Learn about the assay of ferrous sulphate through a laboratory experiment or practical.
Aim:
To perform the assay of ferrous sulphate using standard 0.1 N ceric ammonium sulpahte (Cerimetry).
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade ferrous sulphate (FeSO4), sulphuric acid (H2SO4), and potassium permanganate (KMnO4), ceric ammonium sulphate, arsenic trioxide, potassium iodide, sodium hydroxide, osmic acid, ferroin sulphate, and 1, 10-phenanthroline hydrochloride, etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.
Principle of assay of ferrous sulphate:
The assay of ferrous sulphate is based on redox titration (cerimetry). Ferrous sulphate is used as a reducing agent and is a powerful oxidant. Using ferroin solution as an indication, the known concentration solution of ceric ammonium sulphate is titrated with ferrous sulphate.
Ferrous sulphate is oxidized to ferric sulphate in the presence of dilute H2SO4. When the oxidation of ferrous sulphate is completed, a drop of KMnO4 is added. The endpoint of the titration is determined by the appearance of the permanent pink color and potassium permanganate (KMnO4) acts as a self-indicator.
Preparation and standardization of ceric ammonium sulphate (0.1 M):
Click here to get the procedure for the preparation and standardization of 0.1 M ceric ammonium sulphate.
Preparation of ferroin sulphate solution:
Take 0.7 gm of ferrous sulphate and 01.50 gm of 1, 10- phenanthroline hydrochloride and dissolve in 70 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 100 ml.
Preparation of sulphuric acid solution (1 M):
Click here to get the procedure for the preparation of 1 M sulphuric acid 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 0.5 gm of ferrous sulphate and pour into a conical flask and to dissolve add a mixture of 20 ml sulphuric acid (1 M) and 30 ml of distilled water.
- Add 0.1 ml of ferroin sulphate solution.
- Titrate the sample solution with ceric ammonium sulphate solution until the endpoint is reached. The actual endpoint of the titration is indicated by the disappearance of the red color.
- Properly record the readings of the burette.
- To get accurate results, repeat the titration three times.
- Take their mean and calculate the % purity of ferrous sulphate.
Observation table:-
|
Sr. No. |
Content
in conical flask |
Burette
reading |
Volume
of titrant used (ml) |
|
|
Initial |
Final |
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|
1 |
|
|
|
|
|
2 |
|
|
|
|
|
3 |
|
|
|
|
|
Mean: |
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Calculations:
Percentage purity of NH4Cl = V x E x AN X 100 / W x RN
Where,
V is a volume of KMnO4used
E is an equivalent factor
AN is an actual normality of KMnO4
RM is a required normality of KMnO4
W is the weight of the sample
For 0.1 M NaOH, the equivalent factor of ceric ammonium sulphate is 0.01519
Result:
The percentage purity of the ferrous sulphate (FeSO4) sample was found to be_____.
Commonly asked questions on the assay of ferrous sulphate are as follows.
Which indicator is used in the assay of ferrous sulphate?
No indicator is required in the assay of ferrous sulphate as potassium permanganate is a self-indicator. Generally, ferroin sulphate solution is used as an indicator which is prepared by ferrous sulphate and 1, 10- phenanthroline hydrochloride.
Which method is used for the estimation of ferrous sulphate?
The redox method is used for the estimation of ferrous sulphate from the sample solution.
How do you identify ferrous sulfate?
Ferrous sulfate can be identified by the identification tests are prescribed by pharmacopeias, that is to check the quality of the drugs, pharmaceutical aids, or any reagents necessary for the test.
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