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To find out the Ka of ethanoic acid, chloroethanoic acid and dichloroethanoic acid.

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Introduction

Experiment 17 21-4-99 Aim: To find out the Ka of ethanoic acid, chloroethanoic acid and dichloroethanoic acid. Procedure: 1. The pH meter is calibrated, using a buffer solution of accurately known pH. 2. 20.0cm3 of 0.10M ethanoic acid was pipetted into a conical flask. 3. 0.10M sodium hydroxide solution was titrated using phenolphthalein as indicator, until the solution was just turned pink. 4. A further 20.0cm3 of the same ethanoic acid solution was added to the flask and was mixed thoroughly. 5. The pH of the resulting solution was determined. Result: Volume of NaOH used is recorded below: Trial (cm3) 1st time (cm3) ...read more.

Middle

1 [H+] ? Ka 3. [H+] ? Ka -log Ka = -log [H+] pKa = pH 4. The aim of neutralization is to neutralize all the acid, and make the concentration of the salt same as the concentration of the 20.0cm3 acid. Therefore the titre need not be exactly 20.0cm3. 5. If the titre were, say 22.0cm3, a further 20.0cm3 of acid is still added. The mole of the salt from neutralization is same as the mole of 20.0cm3 acid. As equal mole of salt and acid is needed, a further 20.0cm3 of acid is still added. 6. For CH3COOH, pKa = pH pKa = 4.6 Ka = 2.514 ? ...read more.

Conclusion

9. This method can also be used to determine the dissociation constant of weak bases. For ammonia: Kb = [OH-] ? Kb Procedure 1~5 can be repeated while the acid is replaced by NH3 and NaOH is replaced by HCl. For the pH is known, by 14 - pH = pKb the Kb can be found out. Conclusion: Ka ethanoic acid 2.514 ? 10-5 chloroethanoic acid 0.001 dichloroethanoic acid 6.310 ? 10-3 Discussion: 1. Distilled water can be added to buffer solution. But Distilled water can not be added to the conical flask because it will alter the pH of the solution 2. The pH meter should be calibrated by washing it with deionized water and then with the acid. ...read more.

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