CC11 - extracting Metals & CC12 - reversible reactions and equilibria Flashcards
What is oxidation
When oxygen is added to a substance (loss of electrons)
What is reduction
When oxygen is removed from a substance (gain of electrons)
What is a redox reaction
A reaction where both oxidation and reduction occur
What is a sign that a reaction has occurred
Effervescence (more = higher reactivity)
What gas is produced when metals are reacted with acid
Hydrogen
What is the test for hydrogen
Hold a lit splint to the gas, if hydrogen is present there will be a squeaky pop
Word equation for metals reacting with acid
Metal + acid —> salt + hydrogen
Word equation for metal reacting with water
Metal + water —> metal hydroxide + hydrogen
Example of a redox reaction
Displacement reactions
What occurs during a displacement reaction
A more reactive element reacts to take the place of a less reactive element in a compound
Redox in metal displacement reactions
More reactive metal = lose electrons (oxidation)
Less reactive metal = gain electrons (reduction)
What happens when a reactive metal is put in a solution of a less reactive metal salt
The reactive metal will react to take the place of the less reactive metal in the salt compund
What happens if a less reactive metal is added to a solution of a more reactive metal salt
Nothing, a less reactive metal cannot take the place of a more reactive metal
What happens if a metal is added to a solution of a metal salt of the same metal
Nothing, the same metal cannot displace itself
What is an ore
A rock that contains a compound with enough metal to make extracting the metal economically viable
What is economically viable
It make sense financially eg. Profit can be made
Copper ore
Malachite
Aluminium ore
Bauxite
Iron ore
Hematite
What does the method used to extract the metal from its ore depend on
How reactive it is
Why are gold and platinum present in the earth as uncombined elements
They are very unreactive
What does extracting metals by reduction using carbon depend on
It only works if the metal is less reactive than carbon
Word equation for extraction using carbon
Metal oxide + carbon —> metal + carbon dioxide
How are metals that are more reactive than carbon extracted from their ores
Electrolysis
Why is electrolysis only used for metals more reactive than carbon
It is more expensive to run as it involves large amounts of electricity
It also costs a lot to melt or dissolve the metal ore so it conducts (ions can move)
Why can carbon only be used to extract metals less reactive than itself
Carbon can only take the oxygen (displace) from elements less reactive than iself
Why must ores be molten or dissolved to under go electrolysis
So that the ions can move to the electrodes once electric current is passed through
Where is the metal discharged in electrolysis
Cathode (negative)
Where is the non-metal discharged in electrolysis
Anode (positive)
What happens with oxide ions in electrolysis of aluminium oxide
They produce oxygen gas which reacted with graphite (carbon) anodes to form CO2 gas
Why do anodes need to be replaced at intervals in the electrolysis of aluminium oxide
The carbon is used up producing CO2, and the anode gets smaller over time
reasons that iron nails are galvanised (coated in zinc)
- zinc is a sacrificial coating
- zinc prevents oxygen reaching the iron in the nails
- Its more reactive, so it oxidises in preference to the iron
what are some biological methods of extracting metals
bioleaching and phytoextraction
why may biological methods be used to extract metals from ores
- supply of metal rich ores is limited eg. copper
- demand for metals is increasing: might lead to future shortages
- scientists are looking for ways to extract metals from low-grade ores or from waste currently produced when metals are extracted
what is a low-grade ore
ores that only contain a small percentage of the metal or its compound, it’ll not be as economically viable
what is bioleaching
- bacteria breaks energy bonds between atoms in an ore, separating the metal from the ore
- bacteria produces a solution called leachate which contains the metal compound needed
- the metal can be extracted from the leachate using displacement with carbon, or electrolysis
positives of bioleaching
- more economically viable than just extracting metal from low-grade ores
- better for the environment
negatives of bioleaching
- slow method of extraction
- still not pure metal: displacement with carbon, or electrolysis still needed
what is phytoextraction
- plants grown in soil that contains lowgrade ores
- metal becomes concentrated in plant tissues
- plants are dried and burnt in furnaces, metal compounds are found in the ashes
- metal can be extracted from compound using displacement with carbon, or electrolysis
positives of phytomining
- more economically viable than lowgrade ore displacement
- no heavy machinery needed = better for the environment
negatives of phytomining
still not pure metal other methods such as displacement with carbon, or electrolysis need to be used to extract the metal
what is aluminium oxide dissoved in for electrolysis, and why
molten cryolite, because cryolite has a lower melting point (1000°C) than aluminium oxide (2000 °C) therefore it is more economically viable
how is the position of a metal in the reactivity series is related to its resistance to oxidation
- more reactive metals (top) lose electrons easily and are also oxidised more easily
- less reactive metals (bottom) dont lose electrons as easily and are more resistant to oxidation
how does recycling conserve resources and energy
- extracting raw materials requires lots of energy (from burning fossil fuels)
- fossil fuels are finite so need to be conserved
- recyling uses significantly less energy than extracting new resources
- raw materials are finite: reusing conserves them
how does recycling protect the environment
- mines destroy habitats and ruin the landscape, less mines needed if materials are recycled
- recycling cuts down on waste sent to landfill, landfill takes up space and pollutes surroundings
economic benefits of recycling
- saves money as less energy is used
- saves money on materials that are expensive to buy or extract
- large industry: creates jobs (more than is things were just sent to landfill)
costs of recycling
collection
processing
wages
transport
benefits of recycling aluminium
for every 1kg recycled:
- 95% energy saved than mining new aluminium
- 4kg aluminium ore saved
what do life cycle assessments work out
the total environmental impact of a product over the entire period of its life
what are the stages of LCA
- obtaining and processing raw materials (choice of material)
- manufature
- use of product
- disposal
LCA: obtaining and processing raw materials (choice of material)
- metals have to be mined and extracted (uses lots of energy + causes pollution)
- raw materials and fossil fuels are finite and extraction and refining use lots of energy + pollute
LCA: manufacturing
- uses lots of energy
- causes pollution (fumes eg. CO)
- disposal of waste products from manufacture (can it be recycled?)
- chemical manufacture uses water: don’t put polluted water back in environment after process
LCA: use of product
- paint can gice toxic fumes
- burning fuels releases greenhouse gases
- fertilisers can leach and damage ecosystems
LCA: disposal
- many products disposed at landfill
- pollutes environment and takes up space
- air pollution caused by products that are incinerated
what does ‘⇌’ mean
equilibrium symbol:
the reaction is reversible
what is a reversible reaction
the reaction may proceed in either direction depending on the conditions
reactants can be made into products and products can be made into reactants
what is equilibrium
- when reactants react their conc. fall: foward reaction slows down
- as conc. of products increases: backward reaction speeds up
- at equilibrium the foward and backward reactions are happening at the same rate, both reactions are happening but there’s no overall change
what is dynamic equilibrium
when foward and backward reactions happen at the same time and same rate, and conc. of products and reactants reach a balance and wont change
what does it mean when the equilibrium lies to the right
conc. of products is greater than the conc. of reactants
what does it mean when the equilibrium lies to the left
conc. or reactants is greater than the conc. of products
what can change the position of equilibrium
temperature, pressure (if gases are involved), concentration of products and reactants
what is the harber process
a reversible reaction: nitrogen and hydrogen react to form ammonia
where are the nitrogen and hydrogen gained from for the harber process
N2 = air (78% N)
H3 = natural gas
method of the harber process
- H and N in a reactor
- gases are cooled and ammonia turns into a liquid and is removed
- unreacted H and N recycled, undergo the process again
what are the conditions in the reactor for the harber process
- 450°C
- 200 atmospheres
- iron catalyst
what is the foward reaction in the haber process
N2(g) + H3(g) —–> 2NH3 (g) (EXOTHERMIC)
what is the backwards reaction in the haber process
2NH3 (g) —-> N2(g) + H3(g) (ENDOTHERMIC)
what is le chatelier’s principal
if there is a change in concentreation, pressure or temperature in a reversible reaction, the equilibrium position will move to help counteract the change
le chatelier’s principal: temperature
- all reactions are exothermic in one direction, and endothermic in the other
- if temperature is decrease, the equilibrium will move in the exothermic direction to produce more heat
- if it is increased, the equilibrium will move in the endothermic direction to absorb the extra heat
le chatelier’s principal: pressure
- only affects equilibria involving gases
- if presure is increased, equilibrium will move towards the side that has fewer molecules of gas to reduce pressure
- if pressure is decreased, equilibrium will move towards the side that has more molecules of gas to increase pressure
le chatelier’s principal: concentration
- if conc of reactants is increased, equilibrium will move to the right to use up the reactants (make more products)
- if conc of products in increased, equilibrium will move to left to use up the products (make more reactants)
- decreasing conc has the opposite effect
