CHEMICAL CHANGES

• Metals react with oxygen to produce metal oxides. The reactions are oxidation reactions because the metals gain oxygen
• Metals that can be arranged in order of reactivity in a reactivity series

  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Zinc
  • Iron
  • Copper

  
• Reactivity of a metal

  Related to its tendency to form positive ions
• Deducing an order of reactivity of metals


  Based on experimental results
• Unreactive metals such as gold are found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal
• Metals less reactive than carbon can be extracted from their oxides by reduction with carbon
• Reduction


  Involves the loss of oxygen
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Acids react with some metals to produce salts and hydrogen
• Acids are neutralised by alkalis (eg soluble metal hydroxides) and bases (eg insoluble metal hydroxides and metal oxides) to produce salts and water, and by metal carbonates to produce salts, water and carbon dioxide
• The particular salt produced in any reaction between an acid and a base or alkali depends on:
• Making pure, dry samples of soluble salts


  From information provided
• In neutralisation reactions between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water
• Carrying out titrations using strong acids and strong alkalis


  To find the reacting volumes accurately
• Strong acid


  Completely ionised in aqueous solution
• As the pH decreases by one unit, the hydrogen ion concentration of the solution increases by a factor of 10
• pH


  The lower the pH, the higher the hydrogen ion concentration of the solution
• Students should be able to

  Use and explain the terms dilute and concentrated (in terms of amount of substance), and weak and strong (in terms of the degree of ionisation) in relation to acids
• AT 8


  • An opportunity to measure the pH of different acids at different concentrations
• Students should be able to


  Describe neutrality and relative acidity in terms of the effect on hydrogen ion concentration and the numerical value of pH (whole numbers only)
• Passing an electric current through electrolytes causes

  Positively charged ions move to the negative electrode (the cathode), and negatively charged ions move to the positive electrode (the anode). Ions are discharged at the electrodes producing elements. This process is called electrolysis
• (HT only) Throughout Section 4.4.3 Higher Tier students should be able to write half equations for the reactions occurring at the electrodes during electrolysis, and may be required to complete and balance supplied half equations
• When a simple ionic compound (eg lead bromide) is electrolysed in the molten state using inert electrodes


  The metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode
• Students should be able to

  Predict the products of the electrolysis of binary ionic compounds in the molten state
• Metals can be extracted from molten compounds using electrolysis. Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon. Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current
• Students should be able to

  1. Explain why a mixture is used as the electrolyte

  2. Explain why the positive electrode must be continually replaced
• The ions discharged when an aqueous solution is electrolysed using inert electrodes depend on the relative reactivity of the elements involved
• Students should be able to

  Predict the products of the electrolysis of aqueous solutions containing a single ionic compound
• WS 1.2


  • Required practical 3: investigate what happens when aqueous solutions are electrolysed using inert electrodes. This should be an investigation involving developing a hypothesis. AT skills covered by this practical activity: 3, 7 and 8. This practical activity also provides opportunities to develop WS and MS.
• Reactions at electrodes can be represented by half equations


  • 2H+ + 2e- → H2
  • 4OH- → O2 + 2H2O + 4e-
  • 4OH- – 4e- → O2 + 2H2O
• Students should be able to

  1. Evaluate the use of hydrogen fuel cells in comparison with rechargeable cells and batteries

  2. (HT only) Write the half equations for the electrode reactions in the hydrogen fuel cell
• all hydroxides are ______ (acid/alkali)

  alkali
• metal + oxygen →

  metal oxide
• metal + water →

  metal hydroxide + hydrogen
• metal + acid →

  salt + hydrogen
• metal oxide + acid →

  salt + water
• metal hydroxide + acid →

  salt + water
• metal carbonate + acid →

  salt + water + carbon dioxide
• in a displacement reaction a _____ reactive metal will displace a _____ reactive metal

  more, less