Chemical changes

• What is oxidation/reduction?


  Oxidation: when a substance gains oxygen

  Reduction: when a substance loses oxygen
• What is the reactivity series of metals?

  Metals above H2 react with acid to produce H2

  -> The more reactive the metal is, the quicker and more violent reaction with acid occurs

  > Metals below H2 don’t react with acids

  > Metals above Carbon are extracted via electrolysis

  > Metals below carbon are extracted from oxides by reduction with carbon
• What is a displacement reaction?

  A reaction where a more reactive metal displaces a less reactive metal from a compound
• How are unreactive metals found in earth?

  In their natural state
• How are oxidation and reduction defined in terms of electron transfer?

  Oxidation: loss of electrons

  Reduction: Gain of electrons
• What is the general equation for a reaction between metals and acids?

  Metal + acid -> salt + hydrogen

  -> A redox reaction
• What is the general equation for a neutralisation reaction?

  Base + acid -> salt + water
• What is the general equation for the reaction between metal carbonate and acid?

  Metal carbonate + acid -> salt + water + carbon dioxide
• What is the general equation for the reaction between metal oxides and acids?

  Metal oxide + acid -> salt + water
• Explain in terms of gain or loss of electrons which species has been oxides and which has been reduced when magnesium recast with hydrochloric acid:

  Magnesium has lost electrons and thus has been oxidised

  The hydrogen in HCl has gained electrons and thus has been reduced
• How is a soluble salt formed?

  React the excess acid with some insoluble chemical

  Filter off the leftovers

  Crystallise the product
• What do acids and alkalis produce in aqueous solutions?

  Acids produce hydrogen ions

  Alkalis produce hydroxide ions
• State the general equation for s neutralisation reaction in a short ionic form:

  H+ + OH- -> H2O
• What is a strong and weak acid?

  A strong acid is completely ionised in an aqueous solution

  A weak acid is only partially ionised
• What happens to pH has concentration of H+ increases?

  The pH decreases
• What is a concentrated and dilute acid?

  Concentrated acid has more molecules of acid per unit volume

  Concentration is not the same as strong and weak acids

  -> Strength refers to whether the acid is completely ionised
• As the pH is decreased by one unit, what change is seen in the hydrogen ion concentration?

  Increases by a factor of 10
• Name the following salts: LiNO3, K2CO3, MgBr2, BaSO4

  Lithium nitrate

  Potassium carbonate

  Magnesium bromide

  Barium sulfate
• What is electrolysis?


  The passing of an electric current through ionic substances that are molten or in solution to break them down into elements; ions are discharged at the electrodes
• What is an electrolyte?


  The liquid which conducts electricity
• What is a cathode and what is an anode?

  Cathode is the negative electrode

  Anode is the positive electrode
• What occurs at the cathode and anode during electrolysis?

  Reduction occurs at the cathode

  Oxidation occurs at the anode
• In aqueous electrolysis, what element in discharged at the cathode? What is produced at the anode?

  > The less reactive element discharges at the cathode

  > Hydrogen is produced unless there is a less reactive metal in which case the said metal in produced

  > Oxygen is produced at the anode unless the solution contains haloed ions in which case halogen molecules are produced
• How is aluminium manufactured? 


  Made through the electrolysis of aluminium oxide and cryolite

  Lots of energy is needed to produce the current in electrolysis which makes this process expensive
• What are the half equations in electrolysis of the aqueous Na2SO4?

  2H+ + 2e- -> H2 (cathode)

  4OH- -> 2H2O + O2 + 4e-