Assay of Sodium Chloride by Modified Volhard’s method
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Aim:
To determine the % w/w of NHCI in a given sample of ammonium chloride
Apparatus:
Burette (50ml), pipette (10 ml & 25 ml), beaker (100 ml), conical flask (10 ml), volumetric flask (100 ml).
Chemicals:
Ammonium chloride sample, nitric acid, nitrobenzene, silver nitrate solution, ammonium thiocyanate solution, ferric ammonium sulphate and distilled water.
Chemical reactions: Chemical reaction for standardization
Procedure:
Standardization of silver nitrate solution.
Weigh accurately 0.1g of sodium chloride previously dried at 110°C for 2hours.
Dissolve it in 5ml distilled water.
Add 5ml of acetic acid and 50ml of methanol.
Add a few drops of potassium chromate (5%), stirring preferably with a magnetic stirrer.
Fill the burette with a given solution of silver nitrate.
Remove the air bubble and adjust the zero level.
Titrate the solution in a conical flask by running the solution from the burette.
The appearance of a red precipitate indicates the endpoint.
Report the reading by repeating it three times and calculate the normality of silver nitrate.
Observation Table:
| Sr. No. | Initial Burette Reading (ml) | Final Burette Reading (ml) | Difference |
|---|---|---|---|
| 1 | |||
| 2 | |||
| 3 |
Assay procedure:
Weigh accurately and dissolve about 0.1 g sodium chloride in 50 ml water in a stop flask.
Add 50 mi 0.1N silver nitrate and 3 ml nitric acid.
Shake well and add nitrobenzene, 2 ml ferric ammonium sulphate indicator and titrate with 0.1 N ammo thiocyanate solution with vigorous shaking until reddish precipitate appeared.
Repeat experiment with same quantities of reagent under the same condition without sample differences in the readings give the amount of silver nitrate consumed by sample.
Observation Table:
Standardization calculation for silver nitrate:
| Sr. No. | Initial Burette Reading (ml) | Final Burette Reading (ml) | Difference |
|---|---|---|---|
| 1 | | | |
| 2 | | | |
| 3 | | | |
Normality of silver nitrate=
= ________________N.
Standardization of ammonium thiocyanate.
Pipette out 30 ml of previously standardized silver nitrate solution into a glass stoppered flask, and dilute with 50ml distilled water.
Add 2 ml of nitric acid and 2ml of ferric ammonium sulphate solution.
Titrate this solution with a given solution of ammonium thiocyanate.
The appearance of the red-brown colour indicates points.
Observation Table:
| Sr. No. | Initial Burette Reading (ml) | Final Burette Reading (ml) | Difference |
|---|---|---|---|
| 1 | | | |
| 2 | | | |
| 3 | | | |
Standardization calculation for ammonium thiocyanate:
Ammonium thcyanate = Silver nitrate
= N₁XV₁ = N₂ XV₂
