⭐️SC10, SC11, SC12, SC13-electrolysis, transition metals, reversible reactions Flashcards
What is an electrolyte?
An ionic substance with freely moving ions and so can conduct electricity
What is electrolysis?
Using energy transferred by electricity to decompose electrolytes
What are the two types of ions and what electrode do they move to?
-cations are positively charged and move to the negative cathode
Anions are negatively charged and move to fee positive anode
How can you prove positive ions go to negative cathode and vise versa?
By placing purple potassium magnganate crystal on a piece of damp filter paper attached to a microscope slide and connected to a DC electric supply, the purple colour will spread towards the anode
What happens to ions in terms of the electrons at each cathode and what is each process called?
At the anode, negative ions loose electrons which is oxidation
At the cathode electrons are transferred from electrode to positive ion so it gains electrons
What does oxidation and reduction do to the ions at the electrodes?
It changes charged ions into atoms or molecules resulting in chemical changes at the electrodes
What type of electrolysis uses inert (unreactive) electrodes?
Electrolysis of molten or dissolved ionic salts
What material electrodes are used when electrolysing molten lead bromine?
Usually platinum or graphite electrodes because molten lead bromine is a dissolved ionic salt and needs electrodes to be inert
How is copper purified through electrolysis?
- the copper needing to be purified is used at the anode and the pure one is used at the cathode, in an electrolyte of copper sulphate solution
- copper is one dissolve in the solution and go to the cathode so anode looses mass and the cathode gains mass.
- Impurities from the anode collect under it as a sludge
Why may anode sludge after electrolysis of copper sulphate solution be collected?
Because it could contain valuable metallic elements
What are the half equations at each electrode in the electrolysis of copper sulphate solution?
Anode:
Cu -> Cu2+ - 2e-
Cathode:
Cu2+ + 2e- -> Cu
In electrolysis of salt solution? How do you know if the positive ions or hydrogen ions become atoms at the cathode?
The more reactive ion stays in the solution
At the anode, how do you determine wether a hydroxide ion of the negative salt ion forms?
The salt forms if it’s a halogen so either f+ or cl- otherwise the OH- forms (get their checked)
What do the metals that react with cold water form?
Metal hydroxide and hydrogen
What do the metals that react with steam form?
Hydrogen and a solid metal oxide
What happens if a metal reacts with dilute acids? What can this tell you about the metal?
It forms hydrogen and a salt solution and bubbles of gas will be seen. The more bubbles the more reactive the metal
What does it mean if a metal is higher in the reactivity series in terms of electrons
The higher the metal in the reactivity series, the more easier it looses electrons
How do displacement reactions work?
The more reactive metal displaces the less reactive metal in the salt e.g.
Zn + CuSO4 -> Cu + ZnSO4
What are displacement reactions also known as?
Redox reactions
How do you write ionic equations?
- Write out the full balanced symbol equation with state symbols
- Split the aqueous ionic compounds into the ions they contain
- Cancel the spectator ions
- Write the equation that’s left
What is extraction?
The process of obtaining a metal from it’s naturally occurring 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 and what’s this ore called
Haematite is the ore iron is extracted from by heating the iron oxide with carbon as carbon is more reactive than iron and displaces it
How do you extract metals from their ores if they are more reactive than carbon? Give an example
With electrolysis for example aluminium comes from the ore bauxite and is extracted by the electrolysis of aluminium oxide
Why is electrolysis not used in large scale extraction of zinc
As zinc is less reactive than carbon so can be extracted using a displacement reaction and keeping metal oxides molten for electrolysis requires a lot of energy making it extremely expensive
What is bioleaching? Describe the steps involved of bioleaching to obtain copper
A method of metal extraction
- Bacteria is grown on a low grade ore producing a solution containing the copper ions called the leachate
- The copped is ectracted from the leachate by a displacement reaction using scrap iron
- The copper is then purified using electrolysis
What is phytoextraction?
Where you grow plants that absorb metal compounds and then burn them to form ash from which the metal is extracted
Give advantages and disadvantages of bioleaching
Adv:
-doesn’t require high temps
-no harmful gases produced
-causes less damage to the landscape than mining
-conserves supplies of higher grade ores
Disadv:
-very slow
-toxic substances like sulphuric acid can be produced and damage the environment
Give advantages and disadvantages of phytoextraction
Adv:
-no harmful gases produced
-causes less damage to the landscape than mining
-conserves supplies of higher grade ores
-can extract metals from contaminated soils
Disadv:
-very slow
-more expensive than mining some ores
-growing plants is dependant on weather conditions
What’s oxidation and reduction in terms of oxygen?
Oxidation is the gain of oxygen
Reduction is the loss of oxygen from a substance
What are redox reactions?
Reactions where oxidation and reduction occur?
When oxidation occurs…
Reduction occurs at the same time and so when one substance is oxidised, the other is reduced
What happens in the electrolysis of aluminium oxide to get aluminium?
The Al3+ ions are attracted to the cathode where they gain electrons to become Al and the O2- ions are attracted to the anode where they loose electrons to become O2.
What are the half equations for electrolysis of aluminium oxide to get aluminium?
Cathode: Al3+ + 3e -> Al
Anode: 2O2- -> O2 + 4e
What is the electrolyte when obtaining aluminium using electrolysis?
Aluminium oxide mixed with cryolite as this lowers the high melting point of 2000°C. The lower melting point reduced the amount of energy needed and saves money
In electrolysis of aluminium oxide, why must the anode be regularly replaced?
As At high temps, the oxygen reacts with the graphite anode to form carbon dioxide as graphite is made of carbon hydrogen
What is corrosion?
When a metal reacts with oxygen making the metal weaker over time
What process happens in corrosion?
Oxidation as the metal gains oxygen
What is rusting? What does it require?
The corrosion of iron that requires water as well as oxygen
Why do some fairly reactive metals not corrode quickly?
As they tarnish where their surfaces form a protective oxide layer that prevents further reaction
Give 3 advantages of recycling
- natural reserves of metal ores will last linger
- less waste metal ends up in landfill sites
- the need to mine ores is reduced which is good as mining damages the landscape and creates noise and dust pollution
Give disadvantages of recycling
It can take a lot of energy and ninety to transport, collect and sort the metals to be recycled
What does a lifecycle assessment do?
- works out the environmental impact of the product
- decides wether it’s worth manufacturing a product
- compares the effects of using different materials for the same product
What are the stages in a lifecycle assessment?
- Obtaining and processing raw materials
- Manufacturing and packaging the product
- Using the product
- Disposal of the product
Give 3 questions you would ask for a lifecycle assessment
- what raw materials are needed?
- what will the product be used for?
- how much energy is needed for the manufacture and packaging of the product?
What are reversible reactions?
Where the products react to reform the reactants
What’s significant about the energy transferred in a reversible reaction?
The same amount of energy is transferred in both the forward and backward direction
What is exothermic reaction
One that gives out heat and heats up the surroundings giving a negative energy change in the reaction
What is an endothermic reaction?
One that takes in heat and cools it’s surroundings giving a positive energy change in the reaction
What is dynamic equilibrium?
Where the % of the products are no longer changing despite the forward and backward reactions are still happening and the substances remain in balance.
When does dynamic equilibrium occur?
In a closed system where there is no loss of reactants or products as in an open system, gases could escape so equilibrium wouldn’t be achieved
What process is the manufacture of ammonia by? What does it involve? What changes the equilibrium position?
The Haber process.
Involves a reversible reaction between nitrogen (from air) and hydrogen (from natural gas) that can reach a dynamic equilibrium
The equilibrium position is changed by the reaction conditions?
What are the reaction conditions did in the have process and what are they?
They are to favour the forward reaction and make a large amount of product as cheaply as possible.
Conditions = temp of 450°C, pressure of 200 atmospheres and an iron catalyst
What happens to equilibrium position if you increase the temperature?
It shifts in the endothermic direction
What happens to equilibrium position if you decrease temperature?
It shifts to the exothermic direction
What happens to equilibrium position if you increase pressure?
Shifts to the direction that forms fewer gas molecules
What happens to equilibrium position if you decrease pressure?
Shifts to the direction that forms more gas molecules
What happens to equilibrium position if you increase the concentration?
Shifts in the direction that uses up the substance that’s been added
What happens to equilibrium position if you decrease concentration?
Shifts in the direction that forms more of the substance that’s been added
What are the physical properties of transition metals?
- malleable= they can be hammered or rolled into shape without shattering
- ductile= can be stretched out to make thin wires
- shiny when polished
What’s iron used for and why?
To make buildings, bridges, ships and cars as it’s malleable and strong
What’s copper used for and why?
Electrical wiring because it’s ductile and is a good conductor of electricity
What do household mirrors contain?
A sheet of glass coated with aluminium
What metal is used in infared telescopes? Why isn’t this aluminium
Silver as it’s shinier than aluminium so that’s used for the mirrors in the telescopes instead
Compared to other metals, transition metals typically have…
High melting points
High densities
What are the chemical properties of transition metals?
- form coloured compounds
- can be used as a catalyst
Give an example of transition metals that show they form coloured compounds
Iron oxide is red brown
Tungsten oxide is yellow
Iron (II) hydroxide is pale green
What does the rate of metals oxidising depend on?
Their reactivity as the more reactive they are the quicker they oxidise
What’s a tarnish? Give an example of a metal that forms this
A layer formed on metals when they oxidise that stops oxygen reaching the metal itself preventing further oxidation for example the aluminium oxide on aluminium
When does corrosion happen?
When a metal continues to oxidise making the metal weaker
What is rusting?
The corrosion of iron or steel (mainly iron)
When does iron rust?
It rusts when it reacts with oxygen and water
What is the substance seen on rusty objects, what usually happens to it?
It’s hydrated iron oxide (III) and this flakes off exposing the metal to more more air air and water and so it continues to corrode and weaken
How can you prevent rusting by keeping away the air?
Storing the metal in an unreactive atmosphere of nitrogen or argon
How can you prevent rusting by keeping away both air and water at the same time
Painting, coating with plastic, oiling and greasing
How can you prevent rusting by keeping away water?
using a desiccant powder that absorbs water vapour
What is sacrificial protection
A method of rust prevention that does not rely in keeping away air or water but instead attaches magnesium or zinc to the iron or steel because they oxidise easier than iron and so oxygen reacts with them instead.
How long does sacrificial protection last for?
It continues until the sacrificial metal corrodes away
What does a metals reactivity mean in terms of loss of electrons?
The more reactive the metal is the more easily it loses electrons.
Why does magnesium and zinc oxidise in preference to iron or steel? (In terms of electrons)
As they are more reactive and so lose electrons easier
What is electroplating?
Coating the surface of one metal with a thin layer of another metal
Why may electroplating be done?
- because the metal is expensive so it’s cheaper to electroplate a cheaper metal
- to improve a metals ability to resist corrosion
Give an example where electroplating has been done because a metal is expensive?
Making jewellery by electroplating cheap base metals like iron and nickel with gold or silver so the jewellery is still attractive
Give an example where electroplating has been done to improve a metals resistance to corrosion
Chromium is used to electroplate objects such as vehicle parts or boat parts made from steel making them chrome plated as the thin layer of chromium stops air and water reaching the steel below preventing the object from rusting
How may cables and equipment use electroplating?
As they are usually made of copper or silver as the best electrical conductors but a layer of tarnish can form so they may be electroplated with gold despite its expensive
What do you need to electroplate a metal object?
- an anode made of the playing metal
- an electrolyte that contains the ions of the plating metal
- a cathode which is the metal object itself
Give the half equations at each electrode when copper is electroplated with silver
- anode: Ag -> Ag+ + e-
- cathode: Ag+ + e- -> Ag
What is galvanising?
Where iron and steel objects are protected from rusting by coating them with zinc
Why does galvanising work?
Because the thin layer of zinc improves corrosion resistance by stopping reaching the iron or steel and by acting as a sacrificial metal which can continue even if the zinc is damaged
How can galvanising be carried out?
By using electroplating or dipping the metal into molten zinc
Steel cans are protected on the inside by electroplating with tin. If the tin is damaged what happens to the steel can?
The steel will rust further because iron is more reactive than tin so it is what 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 that are usually metals
What are stainless steel an alloy of? What is their benefits over iron and other steels?
They resist rusting as they contain chromium which reacts with the oxygen in the air forming chromium oxide which is thick enough to stop air and water reaching the metal below yet is thin enough to be transparent. If the metal scratches, more chromium reacts to replace the layer
What makes up ‘tool steels’?
Tungsten and molybdenum in drill bits because they are very strong
How do you make steel harder?
Increase the carbon content, the greater this is, the harder and stronger it will be
Why doesn’t mild steel have a lot of carbon so it’s as strong as possible?
Because it’s purposes still require it to malleable so it has less carbon but contains manganese to increase its strength while maintaining its malleability
What’s mild steel used for?
A building material and car body panels
What do car manufacturers use stronger steel for?
To produce strong but relatively lightweight car bodies
Why are metals malleable and ductile?
Because the atoms are all the same size and are regularly arranged when solid so layers can slide past each other if enough force is applied.
Explain in terms of atoms why alloys are stronger than pure metals
As in alloys the atoms of other elements present may be different sizes, distorting the regular structure making it harder for the layers to slide past each other though this doesn’t present the alloys being ductile and malleable
What does the uses of a metal or alloy depend on?
- chemical properties like resistance to corrosion
- physical properties like density and ability to conduct electricity
Despite both copper and gold are very good at electrical wiring why is copper used?
Because gold is thousands of times more expensive than copper so good is only used in tiny amounts to connect microprocessors and memory chips
Why is aluminium used in overhead cables instead of copper despite it being less good at conducting electricity?
As it resists corrosion, is stronger and cheaper than copper also
Give an example where alloys have more useful properties than the metals they contain?
Brass for e.g. is made of copper and zinc. Both copper and brass resist corrosion. Copper is a better electrical conductor but brass is stronger making it more suitable than copper for electrical plug pins
What is magnalium made up of? What’s it used for?
95% aluminium and 5% magnesium used for aircraft parts and scientific instruments
Why is aluminium and magnesium used together as the alloy magnalium instead of the metals alone?
- magnalium is less dense and almost 4x stronger than aluminium
- magnalium is twice as strong and has better resistance to corrosion than magnesium
