Chemical Changes

Question 1

Electrolysis

Answer 1

• Using electricity to separate elements.
  The positive ions in the electrolyte will move towards the cathode (-ve electrode) and gain electrons so they are reduced.
  The negative ions will move towards the anode (+ve electrode) and lose electrons do they are oxidised.
  Positive metal ions are reduced to the element at the cathode: Pb2+ + 2e-= Pb.
  Negative non- metal ions are oxidised to the element at the anode: 2Br-= Br2 + 2e-.

Question 2

Aluminium Electrolysis

Answer 2

• Very expensive as lots of energy is required to melt the ire and produced the required current.
  1) Aluminium is extracted from the ore bauxite by electrolysis. Bauxite contains aluminium oxide.
  2) Aluminium oxide has a high melting temperature so its mixed with cryolite to lower the melting point.
  3) The molten mixture contains free ions- so it’ll conduct electricity.
  4) The positive Al3+ ions are attracted to the negative electrode where they each pick up three electrons and turn into neutral aluminium atoms. These then sink to the bottom of the electrolysis tank.
  5) The negative O2- ions are attracted to the positive electrode where they each lose two electrons. The neural oxygen atoms will then combine to form O2 molecules.

Question 3

Half equations for Aluminium electrolysis

Answer 3

Al3+ + 3e-= Al
2O2-= O2 + 4e-
Aluminium Oxide= Aluminium + oxygen.
Anode made of carbon reacts with the oxygen to produce carbon dioxide, so must be replaced regularly.

Question 4

Reactivity

Answer 4

Potassium
Sodium    Extracted using 
Lithium.    electrolysis.
Calcium
Magnesium
-Carbon-
Zinc
Iron.        Extracted by reduction using 
Copper   Carbon.

Question 5

Titrations

Answer 5

• a method of analysing the concentrations of solutions.
• allow you to find out how much acid is needed to neutralise a quantity of alkali.
  1) Using a pipette and pipette filler, add a set volume of the alkali to a conical flask. Add two or three drops of indicator too.
  2) Use a funnel to fill a burette with some acid of known concentration. (At eye level so you don’t get acid in your eye if it spills.) Record the initial volume of the acid in the burette.
  3) Using the burette, add the acid to the alkali a bit at a time- giving the conical flask a regular swirl.
  4) The indicator changes colour when all the alkali has been neutralised.
  5) Record the final volume of acid in the burette and use it along with the initial reading, to calculate the volume of acid used to neutralise the alkali.