Chemical Changes

• What happens in an oxidation reaction?

  A substance loses electrons
• What happens in a reduction reaction?

  A substance gains electrons
• What is a displacement reaction?

  A more reactive metal will displace a less reactive metal from a solution of its salt
• How can metals that are less reactive than carbon (e.g. iron and lead) be extracted from their oxides?

  By heating the metal oxides with carbon
• What happens when substances dissolve in water?

  They dissociate into their original ions
• What is an aqueous solution?

  A solution in which the solvent is water
• What is the pH level of a neutral solution?

  7
• What is produced when an acid reacts with an alkali?

  Water
• Acids are neutralised by bases
• What is produced when an acid reacts with a metal oxide or hydroxide?

  Water and salt
• What happens to strong acids in water?

  They are completely split up (ionised)
• What happens to weak acids in water?

  They partially split up
• What can you infer when a solution decreases in pH?

  The number of hydrogen ions has increased
• Metal oxides can be reduced by removing oxygen
• What are indicators?

  Dyes that change colour depending on whether they are in acidic or alkaline solutions
• What is electrolysis?

  The use of electrical current to break down compounds containing ions into their elements
• What are electrodes?

  Solids that conduct electricity during electroylsis
• What is the anode?

  Positive electrode
• What is the cathode?

  Negative electrode
• Why do the negatively charged non metals go to the anode?

  The anode is the positive cathode and the negatively charged non metal ions can go there in order to lose electrons to form non metal atoms and become pure
• What type of reaction happens at the anode?

  Oxidation
• What type of reaction happens at the cathode?

  Reduction
• What is a redox reaction?

  A reaction where both oxidation and reduction take place
• Why is electrolysis expensive?

  It requires a lot of heat and electrical energy
• What is cryolite?

  A compound of aluminium that lowers the melting point of aluminium oxide
• Why do positively charged metals go to the cathode?

  The cathode is the negative electrode and the positively charged metal ions can go there, in order to gain electrons to form metal atoms and become pure