Electrolysis, metals and equilibrium 2 Flashcards
Reactivity series
Potassium K. Most reactive Sodium. Na Calcium Ca Magnesium Mg Aluminium Al Carbon. C Zinc. Zn Iron. Fe Hydrogen H Copper. Cu Silver. Ag Gold Au. Least reactive Please stop calling me a careless zebra instead try learning how copper saves gold.
Oil Rig
Oxidation is loss (of electrons and gain of oxygen) Reduction is Gain (of electrons and loss of oxygen).
Experiment to show that some metals are more reactive than others.
Place little pieces of metals into dilute hydrochloric acid. Show that hydrogen is forming using the burning splint. Louder the pop, more hydrogen made - more reactive.
Magnesium- loud squeaky pop, fizz vigorously.
Aluminium- fair squeaky pop
Zinc- quiet squeaky pop. Bubble a bit.
Iron- very quiet squeaky pop
Copper- no squeaky pop, not react.
The faster the bubbles form, faster the reaction and more reactive the metal.
Metal+ water
Metal + water = metal hydroxide + hydrogen
Very reactive metals will react vigorously with water.
Less reactive metals won’t react with cold water but will react with steam.
Copper won’t react with either.
Displacement reactions.
Example of Redox reactions where more reactive element reacts to take the place of a less reactive element in a compound.
With metal, more reactive metal loses electrons (oxidised) and less reactive metal gains electrons. (Reduced)
Put iron nail in a solution of copper sulphate.
Iron (more reactive) will kick out copper (less reactive) from the salt.
Iron sulphate solution + copper metal.
Put silver metal into solution of copper sulphate.
Nothing will happen. Copper is more reactive than silver.
Ore
Metal ore- a rock which contains enough metal to extract. Ore is an oxide of the metal.
E.g. main aluminium ore is bauxite- aluminium oxide.
Found in earths crust
Unreactive metals are found in earths crust as uncombined elements.
Metals extracted
Metals higher than carbon in reactivity series have to be extracted by electrolysis of molten compounds- expensive.
Metals below carbon are extracted by reduction using carbon.
Extracting metals with electrolysis- what goes to the anode and cathode?
Metal ore is melted (electric current passed through).
Metal discharged at cathode
Non-metal at anode.
E.g. Aluminium extracted using electrolysis with carbon electrodes. Aluminium oxide dissolved in molten cryolite (aluminium compound with lower melting point than aluminium oxide).
Aluminium- cathode
Oxygen- anode
2Al2O3=4Al + 3O2
Prices of extraction with electrolysis and reduction with carbon.
Reduction with carbon is cheaper.
Electricity is expensive +costs to melt a metal ore.
Lower down the reactivity series, cheaper to extract.
Bioleaching + phytoextraction
Bioleaching- uses bacteria to separate metals from their ores.
phytoextraction- Plants grown in soil that contains metal compounds. Metals build up in leaves+ are burned. Ash contains metal compounds.
Recycling materials
Saves energy
Infinite amount of raw materials (renewable unlike fossil fuels).
Cuts down on rubbish sent to landfill ( pollutes surroundings).
Creates jobs
Beneficial to economy to recycle metals that are expensive to extract or buy.
For every 1kg of aluminium recycled you save:
95% of emery needed to mine fresh aluminium.
4kg of aluminium ore
Lots of waste.
Life cycle assessment + environmental impact.
Choice of material: metals mined and extracted - need energy+ cause pollution.
Raw material comes from crude oil (non renewable)
Manufacture: uses energy. Cause pollution- CO or HCL). Waste product disposal- some can be turned into useful chemicals reducing pollution. Make sure businesses don’t put polluted water back in environment.
Product use: paint - toxic fumes
Burning fuels- greenhouse gases + harmful substances.
Fertilisers- leach into streams + damage ecosystem.
Disposal: landfill site- takes up space + pollute land and water.
Incineration- causes air pollution.
Reversible reactions
Products can react to produce original reactants.
Haber process
Example of reversible reaction.
Nitrogen + hydrogen = ammonia N2 + 3H2 = 2NH3.
Nitrogen: obtained from air (78% nitrogen)
Hydrogen: extracted from hydrocarbons from sources e.g. natural gas + crude oil.
Carried out at 450 degrees with pressure of 200 atmospheres and an iron catalyst.
Equilibrium
When the forward reaction is going at the same rate as the backward reaction.
Both reactions are happening but there’s no overall effect.
Can only happen in closed system so no reactants or products can escape.
Sometimes the equilibrium will lie to the left (lots of reactants but not much products) or right (lots of products but not much reactants).
Dynamic equilibrium
Forward and backward reactions happening at the same time and same rate, and concentrations of reactants and products have reached a balance and won’t change.
What can change the position of the equilibrium?
Temperature, pressure (involving gas), concentrations (of reactants or products).
Le Chatelier’s principle
If there’s a change in concentration, pressure or temperature in a reversible reaction, the equilibrium position will move to help counteract that change.
Temperature
Decrease temp- equilibrium will move in exothermic (releases energy) direction to produce more heat.
Increase temp- equilibrium will move in endothermic (absorb energy) direction to absorb extra heat.
Pressure
Only effects equilibria involving gases
Increase pressure- equilibrium will move towards side that has fewer moles of gas to reduce pressure.
Decrease pressure- equilibrium will move towards side that has more moles of gas to increase pressure.
Concentration
Increase concentration of reactants, equilibrium will move to the right to use up the reactants (making more products).
Increase concentration of products, equilibrium will move to the left to use up the products ( making more reactants).
Decreasing concentration will have opposite effect.
How can you increase yield? (How much product you get)
Changing the conditions to shift the equilibrium position to the right (towards the products).
Advantages and disadvantages of bioleaching and phytoextraction
Advantages- no harmful gases
Causes less damage to the landscape than mining
Conserves supplies of higher grade ores
Disadvantage- very slow
Advantages and disadvantages of bioleaching
Advantage- doesn’t require high temperatures
Disadvantage- toxic substances and sulphuric acid can be produced and damage the environment
Advantages and disadvantages of phytoextraction
Advantage- Can extract metals from contaminated soils
Disadvantage- more expensive than mining some ores
Growing plants is dependant on weather conditions
What happens to negative ions at the anode
They lose electrons and are oxidised
What happens to the positive ions at the cathode
Electrons are transferred from the cathode to the positive ions and are reduced
In the electrolysis of copper sulphate solution, what happens to the anode and cathode
Mass of anode decreases
Mass of cathode decreases
Disadvantage of extracting nickel from its ore rather than by phytoextraction
Mining is bad for the environment because it causes habitat loss
