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Introduction

Analysis Experiment 1 Time (minutes) Mass of crystals, crucible + lid (g) 0 23.36 5 22.59 10 22.41 15 22.41 20 22.41 Mass of crucible + lid = 20.82 g Mass of hydrated CuSO4 = 23.36 - 20.82 = 2.54 g Mass of anhydrous CuSO4 = 22.41 - 20.82 = 1.59 g Mass of water = 2.54 - 1.59 = 0.95 g % of water by mass = (0.95/2.54) x 100 = 37.401575 = 37.4 % (3.s.f) Mr of H2O = 18 No. of moles in 2.54g of H2O = 0.95/18 = 0.05278 moles No. of moles in 1g of H2O = 0.05278/2.54 = 0.020778652 moles Experiment 2 Mass of hydrated CuSO4 used = 5.83g Titre Volume (cm3) 1 23.5 2 25.0 (anomalous) 3 24.1 Average titre = (23.5+24.1)/2 = 23.80 cm3 Volume of S2O32- = 23.80 cm3 Concentration of S2O3 = 0.1 mol dm-3 Moles of S2O32- in 25ml = (0.1 x 23.80) / 1000 = 0.00238 moles Moles of S2O32- in 250ml = 10 x 0.00238 = 0.02380 moles To find the number of moles of Cu 2+, we need to see what ratio the Cu 2+ and S2O32- react in: They react in a 1:1 molar ratio. ...read more.

Middle

= +/- 0.24317723 % = +/- 0.2432 (4sf) Total % error in experiment 2: Burette: +/- 100 x [(0.5 x 0.1)/ 23.5] = +/- 0.212765957% +/- 100 x [(0.5 x 0.1)/ 25.0] = +/- 0.200000000% +/- 100 x [(0.5 x 0.1)/ 24.1] = +/- 0.207468879% Mass of crystals: +/- 100 x [(0.5 x 0.01)/5.83] = +/- 0.08576329331 % Pipette: +/- 100 x [(0.5 x 0.06)/25] = +/- 0.12 % +/- 100 x [(0.5 x 0.06)/25] = +/- 0.12 % +/- 100 x [(0.5 x 0.06)/25] = +/- 0.12 % (Combined) = +/- 1.065998129 = +/- 1.066% (4.s.f) In conclusion it appears that in both experiments 1 and 2, the percentage errors are relatively small which shows that my experiments were fairly reliable and accurate. The values for % error give a clear indication as to which experiment was more accurate, its apparent that experiment 1 was a lot more accurate than experiment 2 purely because its percentage error was +/- 0.2432 % which is sufficiently less than that of experiment 2 with +/- 1.066 % error. In experiment 1 the weighing scale gave values to 2 decimal places; however the burette was correct to only 1 decimal place. ...read more.

Conclusion

Most significant error in measurement and modification > From both experiments, the apparatus with the least % accuracy was the burette. It had errors up to +/- 0.212765957% which is the largest error out of all the equipment. This error can be minimised by using a burette with a smaller diameter. This allows the meniscus to be seen easily compared to that with a larger diameter. By doing so a more accurate result is gained, hence a more accurate reading of the volume of solution in the burette is obtained and so the results are more reliable. > Another modification is to use a burette with a much smaller scale. by using a scale which is more accurate than 0.1ml would allow for a more accurate reading of volume during titration. This effectively would allow for more accurate calculations and therefore results of higher accuracy. > A burette which has a much narrower tip should be used. This is allows fewer drops to be added in a given time, in effect colour changes can be spotted more accurately thus preventing an excess amount (which is not required) added. This prevention allows for more accurate results, therefore a more accurate and reliable experiment. ...read more.

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