Chemical changes

• Salt


  A compound where the hydrogen from an acid has been replaced by a metal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


  • hydrochloric acid
  • sulfuric acid
  • nitric acid
• Ions formed in acid solutions


  • H+ and Cl-
  • 2H+ and SO4^2-
  • H+ and NO3-
• Types of salts formed


  • metal chloride
  • metal sulfate
  • metal nitrate
• Sodium salts


  • sodium chloride, NaCl
  • sodium sulfate, Na2SO4
  • sodium nitrate, NaNO3
• Reactions of metals with water and acids depend on the reactivity of the metal
• Reactivity


  How chemically reactive a metal is
• Extraction methods


  • electrolysis
  • reduction with carbon
• Oxidation


  The loss of electrons
• Reduction


  The gain of electrons
• Half equation


  An equation showing half of an ionic equation, either the oxidation or reduction half
• A metal's reactivity depends on how readily it forms an ion by losing electrons
• Displacement reaction


  A more reactive element takes the place of a less reactive element in a compound
• Displacement reaction


  • copper sulfate + iron ➞ iron sulfate + copper
• Acid


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


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


  A measure of acidity and alkalinity, running from 1 to 14
• Indicator


  A substance that can show if something is an acid or an alkali
• Acids react with some metals to form salts and hydrogen gas
• Neutralisation reactions


  1. Acids react with metal hydroxides to form salts and water

  2. Acids react with metal oxides to form salts and water

  3. Acids react with metal carbonates to form salts, water, and carbon dioxide
• Strong acid


  An acid that is completely ionised in water
• Weak acid


  An acid that is only partially ionised in water
• Concentrated acid


  An acid with lots of acid dissolved in a small volume of water
• Dilute acid


  An acid with little acid dissolved in a large volume of water
• Strong acids


  Acids that, when dissolved in water, every molecule splits up into ions - they are completely ionised
• Strong acids


  • H2SO4(aq) ➞ 2H+(aq) + SO4^2−(aq)
  • HNO3(aq) ➞ H+(aq) + NO3^−(aq)
  • HCl(aq) ➞ H+(aq) + Cl^−(aq)
• Weak acids


  Acids where only a percentage of their molecules split up into ions when dissolved in water - they are partially ionised
• For a given concentration


  The stronger the acid, the lower the pH
• Concentration


  How much of a substance is dissolved in water
• Concentration


  • More concentrated acids have lots of acid in a small volume of water
  • Less concentrated (dilute) acids have little acid in a large volume of water
• There are lots of acid ions, they are completely ionised
• There are a few acid ions, they are partially ionised
• There are lots of acid ions, they are partially ionised
• Producing a solid salt from an insoluble base by crystallisation


  1. Choose the correct acid and base

  2. Put dilute acid in flask, heat gently

  3. Add small amount of base and stir

  4. Keep adding base until no more reacts, base is in excess

  5. Filter to remove unreacted base

  6. Add remaining solution to evaporating dish

  7. Evaporate water, salt crystals left behind
• Acid


  A solution with a pH less than 7
• Neutral solution


  A solution with a pH of 7
• Acid (in terms of H+ ions)


  A substance that releases H+ ions when dissolved in water
• Amount of H+ ions in a solution


  The more H+ ions, the lower the pH
• Measuring pH


  Universal indicator or pH probe
• Strong acid


  An acid where the molecules or ions completely ionise in water