To recover CaCO₃ from the given mixture of CaCO₃ and MgCO₃ | NEB Grade XII Chemistry Practical | Nepali Educate

Experiment No.: 02

Name of the Experiment: To Recover Calcium Carbonate from the Given Mixture of Calcium Carbonate and Magnesium Carbonate (Dolomite)

Apparatus Required:

• Beaker
• Porcelain Basin
• Filter paper
• Funnel
• Stand
• Glass rod

Chemicals Required:

• Dolomite
• Dilute Hydrochloric Acid (HCl)
• Ammonium Hydroxide (NH₄OH)
• Ammonium Carbonate ((NH₄)₂CO₃)

Theory

Though CaCO₃ and MgCO₃ are insoluble in water, they are soluble in mineral acids like hydrochloric acid. The addition of suitable reagents precipitates one component selectively. When dolomite is treated with dilute hydrochloric acid, water-soluble chlorides are obtained. The addition of proper amounts of ammonium chlorides, ammonium hydroxide, and ammonium carbonate solutions gives a precipitate of calcium carbonate. Magnesium ions remain in the solution and are washed away.

Reaction Involved:

CaCO₃ + MgCO₃ + 4HCl → CaCl₂ + MgCl₂ + 2H₂O + 2CO₂

CaCl₂ + MgCl₂ + (NH₄)₂CO₃ → CaCO₃ + MgCl₂ + 2NH₄Cl + 2H₂O

The precipitation of CaCO₃ is carried out based on the solubility product principle and common ion effect. Calcium carbonate has a lower solubility product constant value and easily precipitates out.

Procedure:

1. Dolomite was dissolved in a minimum amount of dilute HCl until the solution became clear.
2. One test tube of ammonium chloride and ammonium hydroxide solution was added to the solution to make it alkaline.
3. Ammonium carbonate solution was finally added to the solution, and calcium carbonate precipitated out.
4. The precipitate was settled at the bottom, and filtration was carried out.
5. The precipitate was dried and removed from the filter paper using a spatula.

Observation Table for Complete Precipitation

S.No.	Experiment	Observation	Inference
1.	A few cc of supernatant liquid was White ppt. was not taken into a test tube and a few drops of sodium carbonate.	White ppt. was not obtained.	Incompleteness of precipitation reaction.
2.	A few cc of supernatant liquid was White ppt. was not taken into a test tube and a few drops of sodium carbonate.	White ppt. was obtained.	Completeness of precipitation reaction.

Result:

Hence, the calcium carbonate was recovered from the given mixture of calcium carbonate and magnesium carbonate (dolomite).

Conclusion:

Substances having different solubility products can be separated by the common ion effect principle.

Precautions:

• The mixture should be dissolved in a minimum amount of acid.
• The precipitation should be completed.