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# Determine the concentration of limewater.

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Introduction

To determine the concentration of limewater The aim of my experiment is to find the concentration of limewater solution in gdm. To do this, I am required to construct my own experiment and choosing reliable and appropriate apparatus. I will be provided with 250cm of limewater, which contains approximately 1gdm of calcium hydroxide. I also have hydrochloric acid, which has a concentration of 2.00-mol dm , which is too concentrated and will need diluting. Apparatus, equipment and chemicals Pipette 250cm Burette Conical flask 250cm Volumetric flask 250cm Graduated pipette Clamp + stand White tile Indicator (methyl orange) Limewater (250cm with 1gdm of calcium hydroxide) Hydrochloric acid (2.00-mol dm ) Distilled water Squeezing pump Balanced Equation In order to achieve limewater, dissolved slacked lime in water to get a solution of calcium hydroxide (Ca (OH) 2 ) Quicklime + water --------> slaked lime CaO (s) + H2O (l) --------> CaCl2 (aq) + 2H2O (l) In this reaction it shows the calcium oxide reacts with water to produce calcium hydroxide. After adding more water to calcium hydroxide, it produces the saturated aqueous solution known as limewater. Ca(OH) ...read more.

Middle

Because these are clear it means I can tell when the reaction has finished easier than using other indicators. Limewater, which is calcium hydroxide, is a strong alkali, even though it is only sparing soluble. Its pH is 14. Hydrochloric acid is a strong acid. This means that even if you have quite a weak concentration it completely dissociates in water into H3O+ ions and OH- ions giving a pH of 1 (The pH is a measure of how many hydrogen ions are present in solution). For the reaction of Calcium hydroxide and Hydrochloric acid I would use methyl orange. It changes colour at around pH 4.4 and will change from yellow in acid to pink in alkali by the addition of limewater. To make this experiment as accurate as possible, the pipette, burette and volumetric flask only have a percentage error of + or - 0.1%. This is only a small error. Also making sure the hydrochloric acid is poured into the burette carefully using a funnel will prevent the hydrochloric acid pouring down the side of the burette. Results I worked out the average titre like this: Mean = 13.2 + 13.3 + 13.2 / 3 = 13.2 Calculating the concentration of limewater Ca(OH) ...read more.

Conclusion

2. When you have filled the burette make sure that you have removed the air bubble from below the burette's tap. 3. When transferring the solution into the conical flask always use a graduated pipette. Ensure that the bottom of the meniscus is on the line. 4. Always leave the last drop in the graduated pipette - it is calibrated this way. 5. When adding indicator add only enough drops to get a reasonable colour. Too many drops will affect the end point and hence the accuracy of your results. 6. Always use a white tile so that the colour change at the end point is clear. 7. Before carrying out your first titration remove the filter funnel you used to fill the burette. 8. Record the starting volume and the final volume when the end point is reached. Don't forget to record the volumes to 2 decimal places - i.e. 0.00 means on the line 0.05 means between the lines. 9. Repeat the titrations until you get concordant results i.e. 2 identical titres or 3 within 0.1cm3 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. ...read more.

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1. ## To determine the concentration of limewater

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moles of limewater / volume = 0.013 / 1 = 0.013 mol dm So there is 0.013 mole of Ca(OH) 2 per every 1000cm3 of solution. Therefore 25cm should contain 3.25x10-4 moles of Ca(OH) 2. 0.013/40=3.25x10-4 mole Ratio of limewater: Hydrochloric acid = 1: 2 = 3.25 x 10 :

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The reaction vessel (conical flask) should be rinsed with distilled water for the same reason. Before transferring any limewater solution with the pipette this should also be rinsed out with distilled water to avoid contamination, which may lead to erroneous results. Once all equipment is ready for the process to begin the hydrochloric acid solution

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