Topic 4 - chem changes

• metal oxides and metal hydroxides are bases
• all metal oxides and metal hydroxides react with acids to form a salt and a water
• metal carbonates react with an acid to form a salt, water and carbon dioxide
• some metal oxides and metal hydroxides will dissolve in water, these soluble compounds are alkalis

  alkalis react with acids in neutralisation reactions

  even bases that wont dissolve in water will still take part in neutralisation reactions with acids
• the reaction that seperates a metal from its oxide is called a reduction reaction
• lots of common metals react with oxygen to form oxides this process is called oxidation
• what is oxidation 


  the gain of oxygen
• what is reduction


  the loss of oxygen
• extracting metals with carbon 


  • some metals can be extraxted from their ores (oxides) chemically by reduction using carbon
  • in this reaction the ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidised
  • the position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon
• The reactivity series


  • potassium
  • sodium
  • lithium
  • calcium
  • magnesium
  • carbon
  • zinc
  • iron
  • copper
• the reactivity series and reduction


  • metals higher than carbon have to be extracted using electrolysis which is expensive
  • metals below carbon can be extracted using reduction by carbon
  • this is because carbon can only take the oxygen away from metals which are less reactive than itself
• acids produce protons in water :


  they ionise in aqueous solutions- they produce hydrogen ions H+
• strong acids ionise completely in water, all particles dissociate to release H+ ions
• weak acids do not fully ionise in solution, only a small proportion of acid particles dissociate to release H+ ions
• the ionisation of a weak acid is a reversible reaction which sets up an equilibrium between the undissociated and dissocated acid
• the pH of an acid or an alkali is a measure of the concentration of H+ ions in the solution
• for every decrease of 1 on the pH scale the concentration of H+ ions increases by a factor of 10
• the pH of a strong acid is always less than the pH of a weaker acid if they have the same concentration
• what is acid strength ?


  tells you what proportion of the acid molecules ionise in water
• what is acid concentration ?


  how much acid there is in a certain volume of water
• what is the pH scale ?


  a measure of how acidic or alkaline a solution is
• the lower the pH of a solution the more acidic it is

  the higher the pH of a solution the more alkaline it is
• a neutral substance has a pH of 7
• an acid is a substance that forms aqueous solutions with a pH of less than 7
• a base is a substance with a pH greater than 7
• acid + base --> salt and water
• when an acid neutralises a base the products are neutral, an indicator can be used to show that a neutralisation reaction is over
• metals reactivity is determined by how easily they lose electrons and form positive ions, so the higher the metal is on a reactivity series the more easily it reacts with water or acid
• the more reactive a metal the faster it will react with an acid, very reactive metals like potassium, sodium, lithium and calcium react explosivley but less reactive metals such as magnesium, zinc and iron react less violently. in general copper wont react with cold dilute acids
• metal + water --> metal hydroxide + hydrogen
• potassium, sodium, lithium and calcium will all react with water, less reactive metals like zinc, iron and copper wont react with water
• a loss of electrons is called oxidation and a gain of electrons is called reduction
• Redox reactions :


  • iron atoms are oxidised to Fe2+ ions when they react with a dilute acid : Fe + 2H+ --> Fe2+ + H2
  • the iron atoms lose elctrons, theyre oxidised by the hydrogen atoms Fe - 2e- --> Fe2+
  • the hygrogen atoms gain electrons, they are reduced by the iron atoms 2H+ + 2e- --> H2
• what is a displacement reaction 


  a more reactive metal displacing (kicking out) a less reactive metal from its compound
• in displacement reactions its always the metal ion that gains electrons and is reduced, the metal atom always gains electrons and is oxidised