Unit 10, 11, 12 & 13 - Electrolytic Processes/ Obtaining And Using Metals/ Transition Metals/ Alloys And Corrosion Flashcards
What can acidified water be broken down into by electrolysis?
Hydro peen and oxygen
What is electrolysis?
Using an electrical current to break down substances
What is an electrolyte?
An ionic substance with freely moving ions and can conduct electricity
What happens to the electrolytes during electrolysis?
They move to the opposite charged electrode
What are the electrodes and which is which charge?
Anode: positive
Cathode: negative
What electrolytes move to which electrode?
Cation —> cathode
Anion —> anode
What is the acronym for electrodes
PANIC
What happens at each electrode?
Negative ions lose electrons, positive ions gain electrons
What is the acronym for oxidation and reduction?
OIL RIG
What is oxidisation? (Electrons)
Losing electrons
What is reduction (electrons)
Gaining electrons
Why are there chemical changes at the electrodes?
They change from charged ions to atoms or molecules
What do half equations show? (Electrolysis)
What happens at each electrode
What happens during electrolysis of copper sulphate solution when using a pure copper electrode and an impure copper electrode?
The copper at the impure electrode loses 2 electrons each, the copper ions them dissolve in the solution and move to the negative electrode and become pure copper. The impurities from the other electrode gathers at the bottom. The mass of the impure electrode decreases and the other increases
Explain the core practical - electrolysis of copper sulphate solution
Label a piece of copper the anode and another cathode. Measure the masses. Set up an electrolysis circuit and turn on power to 0.2 A. Leave for 20 minutes. Turn off power, wash in distilled, dip in propane and let the propane evaporate. Measure the masses of the electrodes. Repeat for different currents.
What type of electrodes do molten or dissolved ionic salts use?
Inert (unreactive) electrodes
When a molten salt is electrolysed, how are the ions discharged as?
Atoms or molecules
During electrolysis, what will the salt always decompose into?
It’s elements
Which elements of a salt are produced at which electrode?
Metal at cathode
Non metal at anode
When a solution is dissolved in water, what is important to remember about the ions?
There will be the dissolved ions as well as H+ and OH- ions
Electrolysis: copper chloride in aqueous solution, if the copper chloride decomposes but the water doesn’t change, what is the overall equation?
CuCl2(aq) —> Cu(s) + Cl2(g)
Electrolysis: sodium chloride aqueous solution, sodium chloride decomposes to form hydrogen and chlorine, sodium and hydroxide ions remain in solution, what is overall equation?
2NaCl(aq) + 2H2O(l) —> H2(g) + Cl2(g) + 2NaOH(aq)
What is the rule for the products formed at the cathode?
Least reactive ion
What is the rules for the product formed at the anode?
Halides (chlorine, bromine, iodine) > hydroxide > other ions
What are the 5 least reactive ions (from hydrogen down)
Hydrogen, copper, silver, gold, platinum
What is the reactivity series?
A list of metals in order of reactivity, most reactive at top
What do metals that react with cold water form?
Hydrogen and a metal hydroxide
What do metals that react with steam form?
Hydrogen and a solid metal oxide
What do metals that react with dilute acids form?
Hydrogen and a salt solution
Wha pr happens to a metal when it reacts
They lose electrons
How can the reactivity series help us tell if a reaction will take place
Each metal will react with compounds of the metals below it.
What is a displacement reaction?
When a metal reacts with a metal compound. The metals swap places
Why can displacement reactions only work one way?
Because the metal compound must be less reactive than the metal
What are spectator ions?
Ions that don’t change in a reaction
How do you write an ionic equation?
Remove any ions that remain the same throughout and include charges
What is a redox reaction?
A reaction where one substance is oxidised and another is reduced
What is extraction?
The process of obtaining a metal from its compound
What is an ore?
A rock that contains enough of a compound to extract a metal for profit
How is iron extracted from its ore?
Heating the iron oxide with carbon
When does heating the ore result in the metal?
When the metal is below carbon in the reactivity series
When is electrolysis used to extract metals?
When the metal is above carbon in the reactivity series
What does electrolysis involve?
Passing electricity through a molten ionic compound to decompose it into its elements
Why is electrolysis expensive?
A lot of energy is needed to keep metal oxides molten
What is bioleaching?
A method where bacteria is grown on a low grade ore which produces a solution containing the metal ions called a leachate. The metal is extracted from this by displacement
What is phytoextraction
A process where plants are grown that absorb metal compounds, these are burnt to form ash and the metal is extracted
Give 2 advantages of both bioleaching and phytoextraction
No harmful gases produced
Causes less damage to landscape than mining
Give 1 disadvantage for both bioleaching and phytoextraction
Very slow
What must be removed in order to obtain the metal from its oxide
Oxygen
During electrolysis using aluminium oxide and graphite electrodes, what does the oxygen react with to form
The graphite electrodes to form carbon dioxide
What is rusting
The corrosion of iron that requires water and oxygen
When does corrosion happen
When a metal reacts with oxygen
Why is gold used for jewellery
It doesn’t corrode
Give 3 advantages of recycling metals
Natural reserves of metal ores last longer
Less pollution produced as sulphur dioxide is formed when they are extracted from ores
Less waste metal ends up in landfill sites
Give 3 disadvantages of recycling metals
Expensive as it uses a lot of energy to melt the metal
Transporting the metal
Sorting the metals
What does LCA stand for
Life cycle assessment
What does the LCA help to decide
Whether it is worthwhile to manufacture and recycle a product
What is a reversible reaction
A reaction where the products can react to reform the reactants
What is a dynamic equilibrium
When a reaction is reversible so 2 reactions are constantly reacting but at a rate where the substances remain in balance
What must happen for a dynamic equilibrium to occur
It must be in a closed system
What can alter the equilibrium position
Temperature, pressure and concentration
If the temperature is increased, which way does the equilibrium move
Towards to endothermic as it takes in the extra heat
Which way does the equilibrium move if the pressure is increased
Towards to low pressure side to take in the extra molecules
Which direction does the equilibrium move if the concentration is increased
To the side that uses up the extra substance
What are transition metals used for
Construction, jewellery, vehicles
Why is copper used for electrical wiring?
It is ductile and a good conductor of electricity
What is iron used for
Making buildings, bridges, cars
Do transition metals have higher or lower densities and melting points compared to normal metals
Her
Give an exception for transition metals in terms of melting points
Mercury, liquid at room temp
What type of compounds do transition metals form
Coloured
Give a use of transition metals in terms of chemical reactions
Used as catalysts
What is a tarnish
When metals form a thin layer when they oxidise which stops oxygen reaching the metal
What is corrosion
When a metal continues to oxidise and so the metal becomes weaker
What is rusting
The corrosion of iron or steel
What is the product when iron reacts with oxygen and water
Rust, hydrated iron oxide
What is desiccant powder used for
Preventing rust by absorbing water vapour
How is oxygen kept away from rusting objects
By storing the metal in an unreactive atmosphere of nitrogen or argon
Give 2 ways of preventing rusting
Painting, piling
What is sacrificial protection
A method of preventing rust by attaching a piece of magnesium or zinc to the iron object as it reacts more easily with oxygen
What is electroplating
Coating the surface of a metal with a thin layer of another metal
Why might something be electroplated with silver or gold
They are expensive but attractive
Why might something be electroplated with chromium
It resists corrosion and stops air and water reaching the steel, prevents rusting
Why might connectors be gold-plated
It is the third best electrical conductor but doesn’t tarnish as much
How does electroplating with silver work
Set up electrolysis equipment (anode, cathode, electrolyte)
Anode must be silver plating metal and the electrolyte must have silver ions
The silver ions in the electrolyte move towards the cathode where they get electrons and become atoms
The silver at the anode loses electrons to become ions which move to the cathode
What is galvanising
When iron and steel objects are protected from rusting by coating them with zinc
How does galvanising protect the metal
Sacrificial protection and the zinc papacy’s as a waterproof layer
How can galvanising be carried out (2)
Electroplating, dipping in molten zinc
Why is tin used for the insides of food cans
It doesn’t react with air or water are room temp
What is an alloy
A mixture of a metal element with one or more other elements
How are alloy steels made
By deliberately adding other elements to iron
What is a good and different characteristic of stainless steel compared to other steels
It resists rusting
What does stainless steel contain to help it be resistant to air and water
A layer of chromium oxide
What do ‘tool steels’ contain
Tungsten and molybdenum
What makes a steel stronger
Increased carbon content
Why are alloys stronger than pure metals
In pure metal, all atoms are the same size in layers which can move around but in an alloy, the atoms are different sizes so the layers can’t slide
Give an example of a chemical property
Resistance to corrosion
Give an example of a physical property
Ability to conduct electricity
What metal is normally chosen for electrical wiring
Copper
