4) Acids and Redox

• What element do all acids contain in their chemical formulae?

  Hydrogen
• What ion do all acids release when dissolved in water?

  Hydrogen ion (H+)
• What happens to a strong acid when it dissolves in water/ solution?

  Strong acids completely dissociates and releases all hydrogen atoms as hydrogen ions.
• What happens to a weak acid when it dissolves in water/ solution?

  Weak acids only partially dissociates and releases a small number of hydrogen atoms as hydrogen ions.
• What is a salt?

  A chemical compound formed when hydrogen ions in an acid has been replaced by metal ions, or other positive ions such as ammonium ions.
• What is an alkali?

  • Any base that dissolves in water and releases hydroxide ions (OH-) into the solution.
• What is a base?

  A substance capable of accepting a proton in aqueous solution.
• What is an acid?

  A substance capable of donating a proton (H+ ion) in aqueous solution.

  Therefore increases the concentration of hydrogen ions in the solution.
• What types of salts are formed from HCl, H2SO4, HNO3?

  • Chloride salts
  • Sulfate salts
  • Nitrate salts
• What type of reaction takes places between when an acid and a base react?

  Neutralisation (the acid is neutralised)
• What is the ionic equation that occurs in a neutralisation reaction?

  H+(aq) + OH-(aq) ----> H2O(l)
• Acid + Metal Carbonate 


  Salt + Water + Carbon Dioxide
• Acid + Metal Hydroxide 


  Salt + Water
• Acid + Metal Oxide 


  Salt + Water
• What ions do all alkalis release when dissolved in water?

  Hydroxide ions (OH-)
• Acid + Metal


  Salt + Hydrogen
• Acid + Ammonia


  Ammonium Salt
• Strong Acid Examples:

  • HCL ---> H+ + Cl- (aq)
  • H2SO4 ---> 2H+ + SO4^2- (aq)
  • HNO3 ---> H+ + NO3- (aq)
  • H3PO4 ---> 3H+ + PO4^-3 (aq)
• Weak Acid Example: Ethanoic Acid 


  CH3COOH ⇌ CH3COO- + H+ (aq)
• Examples of Bases:

  • Sodium Hydroxide
  • Copper Oxide
  • Calcium Carbonate
  • Ammonia
• What are concordant results in a titration?

  Concordant results in a titration are titre volumes that are within 0.10 cm3 of each other
• What is the volume of solution added from the burette called?

  Titre (usually acid)
• What is the effect of filling the volumetric flask with distilled water above the graduation line?

  The standard solution will be too dilute, and must be prepared again.
• Preparation of a standard solution:

  1. Weigh the solid accurately
  2. Dissolve the solid in beaker with distilled water
  3. Transfer the solution to a volumetric flask
  4. Rinse the beaker several time with distilled water and transfer the washings to the volumetric flask.
  5. Fill the volumetric flask to the graduation line with distilled water.
  6. Slowly invert the flask several time to mix the solution thoroughly.
• What is a titration?

  A method used to determine the concentration of a solution of known volume.
• What are oxidation numbers?

  A measure of the number of electrons an atom uses to bond with atoms of another element.
• What is the oxidation number of uncombined element?

  0 (e.g. Na)
• What is the oxidation number of simple ions?

  The charge of the ion (e.g. Na+ ; oxidation number is +1)
• • In a compound, the same of the oxidation number is 0.
• • The sum of the oxidation number in a compound ion is equal to the charge of the ion (e.g. CO3^2- ; the sum of the oxidation number of the ion is -2)
• • Fluorine in a compound has an oxidation number of -1. (e.g. NaF)
  • Hydrogen in a compound has an oxidation number of +1 unless it is a metal hydride, where it is -1. (e.g. NaH)
  • Oxygen in a compound has an oxidation number of -2, unless it it bonded to fluorine or in a peroxide. (e.g. F2O ; H2O2)
• Which element always has an oxidation number of -1?

  Fluorine always has an oxidation number of -1 because it is the most electronegative element.
• • Roman numerals indicate the oxidation number of the element, but no sign is displayed.
• Oxidation

  • Gain of oxygen, or
  • Is the loss of electrons, and
  • An increase in oxidation number
• Reduction

  • Loss of oxygen, or
  • Is the gain of electrons, and
  • A decrease in oxidation number
• What is a redox reaction:

  • A redox reaction is a reaction in which oxidation and reduction take place at the same time.
  • This results in a transfer of electron from one species to another.
• How can oxidation numbers be used in redox equation?

  Determines which element has been oxidised and which has been reduced.