10.1 Using the Earth's resources and obtaining potable water

10.1.1 Using the Earth's resources and sustainable development

- Humans can use the Earth's resources to provide warmthm, shelter, food and transport.
- These natural resources are supplemented by agriculture to provide food, timber, clothing, and fuels.
- Finite resources are resources where there is only a limited supply. Finite resources from the Earth, oceans, and atmosphere, are processed to provide energy and materials.
- Finite resources include fossil fuels (oil, coal, and natural gas) and metal ores.
- Renewable resources are resources that can be replaced at the same rate as, or faster than, they are used.
- Examples of renewable resources include timber (if managed correctly), water, and wind energy.
- Sustainable resource management is using resources while leaving enough for future generations to meet their needs.
- Carbon-neutral resources come from plants. The carbon dioxide absorbed by the plants as they grow is equal to the carbon dioxide released when they are burned.

10.1.2 Potable water

- Potable water is water that is safe to drink.
- Fresh water is water that has a low concentration of dissolved salts and microbes.
- Most fresh water is found in lakes, rivers, and groundwater.
- In the UK, fresh water from rivers and lakes is treated to make it potable by:

• choosing an appropriate source of fresh water
• passing the water through filter beds (sand, gravel, and charcoal)
• sterilisation (using chlorine, ozone, or ultraviolet light) to kill microbes

Distillation desalination diagram

Reverse osmosis diagram

Required Practical 8: analysis and purification of water samples from different sources, including pH, dissolved solids and distillation

Required practical: analysis and purification of water samples

• Sampling
  • Collect labelled samples from each source (tap, river, groundwater, seawater, wastewater). Record location, time, temperature.
  • Use clean glassware; avoid cross-contamination; store cold and test promptly.
• pH measurement
  • Calibrate pH meter with pH 4.00 and 7.00 (and 10.00 if necessary). Rinse probe between samples.
  • Measure and record pH and temperature for each sample; optionally compare with universal indicator paper/solution.
  • Notes: pH affects solubility and disinfection effectiveness.
• Dissolved solids (TDS) / total dissolved solids
  • Method A: Conductivity/TDS meter: calibrate, measure conductivity and convert to TDS using device factor; quick non-destructive test.
  • Method B: Gravimetric (precise): filter sample to remove suspended solids, evaporate a known volume to dryness in a pre-weighed crucible (dry at ~105 °C), cool in desiccator, weigh residue. Calculate mg L⁻¹ = (mass residue / volume sample in L) × 1000.
  • Include blanks and repeat measurements; account for hygroscopic salts and volatile losses as uncertainty sources.
• Additional tests (optional)
  • Chloride: titration (AgNO3) or ion-selective electrode.
  • Turbidity: nephelometer or visual comparison.
  • Microbial presence: culture tests (if required) or use membrane filtration methods.
• Purification methods
  • Pre-treatment: coarse filtration/sedimentation to remove suspended solids.
  • Filtration: sand/gravel/activated charcoal for organics and particulates.
  • Sterilisation: boiling, chemical (chlorination), UV or ozone to kill microbes.
  • Desalination/distillation: simple distillation apparatus — heat sample, collect condensate; distilled water should have very low conductivity and low residue on evaporation.
  • Reverse osmosis note: high energy, uses semipermeable membrane (lab demo usually limited to simple distillation).
• Distillation practical notes
  • Set up round-bottom flask, condenser, and receiver; use boiling chips; control heating to avoid bumping.
  • Collect fractions if required; measure pH, conductivity, and TDS of distillate and compare with feed.
  • Record mass/volume of distillate and residue; calculate % removal of dissolved solids.
• Calculations and evaluation
  • Calculate mg L⁻¹ dissolved solids, % removal after purification, and uncertainty (repeatability, instrument calibration, mass balance errors).
  • Discuss limitations: energy cost of distillation, incomplete removal of volatile contaminants, adsorption capacity of charcoal, sampling errors.
  • Safety: handle hot apparatus, corrosive reagents, and contaminated samples with appropriate PPE and waste disposal.

10.1.3 Waste Water Treatment

10.1.4 Alternative methods of extracting metals

- The Earth’s resources of metal ores are limited.
- Traditional open-cast mining takes lots of energy, makes large holes in the ground, and produces large amounts of waste material.
- It can also cause deforestation, habitat loss, and pollution of land and water with chemicals used in the extraction process (e.g. sulphuric acid).
- The mining can use explosives made from crude oil and the transporting, sorting, and refining of the ore all use large amounts of energy from fossil fuels.
- Most copper is extracted by smelting copper rich ores.
- Electrolysis is used to purify impure copper obtained from smelting.
- Sulphuric acid can be used to produce copper sulphate solution from low-grade ores.
- Copper is then extracted from the solution by displacement using scrap iron.
- Phytomining and bioleaching are alternative methods of extracting metals from low-grade ores using plants and bacteria respectively.

Phytomining

- Phytomining uses plants to absorb metal compounds (often from the waste from previous mining).

1. Plants are used to absorb metal compounds.
2. Plants are harvested, then burned to produce ash.
3. An acid is added to the ash to produce a solution containing dissolved metal ions (leachate).
4. Copper can be obtained from the solution by displacement using scrap iron.

Bioleaching

- Bioleaching uses bacteria that feed on low-grade metal ores to produce leachate solutions that contain dissolved metal compounds.
- The metal compounds can then be processed by electrolysis or displacement to obtain the metal.