C5 - Chemical Changes

• What is Oxidation?

  Substance gains oxygen

  Substance loses electrons
• What is Reduction?

  Substance loses oxygen

  Substance gains electrons
• What are the trends in reactivities of metals in reactions with acid/water

  • Metals above H² in the reactivity series react with acids to produce H². The more reactive the metal is, the quicker and more violent the reaction with the acid occurs
  • Not all Metals above H² react with water - Mostly Group 1 and II Metals. Aluminum is the bordeline case.
  • Metals below H² don't react with acids

  
• What is a displacement reaction?

  a reaction where a more reactive metal displaces a less reactive metal from a compound
• How can metals less reactive than carbon be extracted?

  Reduction with carbon. Carbon displaces the metal in a metal oxide - gets oxidised to carbon dioxides.

  Metal fom the metal oxide gets reduced to the pure metal.
• General Equation for reaction between metals and acids

  metal + acid -> salt + hydrogen

  • Redox and Displacement Reaction
• Which mets in the reactivity series will react with acid?

  Those above hydrogen
• General Equation for a neutralisation reaction

  Base + Acid -> Salt + Water
• General equation for the reaction between metal carbonate and acid

  Metal Carbonate + Acid -> Salt + Water + Carbon Dioxide
• General equation between metal oxides and acids

  Metal Oxide + Acid -> Salt + Water
• What is a Redox Reaction

  Reaction where both oxidation and reduction occurs
• How is a soluble salt formed?

  1. React with the excess acid with some insoluble chemical (e.g metal oxide)
  2. Filter off leftovers
  3. Crystalise the product
• What ions do acids and alkalis producd in aqueous solutions?

  Acids

  • Hydrogen Ions H+

  Alkalis

  • Hydroxide Ions OH-
• What is a strong acid?

  An acid that is completely ionised in aqueous solution
• What is a weak acid?

  An acid that is only partially ionised in aqueous solution
• What happens to pH as concentration of H+ increases?

  pH decreases
• What is a concentrated acid?

  More moles of acid per unit volume than dilute

  • Not the same as strength of an acid
• As the pH is decreased by one unit, what change is seen in the hydrogen ion concentration?

  Increases by a factor of 10
• Name the following salts:

  LiNO³ - Lithium nitrate

  K²CO³ - Potassium Carbonate

  MgBr² - Magnesium Bromide

  BaSO⁴ - Barium Sulfate
• What is an Ionic equation?

  gives some substances as ions and has spectator ions removed
• What is a spectator ion?

  ion fhat is unchanged in a reaction
• What is a half equation?

  Equation that shows whether a substance is losing or gaining electrons
• What is a neutralisation reaction?

  a reaction between an acid and base to produce water