Chemical changes

• Reactivity of metals

  How chemically reactive a metal is
• Metals

  • Some react very vigorously with water (high reactivity)
  • Some barely react with water or acid (low reactivity)
• Reactivity series

  Places metals in order of their reactivity
• The reactivity series sometimes includes hydrogen and carbon, even though they are non-metals
• Displacement reactions

  A more reactive element takes the place of a less reactive element in a compound
• Ionic equation

  Represents a chemical reaction by showing the ions involved, with spectator ions removed
• Half equation

  Shows half of an ionic equation, representing the loss or gain of electrons
• Oxidation

  The loss of electrons
• Reduction

  The gain of electrons
• Spectator ion

  An ion that is unchanged in a reaction
• Acid

  A compound that, when dissolved in water, releases H+ ions
• Alkali

  A compound that, when dissolved in water, releases OH- ions
• pH scale

  Measures acidity and alkalinity, from 1 (acidic) to 14 (alkaline), with 7 being neutral
• Indicator

  A substance that can show if something is an acid or an alkali
• Logarithmic scale

  An increase of 1 on the pH scale equals a 10x decrease in the number of H+ ions
• Strong acid

  Completely ionises in water (e.g. sulfuric, nitric, hydrochloric)
• Weak acid

  Partially ionises in water (e.g. ethanoic, citric, carbonic)
• Concentrated acid

  Has lots of acid in a small volume of water
• Dilute acid

  Has little acid in a large volume of water
• Salt

  A compound where the hydrogen from an acid has been replaced by a metal
• Neutralisation reactions

  Reactions of acids with metals or metal compounds to form salts
• Acids react with some metals to form salts and hydrogen gas
• Acids react with metal hydroxides to form salts and water
• Types of ions

  • Lots of acid ions
  • They are partially ionised
• Salts

  Compounds where the hydrogen from an acid has been replaced by a metal
• When acids react with metals or metal compounds, they form salts
• Neutralisation reactions


  Reactions where bases neutralise acids
• Reactions of acids with metals

  Acid + metal -> salt + hydrogen gas
• Reactions of acids with metal hydroxides

  Acid + metal hydroxide -> salt + water
• Reactions of acids with metal oxides

  Acid + metal oxide -> salt + water
• Reactions of acids with metal carbonates

  Acid + metal carbonate -> salt + water + carbon dioxide
• Crystallisation

  Producing a solid salt from an insoluble base
• Crystallisation method

  1. Choose acid and base

  2. Heat dilute acid

  3. Add base until no more reacts

  4. Filter out unreacted base

  5. Evaporate water to leave salt crystals
• Redox reaction

  The reaction of acids with metals, where the metal loses electrons and is oxidised, and the hydrogen gains an electron and is reduced
• Alkalis

  Alkaline solutions formed when some metal hydroxides dissolve in water
• Bases

  Metal oxides and hydroxides that do not dissolve in water
• In the process of electrolysis, an electric current is passed through an electrolyte, causing the ions to move to the electrodes where they form pure elements
• Anode

  Positive electrode where electrons are lost
• Cathode

  Negative electrode where electrons are gained
• Solid ionic compounds do not conduct electricity as the ions cannot move, so they must be molten or dissolved for electrolysis