Chrominfo: Preparation and standardization of 0.1 N ammonium thiocyanate

Learn about the preparation and standardization of 0.1 N ammonium thiocyanate through a laboratory experiment or practical.

Aim:

To prepare and standardize 0.1 N ammonium thiocyanate solution using standard AgNO3 as secondary standard (Volhard’s method).

Requirements:

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

Chemicals: LR grade ammonium thiocyanate (NH4SCN), silver nitrate (AgNO3), nitric acid (HNO3), and ferric ammonium sulphate (NH4Fe(SO4)2), etc.

How to prepare 0.1N ammonium thiocyanate solution:

Take 7.612 gm of ammonium thiocyanate and dissolve in 500 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 1000 ml.

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.
Using pipette take 30.00 ml of freshly prepared 0.1 M silver nitrate solution and into a glass-stoppered flask. To prevent the reducing effect of light on silver nitrate, protect it from light.
After that, add 02.00 ml of nitric acid and 02.00 ml of ferric ammonium sulfate solution.
Titrate the sample solution with ammonium thiocyanate solution until the endpoint is reached.
The actual endpoint is indicated by the appearance of a brown-red.
To get accurate results, repeat the titration three times.
Properly record the readings of the burette.
Take their mean and calculate the molarity of ammonium thiocyanate solution.

Observation table:-

Sr. No.	Content in conical flask	Burette reading		Volume of titrant used (ml)
Sr. No.	Content in conical flask	Initial	Final	Volume of titrant used (ml)
1
2
3
				Mean:

Calculations:

M= Volume of AgNO3 x Normality of AgNO3/ Volume of NH4SCN

Result:

The strength of the prepared ammonium thiocyanate solution was found to be_____N.

Frequently Asked Questions (FAQ):

What is the purpose of adding nitric acid in the standardization of 0.1N ammonia thiocyanate solution?

To avoid hydrolysis of the ferric ammonium sulphate which is used as an indicator, the concentrated nitric acid is added to the standardization of 0.1N ammonium thiocyanate solution.