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Determining the Concentration of Calcium Carbonate in an Unknown Substance through the Methods of Titration Aim:

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Introduction

Amrit Warraich September 30th 2009 Chemistry SL Mr. Ochola Titration Lab Problem Determine the concentration of the unknown ethanoic acid solution by titrating with a known concentration of sodium hydroxide Equipment and Materials * Unknown ethanoic acid * 50cm3 burette * 250cm3 Erlenmeyer flask * 100cm3 beaker (for CH3COOH) * 200cm3 beaker (for NaOH) * 100cm3 beaker (for waste) * Standardized sodium hydroxide solution * Burette clamp * Retort stand * Phenolphthalein indicator * 50cm3 graduated cylinder * Distilled water (to rinse the flask) Procedure: To begin with, obtain approximately 200 cm3 of sodium hydroxide solution. Then, set up the retort stand and burette clamp as indicated in the diagram below. Using two 10 cm3 aliquots of the NaOH solution, rinse the burette twice. Next, fill to above the 0.00cm3 mark and drain down to below the 0.00cm3 mark in order to remove any air bubbles. After that, transfer 50 cm3 of the unknown acid into the 250cm3 flask. Into the same flask, place 2 drops of the phenolphthalein indicator. Finally, add sodium hydroxide from the burette until you reach the endpoint. Procedural Notes To accommodate for the sodium hydroxide that splashes to the sides of the flask, distilled water was used. ...read more.

Middle

The following table represents the results. Results for the calculations of the concentration of ethanoic acid used in each trial Trial Concentration of CH3COOH / mol dm-3 CH3COOH Uncertainties / % 1 0.913 1.3 2 0.913 1.3 3 0.909 1.3 4 0.904 1.3 Average 0.910 1.3 Conclusion: In conclusion, the result of this lab indicates that the concentration of CH3COOH is 0.910 mol dm-3. Using this value, and the actual value of ethnoic acid, 0.9190 mol dm-3 �0.0004 mol dm-3, percent error was calculated as follows: With this, we see that the percent of uncertainties is greater than the percent error. The percent of uncertainties represents the random errors, in which the measured value can either be bigger or smaller than the accepted value, due to an imprecise measurement. To improve these random errors, it is necessary to use more precise equipment and/or repeat measurements. One example of this would be to use a pipette instead of a graduated cylinder, especially because ?0.4 cm3 is a relatively large uncertainty. Consequently, the use of such equipment led to the percent of uncertainties being greater than the percent error. This means that the random errors cover for the errors in this lab. However, there are a couple potential systematic errors that should be appointed in this lab. ...read more.

Conclusion

To improve this, it may be suggested that rinsing the burette 4 times is more sensible, even though it is time consuming. A final systematic error comes when transferring the ethanoic acid from the graduated cylinder. When this happens, some of the ethanoic acid may be retained in the graduated cylinder. This is a systematic error as this always leads to a smaller volume of ethanoic acid than measured. To improve this error, one may pour a tiny bit more than 50 ml of ethanoic acid, and measure that as 50 ml of ethanoic acid. Improving this error leads to a larger volume of ethanoic acid, a lower concentration of ethanoic acid, and once again, an increase in percent error. All in all, it is very interesting how knowing the amount of one substance can help determine the amount of another substance, although it is a topic that appears frequently in chemistry. In this case, knowing the number of moles of sodium hydroxide enabled us to know the concentration of the ethanoic acid. Furthermore, this lab helps one enhance their knowledge on the difficulty of setting up a lab. By reviewing and understanding the errors to a lab, one can relate the improvements to future labs. In a nutshell, this lab exemplified the process of titration, and how useful it can be. ...read more.

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