1.4 Chemical changes

• What is oxidation?

  Oxidation is when a substance gains oxygen.
• What is reduction?

  Reduction is when a substance loses oxygen.
• What does the reactivity series of metals indicate?

  The reactivity series shows metals in order of their reactivity.
• What happens to metals above hydrogen in the reactivity series when they react with acids?

  They react with acids to produce hydrogen gas.
• How does the reactivity of metals affect their reaction with acids?

  The more reactive the metal, the quicker and more violent the reaction with acid occurs.
• Do metals below hydrogen react with acids?

  No, metals below hydrogen do not react with acids.
• Which metals typically react with water?

  Mostly Group I and II metals react with water.
• How are unreactive metals found in Earth?

  Unreactive metals are found in their natural state.
• How can metals less reactive than carbon be extracted?

  They can be extracted by reduction with carbon.
• What happens during the reduction of a metal oxide with carbon?

  Carbon displaces the metal in a metal oxide and gets oxidised to carbon oxides.
• How are metals more reactive than carbon extracted?

  They are extracted by electrolysis.
• How are oxidation and reduction defined in terms of electron transfer?

  Oxidation is the loss of electrons, and reduction is the gain of electrons.
• What is the general equation for a reaction between metals and acids?

  Metal + acid → salt + hydrogen.
• What type of reaction occurs when metals react with acids?

  It is a redox reaction and also a displacement reaction.
• Which metals in the reactivity series will react with acid?

  Those above hydrogen will react with acid.
• What is the general equation for a neutralisation reaction?

  Base + acid → salt + water.
• What is the general equation for the reaction between metal carbonate and acid?

  Metal carbonate + acid → salt + water + carbon dioxide.
• What is the general equation for the reaction between metal oxides and acids?

  Metal oxide + acid → a salt + water.
• What is a redox reaction?

  A redox reaction is a reaction where both oxidation and reduction occur.
• In the reaction between magnesium and hydrochloric acid, which species is oxidised and which is reduced?

  Magnesium is oxidised (loses electrons), and hydrogen is reduced (gains electrons).
• How is a soluble salt formed?

  • React the excess acid with some insoluble chemical (e.g., metal oxide)
  • Filter off the leftovers
  • Crystallise the product
• What do acids produce in aqueous solutions?

  Acids produce hydrogen ions.
• What do alkalis produce in aqueous solutions?

  Alkalis produce hydroxide ions.
• What are bases, acids, and alkalis?

  • Bases neutralise acids
  • Acids produce hydrogen ions in aqueous solutions
  • Alkalis are soluble bases that produce hydroxide ions in aqueous solutions
• What is the pH scale and what does a pH of 7 indicate?

  The pH scale measures acidity/alkalinity; a pH of 7 indicates a neutral solution.
• What is the short ionic form of the general equation for a neutralisation reaction?

  H+ + OH− → H2O.
• What is a strong acid?

  A strong acid is completely ionised in aqueous solution.
• What is a weak acid?

  A weak acid is only partially ionised in aqueous solution.
• What happens to pH as the concentration of H+ increases?

  The pH decreases.
• What is the difference between concentrated and diluted acids?

  • Concentrated acid has more moles of acid per unit volume than dilute acid.
  • Dilute refers to solutions of low concentrations.
  • Concentration is not the same as strength; strength refers to ionisation in water.
• What happens to hydrogen ion concentration as the pH decreases by one unit?

  It increases by a factor of 10.
• Name the following salts: LiNO3, K2CO3, MgBr2, BaSO4.

  • Lithium nitrate
  • Potassium carbonate
  • Magnesium bromide
  • Barium sulfate
• What is electrolysis?

  Electrolysis is the passing of an electric current through ionic substances to break them down into elements.
• What is an electrolyte?

  An electrolyte is the liquid or solution that conducts electricity.
• What is a cathode?

  The cathode is the negative electrode.
• What is an anode?

  The anode is the positive electrode.
• What occurs at the cathode during electrolysis?

  Reduction occurs at the cathode.
• What occurs at the anode during electrolysis?

  Oxidation occurs at the anode.
• In aqueous electrolysis, what is produced at the cathode?

  The less reactive element is discharged at the cathode.
• What is produced at the anode during aqueous electrolysis unless halide ions are present?

  Oxygen is produced at the anode unless halide ions are present.