revision pack

• Advantages and disadvantages of hydrogen-oxygen fuel cells advantages : renewable resource

  releases more energy

  no power is lost in transmission due to no moving parts (it doesn't produce greenhouse gases)

  Disadvantages: expensive

  less efficient

  less hydrogen filling stations
• general principles on electrolysis

  1. Ionic compounds require free moving ions to conduct electricity.
  2. Anode is positive cathode is negative.
  3. Metals and hydrogen form positively charged ions so either metal or hydrogen gas will be formed at the cathode.
  4. Non metals (except hydrogen) will be formed at the anode
  5. Electrolyte is the ionic compound in molten or dissolved solution that conducts electricity.
• Transfer of charge (electrolysis)

  1. Power supply give electrons to the cathode and it becomes negative, the anode is positive so the loss and gain of electrons in ions happens here.
  2. In an external circuit, electrons are the charge carriers and ions are charge carriers in electrolyte.
  3. electrons move from anode to cathode, and -ve ions go to anode and +ve ions go to cathode
• Electrolysis of....

  • molten lead (II) bromide (any halide I think): anode = bromine gas and cathode = grey solid (which is deposited on the surface of electrode)
  • Aqueous sodium chloride: anode = chlorine gas and cathode = hydrogen gas. NaOH is left in the electrolyte.
  • dilute sulfuric acid: anode = oxygen gas and cathode = hydrogen gas (and water is formed when OH- lose electrons)

  ALL USING INERT ELECTRODE MADE OF PLATINUM OR CARBON/GRAPHITE
• Binary compounds

  two elements in a compound joined ionically and to predict their products identify the ions

  product at cathode will always be a metal and product at anode will always be a non metal.
• electrolysis of aqueous solutions

  At the anode : OH- and non metals are attracted, if a halide ions are present then it will discharge Instead of OH- and form halogen (gas). IF NO halide ions are present then OH- will be released and form oxygen gas. SO IF concentrated halide solution is used then halogen forms IF its dilute halide solution, then oxygen forms.

  At cathode : H+ and metal ions are attracted, so one of them will be discharged. if metal is more reactive than hydrogen then hydrogen gas will be discharged and reactive metal ion will remain in solution.
• Electrolysis of aqueous copper sulfate

  Ions present: Cu2+, SO4^2-, H+ and OH-

  product at cathode : copper (half eq: Cu2+ + 2e- ---> Cu)

  product at anode : oxygen gas because OH- lose electrons more easily than SO4^2-. (half eq: 4OH ---> O2 + H2O + 4e-

  What if we use copper electrodes: mass of cathode increases and anode decreases, because copper atoms are oxidized to copper ions at the anode, and they are reduced at the cathode forming copper atoms.
• electroplating

  cathode : place object to be electroplated

  anode : place pure metal you want to coat object with

  Electrolyte: should be aqueous solution of a soluble salt of the pure metal you are using.
• rate of reaction : temperature (collision theory)

  successful collisions depend on : number of particles per unit volume, frequency of collisions and kinetic energy of particles.

  temperature: increases rate of reaction, particles have more kinetic energy than activation energy, causing more frequent collisions and higher concentration of particles thus causing more frequent collisions per second.
• rate of reaction : surface area and catalysts (collision theory)

  surface area: will increase rate of reaction

  produces high number of collisions per second

  catalyst: speed up rate of reaction without being altered, provides a different path for reaction to occur when activation energy is low, thus resulting in more successful collisions per second.
• rate of reaction : concentration (collision theory)


  increases rate of reaction

  number of particles are high in a given volume, allowing more frequent and successful collisions per second.

  FOR A GASEOUS REACTION: pressure increases, concentration increases because number of particles are more in a given volume, increasing number of particles will increase number of collisions
• Position of equilibrium

  1. increasing temperature will shift equilibrium to the reactants side and decreasing will shift in the product side to reverse change
  2. Increasing pressure causes equilibrium to shift in the direction where gas molecules produced are Low, and decrease in pressure shifts it to the side where high number of gas molecules are produced.
  3. Increasing concentration shift equilibrium to the right and decreasing it shifts it to the left.
  4. Catalyst does not affect position of equilibrium, but increases rate at which equilibrium is reached.
• indicators

  litmus = red in acid and blue in base (alkali)

  methyl orange = yellow in alkali and red in acid

  thymolphthalein: blue in alkali and colorless in acid.
• oxides 


  acidic oxides form when non metals react with oxygen and react with bases to form salt and water, when dissolved in water they form acidic solution

  basic oxides form when metals react with oxygen also resulting in salt and water when react and form basic solutions.
• preparing soluble salts

  adding acid to a solid metal, insoluble base or carbonate:

  1. heat/ warm up acid
  2. add insoluble base or carbonate or metal to the mixture, slowly.
  3. stir in until base is in excess (meaning that base stops disappearing and base floats in acid )
  4. filter mixture to remove excess base
  5. heat solution to remove water and if crystals can be seen on the glass rod dipped in mixture, then solution is saturated
  6. finally dry and allow filtrate to crystallize
• reacting dilute acid and alkali (soluble base) = titration

  1. use pipette to add alkali into flask and add few drops of indicator
  2. add acid into flask slowly until indicator changes color (after adding to burette and measuring start volume)
  3. note and record final volume and subtract start - final volume and add amount of volume obtained from this calculation in to the same alkali without indicator
  4. heat (resulting solution to partially evaporate leaving a saturated solution where crystals form on sides of beaker or end of glass rod. )
  5. leave to crystallize, filter wash and dry.
• preparing insoluble salt (with precipitation method)

  dissolve two soluble salts in water and mix with a glass rod, in a beaker

  filter to remove precipitate from mixture

  wash filtrate

  leave in oven to dry
• solubility rules

  ...