metals Flashcards
characteristics of metals (6)
- mallaeble
- good conductors of electricity + heat
- high mp bp
- ductile (beaten into sheets)
- pure metals are too soft (not widely used in industry, may react w water and corrode easily)
who react with cold water to form…?
- K, Ca, Na (3)
- metal hydroxide (aq) + H2
why are metals often used in the form of alloys? (4)
- to make metals Harder and Stronger
- to Improve appearance of metals(shiny)
- To lower Melting point of metals (bcos impurities lower mp)
- to make metals more Resistant to corrosion
hisrm
why are alloys stronger and harder than their constituent metals?
bcos atom of added elements hv a diff since thus disrupting the regular/orderly arrangement so layers of atoms cannot slide over each other easily when a force is applied
what is an alloy
it is a mixture of a metal with one or a few other elements(need not b metal)
steel
alloy of iron and carbon
brass
alloy of copper(70%) and zinc(30%), it is harder and stronger than pure zinc + does not corrode easily, attractive yellow colour(goldish) so used for decorative ornaments, musical instruments and coins
bronze
alloy of copper and tin
pewter
alloy of tin(95%), antimony(3.5%) and copper(1.5%), used as a decorative ornament because of its bright, shiny silverish colour
solder
alloy of tin(50%) and lead(50%), has a lower mp than pure tin or lead and is used for joining metals
cupronickel
alloy of copper and nickel, used in coins as it does not corrode easily
stainless steel
alloy of iron, chromimum, nickel and carbon, resitant to corrosion and used for cutlery, utensils, medical instruments and pipes in chemical industries
who react with steam to form…?
- Mg, Al, Zn, Fe (4)
- metal oxide (s) + H2
Fe will form Fe3O4 (is the red colour cpd in ur bld)
ZnO (s) is yellow when hot, white when cold
who will have no rxn w steam or cold water
lead, copper, silver
who will have explosive rxn w dilute acids, what will they form
- K and Na (2)
- form metal chloride + H2 (if reacted w HCL)
metal salts + h2
who will have violent rxn w dilute acids, what will they form
Calcium (Ca)
- form metal salts + H2
who will have moderately fast rxn w dilute acids, what will they form
- Mg. Al, Zn (3)
- form salt + H2 (g)
who will have slow rxn w dilute acids
- iron, lead
who will have no rxn w dilute acids
- copper, silver
the 2 states of metals, combined and uncombined states, explain
uncombined:
- Gold, Silver, Platinum (unreactive metals)
- copper is also unreactive but not uncombined
combined:
- metal oxides
- metal sulfides
- metal carbonates
- metal chlorides
reactions based on reactivity series:
- metal displacement reaction(btwn solid metal & metal solution)
- metal displacement reaction(btwn a metal & a metal oxide)
- reduction of metal oxides with carbon
- reduction of metal oxides with hydrogen
- thermal decomp of metal carbonates
metal displacement reaction(btwn solid metal & metal solution)
a more reactive metal can displace ions of less reactive metals from its salt solution
metal displacement reaction(btwn a metal & a metal oxide)
a more reactive metal can reduce the oxide of a less reactive metal
- need a fuse(like a magnesium ribbon) to provide enough energy to start the rctn when it ignites
reduction of metal oxides with carbon
- carbon can remove oxygen frm the oxides of metals that r not too high up the reactivity series(oxides of zinc onwards, zinc, iron, lead and copper)
- the lower the position of a metal in the reactivity series, the easier it is for carbon to reduce its oxide
carbon can reduce any metal below it, better RA than hydrogen!
reduction of metal oxides with hydrogen
- hydrogen can remove oxygen from metallic oxides producing the metal and water
- lower the position of a metal in the rs, easier for hydrogen to reduce its metal oxide
- oxides of lead and copper can b reduced to their metals by heating w hydrogen
- must hv an outlet for H2 gas bcos it is very explosive s so an outlet is needed for it to flow out
- heat source is to b removed b4 h2 source so that metal cools down and will not react with air to form back the oxide
thermal decomp of metal carbonates
the more reactive the metal, the more difficult it is to decompose its carbonate by heat
- not all can b decomposed, grp 1 metal carbonates–> highly thermally stable, thus thy do not decompose on prolonged heating
so K2co3 and Na2co3–> unaffected by heat
rest of them from Ca onwards decompose into metal oxide + co2 on heating except for Ag2Co3–> decompose into silver and co2 on heating
whats reactivity
tendency of a metal to lose an electron
- ⬆ reactive, ⬆ reducing power
- grp 1 metals ⬆ reactive than grp 2
cost of metals dependent on… (2)
- abundance of metal
- method of extraction of metal
step 1 of blast furnace
- coke react w oxygen to form carbon dioxide and heat
C (s) + O2(g) –> CO2 (g) - Co2 cant be RA cos max no of OS is + 4, cnt go beyond
step 2 of blast furnace
- Carbon dioxide react w more coke to form carbon mono, which is a good RA
CO2 (g) + C (s) –> 2CO (g)
step 3 of blast furnace
- carbon mono reacts with haematite to prod molten iron
3CO(g) + Fe2O3 (s) –> 2Fe (l) + 3CO2 (g) - molten iron sinks to bottom of furnac as cast iron
- CO2 escapes as hot gas thru top of furnac
step 4 of blast furnace
- limestone thermally decomp to prod calcium oxide * carbon dioxide
CaCO3 (s) –> CaO (s) + CO2 (g) - the CO2 can be recycled again for stage 2
step 5 of blast furnace
acidic impurities like Silicon dioxide react w basic CaO to prod slag (neutralisation rxn, the only non redox ones are stage 4 & 5)
SiO2 (s) + CaO(s) –> CaSiO3 (l)
- molten slag sinks but its less dense than molten iron so it floats on top
the 3 ‘ingredients’ on top of the blast furnace (3)
and other things added (hINt: the air)
- limestone (CaCO3)
- coke (c)
- haematite (Fe2O3)
haematite is most impt ore of iron composed of mainly iron (iii) oxide and sand impurities (SiO2 –> acidic oxides, GMS) - hot air enriched w O2, > 750 degree celcius
blast furnaces surfaces are lined with …? (3)
… ionic cpd which are insoluble + high mp + trap heat
waste gases exiting blast furnace
- N2, CO2
- NO, NO2 (react w high temp, enuf to break N triple N bond, form oxides of nitrogen)
what is steel
- is an alloy of iron & carbon w small amts of other elements
- rusts easily
- very strong
- cheap compared to othr alloys
- most widely used metal alloy
- strong, tougher and harder than pure iron
how to make steel?
- remove all impurities in iron–> done by blowing oxygen gas into molten iron to change impurities into oxides (non-metallic oxides)
- the oxides(acidic) are combines w quicklime(basic, CaO) and removed as slag
- the correct amts of carbon and other metals are added to make steel
mild steel (low-carbon steel) aka wrought iron (composition, special properties, reason and uses)
composition: 99.5% iron, 0.25% carbon
special properties: hard, strong and malleable
reason: diff sizes of carbon atoms disrupt the regular layer of iron atoms, hence conferring strength
uses: carbodies, machinery
hard steel (high-carbon steel) aka cast iron (composition, special properties, reason and uses)
composition: 0.45%-1.5% carbon
special properties: strong but brittle, not very malleable, harder than mild steel
reason: too much disruption to the layers of atoms, when a force is applied metal fractures
uses: knives, hammers, chisels, saws and other cutting tools
manganese steel
composition, special properties, and uses
composition: iron, carbon and manganese
special properties: increased strength and hardness
uses: springs and drills
stainless steel
composition, special properties, and uses
composition: iron, carbon, chromium & nickel
special properties: durable, highly resistant to corrosion
uses: cutlery, surgical instruments & equipment in chemical plants
whats rusting lol
- only used on iron and steel okay, others say corrode cos it issz wat it iss
- need oxygen and water
- gradual oxidation of iron to form hydrated iron (iii) oxide [Fe (s) + 3O2 (g) + 2xH2O (l) ]
- sped up thru NaCl and acidic subs (so houses near sea rust alot cos got NaCl in sea)
rust prevention methods (2)
1) protective layer
- once scratched iron/ steel beneath will rust faster
- exclude water and oxygen
- painting, greasing, plastic coating, electroplating with less reactive metals (canned food in tin plated irol/ steel cans)
2) sacrificial method
a) galvanising (oni Zn)
- coating w zinc (not protective layer ok)
- Zn more reactive than iron, pref oxidise in place of iron
b) attach steel/iron to a more reactive metal
- expensive tho (used on bigger construction)
- more reactive one oxidise pref/ more readily in place of iron
why must we recycle metals?
bcos metals are finite and non-renewable resources
thus recycling makes the supply of metals last longer
how can we conserve metals?
by finding substitutes to replace metals so that we can use the existing metals more sparingly
or
recycling!
price of metal depends on: (2)
- how scarce/ availabiltiy of these metals
- -> that why aluminum is cheaper than gold - methods of extraction
- -> electrolysis is more ex than reduction w carbon
advantages of recylcing metals (4)
- helps to conserve the finitie natural resources
- helps to reduce shortage of landfills required for disposal for unwanted items
- helps to reduce emissions of pollutants caused by extraction of metals such as reduce the emission of sulfur dioxide and co2:
- in iron blast furnace–> co2 & co
- burning of fossil fuels to provide heat for electrolysis - saves cost of extracting metals as less electrical energy/fossil fuels r used
economic issues of recycling metals
can be more expensive than extracting metals directly from ores bcos costs include collecting, sorting, separating, cleaning and transporting
environmental issues of recycling metals
can cause pollution problems such as recylcing car batteries–> release harmful gases into the envo bcos to recycle metals u hv to melt them first, burn fossil fuels
