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Determining the Solubility of Calcium Hydroxide.

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Introduction

Determining the Solubility of Calcium Hydroxide Introduction Calcium Hydroxide Ca(OH)2 dissolves only slightly to form an alkaline solution. This is a saturated solution often called limewater. The solubility of the calcium hydroxide can be found by titrating the saturated solution against a solution of an acid whose concentration is known. I will be using a sample of limewater, containing approximately 0.015 mol dm-3 of calcium hydroxide, and a solution of Hydrochloric Acid, whose concentration is 0.3 mol dm-3. Choosing an Indicator Strong Acid Weak Acid Hydrochloric Acid Ethanoic Acid Nitric Acid Ethandioic Acid Sulphuric Acid Strong Alkali Weak Alkali Sodium Hydroxide Ammonia Solution Potassium Hydroxide Sodium Carbonate Calcium Hydroxide Sodium Hydrogencarbonate The indicator I must use in this titration will depend on the strength of the acid and alkali I use. I will be using Calcium Hydroxide and Hydrochloric Acid. These are a strong alkali and acid respectively. This means I must use an indicator compatible with a strong alkali and strong acid. The 2 indicators I may use are Phenolphthalein and Methyl Orange. I have elected to use Methyl Orange. The colour change I am expecting is; Yellow Red (Alkali) ...read more.

Middle

The amount of Ca(OH)2 used was 25cm3. This means that the concentration can be found from: Concentration = Amount in moles__ Amount used in dm-3 This value is the amount of Calcium Hydroxide present in the saturated solution used. Results & Analysis Repeat Start Point (cm3) End-Point (cm3) Total Used (cm3) ROUGH 0 36 37 1 0.00 36.35 36.35 2 0.00 37.20 37.20 3 0.10 37.25 37.15 4 6.00 43.25 37.25 Mean Average Acid solution Used* : 37.20 * The mean average acid solution used does not include the rough titration, or the first repeat, which was clearly an anomaly. My results show that the mean average volume of acid used was 37.20cm3. The concentration of this acid can be found by a series of steps, based on these results: Original concentration of acid was 0.3M. This was reduced when the acid was diluted. 25cm3 HCl + 225cm3 distilled water 250cm3 hydrochloric acid solution Concentration of HCl used was 0.03 mol dm-3. I can also find the concentration of the Ca(OH)2 used in the experiment: Ca(OH)2 (aq) + 2HCl (aq) CaCl2 (aq) + 2H2O (l) 25cm3 + 37.20cm3 Concentration 0.03mol dm-3 Unknown I can find the number of moles of HCl used by the following method: Moles = Concentration (mol dm-3) ...read more.

Conclusion

This would account for the anomalous result I obtained, which showed a lower concentration than expected. I believe that overall, my evidence was accurate and reliable because I have found 3 values which agree to within 1 decimal place. The apparatus I have used was the most accurate available to me, and the single anomalous result I obtained can possibly be accounted for by an air bubble. The apparatus was all transparent glassware, so I did not have any difficulty reading the endpoint on the burette, or the line on the pipette. To improve the accuracy of the procedure, I could have repeated the experiment more times, or used different concentrations of acid, and different ratios of acid to alkali. Hopefully, these would all have given the same concentration of calcium hydroxide each time. This experiment would improve or verify the accuracy of the results, because it would be necessary to dilute the hydrochloric acid to a different concentration, which would show whether I had made any errors when diluting the HCl whilst gathering my evidence. If such an error had occurred, it would not show on my results, because I had made 250cm3 of diluted 0.03M hydrochloric acid at the start which was used throughout the experiment. Matt Harris Determination of the Solubility of Calcium Hydroxide Pa12 Page 1 ...read more.

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