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Determining a substance by tritration

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Introduction

Amrit Warraich Chemistry SL Mr. Ochola 10/5/09 Determining the Concentration of Calcium Carbonate in an Unknown Substance through the Methods of Titration Aim: Using the procedures of a standard acid base titration lab, the goal of this experiment is identifying the amount of Calcium Carbonate (CaCO3) that is presented in a calcium carbonate substance presented by our teacher. Hypothesis: Due to any unknown substance that we encounter in the chemistry room, we must take serious precaution, as the substance may very well be highly contagious and dangerous to smell, touch or taste directly. The only ability that we posses that can be used to observer this substance is our vision that is going to help us in determining the concentration of the substance. Although that with vision only, it will not suffice the need that is necessary to make that judgment as we need quantitative data (finding the exact concentration of calcium carbonate). Unless we have prior knowledge about this substance, the processes of a titration must be used. My hypothesis begins that this has about 60% concentration. Variables: Independent Variable: There is none in this experiment. The goal of this lab is not to include any variables that will change the concentration of the calcium carbonate. We need constant results for the concentration of the calcium carbonate, as that will determine the actual concentration of the calcium carbonate in our substance. ...read more.

Middle

6. Record both quantitative and qualitative data. 7. Repeat the process of titration three times. Observation (Data Collection): Measurements: * Mass of Calcium Carbonate solution: * Burette: Calcium Carbonate solution made using 250cm3volumetric flask with an uncertainty of ?0.5cm3 * Pipette: 25.0cm3 of 0.100moldm-3 NaOH(aq) ?0.04cm3 Chemical Equations: Before we delve into the calculations, it is best that we list the necessary chemical equations of this lab. One must note that in this experiment, that there were two chemical reactions. Firstly, the first experiment occurs when the white substance mixed with the HCl. The second chemical reaction took place when the HCl solution meets with the .1M of NaOH 1. 2. Qualitative Data: Description of the substance used and produced Hydrochloric Acid Clear, viscous, Calcium Carbonate White, powder form Phenolphthalein Indicator Clear solution, comes in a bottle, add as drops Solution Produced in the end Bubbly, white liquid, most of the unknown mixture dissolved Clear/pink throughout. Quantitative Data: Measurement Recorded During the Experiment Trial 1 2 3 4* Initial Burette Reading (ml?0.05cm3) 0.00 0.00 0.00 0.00 Final Burette Reading (ml?0.05cm3) 5.45 5.90 5.60 5.40 *To note, for the calculations below, the supervisor at the time suggested the best data to use would be the average of the HCl used because the numbers found were very consistent. ...read more.

Conclusion

Though the pink color should indicate when the endpoint is reached, in trial 2 and 3, the solution turned a faint pink color and my partners and I did not know whether that faint pink indicated the endpoint. This could have resulted in a measurement lower than the actual value. To possibly improve this source of error, I believe more time and trials should be allotted to the students. When I was doing my experiment, we were only given a single class time to follow the procedures, write down our notes, and clean up our experiment. If more time was allotted, then higher quality recordings could be made. This would then give us a clearer idea when the endpoint actually is. Next, though it is unlikely, to improve this lab we may have to rinse the burettes and other flasks prior to performing this lab. In my chemistry classroom, burettes and flasks are arranged so that the clean ones are clearly seen and labeled while the used ones are in the sink. However it could be possible that another student may have placed an unclean burette in the cabinet full of clean equipments. Therefore, for accuracy purposes, all equipment should be washed using soap and tissues. Reviewing and understanding the errors can significantly improve this experiment. Though my hypothesis of the concentration being 60% calcium carbonate was wrong, this experiment taught me the value and usefulness of the process of titration. ?? ?? ?? ?? Warraich 1 ...read more.

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