Using resources 1 Flashcards
Corrosion, alloys as useful materials, Earth's resources/sustainable development, LCAs
Corrosion
The process by which metals are slowly broken down by reacting with substances in their environment.
Rusting
The corrosion of iron by reacting with oxygen and water.
What is the word equation for rusting?
Iron + Water + Oxygen → hydrated iron (III) oxide
What do we mean by saying iron is hydrated?
Water molecules are part of the structure.
What is the symbol equation for rusting?
4Fe + H₂O + 3O₂ → 2Fe₂O₃*H₂O
Half equation for rusting (iron)
Fe → Fe³⁺ + 3e⁻
Half equation for rusting (oxygen from the surroundings)
O₂ + 4e⁻ → 2O²⁻
How is rusting an example of a redox reaction?
Iron atoms lose (3) electrons (are oxidised) and oxygen atoms gain (2) electrons (are reduced).
What are the conditions required for rusting?
Water and oxygen must be present.
What are the ways in which we can prevent corrosion?
Applying a coating that acts as a barrier:
-Painting
-Greasing
-Electroplating
-Galvanising
-Sacrificial protection
Painting or greasing
The iron object is coated with layers of paint or grease.
Painting or greasing explanation.
This prevents rusting because the layer acts as a barrier, preventing oxygen or water reaching the iron to react.
Electroplating explanation
This prevents rusting because the layer acts as a barrier, preventing oxygen or water reaching the iron to react.
Electroplating
Electrolysis is used to coat the iron object in a thin layer of another metal.
-The (negatively charged) cathode is the object to be plated
-The (positively charged) anode is the plating metal
-The electrolyte contains ions of the plating metal
Sacrificial protection
Blocks of a metal more reactive than iron (e.g. Magnesium) are attached to an iron object.
Sacrificial protection explanation
The more reactive metal will oxidise in preference to the iron so the iron won’t rust.
Galvanising
The iron object is dipped in molten zinc, giving it a coating of zinc.
Galvanising explanation
The zinc forms a protective coating, but if this coating gets scratched, and the underlying iron is exposed, the zinc will oxidise in preference to the iron (as it’s more reactive).
What determines the reactivity of elements?
How easily they form ions: more reactive metals form ions more easily.
In experiments, how can we tell if an iron object has rusted?
Measure the mass of the iron object before and after it is kept in certain test tube conditions for a specified period of time. If the iron has rusted, mass will increase.
How can an iron object break down completely?
The surface metal rusts, but this flakes off after a time, leaving the next layer of iron exposed to water and oxygen. This layer then rusts and flakes: the process repeats until the iron object is broken down completely.
Corrosion of Aluminium
Only the surface atoms are affected. The top layer of Al atoms is oxidised to form Aluminium oxide (Al₂O₃) which acts as a protective layer for the rest of the Al from substances in the environment.
What does a layer of oil over water in a test tube do?
Stops new oxygen from the air dissolving into the water.
Why might we boil water in the test tube with the oil before an experiment testing for rust?
To remove any oxygen from the water.
Why might we put anhydrous calcium chloride crystals at the bottom of a test tube with oxygen in? (rusting experiment)
To remove any water vapour from the air.
What is an ore?
A rock containing enough metal to be economically worth extracting.
The Earth’s resources of metal ores are…
limited.
Give three disadvantages of extracting metals from the ground.
-Large amounts of waste go to landfill
-Noise and dust pollution from machines
-Destruction of habitats
What is a low grade ore?
A rock that contains a small percentage of a metal or its compound - not enough to be economically worth extracting (using traditional mining methods).
Which ores in particular are becoming scarce?
Copper ores.
Name alternative methods of extracting copper from low-grade ores
Bioleaching
Phytomining
Briefly describe the process of phytomining.
Plants are used to absorb metal compounds.
They are then harvested and burned to produce ash that contains metal compounds.
Describe the process of phytomining:
Plants are grown on a low-grade ore site.
Through active transport, they absorb copper ions from the soil/rock through their roots.
The plants are harvested and then burned to produce ash which will contain copper ions.
The ash is dissolved in water to form a copper solution.
Pure copper can then be extracted by displacement using scrap iron or by electrolysis.
Briefly describe the process of bioleaching.
Bacteria is used to produce leachate solutions that contain metal compounds.
Describe the process of bioleaching:
A low-grade ore site is flooded with bacteria.
These leech copper ions from the ground, then produce leachate solutions (containing the copper ions).
Pure copper can then be extracted by displacement using scrap iron or by electrolysis.
How can metal compounds be processed to obtain pure metals?
By displacement or electrolysis
e.g. copper can be obtained from solutions of copper compounds by displacement using scrap iron or by electrolysis.
Why is extraction by heating with carbon expensive?
Carbon must be heated to high temperatures which requires lots of energy.
What is the ‘normal’ method of extracting metals?
Quarrying/mining
Why does iron displace copper from solutions of copper compounds?
It is more reactive so iron atoms become ions more easily than copper atoms.
What is the equation for the displacement of copper (from copper sulfate) with scrap iron?
CuSO₄ (aq) + Fe (s) → FeSO₄ (aq) + Cu (s)
Explain why the displacement of copper with scrap iron is a redox reaction.
Iron atoms are losing electrons to form 2+ ions and become part of the compound so are oxidised.
Copper ions are gaining 2 electrons to form copper atoms so are reduced.
What do humans use the Earth’s resources for?
To provide warmth, shelter, food, and transport.
What do natural resources provide? (give examples)
Food, timber, (cotton for) clothing, and (oil for) fuel.
What are natural resources?
Resources that form without human input. They include anything that comes from the earth, sea, or air.
What can natural products be replaced with or improved upon by?
Synthetic products
Man-made processes
What can rubber from tree sap be replaced with?
Man-made polymers (for uses such as in tyres).
Chemistry plays an important role in improving…
…agricultural and industrial processes to provide new products and in sustainable development.
Give an example of agriculture providing conditions where natural resources can be enhanced for our needs.
The development of fertilisers has meant we can produce high crop yields.
What is sustainable development?
Development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.
Finite resources from the Earth, oceans and atmosphere are…
… processed to provide energy and materials.
Give an example of a finite resource.
Fossil fuels
Nuclear fuels such as uranium and plutonium
minerals and metals found in ores
What process is used to produce petrol from crude oil?
Fractional distillation
What happens to metal ores to produce pure metals?
They are reduced.
What must people balance when extracting raw, finite resources?
The social, economic, and environmental effects.
Positives of mining metal ores.
Useful products can be made
Provides jobs for local people
Brings money into the area
Negatives of mining metal ores.
Bad for the environment as…
The process uses loads of energy
Scars the landscape
Produces lots of waste
Destroys habitats
What two metals is bronze (alloy) made of?
Copper and Tin.
Alloy
A mixture of metals.