Chemical Changes

• Displacement reaction


  A more reactive metal (one that forms positive ions more easily) can displace a less reactive metal from a compound
• Displacement reactions


  • A metal can only displace another metal from a compound if it is located above it in the reactivity series
• Spectator ions


  Ions that do not change in the reaction
• The reactivity series is used to predict which metal will displace another from its compound
• Acids and alkalis are on the opposite ends of the pH scale. They combine to form water, which is neutral
• Acids


  Substances that form hydrogen (H+) ions when they dissolve in water (aqueous solutions)
• Alkalis


  Substances that form hydroxide (OH-) ions when they dissolve in water (aqueous solutions)
• Alkali


  A type of base
• The acidity and alkalinity of a substance is measured using the pH scale
• Oxidation


  An oxidation reaction involves gaining oxygen. It can also involve losing electrons
• Oxidation


  • When metals react with oxygen, metal oxides are produced: Magnesium + oxygen
• Reduction


  A reduction reaction involves losing oxygen. It can also involve gaining electrons
• Reduction


  • When metal oxides lose oxygen and return to their atomic form: Iron oxide + carbon monoxide
• Oxidation


  Gaining of oxygen in a reaction
• Reduction


  Loss of oxygen in a reaction
• Oxidation


  When a substance is oxidised (gains oxygen), it always loses electrons
• Reduction


  When a substance is reduced (loses oxygen), it always gains electrons
• A useful mnemonic for remembering the difference between oxidation and reduction reactions in terms of electrons is OIL RIG: Oxidation Is Loss, Reduction Is Gain
• Reactions of Reactive Metals with Water

  1. Potassium, sodium, and lithium react quickly with cold water to produce a metal hydroxide and hydrogen gas

  2. Potassium is the most reactive and reacts very quickly, producing hydrogen that ignites instantly and the metal sets alight with a lilac flame

  3. Sodium fizzes rapidly, melts to form a ball that moves around on the water surface

  4. Lithium fizzes steadily, floats, becomes smaller until it eventually disappears
• Reactions of Metals with Dilute Acids

  1. Most metals react with dilute acids to produce a salt and hydrogen gas

  2. Metals that react with dilute acids include magnesium, aluminium, zinc, iron, and lead (iron and lead react slowly)

  3. Metals that don't react with dilute acids are copper, silver, gold, and platinum
• Extraction of Metals


  1. Most metals are found as compounds and need to be extracted from the ore where the metal compound is found

  2. Metals less reactive than carbon can be extracted from their oxides by reducing with carbon

  3. Carbon is used because it is cheap and abundant

  4. In the reduction process, the metal oxide loses oxygen to form a pure metal, often involving heating the metal oxide in the presence of carbon, usually in the form of coal
• In displacement reactions, metals higher up the reactivity series displace those lower down.
• Reactions of Metals with Acids

  When acids react with metals, a hydrogen and a salt are always formed
• Salt name


  The first part of the salt's name comes from the metal involved, the second part of the name comes from the acid
• Redox reactions


  A reduction reaction (one reactant gains electrons) and an oxidation reaction (one reactant loses electrons)
• Spectator ions


  Ions that are unchanged in a reaction and aren't included in the ionic equation
• Neutralisation of Acids


  Acids are neutralised by bases (substances with a pH greater than 7)
• Bases


  • Metal carbonates, metal oxides, metal hydroxides
• Soluble salts


  Salts which dissolve in water
• Making soluble salts


  Reacting acids with solid, insoluble substances such as pure metals, metal oxides, metal hydroxides, or metal carbonates
• Blue copper sulfate


  • Produced by adding black copper oxide to sulfuric acid
• Blue copper sulfate crystals


  • Produced by adding black copper oxide to sulfuric acid
• Reacting acids with solid, insoluble substances

  Produces soluble salts
• Preparation


  Gently warm an acid using a Bunsen burner<br>2. Add the insoluble solid (with stirring) until the reaction stops happening
• Filtration


  Filter the solution to remove the excess insoluble solid<br>This will leave a solution of the salt dissolved in water
• Crystallisation


  Heat the solution in an evaporating basin above a beaker of water<br>The 'water bath' ensures gentle heating<br>2. Leave the solution to cool and allow more water to evaporate<br>As water evaporates, the solution will become more concentrated and the salt will begin to crystallise
• pH Scale


  A scale used to measure the acidity or alkalinity of a substance
• Measuring pH


  1. Two main ways: Universal indicator

  2. pH probe
• Universal indicator


  An indicator that changes to a particular colour depending on the pH
• pH probe


  An instrument that returns a numerical value for the pH of a substance