Dissociation of acetic acid can be given as below
For dilute solutions
The pH of the solution at the equivalence point is
pH = 1/2 pKw + 1/2 pKa - 1/2 pC
= the ionic product of water = 1× 10^14
= the dissociation constant of acetic acid = 1.82 ×10^-5
= the concentration of the salt in moldm-3
Accordingly, for the neutralization of 0.1M acetic acid with 0.1M NaOH at the equivalence point,
pH = 7 + 2.37 - 1/2 (1.3) = 8.37
The initial pH of the 0.1M acetic acid can be calculated using its Ka value to be 2.87.
For other concentrations corresponding pH value can be calculated by,
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Pipette out 25.00mL of the given acetic acid solution into a titration flask and add few drops of thymolphthalein indicator. Titrate this solution with 0.10M NaOH solution.
- Calculate the concentration of the acetic acid solution.
- Sketch the titration curve.
- Comment on choosing indicators for this titration.
- Derive an equation for the effective or conditional formation constant of water on the employment of a weak acid, HA, with an acid dissociation constant (Ka)
- Calculate the conditional formation constant of water for the above titration.
- Calculate the standard free energy change of this titration (Room temperature = 30 oC
- A sample of vinegar, weighing 12.0g, was titrated with a 0.500M NaOH solution. 17.50 mL being required to obtain a phenolphthalein end point and 5.5 mL being required to obtain a methyl orange end point. Explain the use of correct indicator system in this titration and calculate the percentage of acetic acid in vinegar.