c4 - chemical changes

• metals more reactive than carbon have to be extracted by electrolysis
• metals less reactive than carbon can be extracted from their oxides by reduction with carbon
• reduction involves loss of oxygen
• unreactive metals are found as themselves, e.g. gold
• metals react with oxygen to form metal oxides, often the oxides are the ores which the metals are extracted from
• oxidation reaction - gain of oxygen
• reduction is the gain of electrons
• oxidation is the loss of electrons
• Oxidation Is Loss, Reduction Is Gain
• metals are arranged in order of reactivity, hydrogen and carbon are included too
• a more reactive metal will displace a less reactive metal
• reactivity is the tendency to form positive ions
• relative reactions of metals with water produce a metal hydroxide and hydrogen gas
• relative reactions of metals with dilute acids produce a salt and hydrogen gas
• metal carbonates react with acids to produce salt, water and carbon dioxide
• acids form H+ ions in water
• react acids with insoluble bases to form soluble salts
• the pH scale is a measure of acidity/alkalinity of a solution
• As the pH decreases by one unit, the hydrogen ion concentration of the solution increases by a factor of 10
• Strength is different to concentration - concentration refers to amount of substance
• strong acids completely ionise in water
• hydrochloric, nitric and sulfuric acids are all strong acids
• ethanoic and citric acid are weak acids
• splitting up with electricity - electric current passes through the electrolyte, ions move towards the electrodes where they react
• electrolyte - molten or aqueous ionic compound
• electrolytes conduct electricity
• electrodes - solids placed in the electrolyte
• anode - negative ions move towards the anode
• half equations show reduction reactions at the cathode, oxidation reactions at the anode
• molten compounds - non-metal produced at the anode, the metal is produced at the cathode
• at the anode, oxygen is produced unless the solution contains halide ions - then the halogen is produced
• In the electrolysis of aqueous solutions, what is the rule for determining which ion will be oxidised (lose electrons) at the anode (positive electrode)?

  
  

  It will always be the OH-, unless there is a halide ion (such as Cl-, or Br-) present