Chemistry Reference
In-Depth Information
E5.2: X-ray Apparatus for Analyzing Crystals at School
Problem: Most instruments for X-ray analysis are very expensive large-scale devices,
which can be seen in research institutes of science departments at universities. The
teaching aid industry has developed a school device for the X-ray analysis. Besides
the well known shadow pictures of X-rays it can demonstrate the interference patterns
of single crystals of salts (Laue patterns), of crystalline powders (Debye-Scherrer
pattern) and the glancing angles of crystals (Bragg angles).
Material: X-ray apparatus for schools, equipment such as X-ray film or Polaroid-X-
ray-diffraction-cassette; film developer and fixer, lithium fluoride-single crystal
(T), sodium chloride powder.
Procedure: The X-ray apparatus can be introduced with X-ray shadows: the bones of
an animal, metal pieces in a closed wooden container, etc. Then the apparatus is being
converted to take Laue patterns: The single crystal is being adjusted, a photographic
plate or a Polaroid-X-ray-diffraction cassette is being placed behind the crystal, a thin
X-ray beam is to be separated and directed on the crystal. After an adequate exposure
time, the photographic plate is being developed or the Polaroid-picture is being
removed from the cassette. The crystal powder is to be handled likewise.
Observation: Besides the primary X-ray, a symmetrical pattern of diffraction points
can be seen in the first case. In the second case, there is a pattern of diffraction rings.
These phenomena can be explained by the symmetrical order of the ions in the salt
crystal; experts are able to calculate the spatial structure of the salt crystal from data
of the diffraction pattern.
Precautions for the handling of alkaline metal pieces:
1. Put on safety goggles.
2. Do not touch alkaline metals with bare hands, use tweezers instead.
3. Blot the alkaline metal dry with filter paper.
4. Cut off the crust thoroughly with knife and tweezers.
5. Put the alkaline metal crust and remainder in spirit.
6. Let pea-sized pieces of alkaline metals react.
7. Do not extinguish fires of alkaline metals with water, but with sand.
8. Dilute alkaline solutions with water and wash down the sink.
E5.3: Cut Surfaces of Alkaline Metals
Problem: Alkaline metals are stored in kerosene because oxygen and carbon
dioxide of the air or water vapor in the air react with these metals to form oxides,
carbonates or hydroxides. To demonstrate it a big piece of alkaline metal is to be cut
and the cut surface is to be observed.
Material: 3 watch glasses, tweezers and knife, filter paper; lithium (C/F), sodium
(C/F) and potassium (C/F).
Procedure: One piece of metal at a time is to be taken from kerosene, put on filter
paper and cut open. The cut surface is to be observed.
Observation: The silvery cut surface starts tarnishing and darkening fast, going
from lithium over sodium to potassium.
