gcse science chemistry unit C6 cards

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  • Created by: charlie
  • Created on: 08-06-13 22:03

redox reactions

  • if electrons are transferred- O I L R I G 
  • reduction+oxidation happen at the same time 
  • oxdising agents accepts electrons + gets reduced
  • reducing agent dontates electrons + gets oxidised 

e;g- iron atoms oxideised to iron (II) when react with dilute acid 

  • Fe    -   2e- = Fe2+
  • 2H+ +  2e- =  H2

displacement reactions- redox- more reactive metal displaces less reactive metal from compound

  • place reactive metal into solution of dissolved metal compound- reactive will displace 
  • always metal ion that is reduced 
  • always metal atom that is oxidised 
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rusting of iron

  • rusting is redox reaction
  • only happens when in contact with both oxygen + water 
  • iron+oxygen+water= hydrated iron (III) oxide 
  • each iron atom loses electron + becomes oxidise to Fe3+
  • oxygen gains electron when reacts with iron + becomes reduced to O 2-

prevention methods 

  • metals combined to prevent rust- alloys- steel(iron+carbon), stainless stell(iron+carbon+chronium)
  • oil grease- physical barrier- when moving parts are involved 
  • painting  - physical barrier- large structures+looks attractive 
  • coat of tine- physical barrier- cheap- when scratched iron loses e in preference +rust 
  • sacrificial method- glavanising- coat of zinc loses e in preference even when scratched as more reactive- physical barrier 
  • sacrificial method- blocks of more reactive metal bolted to iron- lose e in preference 
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splitting up with electricity 

  • electric current passed through molten/dissolved ionic compound causing it to decompose 
  • crease a flow of charge through electrolyte 
  • postive ions     --->   cathode + gain e 
  • negative ions   --->   anode + lose e 
  • when it loses/ gains e become atoms/molecules + discharged at electrode 

easier to discharge ions from water than solute 

  • in aq solution as well as ions from solute there are  H+, OH- from water 
  • easier to discharge ions from water instead of solute- H2 at cathode + O2 at anode 

eg. aqueous H2SO4 solution-

  • cathode (hydrogen ions)- 2H+ + 2e- = H2    
  • anode (hydroxide ions) -  4OH-  -  4e- = O2+2H2O
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electrolysis part 2

copper sulphate electrolysed to for copper+oxygen:

  • cathode(copper ions)    - Cu2+ + 2e- = Cu
  • anode(hydroxide ions)  - 4OH- - 4e- = 2H2O 
  • copped ions easier to discharge form solution over H+

in molten ionic solids- only one source of ions 

  • ionic solid cant be electrolysed as in fixed positions- molten ionic compounds can 
  • always broken up into their elements:
  • postive metals reduced at cathode-- Pb2+ + 2e- = Pb
  • negative ions oxidised at anode-- 2Br- = Br2 + 2e-

amount of product made depends on no. of electrons- (inc. no. of e inc. substance produced)

  • electrolysing for long time 
  • inc. the current 

amount of product proportional to time+current     Q= I x T

  • (Q-charge in coulombs)    (I- current in amps)    (T- time in seconds)
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fuel cells

  • hydrogen+oxygen give out energy when they react
  •  produce water + exothermic reaction- shown via energy level diagram

use fuel + oxygen to produce electical energy:

  • hydrogen-oygen fuel cell
  • produces water- clean + no pollutants 

hydrogen- oxygen fuel cell involve redox reaction:

  • electrolyte often solution of potassium hydroxide 
  • hydrogen into anode + oxygen into cathode 
  • at -ve cathode O2 - O2 + 4e- + 2H2O = 4OH-
  • OH- ions move to +ve anode
  • 2H2 + 4OH- = 4H2O + 4e-
  • electrons flow through external circuit from anode to cathode 
  • overall reaction- hydrogen+oxygen=water 
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fuel cells part 2

hydrogen-oxygen advantages:

  • much more efficient than power stations/ batteries greater than 80%
  • direct energy transfer + therefore fewer places where heat can be lost 
  • no moving parts so energy isnt lost by friction + no pollutants only water 


  • producing hydrogen needed to power takes energy- may even come from burning fossil fuels
  • contain posionous catalysts have to be eventually disposed- time money+ enviro problems 

used in spacecraft for electricity:

  • readily available from rocket fuel tanks as reaction between O2+H2 happens 
  • light weight, compact, no moving parts, some product used as drinking water, no pollutants 

car industry developing fuel cells 

  • trying to replace petrol/diesel engines, advantage as no pollutants, obtained by electrolysis- renewable 
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CFC's + ozone layer


  • first thought of as great- non-toxic, non-flammable, chemically inert(unreactive), insoluble in water, low BP, + used as collants in refridgerators+ a.c + propellants aersol spray cans 
  • 1974- chlorine destroyed ozone
  • 1985- evidence of dec. ozone levels over antartica 
  • measurements in upper atmosphere show compunds of broken down ozone 
  • ozone (O3) in stratosphere absorbing UV light + breaks down (O3=O+O2)
  • then joins together to make ozone again (O+O2=O3)
  • uv light reaches earth- sun burn, skin cancer, eye cataracts, ageing 

some countries have banned CFC's

  • took a while for something to happen- research fully reveiwed+evaluated 
  • 1978- USA, canada, sweden, norway - banned CFC's as aersol propellants 
  • after ozone hole discovered - countries joined together reduce CFC production + eventually ban CFC's completely 
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CFC's + ozone layer part 2

free radicals made by breaking covalent bonds:

  • covalent bond breaks unevenly to form two ions-   H--H = H+ = H-
  • H+ has both shared electrons + H- has none 
  • covalent bond can break evenly each atoms gets one shared e-  H--H = H. + H. 
  • unpaired electron makes free radical extremely reactive 

UV light makes carbon-chlorine bonds in CFCs break:

  • CCI2F2 = CCIF2. + Cl.
  • O3 + Cl. = ClO. + O2
  • ClO. + O3 = 2O2 + Cl.

happens high in atmosphere where UV light stonger then free radicals react with ozone creates chain reaction- one Cl free radical breaking up loads of ozone molecules 

CFCs stay in stratosphere for ages- not very reactive only break into Cl where high UV light- each CFC produces one Cl atoms which reacts with thousands of ozone molecules 

  • Alkanes- dont react with ozone so safe alternative 
  • HFC's- very similar but dont contain Cl, none of compunds which broken into attack ozone 
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hardness of water

  • hard water makes scum+scale + wont lather with soap 
  • formes limescale (CaCO) as a thermal insulator- on heating element kettles take longer to boil

hardness caused by Ca2+  +  Mg2+

  • as water flows over rocks + through soil these ions dissolve in it 
  • Magnesium sulphate dissovles + calcium sulphate (a little bit) (permanent hardness)
  • calcium carbonate- only reacts with acids: 
  • CO2 dissolves in rain water forming carbonic acid- CO2 + H20 = H2CO3 
  • so calcium carbonate can react- H2CO3 + CaCO3 = Ca(HCO3)2 (aq) (temporary hardness)
  • overall eqation- carbon dioxide+water+calcium carbonate=caclium hydrocarbonate

ways of removing 

  • temporary hardness- boiling Ca(HCO3)2 (aq)= CaCO3(s) + H2O(l) + CO2(g)
  • both types of hardness- adding washing soda (sodium carbonate) - carbonate ions join onto calcium ions to form precip. - Ca2+(aq) + CO3 2- (aq) = CaCO3(s)
  • both types of hardness- ion exchange resin- Na2+/H+ ions exchange for Ca2+/Mg2+
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hardness of water experiments

  • add 100cm^3 of water to concical flask 
  • add 1cm^3 soap solution to water- put bung on + shake
  • repeat till lather formed- record how much soap needed 
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  • alcohols have a general formula -    C (n) H (2n+1) OH
  • methanol--ethanol--propanol--butanol--pentanol...

fermentation produces ethanol (glucose=ethanol+carbon dioxide)

  • enzymes found in yeast, temp controlled, prevent O2 getting in otherwise turns to ethanoic acid (vinegar) once reaction stops- fractional distillation for pure ethanol 

hydrating ethene produces ethanol 

  • how it is usually made industrially- ethene+water(steam) = ethanol 
  • temp of 300d.c + pressure of 70 atmospheres passed over heated catalyst phosphoric acid 


  • batch process slow inefficient/continuous harsher reaction condition + expensive 
  • ethanol is renewable from sugar cane/ethene from crude oil 
  • ethanol isnt pure + needs fractional distillation/much higher purity 
  • lower atoms economy + yield/low but recycled unused reactants so 95% yields 
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fats + oils

comes from animals or plants:

  • animal fats are: lard, blubber, ghee, cod liver oil (plant fats + oils: walnut oil, coconut oil, olive oil, soya oil )
  • fats are solids+oils are liquids at room temp + are both esthers  reacting the alcohol glycerol with fatty acids 
  • important in raw materials for chemical industry- paints, machine lubricants, detergents, cosmetics 

emulsions made from oil+water 

  • oils dont mix in water- immiscible but can make emulsion- small droplets dispersed in another liquid 
  • milk (oil-in-water emulsion) butter (water-in-oil emulsion)

vegetable oils used to produce biodiesel- provide energy, similar properties to diesel  burning in same way so an alternative 

fats + oils used to make soaps-

  • vegetable oil+alkali makes soap- 
  • natural fats+oils boiled with sodium hydroxide splitting the fats + oils producing soap + glycerol (saponification)
  • first breaks up fat or oil producing glycerol + fatty acids (hydrolysis) then react with sodium hydroxide making soap
  • fat+sodium hydroxide = soap + glycerol 
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using plant oils/fats

unsaturated oils contain C=C double bonds:

  • saturated oils have single C-C bonds 
  • unsaturated oils have double C=C bonds 
  • monounsaturated fats contain one C=C bond + polyunsaturated more than one C=C 
  • detected using bromine water- unsaturated decolourises it as additional reaction takes place- double  bond opens + colourless from orange compound is formed 

unsaturated oils hydrogenated 

  • hardened reacting with H2 in presence of nickel catalyst at around 60d.c (hydrogenation) reacting with double bonds to open them up
  • margarine made from partially hydrogenated vegetable oil- it would be too hard to spread if all bonds were opened up - inc. bad cholesterol in blood + dec. amount of good 

vegetable oils in food can affect health 

  • vegetable o/f- unsaturated however animal o/f saturated- inc. bad cholestrol in blood 
  • unsaturated- reduce amount of bad cholesterol in blood 
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  • hydrophilic head (loves drinking water) + hydrophobic tail 
  • hydrophilic forms strong intermolecular forces with water + hydrophobic with oil 
  • when detergents come in contact with oil/fat helps lift it out of fabric 

dry cleaning uses solvents 

  • much better at removing stains that wont dissolve in water 
  • solvent can completely dissolve the grease:
  • weak intermolecular forces between solvent + weak intermolecular forces between grease
  • solvent applied + intermolecular forces formed between solvent + grease which is surrounded 
  • when solvent removed so is grease 

washing clothes at lower temps saves energy 

  • biological detergents contain enzymes which are bilogical catalysts- help break down large insoluble molecules 
  • enzymes work best at lower temp washes 30d.c/40d.c saving money 
  • higher temps denatured + at cooler temp means delicate clothes can be washed 
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