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An investigation into the water of crystallisation present in Hydrated Magnesium Sulphate

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Introduction

An investigation into the water of crystallisation present in Hydrated Magnesium Sulphate Aim The aim of this experiment is to investigate the amount of water of crystallisation is present in the hydrous powder, and to investigate whether or nor the substance is MgSO4.7H2O Hypothesis I predict that if I take a mass of approximately 2.46g of hydrated magnesium sulphate and decompose it by heating until all of the water of crystallisation has been driven off, I should be left with a mass of approximately 1.2g anhydrous Magnesium Sulphate. This size of the starting mass was chosen because it is both practical to the experiment, due to limited time and supplies, but large enough to create accurate readings on a 3 decimal placed set of scales. Calculating the molecular masses of the anhydrous substance created the figures 246 and 120. These calculations follow: Equipment Apparatus Bunsen burner; Heatproof mat; Tripod; Pipe clay Triangle; 10 g Hydrated Magnesium sulphate; Crystallising dish; Sensitive scales; Tongs; Scoop; Stopwatch; Gas supply; Goggles. Diagram Method Firstly, a crystallising dish's mass will be measured on the scales, and will be recorded. Next, approximately 2.46g of Hydrated Magnesium sulphate will be placed into the Crystallising Dish using the scoop. ...read more.

Middle

It is also important to wear goggles in case any hot substances spark off the crystallising dish. Experimental Report An unknown labelling error caused the two substances used in the experiment to differ. This did not change the procedure at all, but it did mean that the average result would simply lie between the two substances rather than be a more accurate result. However, it did soon become clear that heating the substance and fully removing all water was going to take more than 5 minutes, so this period of the experiment was extended to 15 minutes when it was repeated. Table of Results Results set: Total mass (g) Mass of Crucible (g) Mass of Magnesium (g) Mass change (g) % Mass change (to 3 S.F.) Start End Start End 1 15.081 12.467 10.06 5.075 2.407 2.668 52.6 2 36.210 35.992 35.695 0.515 0.297 0.218 42.3 Average / / / / / / 47.45 Analysis MgSO4.xH2O reference table X Molecule MgSO4.xH2O Mr (RMM) of hydrated molecule Mr of the water % of mass that is water Predicted % that would remain 0 MgSO4 120 0 0 100 1 MgSO4.H2O 138 18 13.04348 86.95652 2 MgSO4.2H2O 156 36 23.07692 76.92308 3 MgSO4.3H2O 174 54 31.03448 68.96552 4 MgSO4.4H2O 192 72 37.5 62.5 5 ...read more.

Conclusion

Evaluation If this experiment were to be repeated, there could be a number of amendments to improve the accuracy of results. Firstly, it would have been repeated three times to allow a further error check in case one of the experiments again went wrong. The experiments would also have used the exact same substance allowing averages and anomalous results to be identified, allowing more accurate results to be produced. However, the experiment did produce a result, that the second substance used was MgSO4.5H2O. This is what is suggested by the data, but the data is not very reliable due to there being no way to check the data to see if it was accurate as two completely different chemicals were used. Had the experiment and one chemical was used the results could be declared more accurate and more reliable. This experiment provided a very accurate result, as it fit nearly perfectly with the reference table, but there was no way to prove this was not just co-incidence as the first results were completely unreliable and unusable. But due to the presence of one result that could be backed up by the scientific evidence of relative molecular mass', it is fair to call this experiment a success. 1 ...read more.

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