Earth's Resources and Sustainability
Finite and Renewable Resources
The Earth provides natural resources that humans depend on. Finite resources (also called non-renewable) will eventually run out because they are consumed faster than they form. Examples include fossil fuels (coal, oil, natural gas), which took millions of years to form from the remains of ancient organisms, and metal ores mined from the Earth’s crust. Renewable resources can be replaced at the same rate they are used — examples include wood (from managed forests), crops, wind energy, solar energy and hydroelectric power.
Sustainable development means meeting the needs of the current population without compromising the ability of future generations to meet their own needs. This requires careful management of resources, reducing waste, recycling materials, developing alternatives to finite resources, and ensuring that the environmental costs of production are minimised at every stage. Chemistry plays a central role in sustainable development — from designing industrial processes with higher atom economy and lower waste to developing biodegradable materials, more efficient batteries, and renewable energy technologies such as hydrogen fuel cells.
Sustainable development requires using resources wisely so that future generations can meet their needs. This involves reducing consumption of finite resources, recycling, and developing renewable alternatives.
Potable Water
Potable water is water that is safe to drink. It is not pure in the chemical sense (it still contains dissolved substances such as mineral salts) but has sufficiently low levels of dissolved salts and harmful microbes to be safe for human consumption. The UK is fortunate to have abundant fresh water from rivers, lakes and reservoirs. Potable water is produced from these sources by a multi-stage process that involves:
Step 1: Filtration — passing the water through filter beds (sand and gravel) to remove solid particles and debris. Step 2: Sterilisation — killing harmful bacteria and microorganisms. This can be done using chlorine, ozone or ultraviolet (UV) light. Chlorine is most commonly used in the UK because it is effective, cheap, and continues to kill bacteria as the water travels through the distribution network.
In areas with limited fresh water, sea water or brackish water (slightly salty water) can be made potable by desalination. This can be done by distillation (boiling and condensing) or by reverse osmosis (forcing water through a membrane that blocks dissolved salts). Desalination requires large amounts of energy, making it expensive. In the UK, where rainfall is generally sufficient, fresh water treatment is more cost-effective. In arid countries like Saudi Arabia or the UAE, desalination is essential despite the high energy cost.
Treating Waste Water
Waste water (from homes, industry and agriculture) must be treated before being released back into the environment. Sewage treatment is a multi-stage process: screening and grit removal (removing large solids and debris), primary sedimentation (allowing smaller solids to settle as sludge in settlement tanks), biological treatment (aerobic microorganisms break down dissolved organic matter in aeration tanks), secondary sedimentation, and final filtration and sterilisation before the clean effluent is returned to rivers. Industrial waste water may also contain harmful chemicals such as heavy metals or toxic organic compounds that require specialised treatment before the water can be safely released. Agricultural run-off containing fertilisers can cause eutrophication in waterways if not properly managed.
Atmospheric Pollutants
The combustion of fossil fuels produces several harmful pollutants that damage human health and the environment. You need to know the source, identity and effects of each one:
Carbon monoxide (CO) — produced by incomplete combustion of fuels. It is a toxic, colourless, odourless gas that reduces the blood’s ability to carry oxygen by binding to haemoglobin. Sulfur dioxide (\(SO_2\)) — produced when fossil fuels containing sulfur impurities are burned. It causes acid rain, which damages buildings, harms aquatic life and kills plants. Oxides of nitrogen (\(NO_x\)) — produced at high temperatures in car engines when nitrogen and oxygen from the air react. They also cause acid rain and contribute to smog. Particulates (tiny solid particles, including soot) — produced by incomplete combustion. They cause respiratory problems, reduced visibility, and can contribute to climate change.
Burning fossil fuels produces: carbon monoxide (toxic gas, incomplete combustion), sulfur dioxide (acid rain), oxides of nitrogen (acid rain, smog), and particulates (respiratory problems). These pollutants have serious health and environmental impacts.
Reducing Pollution
Pollution from combustion can be reduced by: using catalytic converters in vehicles (which convert CO and \(NO_x\) to less harmful \(CO_2\) and \(N_2\)), removing sulfur from fuels before burning, using flue gas desulfurisation in power stations, switching to renewable energy sources, and improving engine efficiency. Switching to electric vehicles reduces exhaust emissions at the point of use, though the overall environmental benefit depends on how the electricity is generated. These strategies involve balancing environmental benefits against economic costs, technological feasibility and public willingness to change behaviour.