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Determination of the concentration of lime water solution

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Introduction

Victioria Nicholls Chemistry Coursework Title: Determination of the concentration of lime water solution Objective: The aim of this experiment is to determine the concentration of an unknown limewater solution in g dm-3 as accurately as possible, which contains 1g dm-3 of calcium hydroxide. This will be done by titration with hydrochloric acid. The Reaction occurring is: Ca(OH)2(l) + 2HCl(l) � CaCl2(l) + H2O(l) Apparatus: Metal stand Burette Conical flask 25cm3 Pipette 250cm3 volumetric flask Lime-water solution Hydrochloric acid Methyl-red indicator Diagram Method: 1.Firstly, determination of the concentration of hydrochloric acid to be used is to be carried out, as the 2.00 mol dm-3 solution of hydrochloric acid supplied is too concentrated. This was done by diluting the 2.00 mol dm-3 solution with water to the values 1.00, 0.50, 0.10 and 0.02mol dm-3 of hydrochloric acid. The was done using preliminary results: Concentration of HCl (mol dm-3) Volume of HCl required to neutralise the lime water (cm3) ...read more.

Middle

This is when the solution becomes neutral i.e. pH7. (See method on how to titrate accurately - see appendix 2) 7. So after finding a suitable dilution of hydrochloric acid to use which was 0.02 mol dm3, the burette was filled with 50cm3 of hydrochloric acid, using a measuring cylinder that measures to 1cm3. We had to make sure that there were no air bubbles present in the burette jet, this would have affected the volume of liquid in this method. To avoid this we kept the burette jet running until we could see clear that there were no air bubbles present in the burette to affect the accuracy of our results. 8. We needed an indicator which has an end point is below pH 7 because there is a sharp change below pH7 and a gradual change above pH 7. We needed a sharp change. The colours, ranges and end points vary considerably as can be seen in the table below: Name of dye Colour at low pH pH range End point (Pkind) ...read more.

Conclusion

Results Titration Start (cm3) Finish (cm3) Volume (cm3) Rough 50 19.0 31.00 1 50 19.3 30.70 2 50 19.4 30.60 3 50 19.5 30.50 Average Volume = 30.60cm3 Number of moles of HCl used = volume � concentration 1000 = 30.60 � 0.02 1000 = 0.0006mol dm-3 The reaction occurring is: Ca(OH)2 + 2HCl � CaCl2 + H2O As 2 : 1 HCl Ca(OH)2 0.0006 = 0.0003 moles of Ca(OH)2 2 0.0003 moles in 25cm3 0.0003 � 40 = 0.012 moles ArCa(OH)2 = 74 Moles = Mass � Mass = Moles � Ar Ar = 0.012 � 74 = 0.1g/dm-3 Therefore, the concentration of limewater is 0.1g/dm-3 Safety Substance Risk Precaution - Hydrochloric Acid - CORROSIVE - Can cause severe burns. Can be very dangerous to eyes and skin. Solutions equal to over 0.5m should be labelled corrosive. Those over 0.5m should be relabelled irritant. - Wear gloves and goggles at all times Instructions to follow before starting experiment: - Move all obstructions e.g. stools and bags - Clear work area of unnecessary equipment - Beware of spillage's - Take care with glass equipment - if breakage occurs report immediately ...read more.

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