Equilibrium Constant - Ironisation of Ethanoic Acid

[phoebejean]

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I have a prac assessment in a few days, any help would be great! Thankyou

Design an experiment to calculate the value of the equilibrium constant for the ionisation of ethanoic acid, a weak acid.

Any idea's of the best way to do this? We need to list the equipment we will use and justify our choices and also outline the variables and how we will control them.

sweeeeeeet.

[brenton1987]

Originally Posted by phoebejean

Design an experiment to calculate the value of the equilibrium constant for the ionisation of ethanoic acid, a weak acid.

The dissociation of ethanoic acid will be
CH₃COOH --> H⁺ + CH₃COO^-
K_d = [H⁺] [CH₃COO^-] / [CH₃COOH]

Measuring the pH of a sample of standardised ethanoic acid will allow the calculation of [H+], [CH3COO-], and [CH3COOH].

As ethanoic acid will be an aqueous solution it needs to be standardised against standardised base.

Primary standard --> Determine concentration of base --> Determine concentration of ethanoic acid.

Weigh accurately a sample of primary standard acid (potassium hydrogen phthalate, potassium hydrogen iodate, sulfosalicylic acid double salt, sulfamic acid etc) and make up to volume. Calculate the concentration.

Titrate against the base. Calculate concentration of base. Titrate standardised base against ethanoic acid. Calculate acid concentration.

Pipette a sample of ethanoic acid and measure pH. Calculate [H⁺], which will be the same as [CH₃COO^-]. [CH₃COOH] has be previously calculated.

All titrations should use a pH meter with measurements taken every 1 cm³ to within 5 cm³ of the end point and then every 0.1 cm³. Plot a differential graph to determine volume.