Learn about the assay of ammonium chloride through a laboratory experiment or practical.
Aim:
To determine the percentage purity (assay) of given sample of ammonium chloride using standard 0.1 N NaOH. (Acid-base titration)
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade ammonium chloride (NH4Cl), sodium hydroxide (NaOH), potassium hydrogen phthalate (PHP), and phenolphthalein indicator, etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.
Principle of assay of ammonium chloride:
The indirect assay method is used to perform the assay ammonium chloride. The sample solution is dissolved in water and treated with a formaldehyde solution that has been previously neutralized.
As a result in the quantitative liberation of HCl is equal to NH4Cl. It's an acidic salt that interacts with formaldehyde to liberate free acid, which then reacts with NaOH. 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 (0.1 M):
Click here to get the procedure of preparation and standardization of 0.1 M sodium hydroxide.
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 0.1 gm of ammonium chloride, pour into a conical flask and dissolve in 20 ml distilled water.
- Add a 5 ml mixture of formaldehyde solution and 20 mL distilled water.
- Add 2 drops of phenolphthalein indicator and let stand for two minutes.
- Titrate the sample solution with NaOH until the endpoint is reached. When the solution is swirled for up to 10 seconds, a pink color appears and fades, indicates that the endpoint is approaching. The actual endpoint of the titration 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 % purity of ammonium chloride.
Observation table:-
|
Sr. No. |
Content in conical flask |
Burette
reading |
Volume
of titrant used (ml) |
|
|
Initial |
Final |
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|
1 |
|
|
|
|
|
2 |
|
|
|
|
|
3 |
|
|
|
|
|
Mean: |
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Calculations:
Percentage purity of NH4Cl = V x E x AM X 100 / W x RM
Where,
V is a volume of sodium hydroxide used
E is an equivalent factor
AM is an actual molarity
RM is a required molarity
W is the weight of the sample
For 0.1 M NaOH, the equivalent factor of NH4Cl is 0.005349
Result:
The percentage purity of the ammonium chloride (NH4CL) sample was found to be_____.
Commonly asked questions on the assay of ammonium chloride are as follows.
Assay of ammonium chloride is based on which type of titration?
The assay of ammonium chloride is a type of acid-base titration that is performs based on the indirect process.
Which indicator is used in the assay of ammonium chloride?
Phenolphthalein indicator is used in the assay of ammonium chloride which produces a pink color at equivalence or endpoint of the titration.
Why formaldehyde is used in assay of ammonium chloride?
As mentioned in principle of assay of ammonium chloride, liberated ammonium hydroxide can favor reversible reaction i.e. ammonium hydroxide combined with hydrochloric acid to give ammonium chloride, so to prevent this we use formaldehyde.
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