Electrolysis Flashcards
What is an electrolyte?
An ionic substance with freely moving ions
What is oxidation?
At the anode, where negative ions lose electrons and the gain of oxygen
What is reduction?
At the cathode, where electrons are gained from the electrode to the positive ions and the loss of oxygen
What do ions become at the cathode?
They become atoms
What do ions become at the anode?
They become molecules
What do half equations show?
The change at each electrode
What does inert mean?
Unreactive
Where is the metal produced in the electrolysis of molten salt?
Cathode
Where is the non-metal produced in the electrolysis of molten salt?
Anode
What is an acronym to remember the Reactivity series?
Please Stop Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold
What are displacement reactions also?
Redox reactions - one substance is oxidised and another is reduced
What is extraction?
The process of obtaining a metal from its ore
What is an ore?
A rock that contains enough of a compound to extract a metal for profit
What is a problem with electrolysis?
A lot of energy is needed to keep metal oxides molten for it, making it extremely expensive; and so electrolysis is only used to extract very reactive metals that can’t be obtained by heating their oxides with carbon
What does bioleaching use?
Bacteria grown on a low grade ore; this produces a solution cotnaing copper ions, called a leachate, and then is extracted using displacement using scrap iron, then purified by electrolysis
What does phytoextraction involve?
Growing plants that absorb metal compounds; they are burn to form ash from which the metal is extracted
What is a disadvantage of both bioleaching and phytoextraction?
It is very slow
What is the problem with bioleaching?
Toxic substances can be produced and damage the environment
What is the problem with phytoextraction?
Expensive and growing plants is dependent on weather conditions
What are advanatges of bioleaching and phytoextraction?
Bioleaching - doesn’t require high temperatures
Phytoextraction - can extract metals drom contaminated soils
Both - no harmful gases are produced, less damage to landscape then mining and conserves supplies of higher grade ores
When does corrosion happen?
When a metal react with oxygen, making the metal weaker over time; metal gains oxygen and so is oxidised
What is rusting?
The corrosion of iron or steel
What is the relationship between speed of corrosion and reactivity?
Directly proportional - the more reactive a metal is, the more rappidly it corrodes
How can many metals be recycled?
My melting them down and making them into something new
What are some advantages of using recycing?
- Natural reserves of metal ores
- Mining ores is reduced, so damage to landscape, noise and sound pollution is reduced
- Less energy is needed by recycling than extracting new metal from the ore
- Less waste metal ends up in landfill sites
What are some disadvantages of recycling?
-A lot of cost and energy in collecting, transporting and sorting metals to be recycled
What does the LCA decide?
Whether it is worthwhile to manufacture and recycle a product
What does the LCA compare?
The effect of using different materials for the same product
What are reversible reactions?
In chemical reactions where the products react to reform the reactants
What is dynamic equilibrium?
When the forward and backward reactions are still occuring but the percentages of the reactants and products are no longer changing - reactions still occurring (dynamic), but substances remain in balance (equilibrium)
Where does dynamic equilibrium only occur?
In closed systems
What does the manufacture of ammonia in the Haber process involve?
A reversible reaction between nitrogen (from the air) and hydrgoen (from ntural gas) that can reach a dynamic equilibrium
Wht do the reaction conditions in the Haber process favour?
The forward reaction and make a large amount of product as cheaply as possible
What are the conditions of the Haber process?
Temperature - 450 degrees celsius
Pressure - 200 atmospheres
And the use of an iron catalyst
What happens in the Haber process when you:
- Increase the temp
- Decrease the temp
- Increase gas pressure
- Decrease gas pressure
- Increase a concentration
- Decrease a concentration
- Endothermic direction - transfer energy from surroundings, cooling them down
- Exothermic direction - transger energy to surroundings, heating them up
- Direction that forms fewer gas molecules - reduces pressure
- Directions that forms more gas molecules - increases pressure
- Direction that uses up substance that has been added
- Direction that forms more of the substance that has been removed
What are transition metals?
Elements placed in central block of Periodic Table between groups 2 and 3; include most metals used for construction, vehicles, electrical wiring, jewellery and other everyday uses
What are the physical properties of transtion metals?
-Malleable
-Ductile
-Shiny when polished
Good conductors of electricity
-High melting points
-High density
What are the chemical properties of transition metals?
- Compounds usually coloured
- Show catalytic activity
What do metals form when they oxidise?
A think layer of tarnish that stops oxygen reaching the metal, preventing further oxidation
How can rusting be prevented?
If air or water is kept away, for example using a desiccant powder that absorbs water vapour, painting, coating with plastic, oiling and greasing
What is sacrificial protection?
A method of rust prevention that doesn’t rely on keeping air on water away and instead a piece of magnesium or zinc is attatched to the iron/steel object; they oxidise more easily than iron and so oxygen reacts with them rather than the object. This protection continues to corrode until the sacrificial metal corrodes away
What is electroplating?
Coating the surface of one metal with a thin layer of another metal, which may be used to improve a metal object’s ability to resist corrosion or make jewellery attractive that is cheaper than silver or gold by electroplating it onto cheaper ‘base metals’ like copper or nickel
What is wrong with silver and copper?
Despite being the best conductors of electricity, they both tarnish in air and so may use gold-plateed connectors as it does not tarnish in air and so does not disconnect equpiment with cables, but it more expensive than silver or copper
What do you need to electroplate a metal object?
- An anode, from the plating metal
- An electrolyte, a solution containing ions of the plating metal
- A cathode, the metal object itself
What is galvanisation?
Protecting iron and steel objects from rusting by coating them with zinc; it stops water reaching the object and acts as a sacrificial metal which can continue even if the zinc layer is damaged
How does tin stop food cans from rusting?
It does not react with oxygen or water at room temp., but if the tin layer is damaged, the steel can will rust faster because iron is more reactive then tin, and so acts as a sacrificial metal to protect the tin
What is an alloy?
A mixture of a metal element with one or more other elements, usually metals
How are alloy steels made?
By deliberately adding other elements to iron
What do stainless steels do?
Resist rusting - its thin layer of chromium oxide reacts with oxygeni in the air and is thick enough to stop air and water reaching the metal below, but thin enough to be transparent
Are alloys often stronger or weaker than the pure metals they contain?
Stronger
Why are alloys stronger than the pure metals they contain?
In a solid, the pure metal atoms are the same size in a regular pattern and so easily slide past each other if enough force is applied, making them malleable and ductile; however, in alloys, they distort the regular structure with a mixture of different atoms and so it is more difficult for the atoms to slide past each other
What do the uses of a metal/alloy depend on?
- Chemical properties, like resistance to corrosion
- Physical properties, like density and ability to conduct electricity
What is an example of an alloy that has more useful properties than the metals they contain?
Brass is an alloy of copper and zinc; even though copper is a better conductor of electricity and they both resist corrosion, brass is stronger and so is more suitablr for making electrical plug pins
Name some properties of aluminium
- Resists corrosion
- Doesn’t conduct electricity as well as copper
- Cheaper and less dense than copper
Name some peroperties of gold and copper
- Malleable
- Reist corrosion
- Ductile
- Very good conductors of electricity
- Gold is thousands of times more expensive than copper
