Global Reserves & Potable Water (AQA GCSE Combined Science: Trilogy: Chemistry): Flashcards
Exam code: 8464
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Define finite resources.
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Define finite resources.
Finite resources (also called non-renewable resources) are natural resources that do not reform quickly enough to be replenished within a human timescale, such as mineral ores and fossil fuels.
Give one example of a natural resource that has been replaced by a synthetic alternative, and name the synthetic material.
Rubber is naturally extracted from latex (tree sap) but has been replaced in many products by synthetic polymers specifically engineered to replicate its properties.
True or False?
Timber is a non-renewable resource because forests take many years to grow back.
False.
Timber is a renewable resource because forests can be replanted after harvesting. Although trees take many years to grow, the resource can be replenished within a human timescale. Non-renewable resources do not reform at all or do so too slowly.
Natural resources can be classified as either ________ (replenished within a human timescale) or ________ resources (also called finite, which do not reform quickly enough).
Natural resources can be classified as either renewable (replenished within a human timescale) or non-renewable resources (also called finite, which do not reform quickly enough).
How does chemistry contribute to the sustainable use of natural resources?
Chemistry enables development of synthetic alternatives (e.g. polymers to replace rubber) and processes that improve efficiency (e.g. fertilisers to boost crop yield), allowing current needs to be met without depleting resources needed by future generations.
Give two reasons why extracting non-renewable resources is considered less sustainable.
Reasons why extracting non-renewable resources is considered less sustainable include:
Extraction requires large amounts of energy, contributing to greenhouse gas emissions.
Extraction also depletes finite resources that cannot be replaced, reducing availability for future generations.
Define potable water.
Potable water is water that has been processed to be safe for human consumption. Unlike pure water (which contains only H2O), potable water may contain small, regulated amounts of dissolved minerals and salts, with a pH between 6.5 and 8.5.
What are the two main stages in treating fresh water to make it potable?
The two main stages in treating fresh water to make it potable are:
Filtration: water passes through wire mesh screens and then sand and gravel beds to remove debris.
Sterilisation: chlorine gas, ultraviolet light, or ozone is used to kill bacteria and harmful microbes.
True or False?
Potable water is the same as pure water.
False.
Pure water contains only H2O molecules. Potable water is safe to drink but may contain small, regulated amounts of dissolved minerals and salts. It must have a pH between 6.5 and 8.5 and be free of harmful bacteria.
Two methods of desalination are ________ and ________ osmosis. Both require large amounts of ________, making desalination expensive.
Two methods of desalination are distillation and reverse osmosis. Both require large amounts of energy, making desalination expensive.
What is the difference between surface water and groundwater?
Surface water collects in reservoirs, lakes, and rivers.
Groundwater is stored in aquifers, which are porous rocks that hold water underground.
The source used depends on local climate and geology.
Why is desalination not the preferred method of producing potable water?
Desalination requires large amounts of energy, making it expensive and less sustainable.
It is only used in regions where freshwater sources are very limited, such as hot, arid countries like Saudi Arabia.
What are the two laboratory methods used to analyse and purify water samples?
Two laboratory methods used to analyse and purify water sample are:
Determining the mass of dissolved solids in water samples by evaporation
Purifying a water sample by simple distillation to produce pure water.
How do you determine the mass of dissolved solids in a water sample by evaporation?
Weigh an empty evaporating basin, add 25 cm3 of the water sample, heat gently until the water evaporates and solids remain, allow to cool, then reweigh.
Mass of solids = final basin mass - initial basin mass
True or False?
Overheating an evaporating basin produces more accurate results when determining the mass of dissolved solids in a water sample.
False.
Overheating causes thermal decomposition of some dissolved solids, reducing their mass and giving a falsely low result.
The basin should be heated gently until solids begin to form and most water has evaporated, then left to cool.
In simple distillation, water is heated so it ________. The vapour passes along a delivery tube and is ________ by an ice bath so it ________ into liquid in the collecting tube.
In simple distillation, water is heated so it evaporates; the vapour passes along a delivery tube and is cooled by an ice bath so it condenses into liquid in the collecting tube.
How do you test whether a sample of water is pure?
Measure its boiling point. Pure water boils at exactly 100 °C.
If the sample boils at a different temperature or over a range, it contains dissolved impurities.
Why must the delivery tube sit above the liquid surface in the collecting tube during distillation?
If the tube is submerged, cooling can create a partial vacuum that sucks cold water back up into the hot delivery tube, causing the hot glass to crack or shatter.
Keeping the tube above the liquid prevents this suck-back.
Define effluent in the context of sewage treatment.
Effluent is the lighter liquid layer that floats to the top of the settlement tank during sedimentation. It is removed and treated by aerobic biological digestion to break down organic matter and harmful microbes.
List the four stages of sewage treatment in the correct order.
The four stages of sewage treatment, in the correct order, are:
Screening and grit removal: large particles removed.
Sedimentation: sewage sludge sinks; effluent floats.
Aerobic biological treatment: air pumped into effluent; aerobic bacteria break down organic matter.
Anaerobic digestion: bacteria break down the sludge, releasing methane.
True or False?
Anaerobic digestion in sewage treatment is used to treat the effluent layer.
False.
Anaerobic digestion treats the sewage sludge from the bottom of the settlement tank. The effluent (upper liquid layer) is treated by aerobic biological digestion, which uses air and aerobic bacteria to break down organic matter.
Anaerobic digestion of sewage sludge releases ________ gas as a by-product for use as an energy ________. The remaining digested waste can be used as ________.
Anaerobic digestion of sewage sludge releases methane gas as a by-product for use as an energy source. The remaining digested waste can be used as fertiliser.
Give two sources of waste water other than domestic use.
Sources of waste water other than domestic use include:
Agricultural waste water from animal farms and nutrient run-off from fields
Industrial waste water from chemical processes such as the Haber process
What three types of contaminant must be removed from waste water before it is returned to freshwater sources?
Three contaminants that must be removed are:
Organic matter (from sewage)
Harmful microbes (bacteria and pathogens)
Suspended particulates
Industrial waste water also contains toxic chemicals requiring additional treatment such as membranes, chemical precipitation, or UV radiation.
Define phytomining.
Phytomining is a method of extracting metals from low-grade ores using plants. Plants absorb metal compounds from the soil, are harvested and burned; the ash (containing metal compounds) is dissolved in acid and the metal is recovered by electrolysis or displacement.
What is the correct sequence of steps in phytomining?
The correct sequence of steps in phytomining is:
Plants grow in metal-rich soil and absorb metal compounds through their roots.
Plants are harvested.
Plants are burned.
Ash (containing metal compounds) is dissolved in acid to form a solution.
Metal is extracted from the solution by electrolysis or displacement using scrap iron.
True or False?
Burning plants in phytomining produces ash containing pure metal that can be used directly.
False.
The ash contains metal compounds, not pure metal. The compounds must be dissolved in acid to form a solution, from which the metal is then extracted by electrolysis or displacement using scrap iron.
Bioleaching uses ________ to produce ________ solutions containing metal ions, from which the metal is extracted by ________ or electrolysis.
Bioleaching uses bacteria to produce leachate solutions containing metal ions, from which the metal is extracted by displacement or electrolysis.
Give two disadvantages of phytomining compared with traditional mining.
(Do not refer to carbon dioxide emissions.)
Disadvantages of phytomining compared with traditional mining include:
Phytomining is much slower to produce metal
It requires a large area of land
It typically produces an insufficient yield to meet demand
Why are biological methods of metal extraction being developed for copper and nickel?
High-grade copper and nickel ores are becoming increasingly scarce. Phytomining and bioleaching can extract metals from low-grade ores that are not economically viable to mine by traditional methods, and cause less environmental damage than conventional mining.
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