Learn about the preparation and standardization of 1N hydrochloric acid solution through a laboratory experiment or practical.
To prepare and standardize 1 N HCl using sodium carbonate as a primary standard.
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, wash bottle, etc.
Chemicals: LR grade concentrated hydrochloric acid (HCl), sodium carbonate, (Na2CO3), methyl red indicator, etc.
Apparatus: Digital/analytical balance
Principle of standardization of HCl:
In the titration of hydrochloric acid against the solution of sodium carbonate, methyl red (a weak base) which is yellow in the unionized form is used as an indicator.
When a weak base is used to titrate a solution that is just slightly acidic the endpoint is also slightly acidic. The solution is slightly alkaline when a weak acid is titrated with a strong base because the salt formed is partially hydrolyzed.
The reaction of sodium carbonate with hydrochloric acid is given below:
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
In the process of acid-base titration, the portion of acid becomes chemically equivalent to the quantity of base present. When a strong acid and a strong base are tested at the same time, the solution turns out to be neutral.
Preparation of 1 N HCl solution:
Pipette out accurately 08.50 ml of concentrated hydrochloric acid (HCl) and dilute to 100 ml of distilled water in a volumetric flask, and properly mix it.
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 primary standard anhydrous sodium carbonate (Na2CO3) and dry it at 150°C for 1 hour in a Petri dish or crucible.
- Once it is cool, weigh accurately 01.50 g sodium carbonate and pour it into a conical flask.
- Pour in 100 ml of water and stir the mixture to dissolve.
- Add 2-3 drops of methyl red indicator.
- Titrate the sample solution with the prepared HCl solution until the light pink color appears.
- Heat the solution to boiling until the color returns to yellow, then cool and titrate again until the light pink color is no longer affected by boiling.
- To get accurate results, repeat the titration three times.
- Properly record the readings of the burette.
Observation table:
|
Sr. No. |
Content in
conical flask |
Burette
reading |
Volume of
titrant used (ml) |
|
|
Initial |
Final |
|||
|
1 |
|
|
|
|
|
2 |
|
|
|
|
|
3 |
|
|
|
|
|
|
Mean: |
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Calculations:
Each ml of 1M HCl is equivalent to 0.05299g of Na2CO3.
Calculate the solution's molarity using the following formula.
Molarity = Wt. X 1 / volu. X 0.05299
Where,
Wt. is weight of Na2CO3 used,
Volu. is volume of HCl solution used in titration
Result:
The strength of the prepared hydrochloric acid (HCl) solution was found to be_____N.
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