C6.1 - Metals Flashcards
Ore
= rock / mineral that contains enough metal to make it economical to extract the metal
(Value of metal > cost of extracting it)
List the different ores and the metal compound found in them
- malachite: copper carbonate
- bauxite: aluminium oxide
- haematite: iron(III) oxide
Why are ores mined
To separate the metal compound from the other substances in the ore
What is used to determine what extraction method is used to obtain the metal from the pure metal compound
Depends upon the metals position in the reactivity series
What are the 2 extraction methods & when are they sued
- electrolysis: metal more reactive than carbon
- heating: metal less reactive than carbon
why is heating preferred over electrolysis to extract metal
It is cheaper
Reactivity series (most -> least reactive)
Potassium Sodium Calcium Magnesium Aluminium Carbon Zinc Iron Tin Lead Copper Silver Gold Platinum
What are the 2 stages to extract copper from copper(II) sulfide
1: copper(II) sulfide ‘roasted’ in air
2: copper(II) oxide heated with carbon (/ methane / hydrogen)
Word & symbol equation for stage 1 of copper extraction
Copper(II) sulfide + oxygen —> copper(II) oxide + sulfur dioxide
2CuS (s) + 3O2 (g) —> 2CuO (s) + 2SO2 (g)
Word & symbol equation for stage 2 of copper extraction
Copper(II) oxide + carbon —> copper + carbon dioxide
2CuO (s) + C (s) —> 2Cu (s) + CO2 (g)
Why is stage 2 of copper extraction a redox reaction
- copper(II) oxide loses oxygen = reduced, oxidising agent
- carbon gains oxygen = oxidised, reducing agent
Extracting copper experiment (PAG)
- mix copper(II) oxide & charcoal in crucible
- put lid on top (so powders don’t escape / air doesn’t get in causing carbon to burn during heating)
- heat it strongly
- after few mins, allow crucible to cool
- when cool, transfer contents to breaker of water
- copper sinks to bottom, excess charcoal suspended in water (top)
- separate copper by washing it
Blast furnace
Industrial large reaction vessel for iron production (to extract iron from its ore)
Raw materials added at top of a blast furnace
- iron ore (haematite)
- coke
- limestone (calcium carbonate)
- hot air (forced into bottom)
Why are each of the raw materials needed in the blast furnace
- haematite: source of iron
- coke: source of carbon (coal heated without air)
- limestone: purifies iron
- hot air: source of oxygen
Temperature inside a blast furnace
Varies from
1900ºC at bottom
to 300ºC at top
3 stages of carbon reducing iron(III) oxide to iron in a blast furnace
1: coke burns in hot air, making carbon dioxide
2: more coke reduces carbon dioxide, making carbon monoxide
3: carbon monoxide reduces iron(III) oxide to iron at 1500ºC
Word & symbol equation of stage 1 of iron extraction
Coke (carbon) + oxygen —> carbon dioxide
C (s) + O2 (g) —> CO2 (g)
word & symbol equation of stage 2 of iron extraction
Coke + carbon dioxide —> carbon monoxide
C (s) + CO2 (g) —> 2CO (g)
word & symbol equation for stage 3 of iron extraction
Carbon monoxide + iron(III) oxide —> carbon dioxide + iron
3CO (g) + Fe2O3 (s) —> 3CO2 (g) + 2Fe (l)
What is used to purify the iron extracted & why
- molten iron trickles down in blast furnace
- contains sandy impurities from iron ore
- removed using limestone (calcium carbonate)
How is the iron extraction purified
- calcium carbonate decomposes at high temps
- forms calcium oxide
- calcium oxide reacts with silica (in sandy impurities)
- forms calcium silicate
- molten iron separates & molten calcium silicate(slag) floats on top
- both iron & slag removed separately at bottom of blast furnace
Word & symbol equation for stage 1 of iron purification
Calcium carbonate —> calcium oxide + carbon dioxide
CaCO3 (s) —> CaO (s) + CO2 (g)
Word & symbol equation for stage 2 of iron purification
Calcium oxide + silica —> calcium silicate
CaO (s) + SiO2 (g) —> CaSiO3 (l)
What extraction method is used for aluminium, why
= electrolysis
More reactive than carbon
What ore is pure aluminium extracted from
Aluminium oxide, Al2O3
Found in the ore bauxite
Why can’t aluminium oxide undergo electrolysis
Electrolysis only works in solution / molten form
- not solution: aluminium oxide doesn’t dissolve in water
- not molten: very high melting point (2000ºC), too expensive to heat
Why is aluminium oxide dissolved in molten cryolite for electrolysis
Cryolite has much lower melting point than aluminium oxide (950ºC)
What is the huge electrolysis cell that holds molten mixture of aluminium oxide & cryolite made from
steel, lined with graphite
What is the cathode (-) and anode (+) in the electrolysis of aluminium
Cathode: graphite lining
Anode: series of large graphite blocks
What is produced at the cathode during electrolysis of aluminium, half equation
Aluminium
Al3+ + 3e- —> Al
What is produced at the anode during the electrolysis of aluminium, half equation
Oxygen
2O2- —> O2 + 4e-
Then oxygen reacts with hot graphite anodes, producing carbon dioxide
O2 + C —> CO2
Low grade ore
Ores that contain too little metal for traditional methods to be profitable
Bioleaching
Biological method of metal extraction in which bacteria speed up reactions that release soluble metal compounds from metal sulfides
How does bioleaching work
- bacteria oxidise iron(II) & sulfide ions in low grade ores
- bacteria use energy transferred for respiration
- in the presence of water & oxygen
- oxidised sulfide ions react with water to produce sulfuric acid
- sulfuric acid breaks down other minerals in ore
- releasing metal ions into solution
Advantages of bioleaching over traditional mining for metals
- cheaper
- extracts metals from low-grade ores
- occurs naturally
- doesn’t require special treatment / conditions
- doesn’t release harmful sulfur dioxide into atmosphere
disadvantages of bioleaching over traditional mining for metals
- slower
- other toxic substances sometimes produced
- toxic substances & sulfuric acid can escape into(contaminate) water supply & soil if not careful
What part of the plant absorbed dissolved ions
Where are the absorbed metals stored
= through their roots
- roots
- shoots
- leaves
Phytoextraction
Biological method of metal extraction in which plants absorb metals through their roots & concentrate them in their cells
Explain the process of phytoextraction
- crop planted in soil containing low-grade ore
- crop/plan absorbs metal ions through roots
- crop/plant harvested
- crop/plant burnt
- burning increases concentration of metal in plant
- metal remains in ashes
- ash = high-grade ore, metal then extracted (smelted)
Why may a complexing agent be added during phytoextraction
Helps plants absorb metal ions more easily
Why is phytoextraction a carbon neutral process
- carbon dioxide released when burned
BUT - carbon dioxide absorbed during photosynthesis as they grow
Advantages of phytoextraction over traditional mining of metals
- cheaper
- produces less waste
- involves smaller energy transfers
- more carbon-neutral activity
Disadvantages of phytoextraction over traditional mining of metals
- slower
- crops may need replanting & harvesting for several years before available metal removed / absorbed from soil
Alloy
Mixture of 2 or more elements
At least 1 of which is a metal
Properties of steel (& most other metals)
- high tensile strength
- ductile
List alloys & their typical uses
- Bronze: bells, propellers for ships
- Duralumin: aircraft parts
- Steel: buildings, bridges, cars
- Brass: musical instruments, coins
- Solder: joining electrical components, pipes
what are the main metals in each alloy
- Bronze: copper & tin
- Duralumin: aluminium & copper
- Steel: iron
- Brass: copper & zinc
- Solder: copper & tin
What properties of solder make it useful for joining electrical components without damaging them
- low melting point = melt & flow into gaps between components
- conducts electricity = allows current to pass between components
Corrosion resistant
2 alloy examples:
= doesn’t react easily with water
- brass
- bronze
Why can metals be stretched / bent
- layers of metal atoms
- slide over each other
- as all atoms same size
Why are alloys often stronger & harder than individual metals
Atoms in alloy are of different sizes
So difficult for atoms to slide over each other
Why is brass useful for making pins for electrical plugs
- contains copper, good conductor
- corrosion resistant
- strong
Why is the alloy bronze useful for making propellers for ships
- corrosion resistant
- strong
- hard
Why can the alloy bronze be used for musically instruments & artwork
Molten bronze expands slightly as it solidifies
So can create details
corrosion
Reaction of metal with substances found in its surroundings
Explain the corrosion of silver:
What does it corrode in
Why does it turn black
- doesn’t easily react with oxygen (in air/water)
- does in presence of hydrogen sulfide, H2S (g)
- when oxygen & water also present
- corrodes silver, producing thin layer of black silver sulfide, Ag2S (objects turn black, need to be cleaned)
What metals don’t corrode
Why
- Gold, Au
- Platinum, Pt
As very unreactive metals
Rusting
Corrosion in which iron / steel reacts with oxygen & water to form hydrates iron(III) oxide (rust)
Word equation for rusting of iron
Iron + oxygen + water —> hydrated iron(III) oxide
Redox reaction, iron oxidised
Why does the mass of iron/steel decrease during rusting
- orange-brown rust (hydrated iron(III) oxide)
- easily flakes off surface of object
- exposing fresh metal underneath
- rusting continues till iron / steel object completely corroded away
Testing substances needed for rusting using steel / iron nails
Set up 3 boiling tubes:
1: iron/steel nail & anhydrous calcium chloride
2: iron/steel nail & boiled water
3: iron/steel nail & water
- bung tubes 1 & 2
- leave tubes for few days
- observe & record results
What results are expected during the rusting experiment in each boiling tube, why?
1: no rust (anhydrous calcium chloride prevents water contacting nail but allows oxygen)
2: no rust (boiling removes all gases like oxygen from water but allows water)
3: rust (water & oxygen have access to nail)
What substances cause rust
- air (oxygen)
- water
List methods used to stop air & water reaching surface of metal, preventing corrosion
- painting
- coating with oil, grease, plastic
- plating with zinc (galvanising)
- plating with tin
Sacrificial protection
Rust prevention in which more reactive metal than iron / steel (magnesium, zinc) corrodes in preference to iron / steel
As more reactive metal corrodes first, protecting iron/steel
How does sacrificial protection work in terms of electrons
During resting, iron atoms oxidised (loses electrons) to iron(III) ions
(Fe —> Fe3+ + 3e-)
more reactive metal = more easily loses electrons
So more readily oxidised than iron
Metal plating
Layer of metal plated onto iron / steel object preventing air & water reaching iron / steel below
Eg. Galvanising
Galvanising
Coating iron / steel with thin layer of zinc
What does the layer of zinc in galvanising do
- stops air & water reaching iron / steel below
- acts as sacrificial metal so object protected, even if zinc layer damaged (as more reactive than iron/steel)
How is tin plating done
- electroplating steel object with tin
- dipping it in molten tin
Disadvantage of tin plating
- tin less reactive than iron
- If tin layer damaged, steel acts as sacrificial metal for tin & rusts even faster than normal
