physical chemistry

• Negative bromide ions move to the positive electrode (anode)


  Each loses one electron to form bromine molecules
• There is bubbling at the anode as brown bromine gas is given off
• Positive lead ions move to the negative electrode (cathode)


  They gain electrons to form a grey lead metal which deposits on the surface of the electrode
• Electrolysis of molten lead(II) bromide

  
1. Add lead(II) bromide into a beaker

  2. Heat it so it will turn molten, allowing ions to be free to move and conduct an electric charge

  3. Add two graphite rods as the electrodes and connect this to a power pack or battery

  4. Turn on the power pack or battery and allow electrolysis to take place

  
• solution in electrolysis must have free moving ions
• Sodium chloride

  NaCl
• Reaction

  NaCl + H + OH → NaOH + H + Cl
• Cathode

  • Na+ and H+
  • H+ discharged
  • more OH-
• Anode

  • Cl- and OH-
  • Cl- discharged
  • diluted → OH- will be discharged
• redox reactions --> reduction + oxydation
• oxydation - loss electrons (+n); loose oxygen
• reduction - gain electrons (-n); loose oxygen
• reducing agent - the one who is able to make other elements reduce
• oxydadion agent - the one who is able to make other elements be oxydised
• oxydation n of oxyen?

  -2
• acid + metal --> salt + hydrogen
• acid + carbonate --> salt + CO2 + H20
• base + acid --> salt + water
• Aqueous silver nitrate solution should not be acidified with hydrochloric acid as this will form a white precipitate due to the chloride ion in the acid
• Aqueous barium nitrate / chloride solution should not be acidified with sulfuric acid as this will form a white precipitate due to the sulfate ion in the acid
• Flame test procedure

  1. Dip the loop of an unreactive metal wire such as nichrome or platinum in concentrated acid and then hold it in the blue flame of a Bunsen burner until there is no colour change

  2. This cleans the wire loop and avoids contamination

  3. A small sample of the compound is placed on an unreactive metal wire loop such as nichrome or platinum

  4. Dip the loop into the solid sample / solution and place it in the edge of the blue Bunsen flame

  5. Avoid letting the wire get so hot that it glows red otherwise this can be confused with a flame colour
• calcium white precipitate remains

  copper light blue prec. insoluble

  Iron (2) green prec. insoluble

  Iron (3) reddish brown insoluble

  Zinc white prec. dissolves