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Questions and Answers
What is the primary basis for the technique of crystallisation in purifying solid organic compounds?
What is the primary basis for the technique of crystallisation in purifying solid organic compounds?
The primary basis for crystallisation is the difference in solubilities of the compound and its impurities in a suitable solvent.
Why is it necessary to use a saturated solution during the crystallisation process?
Why is it necessary to use a saturated solution during the crystallisation process?
A nearly saturated solution is necessary to encourage crystallisation when the solution is cooled, allowing pure compound to form.
Describe how distillation separates liquids based on boiling points.
Describe how distillation separates liquids based on boiling points.
Distillation separates liquids by heating them to vaporize at different temperatures, then cooling the vapors to collect the individual liquids.
What role does activated charcoal play in the crystallisation process?
What role does activated charcoal play in the crystallisation process?
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In what scenario might repeated crystallisation be necessary?
In what scenario might repeated crystallisation be necessary?
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What is the process of cooling a nearly saturated solution intended to achieve during crystallisation?
What is the process of cooling a nearly saturated solution intended to achieve during crystallisation?
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Explain how the solubility characteristics of a compound affect the choice of solvent in crystallisation.
Explain how the solubility characteristics of a compound affect the choice of solvent in crystallisation.
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How does the presence of impurities influence the purity of the crystallised compound?
How does the presence of impurities influence the purity of the crystallised compound?
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What role does the filtrate play after the crystallisation process is complete?
What role does the filtrate play after the crystallisation process is complete?
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In what case would one utilize a mixture of solvents during crystallisation?
In what case would one utilize a mixture of solvents during crystallisation?
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Study Notes
Crystallisation
- A common purification technique for solid organic compounds based on solubility differences.
- The impure compound dissolves in a solvent where it's sparingly soluble at room temperature but more soluble at higher temperatures.
- The solution is concentrated to near saturation and then cooled, causing pure crystals to form.
- These crystals are filtered out, leaving impurities in the filtrate (mother liquor).
- For compounds highly soluble in one solvent and poorly soluble in another, crystallization can be performed in a mixture of these solvents.
- Coloured impurities can be removed by adsorption onto activated charcoal.
- Repeated crystallization is necessary for purifying compounds with impurities of similar solubilities.
Distillation
- A method for separating:
- Volatile liquids from nonvolatile impurities.
- Liquids with significant boiling point differences.
- Liquids with different boiling points vaporize at distinct temperatures.
- The vapors are cooled and the liquids condensed are collected separately.
- Example: Chloroform (b.p. 334 K) and aniline (b.p. 457 K) are easily separated by distillation.
Crystallisation
- A common technique for purifying solid organic compounds.
- Based on the difference in solubilities between the compound and its impurities in a chosen solvent.
- The impure compound is dissolved in a solvent where it has low solubility at room temperature but higher solubility at a higher temperature.
- The solution is concentrated to create a near saturated solution.
- Cooling the solution causes the pure compound to crystallise out, which can be removed by filtration.
- The remaining solution (mother liquor) contains impurities and a small amount of the original compound.
- If the compound has high solubility in one solvent and low solubility in another, crystallisation can be performed in a mixture of those solvents.
- Impurities that colour the solution can be removed by adsorption using activated charcoal.
- Repeated crystallisation is necessary for purification of compounds containing impurities with similar solubilities.
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Description
This quiz covers key purification techniques used in organic chemistry, specifically crystallisation and distillation. It explains the principles and methods of each technique, along with their applications in separating impurities from organic compounds. Test your knowledge on these essential processes in chemical analysis and compound purification.
