Topic 5 - Electrolysis, Metals and Extraction, Transition Metals Flashcards
electrolysis
using electricity to brake down substances (decompose electrolytes)
-> separate the elements in insoluble ionic compounds
electrolyte
liquid or solution that contains an ionic compound - ions are free to move - they can conduct electricity
cations
positive ions
anions
negative ions
cathode
negative electrode
anode
positive electrode
electrodes in electrolysis
solid conductors that are immersed in an electrolyte and are connected to a direct current electricity supply to drive a chemical reaction
-> ions are attracted to the two electrons
what are cations attracted to
negative cathode
what are anions attracted to
positive anode
what happens to the ions at the anode (MOLTEN ELECTROLYSIS)
- get discharged
- the negative ions loose electrons - become a neutral atom
what happens to the ions at the cathode (MOLTEN ELECTROLYSIS)
- get discharged
- the electrons are transferred from the electrode to the positive ions (gain electrons) - make a pure neutral molecule
oxidation is..
Loss of electrons
Reduction is..
Gain of electrons
OILRIG stand for
Oxidation Is Loss of electrons
Reduction Is Gain of electrons
where does reduction take place
Cathode
Where does oxidation take place
Anode
what do ions turn into after being at the cathode
atoms
what do ions at the anode turn into
molecules
cathode half equation (reduction)
anode half equation (oxidation)
what type of electrode is used when doing molten electrolysis
an inert (unreactive) electrode - (graphite)
in the electrolysis of a MOLTEN salt what is usually formed at the cathode and anode
just the metals in metal compound
what is attracted and formed at the cathode in AQUEOUS electrolysis
- attracted: the cations and the H+ ions
- formed: if it’s not Cu, Ag, Au then hydrogen is formed
what is attracted and forms to the anode in the AQUEOUS electrolysis
- attracted: anions and OH- ions
- formed: if it’s not a halogen (Cl-, Br-, I-) then oxygen is produced
where do the electrons go after being transferred to the anode
they go round the circuit to the cathode where the cathode gives the electrons to the cation there
reactivity series
a list of metals in order of increasing reactivity (most reactive at the top)
What metals do not react with cold water or steam?
Copper, silver, gold
what are the products if metal reacts with a dilute acid
hydrogen and a salt solution
what do you see when a metal reacts with a dilute acid?
bubbles of gas will be seen
-> more bubbles formed the more reactive metal
what happens to the metals atom in reaction with a dilute acid
- loose electrons to form positive ions (cations)
-> more easily a metal atom loses electrons to the higher the metal is in the reactivity series
displacement reaction
occurs when a more reactive element displace is a less reactive element from a compound that contains a less reactive element
spectator ions
ion that is present in a chemical reaction but does not participate in it
-> this ion gets removed when making an ionic equation as it doesn’t change
redox reaction
a reaction when one substance is oxidised and another is reduced
how are very unreactive metals found naturally
in the native state (as uncombined elements)
how are reactive metals found naturally?
found in compounds in rocks after they have reacted with other elements
Extraction
The process of obtaining a metal from these compounds that they are naturally found in
ore
A rock that contains enough of a compound to extract a metal for profit
What method is used to extract compounds of metals below carbon in the reactivity series
Heated with carbon and carbon is more reactive than the element so displaces it
If a metal is more reactive than carbon. How is it extracted?
Using the electrolysis of a molten compounds
How does electrolysis purify and what happens to the impurities?
The positive ions move to the negative electrode (cathode) where they gain electrons and for deposit of a pure metal
-> impurities from the anode do not form ions and collect below the anode as ‘sludge’
What are biological methods of metal extraction?
- bioleaching
- phytoextraction
bioleaching
- Uses bacteria grown on a low-grade ore
- the bacteria produce a solution containing the metal ions (leachate)
- The metal is extracted from the Leche by displacement using a more reactive metal, then it’s purified by electrolysis
phytoextraction
- involves growing plants that absorb metal compounds
- Plants are burned from ash from which the metal is extracted
+ and - of bioleaching and phytoextraction
What has to be removed in order to obtain a metal from its oxide
oxygen
what happens in metal extraction with a metal oxide - oxidisation and reduction (METAL LESS REACTIVE THAN CARBON)
a metal less reactive that carbon is obtained by removing oxygen from the metal oxide by heating with carbon. The metal oxide is reduced to just the metal; carbon is oxidised to carbon dioxide.
-> metal oxide + carbon -> metal + carbon dioxide
What happens in metal extraction using electrolysis?
- The metal ions attracted to the cathode where they gain electrons to form the metal
- The oxide ions are attracted to the anode where they lose electrons to form oxygen
- At the high temperature in the electrolysis cell the oxygen reacts with the graphite (carbon) anodes to form carbon dioxide
when does corrosion happen
When a metal reacts with oxygen
-> the metal gains oxygen and so is oxidised
rusting
corrosion of iron, which also requires water as well as oxygen
what does it mean if a metal corrodes more quickly
it’s more reactive
What is a metal that does not corrode at all
gold
What is a metal that does not corrode but is quite reactive and why
aluminium because their surfaces form a protective layer (a tarnish) which prevents further reaction
+ and - of recycling metals
+ Natural reserves of metal ores will last longer
+ The need to mine ores is reduced; mining can damage the landscape as well as creating noise and dust pollution
+ less pollution may be produced; for example sulfur dioxide is formed when some metals are extracted from metal sulfide ores
+ many metals need less energy to recycle them them to extract new metal from the ore
+ less waste metal ends up in landfill sites
- cost
- requires energy used in collecting transporting and sorting metals to be recycled - more energy is required to recycle than to extract the new metal
Four stages of a life cycle assessment
- manufacturing and packaging the product
- Using the product
- Disposal of product
- Obtaining and processing raw materials
life cycle assessment (LCA)
Carried out to work out the environmental impact of a product
reversible reaction
both forward and backward reactions occur at the same time
symbol to show reversible reactions
dynamic equilibrium
occurs when the forward and reverse reactions rates are equal
equilibrium
state in which the rate of the forward reaction equals the rate of the backward reaction - reaction comes to a halt
where does dynamic equilibrium only occur
in a closed system
why does dynamic equilibrium not occur in an open system
gases could escape and so equilibrium would not be achieved
harber process
a important chemical reaction which is used to make ammonia gas
how is ammonia gas made
from the reversible reaction of nitrogen from the air and hydrogen from natural gas
equilibrium position
the percentages of the products and reactants at equilibrium
what can alter the equilibrium position
temperature, pressure and concentration
what can alter the equilibrium position
temperature, pressure and concentration
in general equilibrium position shifts to…
minimise the effects of any changes to the system
if you increase temp, where does the equilibrium position shift to
in the endothermic direction (transferring energy from the surroundings, cooling them down)
if you decrease temp, where does the equilibrium position shift to
in the exothermic direction (transferring energy to the surroundings, heating them up)
if you increase pressure, where does the equilibrium position shift to
in the direction that forms fewer gas molecules (as this reduces pressure)
if you decrease pressure, where does the equilibrium position shift to
in the directions that forms more gas molecules (as this increases pressure)
if you increase concentration, where does the equilibrium position shift to
in the direction that used up the substance that has been added
if you decrease concentration, where does the equilibrium position shift to
in the direction that forms more of the substance that has been removed
where are transition metals in the periodic table
in the central block of the periodic table
transition metals physical properties
- malleable (can be hammered or rolled into shape without shattering)
- ductile (can be stretched out to make thin wires)
- good conductors of electricity
- shiny when polished
unlike groups 1&2: - high melting points
- high density’s
how do u identify the transition metals ion present in a substance
the colour it of the transition metals ion present hydroxide
why are transition metals used in catalytic converters in vehicles
because transition metals and their compounds typically show catalytic activity
what happens when metals react w oxygen
they oxidise to form metal oxides
what do metals form on the outside when they oxidise and why
they may form a thin layer of tarnish to stop oxygen reaching the metal preventing further oxidation
what do metals form on the outside when they oxidise and why
they may form a thin layer of tarnish to stop oxygen reaching the metal preventing further oxidation
what protects aluminium from further oxidation
it is protected by a natural layer of its oxide - this layer is thin enough to see the aluminium underneath
When does corrosion happen?
Corrosion happens when a metal continues to oxidise and so the metal becomes weaker over time
Rusting
Corrosion of iron or steel -> iron rust when it reacts to oxygen and water
How can rusting be prevented?
- air is kept away -> this is achieved by storing the metal in an unreactive atmosphere of nitrogen or argon
- If water is kept away -> using a desiccant powder that absorbs water vapour
- Coating/painting with plastic, oiling and greasing
Sacrificial protection
A method of rust prevention that does not rely on keeping air of water away; instead a piece of magnesium or zinc is attached to the iron or steel object
-> magnesium and zinc oxidise more easily than iron so oxygen reacts with them rather than the iron or steel object (they lose electrons more easily) - this protection continues until the sacrificial metal corrode away
What is a electroplating?
It coats the surface of one metal with a thin layer of another metal
When is electroplating used?
- To make cheap jewellery look attractive by coating it in silver or gold
-To improve a metal objects ability to resist corrosion
What metal resist corrosion and is used on vehicles
Chromium -> the thin layer of chromium stops air and water reaching the steel below preventing the object rusting
tarnish
when a metal looses it colour due to chemical reaction and oxidisation
silver and copper cables + and -
+ best electrical conductors
- tarnish in air
+ and - of gold-plated connectors
expensive hi-if cables and electronic equipment use gold-played connectors
+ does not tarnish
- more expensive than silver or copper cables
what do u need to electroplate a metal object
- an anode made from the plating metal
- an electrolyte which is a solution containing ions of the plating material
- a cathode which is the metal object itself
Electroplating
uses electrolysis to deposit a thin layer of one metal onto the surface of another metal
process of electroplating, example: silver onto a copper ring
- a direct flows through the electrodes and the electrolyte
- silver ions in the electrolyte move to the negatively-charged copper ring - they gain electrons and are deposited as silver atoms
- at the silver anode, silver atoms loose electrons or become silver ions, which go into the electrolyte
- the longer the current flows the thicker the silver layer on the ring becomes
what gets formed at the anode in electroplating
the unreactive metal looses electrons and turns from an atom to ions which go into the electrolyte move
what is produced at the cathode in electroplating
The more unreactive metal ions from the anode move to the more reactive metal in the electrolyte, they gain electrons and are deposited as a unreactive metal ion
Half equation at the anode
unreactive metal atom -> unreactive metal ion + e-
half equation at cathode
More unreactive metal ion + e- -> more unreactive atom
galvanising
iron and steel objects can be protected from rusting by coating them with zinc
-> layer of zinc improves corrosion resistance by stopping the water, reaching the iron or steel and by acting as a sacrificial metal - superficial protection can continue even if the zinc layer is damaged
how can galvanising be carried out?
Using electroplating or by dipping the object in molten zinc
alloy
a mixture of a metal elements with one or more other elements, usually elements
alloys steels
made by deliberately adding other elements to iron
what does stainless steel resist
Stainless steel resist rusting, unlike other alloy steels and iron
what does stainless steel contain
contains chromium which reacts with oxygen in the air and a layer of chromium oxide forms - this is thick enough to stop air and water reaching the metal below
How do you know whether steel is stronger or harder?
in general, the greater the carbon content of steel, the string and harder it is
- mild steel has a low carbon content
Explain how are metals are malleable and ductile
In a solid pure metal, the atoms are all the same size and are arranged regular in layers. These layers move past each other if enough force is applied.
Why are alloys stronger than pure metal (structure)
In an alloy the atoms of other elements present may be different sizes, they distort the regular structure making it more difficult for the layers of slide each - This is why alloys are stronger than pure metals.
properties or metal alloys
- chemical properties such as resistance to corrosion
- physical properties, such as density and ability to conduct electricity
Give a use of metals and alloys
- Gold and copper could be electrical wiring
- Aluminium could be used for overhead electrical cables
- brass is used for making electrical plug pins
describe how after power supply has been switched off you can measure the mass of the metal
rise and dry electrode and measure mass of electrode and subtract og mass
what happens to the reading on the voltmeter over a long period of time
- reading stays the same at first
- it will decrease overtime as the solution ionises and electrons stop flowing so no charge is carried
Explain why can sodium carbonate cannot conduct electricity but a solution of sodium carbonate can conduct electricity
- when solid the IONS are in a fixed position and cannot move as they’re held together by strong electrostatic attractions however when aqueous the IONS are free to move and can carry a current
explain why acidified water is an electrolyte
It contains islands from the acid and as it contains irons that can move the water conducts electricity so it’s an electrolyte
What should be done to the electrode after it has been removed from the solution before the final mass is determined
Wash electrode and then leave it to dry
Explain why the appearance of copper sulphate solution did not change during an example of electrolysis
copper ions are made at the anode and moved to the cathode, so no change in the concentration of copper
