Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
-----------------
hydrogen peroxide : H2O2
acetone : CH3 CO CH3
sodium hydroxide : NaOH
sodium sulfide : Na2S . 3H2O
sulphur : S8
Class:
------
elem=S,C
organic
redox
Summary:
--------
Acetone can be mixed with water in any ratio, but when sodium hydroxide
is added, then the liquids are not miscible in any ratio anymore.
Sulphur reacts with acetone in the presence of sodium hydroxide. Sulfide
does not show such a reaction.
Description:
------------
Sequence 1:
-----------
Add some sulphur to a concentrated solution of NaOH: The sulphur does not
dissolve.
Add some acetone and shake well: The acetone does not mix completely with
the aqueous solution. A two layer system is formed. The bottom layer is an
aqueous layer and the top layer is an acetone layer.
The acetone layer turns darkbrown/sepia, the aqueous layer turns pale yellow.
Besides the typical smell of acetone another strong and unpleasant odour
can be observed.
The largest part of the sulphur remains solid and does not dissolve, not even
on heating to appr. 60 C.
Observation sequence 1: Sulphur reacts with acetone when NaOH is present.
Sequence 2:
-----------
Add some acetone to a concentrated solution of NaOH and shake well: After
standing for a while two layers of liquid can be observed. The liquids
cannot be mixed in any ratio.
Add a fairly large amount of sodium sulfide: The sodium sulfide dissolves.
Both layers remain colorless. The separation between the aqueous layer and
the acetone layer becomes less sharp. Many little droplets of acetone
remain floating around in the aqueous layer.
Observation sequence 2: Sulfide does not react with acetone when NaOH is
present.
Sequence 1+2
------------
Mix the resulting two-layer systems of sequence 1 and sequence 2 and
shake: The total system again becomes a two-layer system. The lop layer
is an acetone layer, which is dark brown/sepa. The bottom layer is an
aqueous layer, which is pale yellow.
Add some H2O2 (3% solution) to the mix of sequence 1 and sequence 2: The
acetone layer turns deep red. Still there are two layers. At the boundary
surface between the two layers a colorless solid compound is formed. This
solid layer keeps both liquid layers well-separated from each other. When
the complete system is shaken, then the solid layer breaks into some scales,
which float through the acetone layer. The boundary surface between the
two liquids becomes hard to see, because the index of refraction is almost
the same for both liquids. The boundary surface, however, is a sharp surface,
not cluttered by little drops of one liquid in the other.
No gas-bubbles are evolved when adding H2O2, nor lateron in the experiment.