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Chemistry Vinegar Titration

Experiment: To determine the ethanoic acid (acetic acid) content of white vinegar.

Aim:White vinegar is sold as a 4% solution of ethanoic acid( acetic acid). What is the actual ethanoic acid content of white vinegar. We can determine this using an acid-base titration.

Equipment required:

          Pipette

            Burette

            Volumetric flask

            Clamp stand

            Funnel

            White tile/white cardboard

Solutions required:

Indicator – phenolphthalein   

Standard solution 2.0 mol/L NaOH

White vinegar

Keywords:

Titration – an experimental procedure in which the amount of some substance or ion is determined by measuring the volume of a solution of known concentration that is required to react with it.

Standard solution –  a solution whose exact concentration is known accurately.
Indicator  (also called an acid-base indicator) –  any substance, natural or synthetic, which has one colour in acid solution and another in alkaline solution.
Pipette – used for the transfer of measured volumes of solutions for analysis, or dilution.
Burette – used to measure the volume of a titrant that reacts exactly with the sample.
Endpoint – the point at which the solution changes colour and the reaction is complete.

Procedure:

  1. Secure the burette in the clamp stand.
  • Add 20mL of 2.0mol/L NaOH to the burette.
  • Record the burette reading, reading from the bottom of the meniscus. This is the initial reading.
  • Accurately pipette 25mL of white vinegar into the volumetric flask.
  • Add 2-3 drops of phenolphthalein indicator.
  • Place the white tile/cardboard on the flat surface of the clamp stand.
  • Place the volumetric flask under the burette.
  • Slowly add the NaOH to the volumetric flask swirling the flask constantly.
  • When the colour of the solution in the volumetric flask changes to pink do not add any further NaOH. This is the endpoint of the titration.
  1. Record the burette reading this is the final reading.

Calculation of the results of a titration

  1. Write the balanced equation for the reaction, and establish the proportion in which the substances react.
  • Identify the substance whose amount can be calculated from the information that is available. This information will be in the form of either the mass of a substance or the volume and concentration of a solution. Calculate the amount of this substance.
  • Use the information from steps 1 and 3 to calculate the amount of the other substance.
  • Complete the calculation by presenting this result in the form required, which will either be:

either the mass of the substance

or the concentration of the solution expressed in  mol/L

or the concentration of the solution expressed in g/L

For the titration demonstrated:

Concentration of standard solution of NaOH=2.0 mol/L
Titration: Final burette reading=31.0 mL
Initial burette reading=22.5 mL
Volume of NaOH solution used in titration=8.5 mL
Volume of sample (ethanoic acid) solution=25 mL

Reaction equation:

CH3COOH + NaOH     —–>     H3COONa + H20

            Amount of NaOH used in titration = 2.0    x     8.5  mol

  1. 1000

= 0.017 mol

Since 1 mol CH3COOH     =  1 mol NaOH

Amount of CH3COOH in sample               =  0.0017 mol  x 1000

                                                                                                         25

                                                                     = 0.68 mol/L

Molecular weight (MR) CH3COOH            = 60

Concentration CH3COOH in vinegar         = 60  x 0.68 g/L

                                                                     = 40.8 g/L

Concentration CH3COOH in vinegar         = 4.08g/100mL

                                                                     = 4.08%

Conclusion:
The concentration of ethanoic acid in the white vinegar examined is consistant with the manufacturers claim of 4%.