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Finding the concentration of sodium carbonate.

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Introduction

Finding the concentration of sodium carbonate: Mass (Na2CO3 transferred to volumetric flask) = [mass (weighing bottle) + mass (Na2CO3)]-[mass(weighing bottle after emptying)] =15.24g - 12.59g =2.65g Molar mass (Na2CO3) Na=23 C=12 O=16 2Na x 1C x 3O = molar mass = (2 x 23) + 16 + (3 x 16) =106 Number of mols (Na2CO3) = mass/molar mass =2.65g/106 =0.025mol Number of mols (Na2CO3) = concentration x volume 1000 0.025 mol. = conc. x 250cm3 1000 Concentration (Na2CO3) = 0.1 mol.dm-3 Results Titration Initial Burette Reading (cm3) Final Burette Reading (cm3) Difference (cm3) 1 (rough) 0.00 32.00 32.00 2 5.00 36.25 31.25 3 1.10 32.30 31.20 4 0.00 31.25 31.25 5 10.00 44.30 34.30 The first and last results are not included in the average since the first is only a rough titration so that later ones can be more accurate and the last is an anomalous result. Therefore the average is: (31.25+31.20+31.25) / 3 = 31.23cm3 We can now number of moles of calcium carbonate using this equation: Number of moles = concentration x volume 1000 =0.1x25 1000 =0.0025 mol. ...read more.

Middle

There may also have been errors in the readings. Or simply missing the end point by not swirling enough or turning off the burette quick enough. Out of the 5 results collected 2 have been ignored, this leaves us with only 3 results to find an average with. Another factor to consider is percentage error. % Error = actual error/ size of measurement x 100 The balance that was used has an error of + or - 0.005g. 4 measurements were taken: 12.57g % Error = 0.005/12.57x100 =0.04% 15.24g % Error = 0.005/15.24x100 =0.03% 12.59g % Error = 0.005/12.59x100 =0.04% 2.65g % Error = 0.005/2.65x100 =0.19 One drop from the burette has a volume of approx. 0.05cm3, this gives an error of + or - 0.05. The average titre was 32.23cm3; therefore the following % error occurred: 0.05/32.23x100= 0.16% There may also be error when using the pipette, if used correctly the error is + or - 0.06cm3 therefore: 0.06/25x100=0.24% The volumetric flask could also produce an error; if the bottom of the meniscus rests on the calibration line the error is 0.2cm3. ...read more.

Conclusion

The % error of the experiment was very small (0.78%) this means the three useable results appear to be reasonably accurate. There are many ways to improve the experiment: * More repetitions, the more repetitions you do the more accurate your end point should be and the average would be more accurate as you are taking into account more results. * Ensure the pipette, burette and volumetric flask readings are done at eye level on a horizontal surface. This makes the readings the readings more accurate. * Use a thinner burette so that changes in volume are even more noticeable and lowering % error. * Add the solution in drips rather than a steady stream. This would make the end point much more accurate. If the experiment is performed in pairs it would make the burette readings more accurate, as 1 person could swirl the solution and the other could handle the burette. This would allow the swirling to be constant as the burette handler could concentrate on finding the end point accurately. ...read more.

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