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Determining the concentration of a limewater solution.

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Introduction

Determining the concentration of a limewater solution Task I am provided with 250 cm� of limewater (calcium hydroxide), which has been made such that it contains approximately 1g/dm� of calcium hydroxide. Also available is hydrochloric acid which has a concentration of exactly 2.00-mol/dm�. However, this acid is too concentrated to be used so will need to be diluted for the experiment. My aim is to plan an experiment which will allow me to determine the concentration, in g/dm�, of the limewater as accurately as possible. Normal laboratory equipment is available including indicator solutions but no other chemicals may be used. The apparatus I have chosen: * Pipette (25cm�) - to gain an accurate amount of hydrochloric acid ready for dilution * Volumetric flask (500cm�) - Very accurate equipment used for the dilution of the hydrochloric acid * Conical flask (250cm�) - to put the limewater solution into ready for the titration * Burette (50cm�) - to contain the diluted hydrochloric acid for the titration * White tile - to put underneath the conical flask to clearly see when the colour changes * Clamp and stand - to hold the burette in place * Funnel - to pour the hydrochloric acid into the burette to prevent spillage * Indicator (phenolphthalein) ...read more.

Middle

The equipment I have chosen is very accurate with the greatest uncertainty being only 2% per drop and the most accurate being only 0.08% uncertainty with the volumetric flask which is extremely reliable and unlikely to affect results in any way. However, to maintain this accuracy, all apparatus must be washed with distilled water before and after use as some will be used more than once and any residual chemicals will affect the outcome. 1. To actually dilute the acid you will need the pipette and the pump to collect exactly 25ml taking into account parallax errors where the level of the 25ml line is at the bottom of the meniscus. 2. Place this solution into a 250ml volumetric flask and top it up to 250ml with distilled water. This will have taken the molar down to 0.2M. 3. Place a bung on the solution and shake to mix up the solution. 4. Take another 25ml by the pipette from this solution and place into a different volumetric flask. Top up to 250ml with distilled water. The molar of the acid has now been taken down by a factor of one hundred making it 0.02M which is now ready for the titration. 5. By using the pipette again collect exactly 25ml of the calcium hydroxide and place in a conical flask. ...read more.

Conclusion

I rounded my end result up to 2 decimal places because this represents the reliability of the equipment which is also accurate to 2 decimal places therefore further digits are not required. I felt there were few limitations in the procedure and any limitations there was were minimal. An example of this is when the solution during the titration gets on the walls of the conical flask which may stop it from being neutralised and slightly disturb the experiment. This however can be helped if you swirl the solution around thoroughly during the titration to make sure that it is all mixed together. Some of the errors were likely to have come from measurements. For example a source of error could be a parallax error which involves the meniscus present in the burette and pipette. Another form of human error could be the judgement of colour change in the titration when it reaches neutralisation. The human eye could be wrong which would results in a slight error of results. None of these sources of error could really be improved dramatically. However, if I were to use a larger quantity of limewater for the titrations this would reduce the percentage error. Also, by repeating the experiment several more times would give me a more reliable and accurate set of results from which I could have obtained a better average. ...read more.

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