Chemical changes

• metal oxide is produced when a metal reacts with oxygen
• oxidation is a reaction which results in the loss of electrons and the gain of oxygen
• reduction is a reaction which result to a gain in electrons and a loss in oxygen
• metal atoms form positive ions
• reactivity series:

  • Potassium - most reactive, so most easily forms positive ions
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Aluminium
  • Carbon
  • Zinc
  • Iron
  • Lead
  • Hydrogen
  • Copper - least reactive, so difficulty forming positive ions
  • Silver
  • Gold
• the higher the reactivity of a metal, the easier it is to form positive ionsthe lower the reactivity of a metal, the harder it is to form positive ions
• gold is found in the Earth
• gold is an unreactive metal
• other metals are found as compounds that need chemical reactions in order to be extracted
• metals less reactive than carbon can be extracted from their oxides by reduction
• salt and hydrogen is produced when acid and metals react
• redox reactions are reactions in which both oxidation and reduction occur
• acids are neutralised by alkalis and bases to form water and salt
• the salt produced when acids and bases react depend on:

  • the type of acid used
  • the positive ions in the base or alkali
• soluble salts are made from acids by reacting them with insoluble substances
• salt solutions are crystalised to produce solid salts
• acids produce hydrogen ions in aqueous solutions
• Aqueous solutions of alkalis contain hydroxide ions
• the pH scale is a measure of how acidic or alkali a substance is
• pH can be measured using:

  • universal indicator
  • pH probe
• in a neutralisaion reaction between an acid and alkali:

  • hydrogen ions react with hydroxide ions to produce water
• when universal indicator is added to a solution, it changes to a colour to show its pH level
• a strong acid is an acid that is completely ionised in aqueous solution
• examples of strong acids:

  • hydrochloric acid
  • sulfuric acid
  • nitric acid
• weak acids are acids that are partially ionised in aqueous solution
• examples of weak acids:

  • ethanoic
  • carbonic
  • citric
• dilute means there is a small amount of solute in a solvent
• concentrated means that there is a large amount of solute in a solvent
• when an ionic compound is melted or dissolved:

  • the ions are free to move about within the solution
• electrolytes are substances that release ions in water and are able to conduct electricity
• passing an electric current through electrolytes cause the ions to move to the electrodes
• Positive

  Anode

  Negatice

  Is

  Cathode
• positively charged ions move towards the cathode
• when bromine is electrolysed:

  •  it is electrolysed in its molten state using inert electrodes
  • lead is produced at the cathode and bromine is produced at the anode
• metals can be extracted from molten compounds using electrolysis
• a molten compound is a compound that is formed by heating a solid
• electrolysis is used if the metal is too reactive to be extracted by reduction
• electrolysis is used if the metal reacts with carbon
• large amounts of energy is used during extraction to melt the compounds and to produce the electrical current
• a mixture is used as the electrolyte because ionic compounds conduct electricity when their ions are free to move