In nature there are some salts that will have water in their crystalline structure. These salts are commonly known as hydrated salts. Hydrated Copper (II) sulphate is one of these, as suggested by the use of the word hydrated in its name. Its molecular structure is shown below.
The water that is chemically combined into their structure is called the water of crystallisation. In our experiment the crystal hydrate is heated, this is an endothermic reaction CuSO4.XH2O (bright blue solid) → CuSO4 (dirty white solid) + 5H2O After enough heat has been added to break the bonds, the water of crystallisation is then released in the form of water vapour. When the water has been removed, the Copper Sulphate crystals will then be in their anhydrous form, and therefore amorphous in nature. Amorphous meaning that the crystals absorb water from the atmosphere. It is for this reason that it is necessary to get the lid back on the crucible as soon as the reaction has finished, then place the crucible in the desiccator as soon as possible. The formula of a hydrated salt is written as the number of moles of water existing in one mole of crystalline structure. So, by heating the hydrated copper (II) sulphate we can determine the moles of water lost by weighing the product before and after heating. We will then be able to calculate X. Method
Please refer to page 14 Plymouth University, Chemistry Practical Booklet [Autumn Term 2012]. As can be seen in the picture bellow (left), the crucible is on the pipe-clay triangle with its lid left ajar. Bellow right is a desiccator.
Results| Mass (g)|
1| Mass of Crucible & Lid| 26.6066|
2| Mass of Hydrated CuSO4 + Crucible & Lid| 27.6651| 3| Mass of Hydrated CuSO4 | 1.0585|
4| Mass of anhydrous CuSO4 + Crucible and Lid | 27.2996| 5...