Chemical Changes

• What is oxidation?

  When a substance gains oxygen
• What is reduction?

  When a substance loses oxygen
• What is the reactivity series? Use your mnemonic.

  Potassium - Please

  Sodium - Send

  Lithium - Lions

  Calcium - Cats

  Magnesium - Monkeys

  Aluminium - And

  Carbon - Cute

  Zinc - Zebras

  Iron - Into

  Hydrogen - Hot

  Copper - Countries

  Silver - Signed

  Gold - Gordon
• What happens in the reactivity series?

  Metals above H₂ react with acid to produce H₂.

  Metals below H₂ don't react with acids

  Not all metals above H₂ react with water - Mostly Group I and II, Aluminum being the borderline.
• What is a displacement reaction

  Where a more reactive metal takes the place of a less reactive metal from a compound
• How are unreactive metals found in the Earth

  In their natural state
• Describe how a metal less reactive than carbon can get displaced

  Reduction with carbon. Carbon displaces the less reactive metal in the metal oxide - and gets oxidised to form carbon oxides. Metal from the metal oxide gets reduced to pure metal.

  Metal Oxide + Carbon → Metal + Carbon Dioxide
• How are metals more reactive then carbon extracted?

  By electrolysis.
• Why do we carry out electrolysis?

  It is more economical to carry out electrolysis over displacement.
• How are oxidation and reduction defined in terms of electron transfer?

  Oxidation - Loss of electrons

  Reduction - Gains electrons

  OIL RIG

  O - Oxidation R - Reduction

  I - Is I - Is

  L - Loss G - Gain
• What is the reaction between metals and acids?

  Metal + Acid → Salt + Hydrogen

  Redox Reaction, also a displacement reaction
• What is a redox reaction?

  A redox reaction is a reaction in which both oxidation and reduction occur.
• Which metals in the reactivity series react with acid?

  Those above hydrogen
• What is the general equation for a neutralisation reaction?

  Base + Acid → Salt + Water
• What is the general equation for the reaction between a metal carbonate and an acid?

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

  Metal Oxide + Acid → a salt + water
• Explain in terms of gain or loss of electrons which species has been oxidised and which has been reduced when magnesium reacts with hydrochloric acid.

  Magnesium has lost electrons and thus has been oxidised (Mg to Mg2+)

  The hydrogen in HCl has gained electrons and thus is reduced (H to H₂)
• What do Acids and Alkalis produce in aqueous solutions?

  Acids produce Hydrogen Ions (H+) and Alkalis produce Hydroxide Ions (OH−)
• What are bases, acids, and alkalis?

  Base - Compounds that neutralise acids

  Acid - Produces Hydrogen Ions in aqueous solutions

  Alkali - Produces Hydroxide Ions in aqueous solutions
• What is the pH scale?

  The measure of how alkaline or acidic a substance is
• What does a pH of 7 show?

  Neutral
• What is pH 1-6

  Acid
• What is pH 8-14

  Alkaline
• State the general equation for neutralisation

  $H^+$$+$$OH^- → H₂O$
• What is the difference between a strong and a weak acid?

  A strong acid has fully ionised in an aqueous solution whereas a weak acid has only partially ionised in an aqueous solution
• What happens to the pH as the concentration of hydrogen ions increases?

  The pH decreases
• What is a concentrated acid and what is a dilute acid? Is it the same as a strong and weak acid?

  • Concentrated acids have more moles of acid per unit than dilute
  • It is not the same - concentration is not the same thing as strength
  • Strength refers to when something has fully ionised (strong) or partially ionised (weak) in water
• As the pH is descreased by one unit, what change is seen in the hydrogen ion concentration?

  Increase factor by 10
• State the name of the following salts: LiNO₃, K₂CO₃, MgBr₂, BaSO₄

  Lithium Nitrate

  Potassium Carbonate

  Magnesium Bromide

  Barium Sulfate
• What is electrolysis?

  The passing of an electric current through ionic substances that are molten or in a solution to break them down into elements; ions are discharged (they lose/gain electrons) at electrodes to produce these
• What is an electrolyte

  A liquid which carries electrical charge
• What is a cathode and what is an anode

  A cathode is the negative electrode, and the anode is the positive electrode
• What occurs at the cathode and what occurs at the anode in electrolysis

  Reduction occurs at the cathode

  Oxidation at the anode

  
• In aqueous electrolysis, which element is discharged at the cathode? Oxygen is produced at the anode unless what?


  The less reactive element is discharged at the cathode. Hydrogen is produced unless there is a reactive metal, in which case the said metal is produced. Oxygen is produced at the anode unless the solution contains group 7 ions, called halide ions, then halogen molecules are produced.
• How is aluminium extracted? why is it expensive?

  Aluminium is extracted through the electrolysis of aluminium oxide and cryolite.

  Lots of energy needed to produce the current in electrolysis which makes this process expensive.
• What are the half equations in the extraction of Aluminium?

  Al^3+ 3e- (e- is an electron) → Al (cathode) this is oxidation

  2O^2- → O₂ + 4e- this is reduction
• Why is Cryolite used in the manufacturing of aluminium?

  It lowers the melting point of aluminium oxide, reducing energy costs.