Topic 4: Chemical Changes

• What do acids produce in aqueous solutions?

  Hydrogen ions (H​+​)
• What is the pH range of acids?

  0-6
• What do alkalis produce in aqueous solutions?

  Hydroxide ions (OH​-​)
• What is the pH range of alkalis?

  8-14
• What is crystallisation used for?

  To produce solid crystals from a solution
• What is a displacement reaction?

  A more reactive element displaces a less reactive one
• What is electrolysis?

  Splitting up an ionic compound using electricity
• What happens during electrolysis?

  Chemical reactions occur at the electrodes
• What is an electrolyte?

  A solution containing free ions
• What is the purpose of extraction techniques?

  To separate a desired substance from others
• What is filtration used for?

  To separate solids from liquids
• What occurs at the negative electrode (cathode)?

  Hydrogen is produced if metal is more reactive
• What is neutralisation?

  Reaction of an acid and a base
• What is oxidation in a chemical reaction?

  Gain of oxygen or loss of electrons
• What is the pH scale range?

  0 to 14
• How can pH be measured?

  Using universal indicator or pH probe
• What is produced at the positive electrode (anode)?

  Oxygen unless halide ions are present
• What is a redox reaction?

  A reaction involving both oxidation and reduction
• What is reduction in a chemical reaction?

  Loss of oxygen or gain of electrons
• How can metals less reactive than carbon be extracted?

  By reduction with carbon
• What defines a strong acid?

  Completely ionised in aqueous solution
• Give examples of strong acids.

  Hydrochloric, nitric, and sulfuric acids
• What is the reactivity series?

  Order of metals by their reactivity
• What is the purpose of titration?

  To determine the concentration of an unknown solution
• What is a universal indicator?

  A mixture of dyes that changes color
• What defines a weak acid?

  Partially ionised in aqueous solution
• Give examples of weak acids.

  Ethanoic, citric, and carbonic acids
• What do metals react with to form metal oxides?

  Oxygen
• Why are these reactions called oxidation reactions?

  Because metals gain oxygen
• What does reduction involve in terms of oxygen?

  Loss of oxygen
• What does oxidation involve in terms of oxygen?

  Gain of oxygen
• What do metal atoms form when they react with other substances?

  Positive ions
• How is the reactivity of a metal related to its ions?

  It relates to forming positive ions
• What is the reactivity series?

  Order of metals by reactivity
• How does potassium react with water?

  Violently
• Which metals are included in the reactivity series?

  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Zinc
  • Iron
  • Copper
• How does sodium react with water?

  Very quick
• How does lithium react with water?

  Quick
• How does calcium react with water?

  More slow
• How does calcium react with dilute acid?

  Very quick