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Estimation of Chlorine in Household Bleach.

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Introduction

Estimation of Chlorine in Household Bleach In this investigation, I am looking to determine the amount of chlorine present in household bleach. However, in order to do this I would have to calculate the mass represented by chlorine in the mass of the household bleach. After doing that, I would then have to represent this as a percentage. In order to calculate the mass represented by the chlorine in the mass of the household bleach, I would have to titrate this solution, along with an excess of potassium iodide and ethanoic acid against sodium thiosulphate from the burette using starch solution as an indicator. The reason for this choice of indicator is that iodine is turned blue black by the starch solution, and this therefore helps to indicate any colour change that occurs. I began my investigation by measuring out 10mls of household bleach using a measuring cylinder. I poured this into a volumetric flask, and used distilled water to ensure that all 10mls of the bleach were in the volumetric flask and not in the measuring cylinder. This was then topped up to 250ml using distilled water in the volumetric flask. I had to make sure that the bleach solution is mixed completely and shook the flask from top to bottom. ...read more.

Middle

This is known as the 'end-point' of the titration. In this case, the colour of the solution would change from blue-back to cream/colourless. After stopping the tap, I would have to read the burette again (V2). Then I would have to subtract this from the previous reading of the bottom of the meniscus (V1) to give the volume of sodium thiosulphate required to react with the ethanoic acid. This titration should be repeated, so an average titre is obtained. From this volume, we can now determine the percentage of chlorine present in household bleach. My results are shown in the table below: - V1, the bottom of the meniscus V2, alkali used to neutralise the acid V2- V1, the amount of alkali used AVERAGE 0.4 21.0 20.6 20.1 0.2 20.4 20.2 0.6 20.1 19.5 During the experiment, the bleach liberates chlorine readily when reacting with the ethanoic acid: - ClO-(aq) + 2H+ (aq) + Cl- (aq) � Cl2 (aq) + H2O (l) (1). The amount of chlorine present in the household bleach, which contains Sodium Chlorate (I) can be found by allowing the bleach to react with an iodide solution to react with an iodide solution to form, and then titrating with thiosulphate solution: - ClO- (aq) ...read more.

Conclusion

These improvements could include more co-ordination between my partner and I, which had resulted in the first attempt of the back titration, where I had closed the tap a bit late due to a late call from my partner to call 'stop' when the end-point had been reached. Normally, the amount of sodium thiosulphate solution required to neutralise the amount of ethanoic acid is the same, but in the case of my investigation, they differ by quite a large range. They differ by 1.1, which is quite big, but the gap is not big enough to affect the results I get. Despite that, no anomalies had occurred throughout the investigation. Possible changes to how investigation was carried out could be that the attempts could have been done separately. My investigation was carried straight after one another, as a result of a lack of sodium thiosulphate, after washing the vessels, which was needed to prevent any interference from the previous attempt. This could have led to more accurate results and better reading of the meniscus. My partner and I had completed the investigation quickly meaning that the investigation lacked some accuracy. So to change this, I would have preferred to complete the investigation with a bit more haste. Also to improve my investigation, I could have used more technologically advanced equipment, but unfortunately these were unavailable. Danny Basil Kannan Vincent ...read more.

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