Learn about the assay of acetic acid in a given sample of vinegar using 0.1 n sodium hydroxide through a laboratory experiment or practical.
To determine the percentage purity of acetic acid in a given sample of vinegar using 0.1 n NaOH
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, wash bottle, etc.
Chemicals: LR grade sodium hydroxide (NaOH), acetic acid (CH3COOH), phenolphthalein indicator, etc.
Apparatus: Digital/analytical balance
The determination of acetic acid in vinegar by direct titration:
The major components in vinegar are acetic acid and water. It is a carbon-based compound with a –COOH functional moiety with a single ionizable proton. Vinegar derives its acidity from acetic acid (CH3COOH or HC2H2O2). Acetic acid, (Ethanoic acid), is a weak acid that is a type of organic acid (carboxylic acid).
CH3COOH(aq) + NaOH(aq) -> CH3COONa(aq) + H2O(l)
Phenolphthalein or thymol blue are ideal indicators for this titration since the pH at the equivalence point will be larger than 07 when weak acids like acetic acid are titrated with strong bases like NaOH solution.
By titrating an appropriate sample of commercial vinegar with the standardized NaOH solution, it is simple to determine the amount of acetic acid (CH3COOH) present in the vinegar. This experiment requires two steps; first, we must standardize the sodium hydroxide standard solution, followed by the acetic acid test.
Click here to get the procedure for standardization of the sodium hydroxide solution:
Titration procedure:
- All glassware should be cleaned and dried according to standard laboratory procedures.
- Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
- Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
- Remove air bubbles from the burette and adjust the reading to zero.
- Take 10.00 ml of commercial vinegar sample and pour it into a 250 ml conical flask.
- Add 5 ml of distilled water using a pipette.
- Add 2-4 drops of phenolphthalein indicator and thoroughly mix the mixture.
- Titrate this solution with NaOH solution until the endpoint is reached.
- The actual endpoint is indicated by the appearance of a pale pink color.
- To get accurate results, repeat the titration three times.
- Properly record the readings of the burette.
- Take their mean and calculate the % acetic acid in vinegar.
Observation table:
|
Sr. No. |
Content in
conical flask |
Burette
reading |
Volume of
titrant used (ml) |
|
|
Initial |
Final |
|||
|
1 |
|
|
|
|
|
2 |
|
|
|
|
|
3 |
|
|
|
|
|
|
Mean: |
|||
Calculations:
Calculate the solution's molarity
using the following formula.
Moles of acetic acid = (MNaOH)(VNaOH)
Grams of acetic
acid = (moles of acetic acid)(MW)
Grams of vinegar
=(volume of vinegar)(density of vinegar)
% acetic acid =
(grams of acetic acid / grams of vinegar) x 100
Result:
The concentration of acetic acid in the vinegar solution: _________ %.
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