What substances are used to make crucibles

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preparation

A porcelain crucible is filled with deionized water inside and out1) rinsed, rubbed with a lint-free cloth and annealed on the burner using the clay triangle or in the crucible furnace. Here organic substances burn, volatile compounds are expelled and the water adsorbed on the surface of the crucible is removed.

The crucible is placed in a desiccator with the aid of crucible tongs and the stopcock or stopper on the side is opened. In order to avoid overpressure as a result of heated air, the desiccator is only closed completely after approx. After the crucible has cooled to room temperature (after to), the crucible is placed in the desiccator and placed in the analytical balance; then place it on the scale with your fingers covered with paper or pieces of rubber tubing and weigh it. The mass of the crucible is noted. Note: If the crucible is even warmer than its surroundings, you will not be able to read a constant value.

Repeat the annealing and cooling of the crucible until there are no deviations of more than until the weighing results.

execution

  1. Approx. (Laboratory balance) of the salt received upon dispensing is ground in the mortar, transferred to the crucible and the crucible with salt is weighed again on the analytical balance.
  2. Using a clay triangle, the crucible is heated moderately with the burner, the water of crystallization gradually escaping. Avoid excessive heating, which can cause the salt to melt and decompose. If the salt dissolves in your own crystal water when heated, you should be particularly careful and slow to warm it up so that there is no loss of substance through splashing.
  3. After cooling in the desiccator, it is weighed again. To check whether all the water has been removed, it is heated a little more than the first time and then weighed again after it has cooled down. When all the water has been driven off, the last two weighings will be the same. If there are significant differences, heating must be continued until the water is completely drained.
Disposal of waste
Salt residue: sink. Rinse with water.