C4-Chemical Changes

• what is a base?

  substance with a PH greater than 7
• what is the neutralisation equation?

  acid + base = salt + water
• what happens to strong acids in water?

  ionise completely

  particles dissociate to release H+ ions
• what happens to weak acids in water?

  do not fully ionise

  small amount of particles dissociate and release H+ ions
• what is the Ph of an acid and alkali?

  measure of the concentration of H+ ions
• for every decrease in PH the concentration of H+ ions increases by a factor of 10
• acid + metal oxide = salt + water
• acid + metal hydroxide = salt + water
• acid + metal carbonate = salt + water + carbon dioxide
• what happens to elements higher in the reactivity series?

  easier to lose electrons forming positive ions
• what is the recativity series?

  Potassium

  Sodium

  Lithium

  Calcium

  Magnesium

  Carbon

  Zinc

  Iron

  Hydrogen

  Copper
• acid + metal = salt + hydrogen
• metal + water = metal hydroxide + hydrogen
• oxidation

  gain of oxygen
• reduction

  loss of oxygen
• how are metals higher than carbon extracted?

  electrolysis
• what how are metals below carbon extracted?

  reduction by carbon
• what happens to electrons in oxidation?

  lost
• what happens to electrons in reduction?

  gained
• what is displacement?

  more reactive metal will kick out a less reactive metal from the compound
• what happens at the cathode?

  positive ions gain electrons
• what happens at the anode?

  negative ions lose electrons
• what compounds can be electrolysed?

  molten ionic compounds because the ions can move freely and conduct electricity
• what are molten ionic liquids broken into?

  their elements
• what happens at the negative electrode?

  reduction = gain of electrons

  metals form positive ions so are attracted to negative electrode

  metal is produced
• what happens at the positive electrode?

  oxidation = loss of electrons

  non metals form negative ions so are attracted to the positive electrode

  gas is produced
• what ions are produced during electrolysis of aqueous solutions?

  hydrogen and hydroxide ions from the water
• what ions are present at the cathode?

  H+ ions

  metal ions
• what happens at the cathode if the metal is more reactive than hydrogen?

  hydrogen gas is produced
• what happens at the cathode if a metal is formed that is less reactive than hydrogen?

  solid layer of the pure metal is produced
• what happens at the anode if OH- and halide ions are present?

  molecules of chlorine, bromine or iodine are formed
• what happens at the anode is no halide ions are present?

  OH- ions are discharged and oxygen is formed
• what is the half equation at the negative electrode?

  2H+ + 2e- = H2
• what is the half equation at the positive electrode?

  2CL- = CL2 +2e-