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Investigation to Identify the Formula of Hydrated Copper Sulphate and in doing so Find what x represents in the Formula CuSO4xH2O

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Introduction

Science Coursework: Investigation to Identify the Formula of Hydrated Copper Sulphate and in doing so Find what x represents in the Formula CuSO4�xH2O Name: Matthew Dobson Partner: Jamie Barton? Date(s) Conducted: 23/04/05 - 06/05/05 Topic: Chemistry - Moles and Empirical Formulas Experiment: The Degree of Hydration of Copper (II) Sulfate, CuSO4 � xH2O Aim: I plan to investigate the formula of Hydrated Copper Sulphate and, more importantly, what x stands for in the formula (CuSO4.xH2O). This will tell me how many molecules of water surround each molecule of Copper Sulphate. To do this I plan to work out the amount of water a set mass of Hydrated Copper Sulphate loses when it becomes anhydrous. I will work this out by measuring the difference in mass between the two states. And thus ascertain the degree of hydration. I predict that because it is hydrated copper sulphate and it is blue that it will contain water of crystallization surrounding the copper sulphate. The number of water molecules per copper sulphate molecule should fall somewhere between 1 and 5 as 1:5 is the largest ratio of copper sulphate to water this molecule can contain. Apparatus: MATERIALS: Hydrated copper (II) sulphate GENERAL: * * Heatproof mat, * Tripod, * Bunsen burner, * Pipe clay triangle, * Crucible, * Metal tongs, * Glass mixing rod, * Spatula, * Electronic-Balance SAFETY: Lab coat and safety glasses to be worn at all times and care to be taken when handling hot objects. Method: 1. Set up apparatus as shown in the diagram. ...read more.

Middle

- m(CuSO4) = 2.034 - 1.267 m(xH2O) = 0.767g ? 0.008g Solving to find "x" in (CuSO4 � xH2O) is now a simple matter of deducing the amount in moles of each compound, and finding the simplest integer ratio between CuSO4 and H2O. See: CuSO4 xH2O 1.267g ? 0.004g 0.767g ? 0.008g Using the formula: n = m/M, where n = moles, m = mass of sample, and M = relative atomic mass of compound n(CuSO4) = 1.267g/[63.55 + 32.06 + 4(16.00)] = 1.267/159.61 mol n(CuSO4) ? 0.00794 mol ? 2.5x10-5 mol n(H2O) = 0.767g/[2(1.01) + 16.00] = 0.767/18.02 mol n(H2O) ? 0.0426 mol ? 4.4x10-4 mol The ratio can now be easily determined: CuSO4 : H2O n(CuSO4)/ n(CuSO4) : n(H2O)/n(CuSO4) (1.267/159.61)/( 1.267/159.61) mol : (0.767/18.02)/(1.267/159.61) mol ? 0.00794/0.00794 mol : ? 0.0426mol/0.00794mol 1 : ? 5.36 So both the exact and the approximate ratio have been determined. However, presumably due to experimental errors the ratio is, of course, not a perfect integer. This can be dealt with in two ways: a) the ratio of 1 : ? 5.36 can be rounded to a ratio of 1 : 5 (which gives the formula of the hydrate as 5H2O) - but since 5.36 does not closely approximate 5.00, this is not an appropriate assumption. b) Alternately, a smaller rounding gives a ratio of 1 : 5.4 and this ratio can be easily multiplied to give an integer ratio as such: 5 x (1 : 5.4) ...read more.

Conclusion

It is likely that a culmination of these errors - with an emphasis on burning the sample - resulted in a degree of imprecision in these results. Regardless, the results were still quite conclusive. Improvements: Several aspects of this experiment could be developed to yield more accurate and precise results. The key improvement to this experiment would probably be to decrease the intensity with which flame is applied to the crucible. This would be to reduce the possibility of overheating, and increase the period of time spent dehydrating the sample to ensure a slower, more thorough (i.e. ensuring that most of the sample is anhydrous) and less intense dehydration. This improvement would allow a more thorough development of the sample, and more frequent processing on the scales. Another main improvement that could be implemented had the equipment been available would be to completely automate the experiment to remove the degree of human error. This would involve using very accurate robotic machines to precisely measure the amount of copper sulphate used and the mass of everything. It would also heat it for the exact amount of time to prevent burning (oxidization) or to not be fully dehydrated. In addition to this, either repetition of the experiment to obtain a broader spread of results or a collation of class results may have yielded more accurate results, as the mean of the results would probably have given a ratio for hydrated copper (II) sulfate much closer the accepted literature value of 1 : 5, or CuSO4 � 5H2O. Matthew Dobson Matthew Dobson 01/05/2007 Mr Robertson Chemistry pg1 ...read more.

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