Analysis of Hydrated Copper Sulphate
The above experiment was conducted to determine the amount of Copper and water present in the given sample of hydrated Copper (II) Sulphate.
Introduction
Gravimetric analysis used in this experiment refers to a set of techniques in analytical chemistry aimed at the quantitative determination of an analyte based on the mass of a given solid. In most gravimetric methods the analyte, in this case hydrated Copper Sulphate, is first converted to solid by precipitation with an appropriate reagent, Oxine in this case. The solid precipitate is then collected by filtration (precipitation). The lab scientist washes the precipitate since it is insoluble in water, dries it to remove any traces of moisture, and then weighs the by-product. Finally, the amount of analyte in the original sample is calculated from the mass of the precipitate and its chemical composition determined (Holler).
Experimental Procedure
- Determination of percent copper by Oxine precipitation
In determining the amount of Cu2+ present in the given amount of sample, hydrated Copper Sulphate was reacted with Oxine. Copper (II) Oxine complex (C18-H12-Cu-N2-02 with a mass of 351.85gm/mol) was formed as a result. Secondly, 0.3gms of hydrated Copper Sulphate was weighed and dissolved in 100ml distilled water contained in a beaker. Next, 1.5gms of Ammonium Acetate and 5ml of glacial acetic acid was added to the reactants before heating the solution to about 700C using a hot plate. Oxine was added drop-wise to the concoction upon stirring until precipitation was complete. The final step involved the filtration of the supernatant liquid into the previously weighted filter apparatus. The collected residue was then dried and weighed. The weighted results were then used to calculate the amount of Copper ion present.
B. Determination of present Hydration
In determining the amount of water present in the compound sample given, clean, dry and covered crucible was heated for about 5 minutes. It was then allowed to cool, and its weight determined. Approximately 2.0gms of hydrated Copper Sulphate was then added to the crucible, and the total weight recorded. The weights were recorded to the nearest mg.
The crucible and its content were transferred to the heating apparatus and heated again, but this time very gently over a low flame while partially covered. The materials were stirred periodically during the heating process. After about 15 minutes, the crucible was removed from the heating process, covered completely and allowed to cool to room temperature. After completely cooling, the cover was removed, and the crucible and its contents weighed. The lab scientists repeated this procedure until they obtained successive weight recordings that differed by not more than a centigram.
Results
- Determining amount of copper by Oxine precipitation
Mass of Cu (C9H6NO) 2 / AW of Cu = 0.0705 g
MW of (C9H6NO) 2
Mass of copper in (C9H6NO) 2 = 0.0705g
Mass of Cux (SO4) y. 2H2O SAMPLE = 0.315g
% Cu in Cux (SO4) y. 2H2O = Mass of copper in (C9H6NO) 2 * 100%
Mass of Cux (SO4) y. 2H2O SAMPLE
= %22.3809
- Determination of percent Hydration
Mass of Cux (SO4) y. 2H2O = 2.014g
Crucible after heating = 45.902g
Mass of water loss = 0.763g
% water in Cux (SO4) y. 2H2O = Mass of water lost * 100%
Mass of Cux (SO4) y. 2H2O SAMPLE
= 0.7639/2.014 * 100%
= % 37.88
Discussion
Gravimetric analysis was employed in this experiment to ascertain the amount of Cu2+ present in the given sample of hydrated Copper Sulphate. The underlying principle of this method is to react the compound under investigation with another substance so as to form solid components of known chemical composition and mass. All gravimetric analyses depend on determination of weight of some final compound in order to measure an analyte. This is because weight is one of the physical characteristics of matter that can be measured with a higher degree of accuracy (Rubinson). However, the process may be lengthy and tiresome since it involves a number of repetitive steps.
In this practical of analysis of copper ion, the given sample of hydrated Copper Sulphate was reacted with Oxine to produce an insoluble solid Copper complex of known chemical composition and formula weight. This compound, being insoluble, is washed in water to remove traces of the solution. Rubinson asserts that this cleaning process does not work on all precipitates, as some have to be ‘extensively treated to remove interfering substances’. This, he affirms, is the reason why ‘very few gravimetric methods are currently used in environmental analysis’.
Some precipitates are hygroscopic in nature, and will increase in weight when exposed to air. Therefore, the sample should be dried in ‘a 103° C to 110° C oven for about 1 hour and allowed to cool to room temperature in a desiccator’ to prevent exposure to air. Finally, the percentage hydration available in the given sample is deducted from the difference between the dry and wet weights of the sample before and after heating just as indicated above.
In conclusion, gravimetric analysis produces results with very small margin of error, thus was used to find the atomic masses of many elements in the past. In addition, the method does not need expensive lab equipment. However, this method can only be used to analyze one element or a small group of elements at a time. This may not be appropriate in today’s fast-paced world where many variables have to be determined at the same time for quick decision-making. All in all, it is still a valuable method of analysis in chemistry today.
Work Cited
Holler, F. J., Skoog, D.A. & West, D. M. Fundamentals of Analytical Chemistry. Philadelphia: Saunders College Publisher, 1996. Print.
Rubinson, K.A. Chemical Analysis. Boston: Little, Brown & Co., Publisher, 1987. 178-179, 243-245. Print.
