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Pka of ethanoic acid

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Introduction

Determining the pka value of ethanoic acid A titration is a procedure that can be used in analytical chemistry to determine certain value or concentration of a substance. The aim of this experiment is to determine the pka value of ethanoic acid. Every acid has its own specific dissociation constant, ka, which measures the strength of the acid. pka is equal to the negative logarithm of ka .In order to determine the pka constant for ethanoic acid it was titrated with NaOH. The reaction is as below CH3COOH + NaOH (aq) � CH3COO- + Na+ + H2O ka = [CH3COO-][H+] [CH3COOH ] pka = - log ka Materials: - NaOH (0.1 mol dm-3), CH3COOH (0.1 mol dm-3), pH meter, stand, clamp, thermometer, beakers, pipette, magnetic spin, titration pipette. Methods:- 1. 25 ml of ethanoic acid was poured into a beaker and placed below the titration pipette. ...read more.

Middle

The pH value also took an abrupt increase from 5.89�0.01 to 11.31�0.01 as the volume of NaOH increased from 15�0.05 to 16�0.05 ml. Graph 1. Change in the pH value of Ethanoic acid as the volume of NaOH increases As seen from Graph 1 the pH value gradually increases up to a point where it drastically show increase in the pH value. Then it begins to increase gradually again. All of this is due to the change of ethanoic acid to its conjugate base as more and more sodium hydroxide is added. The pka value of ethanoic acid can be found by analyzing the above titration graph. From the graph it is possible to find the equivalence point. The equivalence point is a point where the acid-base solution is neutral. This means that all of the acid has been consumed and will have a pH value greater than 7 since ethanoic acid is a weak acid and NaOH is strong acid. ...read more.

Conclusion

Dividing this value by two will result in 7.75�0.32 ml. (The new uncertainty was found by calculating the percentage uncertainty of 15.5). The pH value at 7.75�0.32 ml is 4.60�0.01. The literature pka value of ethanoic acid is found to be 4.76. Therefore the experimental value calculated here is very close. The difference may be due to uncertainties and limitations of the experiment. Conclusion: - according to this experiment the pka value of ethanoic acid was found to be 4.60. This is a very close result to the literature value which is 4.76. The difference may be a result of uncertainties and limitations. Limitations: - the volume used for titration was 25 ml. instead using higher volumes of sodium hydroxide and ethanoic acid would allow the effect of one drop to be more accurate and it will also minimize the random/systematic errors on the final result. Improvements: - using higher volumes such as 100ml of sodium hydroxide and ethanoic acid. ?? ?? ?? ?? ...read more.

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