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Chemistry concentration of lime water.

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Introduction

Chemistry concentration of lime water. AS- Assessed Practical By Nazir Jauhar Zarnosh Introduction: I am required to plan an experiment to find the concentration in g/dm� of a 250Cm� sample of limewater. This has been made such that it contains 1 g/dm� of Calcium hydroxide. Also available to me is Hydrochloric acid which has a concentration of 2.00mol/dm�. This concentration is too high therefore I am required to dilute it. Limewater is formed by the reaction of Calcium Oxide with water this forms slaked lime, which is then dissolved with water. Quicklime + Water Slaked lime CaO(s) + H2O(l) Ca(OH)2(s) It is necessary to react Hydrochloric acid with the Limewater so that the concentration of the Limewater can be established. The reaction that takes place is: Limewater + Hydrochloric acid Calcium chloride + Water + Hydrogen Ca(OH)2(aq) + 2HCl CaCl2 + 2H2O Apparatus: The, equipment and chemicals that I will use are as follows: - 1) Pipette 25cm� 2) Volumetric flask 500cm� 3) Conical flask 250cm� 4) Burette 5) White tile 6) Clamp and stand 7) Indicator (methyl orange) 8) Limewater (250cm� with 1g/dm� of calcium hydroxide) ...read more.

Middle

An accurate way of doing this is to use a volumetric flask and pipette. I want to dilute the acid to 0.1 moles, so I pipette 25.0cm3 of HCl from the original bottle and place it in the 500cm3 volumetric flask. Then I add 475cm3 of distilled water to the same volumetric flask, I measure the amount of water by looking at the graduated mark on the flask and fill until the 500cm3 mark. Once I have obtained the correct concentration of Hydrochloric acid I can precede to the rest of the experiment. First I must set up the apparatus as I have indicated in my diagram. 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. ...read more.

Conclusion

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 dm?3 rather than 0.02 mol dm?3. 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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