metals ! Flashcards
physical properties of metals !
high melting boiling points malleable & ductile good conductors of heat & electricity strong and shiny high density
alloys !
mixture containing metal + other elements
- brass (Cu, Zn)
- stainless steel (Fe, Ni, C, Cr)
- steel (Fe, C)
alloy properties + why alloys !
harder & stronger enhances appearance of metal makes metal more resistant to corrosion lowers melting point : reduces energy to melt electrolyte for electrolysis less malleable
steel !
high carbon steel : strong but brittle
low carbon steel : hard, strong & malleable
- stainless steel : highly resistant to corrosion, durable
- manganese steel : strong & hard
structure of metals !
atoms are arranged in neat layers : lie on top of one another
- easy for layers to slide over each other when force is applied -> malleable + ductile
structure of alloys !
different atomic sizes : disrupts regular arrangement of metal layers
- atoms : unable to slide past each other easily
metal reactivity series !
K Na Ca Mg C Al Zn Fe Pb H Cu Ag Au
metal + water
- > metal hydroxide + hydrogen
- metals below Mg do not react with water
metal + HCl
- > metal chloride + hydrogen
- metals below lead do not react with HCl
metal + steam
- > metal oxide + hydrogen
- metals below iron do not react with steam
metal + water vs metal + steam
similarity : both produce H2
diff 1 : steam -> more vigorous
diff 2 : steam -> metal oxide, water -> metal hydroxide
displacement reactions !
more reactive metal displaces less reactive metal from its salt solution
- metals from salt solution
- metallic oxides from reactive metals
- reduction of metal oxides with carbon : oxides of metals above Zn cannot be reduced by carbon (lower than carbon can be reduced)
- reduction of metal oxides with hydrogen : oxides of metals above Cu cannot be reduced by hydrogen (lower than hydrogen can be reduced)
stability of metal oxide
more reactive a meatal -> more stable the metal oxide is
thermal decomposition of metal carbonates !
- > metal oxide + hydrogen
- more reactive a metal is, the greater the thermal stability of metal carbonate
metal carbonates above Ca : thermally stable, unaffected by heat
Ca to Cu : -> metal oxide + CO2
Ag : silver oxide + CO2 + O2
extraction of metals !
reactive metals : K to Al
- electrolysis
moderatelt reactive metals : Zn to Ag
- reducing agents (carbon)
unreactive metals : Au
- often found in its native state
CARBON : NIL
extracting iron ! pt1
extracted from ore in blast furnace : haematitie -> containing Iron 3 oxide, clay & sand
- haematitie (iron ore), limestone (CaCO3), coke (carbon) : fed at the top of the furnance
- hot air : fed into furnance near the bottom
- temp : 1500 celsius
- molten + slag : collected at bottom of furnance -> slag is less dense than iron -> float on top of molten iron
extracting iron ! p2
- C (s) + O2 (g) -> CO2
- CO2 (g) + C (s) -> CO (g) : carbon monoxide - reducing agent
- Fe2O3 (s) + 3CO (g) -> 2Fe (liquid) + 3CO2 (g) : CO reduces Fe2O3 -> molten iron
- CaCo3 (s) -> CaO (s) + CO2 (g) : limestone is added & will decompose to form CaO (basic)
- CaO (s) + SiO2 (s) -> CaSiO3 (liquid) : CaO (basic) will neutralise acidic impurity SiO2 -> CaSiO3 slag
extracting iron ! p3
hot waste gases containing CO, CO2 & N2 (from air) : escape through top of furnance
rusting !
process where iron/steel is oxidised to hydrated iron 3 oxide (rust)
- exothermic reaction
rust prevention ! p1
use protective layer : place barrier around metal
- coat with paint/grease
- cover with plastic
- electroplating with tin, chromium, copper, silver
-> layer stops O2 & H2O from reaching iron -> no rust
rust prevention ! p2
sacrifical protection : sacrificing a more reactive metal which will corrode preferentially instead of iron
- galvanising : coating Zn on surface to prevent air and moisture from reaching iron/steel
reasons for recycling !
metals : finite resources
- limited, will can used up one day
advantages of recycling !
envionmentally : prolong supply of metal, reduces amt of discarded wastes in landfills -> reduce environmental pollution
economically : saves cost of digging up huge landfills
disadvanatges of recycling !
economically : overall cost of recycling is more than extracting metals
social : not a lifestyle easily adopted by everyone
environmentally : can cause pollution
