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Thursday, August 19, 2021

Preparation and standardization of 0.1 m NaOH

Learn about the preparation and standardization of 0.1 M sodium hydroxide through a laboratory experiment or practical.

Aim:

To prepare and standardization of 0.1 M sodium hydroxide solution (NaOH) using the primary standard potassium hydrogen phthalate.

Reference: Indian Pharmacopoeia (IP), 2007, Volume-1, Page no. 316

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade sodium hydroxide (NaOH), potassium hydrogen phthalate (KHP), and phenolphthalein indicator, etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.

Principle:

Potassium hydrogen phthalate is directly titrated with sodium hydroxide to determine its strength. Using phenolphthalein as an indication, the endpoint of the titration is determined. The following is the reaction that is involved in this titration.

preparation and standardization of sodium hydroxide

The molecular weight of sodium hydroxide (NaOH) is 39.997 g/mol.

Preparation of 0.1 M NaOH:

  • Add 100 mL distilled water to a 1000 mL volumetric flask that has been cleaned and dried.
  • Weigh accurately 04.00 gm of sodium hydroxide and mix well.
  • Allow the solution to cool to ambient temperature and make up the volume to 1000 ml and properly mixing 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.
  • Accurately weigh 01.00 gm of previously dried potassium hydrogen phthalate and pour into a conical flask.
  • To dissolve adequately, add 15 ml distilled water and sonicate for 5 minutes on a sonicator.
  • Add 2 drops of phenolphthalein indicator once it has been solubilized.
  • Titrate the sample solution with NaOH until the endpoint is reached. A pink color appears and disappears, indicating that the endpoint is approaching, when the solution is swirled for up to 10 seconds. The actual endpoint is indicated by a pink color that lasts longer than 30 seconds.
  • Properly record the readings of the burette.
  • To get accurate results, repeat the titration three times.
  • Take their mean and calculate the molarity of NaOH.

Observation table:

Sr. No.

Content in conical flask

 

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

2

 

 

 

3

 

 

 

 

Mean:

Calculations:

Molarity of NaOH = W x RM / V x E
Where,
W is a weight of primary standard
E is an equivalent factor of primary standard
RM is a required molarity
V = volume of NaOH used
For 0.1 M NaOH, the equivalent factor of PHP is 0.020422.

Result:-

The strength of the prepared sodium hydroxide solution was found to be_____M.


Commonly asked quetions on titration are as follows.

Why does the NaOH solution need to be standardized?
To determine the exact concentration (Molarity/Normality) of NaOH solution it needs to be standardized. Because solid NaOH is extremely hygroscopic, it cannot be precisely weighed. The concentration of sodium hydroxide may be determined extremely precisely by titrating a KHP sample of known mass/mole with the NaOH solution.

What is standardization?
The process of determining the precise concentration (molarity) of a solution is known as standardization.

What are the types of titration?
Based on the chemical reaction taking place between the titrant and solute or analyte, there are four types of titrations such as acid-base, redox, complexometric, and precipitation.


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