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The experiment is the mixing of hydrochloric acid and calcium hydroxide together and using an appropriate method to find the concentration of limewater.

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Introduction

Chemistry Assessed Practical 2 Jared Ching Planning: Introduction and background: The experiment is the mixing of hydrochloric acid and calcium hydroxide together and using an appropriate method to find the concentration of limewater. This is the equation of the reaction: Ca(OH)2(aq) +2HCl(l) CaCl2(aq)+2H2O(l) Knowing this and using calculations we can work out the concentration of limewater having titrated the two solutions, from the volumes and concentration of HCl. In the presence of Phenolphthalein hydroxides turn pink, when neutralized, go colourless, this will be the indication of the end of the reaction, when all limewater is reacted. However as stated in "Chemistry in context", phenolphthalein has a very high end point to its pH scale, making it suitable for use in titrations with fairly high concentrations. But clearly using a weak base like calcium hydroxide would make methyl orange a better choice. Using phenolphthalein would change in colour before the point of balance between acid and base, thus giving inaccurate results. Method: In order to find out concentration of the limewater, we need to dilute the hydrochloric acid to a very low concentration, so that it neutralizes the limewater slowly enough to record the change in volume of acid titrated. ...read more.

Middle

5. Take an accurate reading of the final burette reading, record this. 6. Using a new flask with fresh solution of the same volume repeat the titration. Take 5 repeats including one rough reading. 7. Using calculations find out the concentration of calcium hydroxide. This can be done by using the equation: Concentration=Moles x Volume. See preliminary calculations sheet over page. The results will be recorded in a table like this: Rough 1 2 3 4 Initial Burette reading (cm3) Final burette reading (cm3) Volume of 0.02Mol/ dm3 HCl used Safety/Precautions: Always wear a lab coat and safety spectacles. Great care must me taken when handling the concentrated HCL, it is corrosive and will damage bare skin, and especially eyes, care must be taken to not spill the substances on your hands. Precision and accuracy: * I have chosen the apparatus such that it provides the most accurate answers possible. Glass pipettes and volumetric flasks are the most accurate way of measuring out volumes; and burettes. These instruments carry accuracy of +/-0.05 cm3, clearly the small error should not place the results very close to actual volumes. ...read more.

Conclusion

Another cause for the possible inaccuracy is the calcium hydroxide solution decanted- a white solid deposited on the base of the large flask containing the calcium hydroxide solution. This would have caused the solution to be a different concentration completely. Thus I swirled it in order to get a constant concentration throughout the solution. However, the constant effect of the particles depositing leads me to conclude that each titration was different in its results as the concentration of the calcium hydroxide varied each time. Overall, the results were prove to be concurrent and accurate, however there was still error accounted for due to the way calcium hydroxide solution acts and due to the colour change observed not being definite. After the practical we collected results from everyone in the class in order to see what the average concentration of limewater. This is a table of everyone's results: Name Concentration Me 1.006 Adam 0.913 Scott 1.04 Mehul 1.934 Maneesh 0.8151 Raj 0.868 Unni 0.91 Average: 0.941g/dm3 The average concentration indicates that my result was very close, thus I can conclude that I came very close to the actual concentration of the limewater solution. ...read more.

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