Crystallization of Potassium alum from a supersaturated solution.
By Sara Ceccarini; Mara Di Capua; Laura Mazzi.
ABSTRACT:
In chemistry, a solution is a homogeneous mixture composed of
two or more substances. In such a mixture, a solute is a substance
dissolved in another substance, known as a solvent. In this
experiment we made a supersatured solution to create crystals. A
supersaturated contains more solute than could be dissolved
under normal circumstances.
We obtained a crystal (a solid material whose constituents are
arranged in a highly ordered microscopic structure) using the
precipitation method. Precipitation is the creation of a solid from a
solution. When the reaction occurs in a liquid solution, the solid
formed is called the 'precipitate'. This method is the same that formed the crystals of NAICA.
Macroscopic single crystals are usually identifiable by their geometrical shape, consisting of flat faces
with specific, characteristic orientations.
MATERIALS AND METHODS:
We weighed 2,78 grams of potassium sulphate content in the
becker and dissolved them in 20 milliliters of water measured in
the graduated cylinder We put the becker on the heating device to
warm it for 1 minute and 30 seconds. Than we weighed 10,64
grams of Aluminium sulphate on a technical balance and dissolved
them in 30 milliliters of water. Finally we heated it for about 2
minutes. We united the two solutions and heated them for 40
seconds while stirring. We put a bit of the solution in a petri dish
and a bit in a 100 ml jar
A week later we scraped at the
bottom of the petri plate to
remove some small pieces of
crystals. We put them on a
black piece of paper to observe
them. We cleaned the petri plate using simply a napkin, we took
one by one the small pieces of crystals to put them in the cleaned
petri plate. Finally we prepared some new solution and added to
the newly cleaned Petri dish so that all the crystals germs were
submerged
DISCUSSION
:
We have noted that every time we went to the laboratory to see the results, the shapes and sizes of
our crystals changed a lot. At the beginning our crystals were small, and they hadn’t a well defined
shape, which was like a circle with some irregularities. As time went on we discovered that the crystals
grew up thanks to the solution, which progressively we added to the germs. Their shape became more
regular, with the outlines well defined and their color became more transparent. That’s why they
incorporated the supersaturated solution in them.