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Wednesday, August 17, 2022

Standardization of NaOH with KHP

Learn about the preparation and standardization of NaOH solution through a laboratory experiment or practical.

To prepare and standardize 0.1N sodium hydroxide solution with potassium hydrogen phthalate by acid-base titration.


Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, wash bottle, etc.

Chemicals: LR grade potassium hydrogen phthalate (C8H5KO4), sodium hydroxide (NaOH), phenolphthalein indicator, etc.

Apparatus: Digital/analytical balance

Theory for standardization of NaOH:


When sodium hydroxide is weighed, it takes moisture from the air because it is hygroscopic. Because of this water, we will not be able to find out the exact mass of NaOH. Therefore to determine the exact concentration of prepared sodium hydroxide solution, titration with a solid acid that is not hygroscopic is required.

KHP, also known as potassium hydrogen phthalate, is an acidic salt compound. It is used as the primary standard because it has high purity, is non-toxic, has a high molecular weight, is non-hygroscopic, and is easy to weigh. For the purpose of determining the concentration of a solution containing sodium hydroxide, we will use this primary standard.

It is an acid-base titration in which sodium hydroxide is a strong base and potassium hydrogen phthalate is a weak acid. By direct titration, we standardize the 0.1 N NaOH solution (the titrant) with potassium hydrogen phthalate (KHP, KC8H4O4H) using phenolphthalein as an indicator.

KHP is a weak acid, and its reactions with bases are as follows:

Standardization of NaOH

Preparation of 0.1N NaOH solution:

Weigh accurately 0.2 gm of sodium hydroxide and dissolve in 40 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 50 ml with distilled water.

Preparation of 0.1N KHP solution:

Weigh accurately 1.02 gm of potassium hydrogen phthalate and dissolve in 40 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 50 ml with distilled 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 05.00 ml of prepared KHP solution and pour it into a conical flask.
  • Add 2-3 drops of phenolphthalein indicator.
  • Titrate the sample solution with the sodium hydroxide (NaOH) solution until the color of the solution is discharged.
  • 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:

Calculations:

Calculate the normality and % of NaOH.

meq. NaOH = meq KHP

(N * V)NaOH = (N * V)KHP

Wt./ Eq.Wt * 1000 = ( N * V) KHP

Wt./40*1000 = 0.1 x V1 X V2 X V3/3

% NaOH = Wt./Wt. of sample X 100


Result:

The strength of the prepared NaOH solution was found to be_____M.




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