Fo/Chem-Acid&BaSE

• Specification


  • Acids, Bases and Salts
  • Acid-base Equilibrium
  • pH Scale
  • Titrations
  • Salts
• Bronsted-Lowry acid-base equilibrium


  Acids as H+ donors and bases as H+ acceptors
• Strong and weak acids/bases

  Strength refers to the degree of dissociation in water
• pH scale


  Measure of the strength of acids and alkalis
• Acid-base titrations


  Use of indicators
• Acid


  Solution with an excess of H+ ions
• Properties of acids


  • Taste sour
  • Conduct electricity
  • Corrosive
  • React with metals
  • Turn blue litmus paper red

  
• Common acids


  • HCl
  • HNO3
  • H3PO4
  • H2SO4
  • CH3COOH
• Base


  Solution with an excess of OH- ions
• Properties of bases


  • Feel slippery
  • Taste bitter
  • Corrosive
  • Conduct electricity
  • Do not react with metals
  • Turn red litmus paper blue
• Common bases


  • NaOH
  • KOH
  • Ba(OH)2
  • Mg(OH)2
  • Al(OH)3
• pH scale


  Measure of how acidic or basic a solution is, ranging from 0 to 14
• Acidic solutions have pH values below 7, neutral solutions have pH 7, basic solutions have pH above 7
• A change of 1 pH unit represents a tenfold change in the acidity of the solution
• Arrhenius theory


  Acids dissociate in water to produce H+ ions, bases dissociate in water to produce OH- ions

  
• Strong acids


  Ionise completely when dissolved in water
• Weak acids


  Only partially dissociate in water, with a proportion remaining undissociated
• Bronsted-Lowry theory


  H+ ions associate with water to form hydronium ions (H3O+)
• Acid-base reaction


  Neutralisation, forming water and a salt

  
• Acid reactions to form salts

  Acid + Base -> Salt + Water

  Acid + Metal -> Salt + Hydrogen

  Acid + Carbonate -> Salt + Water + Carbon Dioxide

  
• Indicators


  Change colour in acidic or basic solutions
• Indicators


  • Methyl orange

  Phenolphthalein
• Sodium hydroxide neutralises sulfuric acid
• Strong acid


  Completely dissociates in water
• Titration


  Using a pipette to add sodium hydroxide of unknown concentration, then titrating with sulfuric acid of known concentration to find the volume needed for neutralisation
• Concordant results are within 0.10 cm3 of each other
• 2NaOH + H2SO4 -> Na2SO4 + 2H2O
• Titration procedure


  1. Carry out five titrations

  2. Record volume of 0.100 mol/dm3 sulfuric acid in cm3 for each titration
• Concordant results


  Within 0.10 cm3 of each other
• Calculating mean volume


  1. Use concordant results

  2. Calculate mean volume of 0.100 mol/dm3 sulfuric acid added
• Mean volume = ......................... cm3
• Equation for the reaction

  2NaOH + H2SO4 → Na2SO4 + 2H2O
• Calculating concentration of sodium hydroxide


  1. Use equation and mean volume

  2. Calculate concentration to 3 significant figures
• Concentration = ......................... mol/dm3
• Calculating mass of sodium hydroxide

  1. Use 20 cm3 of 0.18 mol/dm3 sodium hydroxide solution

  2. Calculate mass using relative formula mass of NaOH
• Mass = ......................... g
• A student has to check if two samples of hydrochloric acid, A and B, are the same concentration
• Titration procedure to check concentration


  1. Use apparatus and solutions in diagram

  2. Carry out titrations
• Sodium chloride is produced by reacting sodium with chlorine
• Electrons in sodium and chlorine reaction

  • Sodium atom loses electrons
  • Chlorine atom gains electrons
  • Forming ionic bond in sodium chloride