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Crystallization techniques in the laboratory
A topic from the subject of Crystallization in Chemistry.
Crystallization Techniques in the Laboratory
Crystallization is a purification technique commonly used in chemistry to separate and purify compounds.
Key Points
- Involves dissolving the impure compound in a suitable solvent and allowing it to crystallize.
- The crystals formed are filtered and recrystallized to remove impurities.
- The choice of solvent depends on the solubility of the compound being crystallized.
- Impurities can be removed by washing the crystals with a cold solvent.
Main Concepts
- Solubility : The ability of a solute to dissolve in a solvent. Different solvents have different solubilities for the same compound.
- Supersaturation : A solution that contains more dissolved solute than it can normally hold at a given temperature.
- Nucleation : The process by which crystals start to form from a supersaturated solution.
- Crystal growth : The process by which crystals grow in size.
- Recrystallization : The process of dissolving the crystals obtained from the first crystallization in a fresh solvent and allowing them to recrystallize to remove remaining impurities.
Crystallization is a valuable technique for purifying compounds and is widely used in various fields of chemistry and industry.
Crystallization Techniques in the Laboratory: An Experiment
Materials
- Impure solid salt sample (e.g., sodium chloride)
- Distilled water
- Beaker
- Glass stir rod
- Filter paper
- Funnel
- Petri dish
Step-by-Step Procedure
1. Dissolution
- Weigh a small amount (e.g., 10 g) of the impure salt sample.
- Place the salt sample in a beaker and add a small amount of distilled water (e.g., 50 mL).
- Heat the mixture while stirring continuously to dissolve the salt completely.
2. Filtration
- Line a funnel with filter paper and place it over a Petri dish.
- Carefully pour the hot salt solution through the filter paper into the Petri dish.
- This step removes any solid impurities present in the solution.
3. Crystallization
- Allow the filtered solution to cool slowly to room temperature.
- As the solution cools, the salt will start to crystallize out of the solution.
- Monitor the solution and gently agitate it to prevent large, uneven crystals from forming.
4. Vacuum Filtration
- Use a vacuum filter to remove the crystals from the remaining solution.
- Connect the vacuum filter to a vacuum source and place a filter paper on top.
- Pour the cooled solution onto the filter paper and apply vacuum to draw the crystals onto the filter.
5. Drying
- Transfer the crystals to a clean Petri dish and place it in a warm, dry place to allow them to dry completely.
- Drying prevents the crystals from redissolving in the remaining moisture.
Significance
Crystallization is an important technique in chemistry for:- Purifying impure substances by removing solid impurities.
- Obtaining well-defined and uniform crystals for analytical purposes.
- Preparing crystals of substances that do not exist naturally in crystalline form.
- Studying the crystal structure and properties of materials.