C4 chemical changes

• What is the reactivity series?

  A list of elements ordered by their reactivity
• How can metals be placed in order of their reactivity?

  Add the metals to water or acid and see which ones react the most (by how much fizzing there is)
• What is the name for a reaction where oxygen is removed from a compound?

  Reduction
• Explain why zinc can be extracted from zinc oxide with carbon but magnesium cannot be extracted from magnesium oxide with carbon

  Magnesium is more reactive than carbon (1), Zinc is less reactive than carbon (1), Carbon can therefore remove oxygen from zinc oxide but not magnesium oxide (1)
• Explain why gold and silver can be found naturally in the Earth's crust

  It is very unreactive
• What process is used to extract metals more reactive than carbon

  Electrolysis
• Define an ore


  A material containing enough metal in it for it to be economically worthwhile to extract the metal.
• Define a displacement reaction

  A reaction in which a more reactive element takes the place of a less reactive element in one of its compounds or in solution
• Define oxidation in the context of loss and gain of electrons

  Oxidation is the loss of electrons
• Define reduction in the context of loss and gain of electrons

  Reduction is the gain of electrons
• Which of the substances below has been oxidized and which has been reduced? Al³⁺ + Fe → Fe³⁺ + Al

  Aluminium has been reduced and iron has been oxidised
• Show two half equations for the reaction below: Al³⁺ + Fe → Fe³⁺ + Al


  Al³⁺ + 3e⁻ → Al, Fe → Fe³⁺ + 3e-
• Define acid in terms of pH

  A substance with a pH of less than 7
• Define acids in terms of ions

  A substance which releases H⁺ ions in solution
• What does (aq) stand for?

  Aqueous: when something is dissolved in water. E.g. NaCl(aq) is salt water
• State the three common acids and give their formulae

  Hydrochloric acid, HCl(aq), Sulphuric acid, H₂SO₄(aq), Nitric acid, HNO₃
• Which ions do the common acids form in solution?

  HCl forms H⁺ and Cl⁻, H₂SO₄ forms 2H⁺ and SO₄²⁻, HNO₃ forms H⁺ and NO₃⁻
• What is a neutral solution?

  A solution with a pH of 7. Water is an example.
• How do you measure pH?


  With an indicator or pH probe.
• What is a base?

  A metal oxide, hydroxide or carbonate that will react with an acid. E.g. copper oxide
• What is an alkali?


  A soluble base. E.g. sodium hydroxide
• Which ions are always present in a solution of an alkali?

  OH⁻
• What is a salt?


  A compound formed when some or all of the hydrogen from an acid is replaced by a metal. E.g. CuSO₄, copper sulphate, where copper has replaced H from H₂SO₄
• What type of salts are formed by the three main acids?

  Hydrochloric acid produces chlorides, sulphuric acid = sulphates, nitric acid = nitrates
• What is a neutralisation reaction?

  A reaction involving an acid that results in a neutral solution
• Which ions always react together in a neutralization reactions between acids and alkalis?

  H⁺ and OH⁻
• Write the equation showing the reaction between H⁺ and OH⁻ ions

  H⁺ + OH⁻ → H₂O
• metal + acid →

  → salt + hydrogen gas
• metal hydroxide + acid →

  → salt + water
• metal oxide + acid →


  → salt + water
• metal carbonate + acid →

  → salt + water + carbon dioxide
• How do you make a soluble salt from an acid?

  React the acid with a base. E.g. to make copper sulphate react copper oxide with sulphuric acid
• If a salt is in solution, how do you extract it as a solid?

  Allow the water to evaporate off and it will leave the salt behind as a solid.
• What is a strong acid?

  An acid which completely splits up into its ions in water. E.g. when HCl is in water all the HCl molecules split up into H⁺ and Cl⁻
• What is a weak acid?

  An acid which will have some molecules which do not split up into their ions. E.g. in ethanoic acid only some of the molecules will have split up into the ethanoate ion and H⁺ ions.
• What is the relationship between the strength of an acid and its pH?

  As an acid increases in strength the pH decreases.
• What is a concentrated acid?

  An acid where there are lots of acid particles in the water.
• What is a dilute acid?

  An acid where there are fewer acid particles in the water.
• How is pH measured?

  pH is related to the concentration of H⁺ in a solution.
• Which ions are in NaCl

  Na⁺ and Cl⁻