revision for electrolysis test

• the cathode is the negative electrode
• the anode is the positive electrode
• oxide ions lose 2 electrons at the anode forming oxygen. oxygen reacts with the graphite in the cathode to form carbon dioxide. this is the anode burning.
• equation for anode burning = carbon + oxygen -> carbon dioxide
• why does graphite conduct electricity?

  each carbon atom forms three bonds with other carbon atoms therefore graphite has one free (delocalised) electron per carbon that can move throughout the structure and carry charge .
• why is a mixture used as the electrolyte?

  cryolite reduces the melting point of aluminium oxide to 905 degrees so that less energy is needed to separate the ion, deeming it more cost effective and better globally.
• aluminium oxide oxygen equation = 2O2- -> O2 + 4e-
• aluminium oxide aluminium equation = al3+ + 3e- -> al
• graphite? unreactive, high melting point and conductive
• thiosulfate disappearing cross investigation?

  as the temp increases, the rate of reaction increases. the thermal energy increases so so does the kinetic energy. there is higher frequency of collisions. the particles overcome the activation energy leading to successful collision.
• rate of reaction?

  mass of reactant used up (g) / time (s)
• marble chips?

  the larger the marble chips, the lower the surface area, the slower the rte of reaction.
• explain in terms of collision theory why increasing concentration increases rate of reaction?

  increasing concentration means there are more particles in a fixed volume. collisions are likely so the frequency of collisions increase
• explain in terms of collision theory why increasing pressure increases rate of reaction?

  increasing pressure means there are more particles in a fixed volume. collisions are likely so the frequency of collisions increase.
• explain in terms of collision theory why increasing surface area increases rate of reaction?

  larger SA has more particles exposed to collide with.
• explain in terms of collision theory why increasing temperature increases the rate of reaction: as the particles have more kinetic energy, they collide more frequently. particles have more energy so when they collide, they overcome the activation energy.
• oxide ions lose electrons at the anode and become oxygen atoms the oxygen atom reacts with the carbon in the graphite and forms carbon dioxide, this burns the anode so it needs replacing