IB Colourful Solutions in Chemistry

Commercial white vinegar is a dilute solution of ethanoic acid, CH₃COOH, of between 5% and 10% w/v. The purpose of this experiment is to determine the concentration in mol dm^-3 of ethanoic acid in the vinegar by direct titration using phenolphthalein indicator.

Note: Titrations work better with solution concentrations of between 0.01 and 0.2 mol dm^-3.

Background
Requirements
Procedure

Background

Ethanoic acid, CH₃COOH, is a weak monoprotic acid (contains one acidic hydrogen atom) that reacts stoichiometrically (according to the equation) with a base.

Neutralisation of ethanoic acid

CH₃COOH(aq) + NaOH(aq) → CH₃COONa(aq) + H₂O(l)

If the mol of NaOH used in the neutralisation is known then the mol of ethanoic acid must be the same. Using the volume of the ethanoic acid, the concentration can be calculated.

concentration = mol/vol(in dm^-3)

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Requirements

Chemicals

Commercial vinegar
Sodium hydroxide (solid)
Phenolphthalein solution

Apparatus

50ml pipette
25ml pipette
pipette pump filler
250ml conical flask
2 x 250ml volumetric flask
Wash bottle
50ml burette
clamp and stand
white tile

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Procedure

1. Transfer a 25 cm³ sample of the commercial vinegar into a 250 cm3 volumetric flask and make up to the mark with water. Shake and label.
2. Prepare 250 cm³ of approximately 0.1 mol dm^-3 NaOH(aq) by direct dissolution of the solid.
3. Titrate 25ml aliquots of the diluted vinegar solution against sodium hydroxide from the burette using 5 drops of phenolphthalein indicator.
4. Repeat until concordant results are obtained

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Titrations