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Find the concentration of a sample of limewater solution in g dm3.

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Introduction

Plan The aim of this experiment is to find the concentration of a sample of limewater solution in g dm3. I am required to design my own experiment and choose a range of appropriate equipment and apparatus. The indicator will be supplied to me. I am provided with 250 cm3 of limewater, which has been made such that it contains approximately 1g dm3 of calcium hydroxide. Also available is hydrochloric acid which has a concentration of 2.00 mol dm3, this concentration is too much though so it is necessary to dilute it. Apparatus and chemicals- Pipette 25cm3, Volumetric flask 500cm3, Conical flask 250cm3, Burette, White tile, Clamp and stand, Indicator (methyl orange), Limewater (250cm3 with 1g dm3 of calcium hydroxide), Hydrochloric acid- standard solution (conc. 2.00 mol dm3),Distilled water. Acid + Metal Hydroxide => Salt + Water Limewater + Hydrochloric acid => Calcium chloride + Water + Hydrogen Ca(OH)2(aq) + 2HCl(aq) => CaCl2 + 2H2O(aq) In order for the experiment to be accurate and reliable it will be necessary to dilute the Hydrochloric acid significantly. It is in my belief that a concentration of 0.1mol dm3 would enable me to achieve reliable results. ...read more.

Middle

I will be using 25.0cm3 of limewater and I will transfer it into the conical flask using a 25.0cm3 pipette. It is also important to add the indicator into the conical flask so that the neutralisation point can be obtained, where five drops of methyl orange should be appropriate. When the indicator is added the colour of the solution is light, clear, orange and this should turn to pink by the end of the titration. In order to obtain consistent and reliable results it is necessary to repeat the experiment several times. After this it the results must be noted in a table as I have indicated in the table below. Titration 1 Titration 2 Titration 3 Final Reading 6.70 cm3 12.30 cm3 17.90 cm3 Initial Reading 1.00 cm3 6.70 cm3 12.30 cm3 Titer 5.70 cm3 5.60 cm3 5.60 cm3 Average titre 5.70cm3 + 5.60cm3 + 5.60cm3 = 5.63cm3 Conclusion Number of moles of HCl: 1dm3= 10*10*10cm3= 1000cm3 Number of moles= concentration * volume 0.10 mol dm? 3* 5.63cm3 = 5.63*10 mol 1000 Number of moles of Ca(OH)2 (Calcium hydroxide): Reacting ratio: 1 Ca(OH)2 : 2 HCl 5.63*10�@ mol = 2.82*10mol Concentration of Limewater in mol dm3: 25.0cm3 = 25.0 dm3 = 2.50*10?2 dm3 2.82*10?@ mol dm3 2.50*10?2 = 1.13*10?2 mol d?3 Concentration of ...read more.

Conclusion

Another form of human error would be the judgment in colour change. In titration it is impossible for one to judge the solution during the end point of the indicator to be the exact same colour all three times with just the naked eye. This is another limitation in the procedure. During titration the colour change can be rapid to counter this I have used a weak concentration of HCl, which is why I have used a concentration of 0.01 mol dm3 rather than 0.02 mol dm3. The experiment can be improved by using a computer and a real time video camera. If the computer could hold the colour of the initial titration then one could do the second titration while looking at the computer screen, so both titrations would be stopped at exactly the same colour. This would totally reduce the human error when it comes to the colour change of the indicator, making the results more fair, accurate and reliable. Another way I could have improved the experiment was if I was to use a larger quantity of limewater for the titrations and, as a whole would reduce the percentage error. Also by repeating the experiment several more times I could have obtained a better average result. My results are reliable as they are consistent with each other and I have managed to refrain from making any large errors. ...read more.

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