Learn about the preparation and standardization of 0.1 N potassium dichromate solution through a laboratory experiment or practical.
Aim:
To prepare and standardize 0.1 N potassium dichromate solution using standard sodium chloride (volumetric solution).
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: Potassium dichromate (K2Cr2O7), potassium iodide (KI), hydrochloric acid (HCL), sodium thiosulphate (Na2S2O3), and starch solution, etc.
Preparation of 0.1N potassium dichromate solution:
Take properly weighed 06.00 gm of potassium dichromate (It should be previously dried at 1200 C for 4 hours and cool in a desiccator) and add in 100 ml of distilled water, Once it has completely dissolved, make up the volume to 1000 ml with water.
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 40.00 ml of water and add 40.00 ml of prepared potassium dichromate solution in a stoppered flask.
- Add 03.00 gm of potassium iodide and 05.00 ml of HCl.
- Stopper the flask immediately, swirl to ensure even mixing, and then let stand for 10 minutes in the dark.
- Rinse the stopper and interior walls of the flask with water, and titrate with freshly standardized 0.1N sodium thiosulphate solution until the solution becomes yellowish green.
- Add 02.00 ml starch solution and continue the titration until the blue color disappears.
- To get accurate results, repeat the titration three times.
- Properly record the readings of the burette.
- Take their mean and calculate the normality of the potassium dichromate solution.
- 1 ml of 0.1 M sodium thiosulphate is equivalent to 0.0049 g of potassium dichromate.
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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Calculation:
A = B X C / D
Where,
A =normality of K2Cr2O7 solution
B = Na2S2O3 solution (ml) required for titration
C = Normality Na2S2O3 solution
D = K2Cr2O7 solution used
Result:
The strength of the prepared potassium dichromate solution was found to be_____N.
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