Learn about the preparation and standardization of perchloric acid through a laboratory experiment or practical.
Aim:
To prepare and standardize 0.1 M perchloric acid using potassium hydrogen phthalate as primary standard.
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade glacial acetic acid (CH3COOH), perchloric (HClO4), potassium hydrogen phthalate (KHP), acetic anhydride (C4H6O3), and crystal violet, etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.
Principle:
It is a type of non-aqueous titration in which water is removed by the reaction with the acetic anhydride.
The endpoint of reaction is determined by titrating a known amount of potassium hydrogen phthalate with perchloric acid in glacial acetic acid, in which crystal violet solution is used as an indicator.
The molecular weight of perchloric acid (HClO4) is 100.46 g/mol.
Preparation of crystal violet indicator solution:
Take 54 mg of crystal violet 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.
Preparation of 0.1 M perchloric acid:
Take 08.50 ml of perchloric acid using a pipette in a volumetric flask, mix with 500 ml anhydrous glacial acetic acid and 25.00 ml of acetic anhydride. Allow to cool at room temperature and make up the volume to 1000 ml with anhydrous glacial acetic acid.
Let allows the mixture to stand for one day and determining the water content. If it exceeds 0.5 percent, add extra acetic anhydride and let it stand again. The amount of water in the solution must be between 0.2 and 0.5 %.
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 0.35 gm of previously heated (120°C for 2 hours) KHP and pour it into a conical flask.
- Add 50.00 ml anhydrous glacial acetic acid.
- Then add 2 drops of crystal violet 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 molarity of a perchloric acid solution.
- For the blank determination, repeat the titration as directed above but without the potassium hydrogen phthalate (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:
Molarity of perchloric acid = W x RM / V x E
Where,
W is a weight of KHP
E is an equivalent factor of KHP
RM is a required molarity
V is the volume of perchloric acid solution used
V= A-B
A is the volume of perchloric acid solution used in titration with KHP
B is the volume of perchloric acid solution used in titration without KHP
For 0.1 M perchloric acid solution, the equivalent factor of PHP is 0.020422.
Result:
The strength of the prepared perchloric acid solution was found to be_____M.
Commonly asked questions on titration are as follows.
Which indicator is used in the standardization of perchloric acid solution?
Crystal violet is used as an indicator in the standardization of perchloric acid solution which produces emerald green at the endpoint or equivalence point.
Why do we standardize perchloric acid solution?
Standardization of a prepared perchloric acid solution is performed to determine its exact molarity.
What type of titration is the standardization of perchloric acid?
Standardization of perchloric acid is a type of non-aqueous titration.
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