Experiment 2- Gravimetric Analysis

  • You are given an aqueous solution of Al(NO3)3 with unknown concentration.

  • Your goal: Determine the concentration of Al3+

  • Method: Convert the soluble Al3+ species to an insoluble form

  • Insoluble species: 8-hydroxyquinolone

    • The lone pairs in N will bind with Al3+ three times to form Al(hq)3

  • We need to maintain the pH approximately 4 with a buffer called ammonium acetate

  • To bind to all of the aluminum, it’s just a matter of time (Dynamic equilibrium)

  • What species do we want in excess (limiting reagent)? hq

  • Get three crucibles. Wash and label.

  • Insert one filter paper in each crucible

  • Place crucibles in beaker.

  • TA will remove crucibles from the oven

  • Allow crucibles to cool in desiccator

  • Weigh each crucible with filter paper

  • The first measurement when weighing it is the correct measurement, because the crucible hasn’t absorbed moisture

  • Obtain your unknown. Do 3 trials. Record the sample number immediately (10.00mL + 10mL DI water)

  • Heat one of the samples

  • Add 8 mL of Hhq (ligand). Precipitate will form.

  • Stir to redissolve the precipitate. Add HCl if needed.

  • While still warm, add 20% w/v acetate buffer dropwise. Drop, bloom, stir.

  • Continue to add buffer until precipitate does not redissolve upon stirring

  • Add another 10mL