Titrations

• What can a soluble salt be prepared from?

  By reacting an acid with a dilute solution of an alkali
• What are the main steps to prepare a soluble salt?

  1. Carry out a titration to determine volumes of acid and alkali.
  2. Mix acid and alkali in correct proportions without an indicator.
  3. Produce pure dry crystals by crystallisation and drying.
• What is the purpose of carrying out a titration?

  To determine the volumes of acid and alkali needed to obtain salt and water
• What apparatus is needed for the titration process?

  A pipette and a burette
• What is the function of a pipette in the titration process?


  To accurately measure the volume of a reactant
• What is the function of a burette in the titration process?


  To add small, measured volumes of one reactant to another
• What is the method for carrying out a titration with hydrochloric acid?


  Use a pipette to add sodium hydroxide, then add hydrochloric acid from a burette until the end-point is reached
• What indicates the end-point in a titration?


  When the indicator first permanently changes color
• What should be done to obtain more accurate results near the end-point of a titration?


  Add the acid drop by drop
• What are the aims of the titration practical?


  • To determine the reacting volumes of solutions of an acid and alkali.
  • To determine the concentration of one of the solutions in mol/dm³ and g/dm³ (Higher tier only).
• What points should the plan for the titration address?


  • Which apparatus to use
  • Which reagents to use
  • Consideration of hazards, risks, and precautions
• What are the required apparatus for the titration?


  Burette, pipette and filler, conical flask, and white tile
• What reagents are used in the titration process?


  An acid of unknown concentration and sodium hydroxide solution of known concentration
• What is a suitable indicator for the titration?


  Methyl orange or phenolphthalein
• What are the hazards, risks, and precautions associated with the titration practical?


  • Concentrated hydrochloric acid is corrosive; use dilute acid as a precaution.
  • Bunsen burner can cause burns; do not touch hot apparatus.
  • Hair and loose clothing can catch fire; tie back long hair and tuck in loose clothing.
• What volume of alkali should be added to the conical flask for the titration?


  25 cm³
• What should be done after adding the indicator to the alkali in the conical flask?


  Put the conical flask on a white tile
• What should be noted after filling the burette with acid?


  The starting volume of the acid
• What should be done after reaching the end-point in the titration?


  Note the final volume reading
• What is the purpose of adding a few drops of indicator to the alkali?


  To visually signal the end-point of the titration
• What should you do while adding acid from the burette to the alkali?


  Swirl to mix
• What indicates that the end-point has been reached in a titration?


  The indicator first permanently changes colour
• Why is it more accurate to add acid drop by drop near the end-point?


  It allows for precise control over the reaction