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Find the solubility of a sodium hydroxide solution (lime water).

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Introduction

Chemistry coursework assessment November2002 AN EXPERIMENT TO DETERMINE OF THE SOLUBILITY OF CALCIUM HYDROXIDE Giles Greenwell Aim To find the solubility of a sodium hydroxide solution (lime water). In this investigation, I intend to find the solubility of calcium hydroxide in water. Calcium hydroxide dissolves in water to form an alkaline solution. To find the solubility, I need to find the concentration of a saturated solution. To do this, I will titrate an acid of a known concentration, until I have a neutral solution. I can then find the number of moles of acid that reacted with the alkali, and so find the number of moles of calcium hydroxide. As the volume is known, the concentration, and therefore the solubility, can be found. Ca(OH)2 + 2HCl CaCl2 + 2H2O 1 2 1 2 You can see from the equation above that reacting with each mole of calcium hydroxide are two moles of hydrochloric acid. Therefore if the calcium hydroxide concentration was 1 mole dm-3, and the volume was 25 cm3, 50 cm3 of 1 mol dm-3 hydrochloric acid would be needed to react with it. However, It is stated that the concentration of the hydrochloric acid is 0.3 mol dm-3, and the concentration of the lime water is approximately 0.015 mol dm-3. ...read more.

Middle

To conduct the experiment once, I will need 50cm3. to do this, I will use a volumetric flask. I will mix 5 cm3 of hydrochloric acid with 50 cm3 of distilled water. I will fill the burette with 50 cm3 of this solution. I will transfer 25 cm3 of lime water into the conical flask, using a measuring cylinder, and place it on the white tile below the burette. I will put a few drops of methyl orange in the conical flask. I will run the acid into the alkali until a change in colour is seen. At this point I will note the volume of acid used. In order to make the experiment more accurate, I will repeat this process, and take an average (mean) reading. From this, I will be able to find the exact concentration of the calcium hydroxide. Before I perform the experiment, I must take care to rinse out all of the insides of the apparatus, for example the burette, pipette etc. This is top ensure that the apparatus is not contaminated with other chemicals, which could well affect the outcome of the experiment. ...read more.

Conclusion

I worked out the concentration of the calcium hydroxide solution as 0.00089 (2 significant figures). In conclusion, it is clear from the results, and the subsequent calculations that calcium hydroxide is reasonably insoluble, in comparison with other compounds. The results also show that the calculated concentration I found from the experiment was much lower than the approximate calculation that was given. Evaluation From the percentage error calculation, and by the deviation of the results, shown by the calculated value for standard deviation, (2.5) it is clear that there were sources of error in the experiment. I felt that although the apparatus provided a slight source of error during the experiment, the main source of error was my own judgement of when the indicator had changed colour. I felt that it was difficult to judge the same colour change every time. I think this was the main cause for the results deviation that can be seen from the results. This could not be included in the percentage error calculation, however, because of the difficulty in actually measuring this. It would be difficult to improve in a future experiment, but the experiment would have been improved if the human error factor was removed. A way of doing this could have been an electronic system involving a filter allowing only a certain colour of light, and an LDR, with a voltmeter. ...read more.

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