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10:37 AM
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Experiment
Richard Megna/Fundamental Photographs
exp10.qxd
10
Vinegar Analysis
Vinegar is a 4–5% (by mass) solution in acetic acid.
• To determine the percent by mass of acetic acid in vinegar
Objective
The following techniques are used in the Experimental Procedure:
Techniques
Household vinegar is a 4–5% (by mass) acetic acid, CH3COOH, solution (4% is the
minimum federal standard). Generally, caramel flavoring and coloring are also added
to make the product aesthetically more appealing.
A volumetric analysis using the titration technique is the method used for determining the percent by mass of acetic acid in vinegar. A measured mass of vinegar is titrated
to the phenolphthalein endpoint with a measured volume of a standardized sodium
hydroxide solution. Since the volume and molar concentration of the standardized NaOH
solution are known, the moles of NaOH used for the analysis are also known.
Introduction
mol NaOH = L NaOH solution
mol NaOH
L NaOH solution
(10.1)
From the balanced equation:
CH3COOH(aq) + NaOH(aq) —› NaCH3CO2(aq) + H2O(l)
(10.2)
mol CH3COOH = mol NaOH
(10.3)
The mass of CH3COOH in the vinegar is calculated from the measured moles of
CH3COOH neutralized in the reaction and its molar mass, 60.05 g/mol:
mass(g) of CH3COOH = mol CH3COOH
60.05 g CH3COOH
mol CH3COOH
(10.4)
Finally, the percent by mass of CH3COOH in vinegar is calculated:
% by mass of CH3COOH =
mass (g) of CH3COOH
mass (g) of vinegar
100
(10.5)
Procedure Overview: Samples of one or two vinegars are analyzed for the amount
of acetic acid in the sample. A titration setup is used for the analysis, using a standardized NaOH solution as the titrant and phenolphthalein as the indicator.
Experimental
Procedure
Experiment 10
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