Stoichiometry and Empirical Formulae: Conclusion and Evaluation

Topics: Measurement, Observational error, Error Pages: 2 (692 words) Published: June 24, 2013
Stoichiometry and empirical formulae- Conclusion and evaluation

The composition of hydrated crystals is obtained by weighing before and after heating. X, the ratio of moles of water for each mole of copper sulfate, is determined through calculation. It is assumed that when hydrated crystals are heated only the water in the crystal structure is driven off and that no decomposition has occurred.

Mass of anhydrous copper sulfate= 28.780-28.190= 0.590g ±0.002 No. of moles of anhydrous copper sulfate= 0.590/(63.55+32.06+4(16))= 0.0036965mol ± 0.33898%= 0.00370mol ±0.00001 Mass of water= 29.203-28.780= 0.423g ±0.002

No. of moles of water= 0.423/(2(1.01)+16)= 0.02347391787mol ±0.00000846%= 0.023473918mol ±0.000000002 X= 0.0036965/0.02347= 6.349± 0.33898846%= 6.35 ± 0.02
% precision Uncertainty= 0.339%
% Error= (6.349-5)/5×100= 27.0%

Av. % precision uncertainty of class data= 0.317%
% Error= (5.59208-5)/5×100= 11.8%
% uncertainty of mean ratio= 7.96%
Since % uncertainty of mean ratio is higher than the av. % uncertainty, 7.96% is used instead.

The class results are more accurate (5.59) compared to my results (6.35). The class results are not consistent as the range (3.88) and % uncertainty (7.96%) is large. Both readings are precise as the % precision errors are low. The % error (27.0%) of my readings is larger than my % precision uncertainty (0.339%) readings. The % error (11.8%) of the class readings is larger than their % precision uncertainty (7.96%) readings. Thus, systematic and random errors are present in both cases. Most of the class data is noted to be higher than the literature value (5).

The errors that may have caused my and most of the class’s x to be higher are: 1. (Systematic error) The crystals were observed to not flow but stick to each other. The copper sulfate was wet and had more water of crystallization. This is because water may have been absorbed from the atmosphere. Thus the mass of water present in the copper sulfate was...
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