Ib Chemistry-Sl-Water of Crystallizationdy
Aim
To Find the Number of Moles of Water of Crystallisation in Copper (II) Sulphate salt.
Introduction
Water of crystallisation is the term given to the molecules of water that are used to build up a crystal lattice in some ionic compounds.In copper II sulphate the blue crystals would be impossible without using water molecules to act as ’scaffolding’ within the structure CuSO4.5H2O. When this is heated the water molecules are driven off and the blue crystals become a white powder.
As most crystals are made by evaporation from an aqueous solution, it makes sense that water molecules can incorporate themselves into the ionic crystal structure. Water, after all, has an oxygen atom with two lone pairs capable of behaving as a Lewis base; it bonds easily to metal ions as evidenced by complex ions in transition metal chemistry. The metal ions and the water molecules are bonded by dative coordinate bonds from the oxygen atom of the water.
Therefore, Water of crystallization is water that is stoichiometrically bound into a crystal.
Crystal salts containing water of crystallization are called hydrates. * Eg. CuSO4·5H2O cyrstals (copper(II) sulfate pentahydrate)
Hypothesis
In the hydrate copper (II) sulfate one mole of salt is believed to be combined with five moles of water. Bearing this in mind the following hypothesis was made: If the hydrate is heated until there is no further loss in weight, five moles of water will be lost from one mole of salt. I have applied this concept and determined the weight of hydrated salt and subtracted the weight of dehydrated salt from the former to get the mass of water present in the sample. Dividing this mass of water with Molar Mass of water (ie 18g), gave the number of moles of water present in the sample.
Materials * Tripod * Pipe clay triangle * Crucible * Access to a balance (±0.01 g) * Bunsen burner * Tongs
Variables
Independent Variable * Thermal treatment ( heating and
To Find the Number of Moles of Water of Crystallisation in Copper (II) Sulphate salt.
Introduction
Water of crystallisation is the term given to the molecules of water that are used to build up a crystal lattice in some ionic compounds.In copper II sulphate the blue crystals would be impossible without using water molecules to act as ’scaffolding’ within the structure CuSO4.5H2O. When this is heated the water molecules are driven off and the blue crystals become a white powder.
As most crystals are made by evaporation from an aqueous solution, it makes sense that water molecules can incorporate themselves into the ionic crystal structure. Water, after all, has an oxygen atom with two lone pairs capable of behaving as a Lewis base; it bonds easily to metal ions as evidenced by complex ions in transition metal chemistry. The metal ions and the water molecules are bonded by dative coordinate bonds from the oxygen atom of the water.
Therefore, Water of crystallization is water that is stoichiometrically bound into a crystal.
Crystal salts containing water of crystallization are called hydrates. * Eg. CuSO4·5H2O cyrstals (copper(II) sulfate pentahydrate)
Hypothesis
In the hydrate copper (II) sulfate one mole of salt is believed to be combined with five moles of water. Bearing this in mind the following hypothesis was made: If the hydrate is heated until there is no further loss in weight, five moles of water will be lost from one mole of salt. I have applied this concept and determined the weight of hydrated salt and subtracted the weight of dehydrated salt from the former to get the mass of water present in the sample. Dividing this mass of water with Molar Mass of water (ie 18g), gave the number of moles of water present in the sample.
Materials * Tripod * Pipe clay triangle * Crucible * Access to a balance (±0.01 g) * Bunsen burner * Tongs
Variables
Independent Variable * Thermal treatment ( heating and
References: * http://www.rsc.org/learn-chemistry/resource/res00000436/classic-chemistry-experiments-to-find-the-formula-of-hydrated-copper-ii-sulfate * http://www.rsc.org/learn-chemistry/content/filerepository/CMP/00/000/506/cce-52.pdf * http://www.friendlyscience.com/index.php?option=com_content&view=article&id=20&Itemid=27