Chemistry Paper 1

• mass MF/mass EF = n

  MF = n x EF

  if data given is EF and Mr of MF

  MrMF/mass EF = n
• Diamond

  Arrangement

  • tetrahedral
  • C-C covalent bond
  • each C atom bonds with 4 other C atoms
  • no free electrons

  Properties

  • hard, no layers to shift
  • high melting and boiling point, actual C-C covalent bond needs to break, needing lots of energy
  • doesn't conduct electricity, no delocalized electrons
  • insoluble in water and other solvents
• Graphite

  Arrangement

  • layer structure with hexagonal rings
  • C-C covalent bond
  • each C bonds with 3 other C atoms
  • 1 free delocalized electron per C atom

  Properties

  • soft, weak forces between layers
  • high melting and boiling point, strong covalent bonds in hexagons that need to break
  • conducts electricity, delocalized electrons free to move around structure
  • insoluble in water and other solvents
  • less dense than diamond, gap between layers, spaced out
• Fullerene, C60

  Arrangement

  • sphere of hexagonal and pentagonal rings
  • C-C bond
  • each C bonds with 3 other C atoms
  • one delocalized electron per C atom

  Properties

  • soft, not a lot of energy needed to break weak intermolecular forces
  • low melting and boiling point, although there are strong C-C covalent bonds, there are weak intermolecular forces between fullerene molecules
  • doesn't conduct electricity, delocalized electron can't jump from molecule to molecule
  • less dense than diamond
  • dissolves in some solvents
• In dry air

  • Nitrogen = 78%
  • Oxygen = 21%
  • Argon = 0.93%
  • CO2 and others = 0.04%
• MOST REACTIVE

  Potassium

  Sodium

  Lithium

  Calcium

  Magnesium

  Aluminium

  Carbon

  Zinc

  Iron

  Tin

  Lead

  Hydrogen

  Copper

  Silver

  Gold

  LEAST REACTIVE

  All metals above hydrogen react with acid
• Barrier methods = creates barrier between iron and surrounding environment, like air and water, that would make it rust

  • painting, car/bicycle body/railway bridge
  • coating in oil/grease, car engine/bicycle chain
  • cover in plastic, coat in less reactive metal
• Galvanizing = coating with zinc

  Zinc is more reactive than iron, so even if scratched away. zinc reacts more readily than iron

  Bucket/railway bridge/car body
• Sacrifical protection = coat with more reactive material, so it gets oxidized first

  Ships
• Ammonium nitrate is acidid
• Ammonia is a base
• Preparing a pure, dry sample of a soluble salt, starting from an insoluble reactant:

  • warm the acid
  • react with excess solid
  • filter unused solid
  • heat leftover salt solution to concentrate it
  • check saturation using glass rod
  • allow solution to cool so crystals can form
  • filter excess liquid
  • let crystals dry in warm oven or pat dry with filter paper
• Testing for ammonia = damp red litmus paper turns blue
• Flame tests (cations)

  • dip nichrome wire into concentrated HCl
  • put wire into hottest part of blue bunsen burner flame
  • repeat until no color is seen in the flame, removes impurities
  • dip again into concentrated HCl and into compound
  • place wire in hottest part of bunsen flame and record color

  Li+ = red

  Na+ = yellow

  K+ = lilac

  Ca2+ = orange-red

  Cu2+ = blue-green
• Hydroxide tests, precipitation reaction

  • add solution to test tube
  • add up to 10 drops of NaOH to test tube

  Cu2+ = blue

  Fe2+ = green

  Fe3+ = brown
• NH4+ ions:

  • add up to 10 drops of NaOH
  • gently heat contents of test tube
  • damp red litmus paper turns blue due to ammonia liberated
• Surface Area

  • reducing the size of particles increases surface area
  • this increases the number of collisions per second
  • resulting in more frequent successful collisions
  • this increases the rate of reaction
• Concentration

  • increasing the concentration of a solution
  • increases the number of particles per unit volume
  • increasing the number of collisions per second
  • this results in more frequent successful collisions
  • therefore increasing the rate of reaction
• Temperature

  • as temperature increases, particles gain more kinetic energy
  • so more particles have energy greater than or equal to the activation energy
  • this results in an increase in the number of collisions per second
  • resulting in more frequent successful collisions
  • therefore increasing the rate of reaction
• Pressure (gases)

  • increasing the pressure (or decreasing volume) increases concentration
  • same amount of particles in smaller volume
  • so there are more collisions per second
  • resulting in more frequent successful collisions
  • increasing the rate of reaction
• Catalyst

  • substance that increases the rate of reaction but itself remains chemically unchanged
  • provides an alternative route for the reaction with lower activation energy
  • more collisions per second
  • resulting in more frequent and successful collisions
  • increasing the rate of reaction

  Industry: saves money, helps reaction take place at lower temperature and pressure
• Substitution reaction (ALKANES)

  • two products given, only occurs under UV light
  • bromoethane

  propane + bromine + 1-bromopropane + hydrogen bromide

  orange to colorless, ONLY UNDER UV LIGHT

  
• Addition reaction (ALKENE)

  • UV not needed
  • one product
  • dibromoalkane

  orange to colorless

  
• Alkane:

  • doesn't react with bromine water
  • doesn't decolorize bromine water

  Alkene:

  • reacts with bromine water
  • decolorizes bromine water; because bromine no longer exists as its molecule
• Disposal of addition polymers

  • unreactive and chemically inert, so aren't biodegradable
  • takes up valuable land
  • non-biodegradable so landfill sites quickly fill up
  • produce CO2 when burnt
  • greenhouse gas that contributes to climate change
  • if incomplete combustion, CO produced; toxic gas
  • if polymer contains chlorine, hydrogen chloride gas gets produced; toxic gas
  • recycling; different polymers need to be separated from each other; difficult and expensive process
• Fractional Distillation (Crude Oil)

  • crude oil is heated at bottom of column
  • fractionating column has a heating gradient, so it's hotter at the bottom and cooler at the top
  • the fractions separate at different heights
  • because different hydrocarbons have different boiling points
  • shorter hydrocarbons have lower melting points and rise to the top
  • hydrocarbons condense at different levels depending on their boiling point

  
• Cracking = long chain hydrocarbons break down into shorter chain alkanes and alkenes

  • alkenes needed to make polymers
  • shorter-chain alkanes are in higher demand
  • oil fraction heated to around 600-700 degrees Celsius to vaporize them
  • vapors pass over catalyst of silica or aluminium oxide
  • breaks covalent compounds in the molecules
  • produces a mixture of smaller alkanes and alkenes
  • higher proportions of alkenes formed at higher temperatures and pressures
• Mg VS Na


  Higher melting point:

  • Mg will have a higher melting point
  • higher number of delocalized electrons
  • higher charge of cation
  • stronger electrostatic forces of attraction
  • stronger bond
  • higher amount of energy needed to break these bonds
  • so therefore a higher melting point
• Physical properties of metals

  high m.p and b.p: strong forces of attraction that need to be overcome

  conduct electricity: delocalized electrons that move freely throughout the structure

  malleable and ductile: layers of atoms can slide over one another; when a force is applied, the layers of ions shift and stay in their new position
• Electrolysis of aqueous solutions:

  adding dilute acid increases electrical conductivity;

  • if metal is more reactive than hydrogen, H+ gets discharged at cathode
  • if halides (Cl-, Br-, I-) are present, they react; if not, OH- discharges at anode
• Electrolysis of aqueous solutions, formulas

  If H+ is present in electrolyte:

  2H+ + 2e- --> H2 (g)

  If H+ is absent in electrolyte:

  2H2O + 2e- --> H2 (g) + 2OH- (aq)

  If OH- is present in electrolyte:

  4OH- --> O2 + 2H2O + 4e-

  If OH- is absent in electrolyte:

  2H2O --> 4H+ + O2 + 4e-
• Extraction of Aluminium


  Use bauxite dissolved in cryolite, (Na3AlF6)

  • cryolite = aluminium compound that melts at a more reasonable temperature: used to save energy and money
  • Al2O3 + cryolite mixture melts at a lower temperature, around 1000 degrees Celsius

  cathode: Al3+ + 3e- --> Al

  anode: 2O2- --> O2 + 4e- AND ALSO C + O2 --> CO2

  • mixture electrolyzed with graphite electrodes
  • due to high temperature, carbon at anode reacts with oxygen, forming CO2
  • gets burned away, needs to be replaced regularly
• Extraction of Iron


  Blast furnace

  Starting materials:

  • iron ore, Fe2O3
  • coke, C
  • limestone, CaCO3

  Waste gases: CO2 and CO

  Slag: everything left that isn't iron
• steel = iron + carbon

  advantages:

  • low cost
  • very strong
  • easy to work with

  disadvantages:

  • rusts
• Acid-alkali titration


  • fill burette with alkali, rinsed with alkali beforehand
  • more precise than measuring cylinder
  • use pipette to add acid to conical flask
  • more precise than measuring cylinder
  • conical flask rinsed with distilled water
  • add indicator to acid
  • slowly add alkali to acid
  • swirl flask
  • add alkali dropwise towards end point
  • stop adding alkali when there's a permanent color change
  • record titre (alkali volume delivered)
  • repeat titration, until concordant results are obtained
• Exothermic reactions


  ΔH < 0 , negative

  • bond-making, releases energy
  • heat energy given out, surroundings get warmer
  • more energy is released than energy is needed to break the bonds
  • the stronger the bond, the more energy is needed
  • combustion, neutralization

  
• Endothermic reactions


  ΔH > 0, positive

  • bond-breaking, needs energy
  • heat energy absorbed, surroundings get cooler
  • more energy needed to break bonds than energy released when new bonds are formed
  • thermal decomposition, displacement

  
• Reaction profile diagrams

  
• Dynamic equilibrium 


  two reactions occurring simultaneously, and at the same speed

  so concentration of reactants and products remains constant
• Ethanol's oxidation:


  Combustion:

  CnH2n+1OH + O2 --> CO2 + H2O

  
  

  Oxygen in air, to form ethanoic acid:

  CH3CH2OH + O2 --> CH3COOH

  
  

  Reaction with potassium dichromate, K2Cr2O7, and sulfuric acid:

  CH3CH2OH + 2[O] --> CH3COOH