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The aim of this experiment is to determine as accurately as possible the concentration of a limewater solution

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Introduction

Plan Aim The aim of this experiment is to determine as accurately as possible the concentration of a limewater solution. I have decided that in order for the experiment to work best, giving me an accurate as possible result, I will titrate the limewater with Hydrochloric Acid. I will ensure all necessary safety precautions are followed. The problem that may arise during this experiment is that there will be a different amount of Hydrochloric acid needed for each titration. This problem could arise because the limewater is sparingly soluble, meaning it has not completely dissolved. Therefore each 25 cm3 pipette of limewater will require different amounts of Hydrochloric acid. To help overcoming this problem I am going perform the titration experiment 5 times. From these results I will be able to calculate an average for the amount of Hydrochloric acid required to titrate 25cm3 limewater. The first thing I must do in this experiment is to calculate the concentration of Hydrochloric acid that can be used on a reasonable amount of limewater. I will than dilute the Hydrochloric acid given which is of 2.00mol dm-3 to that I have calculated. Following this I will be able to measure out the limewater ready for titration with the Hydrochloric acid. My chosen indicator is phenolphthalein because I believe it will give the clearest colour change, making it easily noticeable as to when the required amount of Hydrochloric acid to neutralise the limewater has be added. ...read more.

Middle

Method to Titrate hydrochloric acid and Limewater 2HCl(aq) + Ca(OH)2(aq) � CaCl2(aq) + 2H2O The safety precautions required for this experiment to be safe, is that I will require goggles to wear. The concentration of solution I am using is not that high, therefore there are not many dangers in using these solutions. I am going to find out the amount of 0.02 mol dm-3 Hydrochloric acid required to titrate 25cm3 of limewater. In order to do this I will accurately pipette 25cm3 of limewater. I will be provided with limewater in a large beaker, from this I can use a pipette to remove 25cm3, when drawing the limewater out I may overflow the 25cm3 mark. To remove a slight amount from the pipette, I will place my thumb over the top of the pipette and gentle wiggle it, this will let a minimal amount of air enter the pipette so that a slight amount of limewater is removed. To ensure the bottom the meniscus is level with the 25cm3 mark, I will keep the mark at my eye level. My thumb will tightly be kept over the top of the pipette when the pipette filler is removed. I will pipette the limewater 5 times, into separate conical flasks. I will stir the limewater solution before I take each 25cm3 aliquot to try to ensure as much calcium hydroxide has dissolved as possible. ...read more.

Conclusion

Calculations I am provided with 250cm3 1gdm-3 Ca(OH)2 This means I have 1g Ca(OH)2 in 1000cm-3 water We only want 250cm3 not 1000cm3 1000 250 = 4 Grams of Ca(OH)2= 1.00 4 = 0.25g We are going to use 25cm3 pipette of Ca(OH)2 Grams in 25cm3 = 0.025g Ca(OH)2 + 2HCl CaCl2 + 2H2 O 1 mole Ca(OH) 2 = mass = 0.025 Mr 74.1 = 0.000337moles Got 0.000337 moles Ca(OH)2 in 25cm3 1 Ca(OH)2 : 2 HCl 0.000337 : 0.000674 moles I am using 2.00 mol dm-3 HCl Volume = moles x 1000 Concn Volume = 0.000674 x 1000 = 0.337cm3 2.00 0.337cm3 : This volume of HCl is too small. I will be using a 50cm3 pipette, the accuracy will be too difficult to obtain. A reasonable volume will be between 20-35 cm3. In order to achieve a volume between 20-35 cm3 I will decrease the concentration. If 0.02mol dm -3 HCl is used: Volume = 0.000674 x 1000 = 33.7 cm3 0.02 This is a reasonable amount. Dilute HCl from 2.00 moldm-3 0.02 mol dm-3 In a 250 cm3 volumetric flask. 2 ? 0.02 = 100 This means 0.02 mol dm-3 HCl is 100 times weaker than 2.00 mol dm-3. 250cm3 ? 100 = 2.5cm3 Therefore I need 2.5 cm3 2.00 mol dm-3 HCl and dilute it to 250 cm3 with distilled water. A 10cm3 graduated burette will need to be used to get an accurate 2.5cm3 reading. ...read more.

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