Back Titration Lab Report. In my experiment, I hoped to find the amount of calcium carbonate in some mineral limestone using the back titration method
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Back Titration Lab Report Aim: Determining the percentage purity of calcium carbonate in a sample of limestone. Introduction: In my experiment, I hoped to find the amount of calcium carbonate in some mineral limestone using the back titration method The equation of the reaction is as follows: 2HCl + CaCO3 CaCl2 + CO2 + H2O As not all the acid will be used up in the above reaction, I plan to obtain the amount of acid not used up and consequently the amount of calcium carbonate in the limestone, by titrating it with known sodium hydroxide solution. The equation of the reaction is as follows: HCl + NaOH NaCl + H2O Apparatus: The equipment and reagents that I used are as follows: 250 cm3 beaker Electronic balance (± 0.01 g)
I repeated the procedure to obtain 3 sets of readings and will take the average value as my result. Data processing and presentation: With all the above processes being done, I wrote down the values which I obtained in the raw data table below. Raw data Raw Data Measure Volume of acid used / cm3 (± 0.05 cm3) 1 41.6 2 41.4 3 41.5 I then processed my data to find the average volume of acid used. Vavg = V1+V2+V3 3 Vavg = 41.6 + 41.4 + 3 Vavg = 41.5 (± 0.05 cm3) Now I used the various formulas related to the mole concept to find the amount of calcium carbonate in the sample of limestone. The equations of the reactions are as follows: 1) 2HCl + CaCO3 CaCl2 + CO2 + H2O 2)
2 = 4.075 x 10-3 moles Mass of CaCO3 in 1.5g of limestone = Moles x RMM (RMM of CaCO3 = 100) = 4.075 x 10-3 x 100 = 0.41g Percentage purity of calcium carbonate = 0.41 x 100 1.5 = 27.3 ± 0.35 % Conclusion: A possible source of error in this experiment is the determination of the end-point, which is characterised by the solution just turning orange. This is because a slightly greater volume of acid may have been used than required to produce the pink colour. To try to reduce the effects of this error I would like to carry out a large number of titrations and their average used in the calculation. Another possible way to reduce error is by using more accurate measuring instruments like a more precise burette so as to reduce the uncertainty of the measurements. ?? ?? ?? ??
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This is a four star piece of work with excellent scientific knowledge of molar calculations and demonstrated great skill in their work. A clear, concise piece of work but they could have put more into the introduction and conclusion.
Marked by teacher Patricia McHugh 01/12/2012
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