The Formation of Alum Crystals from Solutions in Different Thermal Conditions

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  • Topic: Crystallization, Crystal, Seed crystal
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  • Published : December 10, 2012
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The Formation of Alum Crystals from Solutions in Two Different Thermal Conditions Burce P.J., Cachuela J.A.A., Capistrano M.M.

I. Objectives
The experiment aims to describe crystals and its aggregates by creating crystals of Alum (AlK (SO4)2 ∙12H2O), commonly known as Tawas, from solution. Two setups will be created; crystals from each setup will be allowed to form at two different thermal conditions. With this, the experiment also aims to describe how temperature affects the formation of crystals.

II. Methodology
First, 2 liters of water was boiled. Two hundred grams of alum was dissolved to the water while constantly stirring. After this, more alum was added to the mixture while constantly stirring until the solution can no longer dissolve alum. The solution was allowed to cool down to less than its boiling temperature. Two jars were prepared and were marked as set-ups A and B. The cooled solution was divided into two and was poured into each of the jars. Two small chunks of alum, measuring about 1 cm by 2 cm each, was tied to a string. These chunks of alums will be the seed crystals. The other end of the string was tied to the middle portion of a stick. One seed crystal was hanged in each of the jars, with the alum chunks being submerged in the solution. Set-up A was left in a place where it will not be disturbed at room temperature. Set-up B was placed in the freezer. The solutions were allowed to crystallize and were observed for 24 hours.

III. Results and Discussion
The observations for both set-ups were summarized in Table 1. Table 1. Comparison of Observations for the two Set-ups
| Set-up A (room temperature)| Set-up B (freezer temperature)| Rate of Crystallization| Slower| Faster |
Relative Crystal Size| Relatively larger crystals| Relatively smaller crystals| Crystal Shape| Octahedron| Octahedron|
Crystal Abundance| Relatively fewer crystals| Relatively more crystals|

The alum crystals were formed from...
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