finite (metal ores, fossil fuels) and renewable (managed timber, crops) categories. Sustainable development balances current needs with future resource availability. Life cycle assessments evaluate products through extraction, manufacture, use and disposal stages, though quantifying impacts involves subjectivity. Potable water production varies by region: the UK uses filtration and chlorination of fresh water, while water-scarce areas employ expensive desalination. Phytomining and bioleaching extract metals from low-grade ores using plants and bacteria respectively. Recycling, particularly of metals, conserves resources and reduces energy consumption compared to extraction from ores.