A hydrate is a compound, typically a crystalline (ionic) one, in which water molecules are chemically bound to another compound or an element. Hydrates naturally form when ionic compounds come in contact air and make bonds with water molecules. These bonds occur between the cation of the molecule and the water molecule (Gillespie, 2018).
There are three types of hydrates; inorganic hydrates, organic hydrates, and gas (or clathrate) hydrates (Crampton, 2017). Substances that absorb water from the atmosphere in a spontaneous manner to form hydrates are called hygroscopic or deliquescent, while hydrates which lose water of hydration or crystallization to form anhydrous substances are efflorescent.
In most scenarios, the loss or uptake of water through processes such as heating or decreasing pressure are reversible processes. Sometimes, such processes are accompanied by changes in colour in the hydrate sample (Kauffman, 2016). An anhydrous compound (an anhydrate) is a compound with no water in its structure after water is removed from a hydrate. An anhydrate from a hydrate is usually highly soluble in water, and when dissolved in water it will be a similar colour to that of the original hydrate, even after the original colour change from hydrate to anhydrate (Gillespie, 2018). Anhydrous solvents are important for performing particular chemical reactions that, in the presence of water, either cannot proceed or yield unwanted products (Helmenstine, 2018).
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Copper (II) sulphate is the most widely used copper compound, used in agriculture, electrical applications, the production of other chemicals, and in other industrial and commercial applications (Copper Development Association). This material is known to increase the rate of a chemical reaction without any alteration in its own chemical structure. Copper (II) sulphate is an inorganic hydrate which has a dramatic difference in colour between its hydrated and anhydrous forms (Crampton, 2017). This compound is a white crystalline powder in its anhydrous state, but is most commonly found in its pentahydrate form, CuSO4·5H2O, which is a blue granular crystalline solid (Schlager, Weisblatt, & Newton, 2006).The purpose of this lab is to determine the percentage composition of water in the hydrated form of Copper(II) sulphate. This information will help determine the chemical formula of the hydrate. Because the colours of the hydrated and anhydrous Copper(II) sulphate have a dramatic variance, this compound serves as a good model to identify the percentage composition of water. By measuring the compound before heating and after, the amount of water in the original hydrate can be determined and the formula discovered. When hydrated Copper(II) sulphate is heated, it loses its water of hydration and returns to its white, powdery anhydrous state. The anhydrous powder is weighed and the mass is divided by the molar mass to get the mol value. A mol ratio is used to determine the moles of water there are per mol of the anhydrous salt. This number is the coefficient for H2O in the chemical formula of copper (II) sulphate pentahydrate (CuSO4·5H2O). Similarly, from the difference in the mass of the hydrated and the anhydrous copper (II) sulphate, the mass of water liberated can be found. Dividing this number by the original mass will give the percent water in the hydrate.
Thus, in this lab, the purpose to determine the percent of water in an unknown hydrate, as well as the formula of the hydrate, is done through knowledge of finding empirical formulas and percent composition. References Copper Development Association. (n.d.). Uses of copper sulphate for agriculture, industry and medicine.
References
- Retrieved from https://copperalliance.org.uk/about-copper/copper-compounds/uses-copper-sulphate/Copper(II) Sulfate. (2006). In N. Schlager, J. Weisblatt, & D. E. Newton (Eds.), Chemical Compounds. Detroit, MI: UXL.
- Retrieved from http://link.galegroup.com/apps/doc/UVZSUW265796152/SCIC?u=miss91533&sid=SCIC&xid=25372addCrampton, L. (2017, October 10). What Is a Hydrate (Chemistry)?
- Retrieved from https://owlcation.com/stem/What-is-a-Hydrate-ChemistryGillespie, C. (2019, March 02). Hydrous Vs. Anhydrous.
- Retrieved from https://sciencing.com/hydrous-vs-anhydrous-5554365.htmlHelmenstine, A. M. (2018, December 03). What Is an Anhydrous Compound?
- Retrieved from https://www.thoughtco.com/anhydrous-chemistry-definition-603387Kauffman, G. B. (2016, March 21). Hydrate.
- Retrieved from https://www.britannica.com/science/hydrate
