Acids/alkalis

• Oxidation reaction


  When a substance reacts and combines with oxygen
• Oxidation reactions


  • Combustion
  • Rusting
• Metal oxide


  Product when a metal reacts with oxygen
• Reactivity of metals with oxygen


  • Most reactive metals react violently when heated in oxygen, burning with a bright flame
  • Less reactive metals react more slowly when heated in oxygen
• Metals reacting with oxygen

  • zinc + oxygen
  • magnesium + oxygen
• Reaction of metals with water or steam


  • Metal + Water/Steam → Metal Hydroxide + Hydrogen
  • Metal Oxide + Hydrogen
• Reactivity of metals with water/steam

  • Most reactive metals react vigorously with cold water to produce hydroxides
  • Less reactive metals react with steam to make oxides
• Metals reacting with water/steam

  • sodium + water → sodium hydroxide + hydrogen
  • magnesium + steam → magnesium oxide + hydrogen
• Magnesium reacts very slowly with cold water but vigorously with steam
• Experiment to show magnesium reacting with steam

  1. Wet mineral wool placed in boiling tube

  2. Magnesium ribbon added

  3. Tube sealed with bung and glass tube

  4. Magnesium glows brightly as it reacts with steam

  5. Hydrogen produced shown by squeaky pop
• Rusting


  Formation of iron oxide
• Rusting is an example of an oxidation reaction
• Rusting of iron


  1. Iron + oxygen + water → iron oxide (rust)

  2. Rust forms on surface of iron

  3. Rust is a soft crumbly solid that flakes off, exposing more iron to rust
• Both air and water are needed for iron to rust
• Experiments to show air and water needed for rusting

  1. Iron nail in boiled water with oil - no rusting

  2. Iron nail in air with calcium chloride - no rusting

  3. Iron nail in air and water - rusting
• Ways to prevent rusting

  • Coating iron with barrier to keep out water and oxygen (paint, plastic, different metal)
  • Sacrificial method - placing more reactive metal with iron
• pH scale


  Describes how acidic or alkaline a substance is, from 0 (strongest acid) to 14 (strongest alkali), with 7 being neutral
• Acid


  Substance with pH below 7
• Alkali


  Substance with pH above 7
• Indicator


  Substance that changes colour depending on whether it's in an acid or alkali
• Indicators


  • Litmus paper
  • Universal indicator solution
• Using universal indicator


  1. Put drops on dimple tile

  2. Add universal indicator

  3. Match colour to pH chart
• pH meter


  More accurate than indicators for measuring pH
• Neutralisation reaction


  Reaction between an acid and a base to form a salt and water
• Making salts by neutralisation

  1. Add base to acid in small amounts

  2. Test pH after each addition until neutral

  3. Evaporate solution to form salt crystals
• Salt


  Product of neutralisation reaction, depends on the acid used
• Reaction of metals with dilute acid

  Metal + Acid → Salt + Hydrogen
• To Change the Salt, You Must Change the Acid

  1. The salt you get out of a neutralisation reaction depends on the acid you use

  2. The clue is normally in the name: Hydrochloric acid reacts to make chloride salts, Sulfuric acid reacts to make sulfate salts, Nitric acid reacts to make nitrate salts
• Reactions of Metals with Acids

  1. Most metals will react with acids to make a salt and hydrogen

  2. The speed of reaction is indicated by the rate at which the bubbles of hydrogen are given off

  3. The more reactive the metal, the faster the reaction will go
• Reacting Metals With Dilute Acid

  • Magnesium and hydrochloric acid
  • Zinc and sulfuric acid
• Magnesium


  • Reacts quickly with dilute acids and produces loads of bubbles
• Zinc


  • Reacts more slowly with dilute acids and does not produce many bubbles
• The Test for Hydrogen


  Hydrogen makes a "squeaky pop" with a lit spline
• Reactions of Oxides with Acids


  1. Metal oxides are alkaline and react with acids to make a salt and water

  2. Non-metal oxides are acidic and react with alkalis to make a salt and water
• Copper oxide and sulfuric acid

  • Copper oxide + sulfuric acid → copper sulfate + water
• Metal oxides are alkaline, non-metal oxides are acidic
• Limestone is mainly calcium carbonate (CaCO3) and is quarried out of the ground
• Limestone


  • It has lots of different uses in construction
  • It is great for making into blocks for building with
  • Fine old buildings like cathedrals are often made purely from limestone blocks
  • It is used in the manufacture of cement, mortar, concrete and glass, as well as in the extraction of iron from iron ore
  • It is also heated to produce quicklime (calcium oxide), which can be used as a building material
• Limestone reacts with acids


  Limestone reacts with dilute hydrochloric acid to make a salt, water and carbon dioxide
• Acid rain can damage limestone buildings