Learn about the assay of calcium lactate through a laboratory experiment or practical.
Aim:
To perform an assay of a given sample of calcium lactate.
Requirements:
Glasswares: Burette, burette stand, conical flask, pipette, beaker, volumetric flask, funnel, glass rod, wash bottle, etc.
Chemicals: Calcium lactate (C6H10CaO6), calcium chloride (CaCl2), EDTA (C10H16N2O8), magnesium sulphate (MgSO4), ammonium chloride (NH4Cl), ammonia (NH3), and eriochrome black-T (C20H12N3O7SNa ) etc.
Apparatus: Digital/analytical balance, pH meter.
Theory of assay of calcium lactate:
The calcium lactate is a white crystalline salt (granules or powder) with formula C6H10CaO, it is odorless or with a slight but not unpleasant odor. It has 218.2 g/mol. molecular weight, and is soluble in water, very soluble in methanol, and insoluble in ethanol. Calcium lactate is a specific antacid that is also used to treat calcium deficiency.
This titration (assay) is an example of complexometric titration. Complexometric titration is a reaction in which a metal ion is converted into a stable complex ion by the addition of a reagent or ligand. Eriochrome Black-T is used as an indicator, which produces a blue endpoint, is used as an indicator.
Reaction involved in the assay of calcium lactate is as follows.
Preparation of 0.05 M disodium edetate solution:
Take 18.60 gm of disodium edetate and dissolve in 800 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 1000 ml with water.
Preparation of 0.05 M calcium chloride solution:
Take 14.70 gm of calcium chloride and dissolve in 800 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 1000 ml with water.
Preparation of ammonia buffer (pH 10):
Take 05.40 gm of ammonium chloride and dissolve in 20 ml of distilled water in a volumetric flask, add 35 ml of 10 M ammonia and properly mix it. Once it has completely dissolved, make up the volume to 100 ml with water.
Preparation of 0.05 M magnesium sulphate solution:
Take 12.50 gm of magnesium sulphate and dissolve in 800 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 1000 ml with water.
Procedure:
Standardization of EDTA solution:
- 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 10 ml of 0.5 M calcium chloride solution and pour it into a conical.
- Add 2-3 drops of Eriochrome Black-T indicator and properly mix it.
- Titrate the sample solution with 0.05M EDTA until the endpoint is reached. The actual endpoint of the titration is indicated by a change in color from red to blue.
- Properly record the readings of the burette.
- To get accurate results, repeat the titration three times.
- Take their mean and calculate the molarity of 0.05M EDTA solution.
Procedure for assay of calcium lactate:
- Accurately weigh 00.3 gm of calcium lactate and pour into a conical and add 50.00 ml of distilled water to dissolve it.
- Add 5.0 ml of 0.05 of magnesium sulphate and 10.00 ml of strong ammonia solution.
- Add 2-3 drops of Eriochrome Black-T indicator.
- Titrate the sample solution with 0.05M EDTA until the endpoint is reached.
- Properly record the readings of the burette.
- Subtract the volume of magnesium sulphate solution added from the volume of 0.05 M disodium edetate needed.
- To get accurate results, repeat the titration three times.
- Take their mean and calculate the percentage purity of calcium lactate.
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 C6H10CaO6= V x E x AM X 100 / W x RM
Where,
V is a volume of EDTA used
E is an equivalent factor
AM is an actual molarity
RM is a required molarity
W is the weight of the sample
Each mL of 0.05M disodium edetate is equivalent to 0.001091 gm of C6H10CaO6.
Result:
The percentage purity of the given sample calcium lactate was found to be_____.
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