Experiments for better teaching

Acid Synthesis I:
from Nonmetals

P

time requ.: 10 minutes.
objective: Reactions of nonmetals with oxygen gives oxides. Solutions of nonmetal oxides in water gives acids.
material:
  • combustion spoon
  • lighter
  • burner
  • cylinder 250ml
  • fitting stopper or plastic foil
  • indicator paper
chemicals:
  • (oxygen gas)
  • sulphur
  • water
  • red phosphorus
procedure 1: Fill the cylinder with approx. 10ml of water and oxygen gas (or air). Give some sulphur into a combustion spoon, ignite it and sink the spoon into the cylinder (use smoke hood). After reacting dissolve the gaseous product in the water by shaking the cylinder. Test the solution with indicator paper.
observation 1: Acidic reaction.
interpretation 1:      S   +   O2   --->   SO2
sulphur  oxygen      sulphur(IV)-oxide

     SO2         +         H2O   --->   H2SO3         as 2H3O+ + SO32-
sulphur(IV)-oxide      water       sulphuric acid
procedure 2: Repeat the procedure with red phosphorus. ATTENTION: before using the combustion spoon with red phosphorus heat it in the flame until all sulphur is burned!!! Else danger of explosion!!!
observation 2: Acidic reaction.
interpretation 2:        4 P          +   3O2   --->      P4O6
phosphorus     oxygen    phosphorus(III)-oxide

          P4O6            +   6 H2O   --->   4 H3PO3       as 3H3O+ + PO33-
phosphorus(III)-oxide     water      phosphoric acid
disposal of: Sink.
source: from Barke, H.-D. et al.: One Hundred Chemistry-Experiments to Avoid Chalk and Talk; University of Muenster, 2004.

 

© Walter.Wagner ät uni-bayreuth.de, version 09.06.11

Didaktik der Chemie
Universität Bayreuth