Chapter 7: Acids and Alkali

• Acids


  Substances which produce H+ (aq) ions when added to water
• Hydrogen ions, H+ (aq)


  Make solutions acidic
• Hydroxide ions, OH- (aq)


  Make solutions alkaline
• pH scale


  Measure of the acidity or alkalinity of a solution
• Acids are substances which produce H+ (aq) ions when added to water
• Metal oxides and hydroxides are bases
• Soluble hydroxides are called alkalis
• Hydrogen ions, H+ (aq), make solutions acidic
• Hydroxide ions, OH- (aq), make solutions alkaline
• The pH scale is a measure of the acidity or alkalinity of a solution
• Salt


  A chemical compound formed by the reaction of an acid and a base
• The general equation for making salts from metals is: Acid + metal → salt + hydrogen
• The general equation for making salts from insoluble bases is: Acid + insoluble base → salt + water
• Salts

  • Magnesium chloride
  • Copper sulfate
• Making soluble salts from metals

  Acid + metal → salt + hydrogen
• Making soluble salts from insoluble bases


  Acid + insoluble base → salt + water
• Copper is less reactive than hydrogen
• Methods of making salts


  • Acid + metal
  • Acid + insoluble base
• Soluble salts can be made from acids by reacting them with metals (not all metals) and insoluble bases
• Making zinc chloride salt

  1. Zn + HCl → ZnCl2

  2. ZnO + HCl → ZnCl2
• Salt solutions can be crystallised to produce solid salts
• The particular salt produced depends on the acid used and the metal in the base or alkali (hydrochloric acid → chlorides, nitric acid → nitrates, sulfuric acid → sulfates)
• Cu2+ ions
• Residue and filtrate
• Video 7.2A, B, C, Textbook Page 92-93, Worksheet C5.4 Salts from metals
• Neutralisation reaction


  Acid reacts with base to form salt
• Making salts by neutralisation or precipitation

  1. Acid + metal → salt + hydrogen

  2. Acid + insoluble base → salt + water

  3. Acid + soluble base (alkali) → salt + water
• Neutralisation


  Reaction where hydrogen ions react with hydroxide ions to produce water
• Titration


  • Indicator can be used to show the neutralisation point
• Precipitation


  Mixing appropriate solutions of ions so that a precipitate is formed
• Precipitation


  • Can be used to remove unwanted ions from solutions, e.g. in treating water for drinking or in treating effluent (wastewater)
• Acids react with bases to form salts. These reactions are called neutralisation reactions
• In neutralisation reactions, hydrogen ions react with hydroxide ions to produce water
• In titration, an indicator can be used to show the neutralisation point
• Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed
• Precipitation can be used to remove unwanted ions from solutions: for example, in treating water for drinking or in treating effluent (wastewater)
• A precipitate is a solid that forms and settles out of a liquid solution
• Positive test for carbon dioxide gas

  1. Carbonates react with dilute acids to form carbon dioxide

  2. Carbon dioxide produces a white precipitate with limewater (calcium hydroxide), which turns limewater cloudy white (calcium carbonate)
• Ammonia is soluble in water and forms an alkaline solution
• Formation of ammonium hydroxide (ammonia solution)


  Ammonia (g) + water (l) ⇌ ammonium hydroxide (aq)