Learn about the assay of sodium benzoate through a laboratory experiment or practical.
Aim:
To determine the percentage purity of sodium benzoate using standard 0.1 N perchloric acid (non-aqueous titration).
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade sodium benzoate (C7H5O2Na), glacial acetic acid (CH3COOH), potassium hydrogen phthalate (KHP), acetic anhydride (C4H6O3), 1-naphtholbenzein and crystal violet, etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.
Principle of assay of sodium benzoate:
Sodium benzoate is a preservative that comes in the form of a white granular or crystalline powder. The base sodium benzoate is dissolved in glacial acetic acid that increases the strength of weak base sodium benzoate. Acetic acid acts as a base during the titration with strong acid, allowing an accurate endpoint to be determined. As an indication, the 1-naphtholbenzein solution is used to detect the endpoint of the reaction.
This practical is divided into two parts:
A: Preparation and standardization of perchloric acid (0.1M).
B: To perform the assay of sodium benzoate.
Preparation and standardization of 0.1 M perchloric acid:
Click here to get the procedure to prepare and standardize perchloric acid (0.1M).
Preparation of 1-naphtholbenzein indicator solution:
Take 200 mg of 1-naphtholbenzein and dissolve in 50 ml of anhydrous glacial acetic acid in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 100 ml.
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.
- Note: Since it is a non-aqueous titration, it needs to be extra careful during the cleaning and drying of glassware. Glassware is required to be clean with acetone and dried for purpose.
- 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 0.25 gm of sodium benzoate and pour it into a conical flask.
- Add 20.00 ml anhydrous glacial acetic acid, sonicate to dissolve, and if required warm it at 50°C.
- Then add 2 drops of 1-naphtholbenzein indicator solution.
- Titrate the sample solution with the perchloric acid solution until the endpoint is reached.
- The actual endpoint of the titration is indicated by a change of violet color to emerald green.
- To get accurate results, repeat the titration three times.
- Properly record the readings of the burette.
- Take their mean and calculate the percentage purity of sodium benzoate.
- For the blank determination, repeat the titration as directed above but without the sodium benzoate (B).
Observation
table:
A. For
titration of sample
|
Sr. No. |
Content
in conical flask |
Burette
reading |
Volume
of titrant used (ml) |
|
|
Initial |
Final |
|||
|
1 |
|
|
|
|
|
2 |
|
|
|
|
|
3 |
|
|
|
|
|
Mean: |
|||
B. For
titration of blank
|
Sr. No. |
Content
in conical flask |
Burette
reading |
Volume
of titrant used (ml) |
|
|
Initial |
Final |
|||
|
1 |
|
|
|
|
Calculations:
% purity of sodium benzoate = V x E x AM x 100 / W x RM
Where,
V is the volume of perchloric acid solution used
V= A-B
A is a volume of perchloric acid solution used in titration with sodium benzoate
B is a volume of perchloric acid solution used in titration without sodium benzoate
E is an equivalent factor
AM is actual molarity
RM is a required molarity
W is the weight of the sample
For 0.1 M perchloric acid solution, the equivalent factor of PHP is 0.01441.
Result:
The percentage purity of sodium benzoate was found to be_____M.
Commonly asked questions on titration are as follows.
Sodium benzoate can be estimated by which titration?
Sodium benzoate can be estimated by the non-aqueous titration method in which it is dissolved in anhydrous glacial acetic acid, which increases the strength of sodium benzoate, a weak basic.
Which indicator is used in sodium benzoate assay?
1-naphtholbenzein indicator solution is used in sodium benzoate assay which produces emerald green at the endpoint or equivalence point.
Which titrant used in the assay of sodium benzoate?
The perchloric acid solution is used as a titrant in the assay of sodium benzoate by non-aqueous titration.
You may also like this
No comments:
Post a Comment