Podcast
Questions and Answers
What are the two primary methods for purifying solid organic compounds mentioned?
What are the two primary methods for purifying solid organic compounds mentioned?
Sublimation and Recrystallization.
What is sublimation?
What is sublimation?
The process where a solid compound evaporates directly into the gas phase without becoming a liquid.
Sublimation involves the direct transition of a substance from the _____ phase to the _____ phase.
Sublimation involves the direct transition of a substance from the _____ phase to the _____ phase.
solid, gas
According to a typical phase diagram, sublimation occurs at conditions _____ the triple point.
According to a typical phase diagram, sublimation occurs at conditions _____ the triple point.
Sublimation is used for purifying solids that have a significant _____ _____.
Sublimation is used for purifying solids that have a significant _____ _____.
For sublimation to occur readily, the total pressure of the atmosphere (or surrounding environment) should ideally be _____ the vapor pressure of the solid at that temperature.
For sublimation to occur readily, the total pressure of the atmosphere (or surrounding environment) should ideally be _____ the vapor pressure of the solid at that temperature.
Sublimation occurs at temperatures and pressures _____ the substance's triple point.
Sublimation occurs at temperatures and pressures _____ the substance's triple point.
During the purification of an impure sample by sublimation, which component preferentially sublimes?
During the purification of an impure sample by sublimation, which component preferentially sublimes?
What are the two main steps involved in the process of purification by sublimation?
What are the two main steps involved in the process of purification by sublimation?
What is a primary advantage of using sublimation over recrystallization for purification?
What is a primary advantage of using sublimation over recrystallization for purification?
What is a potential disadvantage of sublimation?
What is a potential disadvantage of sublimation?
How is the recovery percentage calculated in a sublimation experiment?
How is the recovery percentage calculated in a sublimation experiment?
What are the two types of sublimation techniques mentioned?
What are the two types of sublimation techniques mentioned?
Vacuum sublimation typically allows the process to occur at a _____ temperature compared to normal pressure sublimation.
Vacuum sublimation typically allows the process to occur at a _____ temperature compared to normal pressure sublimation.
For which two types of compounds is vacuum sublimation particularly useful?
For which two types of compounds is vacuum sublimation particularly useful?
True or False: Benzoic acid can be purified by sublimation.
True or False: Benzoic acid can be purified by sublimation.
Which of the following organic compounds are listed as examples that can be purified by sublimation?
Which of the following organic compounds are listed as examples that can be purified by sublimation?
In the sublimation procedure described using masses $m_1$ and $m_2$, what does $m_1$ represent?
In the sublimation procedure described using masses $m_1$ and $m_2$, what does $m_1$ represent?
In the sublimation procedure described using masses $m_1$ and $m_2$, what does $m_2$ represent?
In the sublimation procedure described using masses $m_1$ and $m_2$, what does $m_2$ represent?
Using the variables from the described procedure, how is the mass of the recovered compound calculated?
Using the variables from the described procedure, how is the mass of the recovered compound calculated?
What is the fundamental difference between Recovery % and Yield % in a laboratory context?
What is the fundamental difference between Recovery % and Yield % in a laboratory context?
Why is it important to use very low or gentle heating during sublimation?
Why is it important to use very low or gentle heating during sublimation?
Flashcards
What is Sublimation?
What is Sublimation?
A purification method where a solid transitions directly to the gas phase, bypassing the liquid phase.
When is sublimation used?
When is sublimation used?
Sublimation is effective for solids with a high tendency to vaporize, at or above atmospheric pressure.
Describe the Sublimation Process
Describe the Sublimation Process
In sublimation, the impure solid is heated, turning it into gas (sublimation), then the gas cools and becomes pure solid crystals (deposition).
Advantage of sublimation
Advantage of sublimation
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Disadvantages of Sublimation
Disadvantages of Sublimation
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Normal Pressure Sublimation
Normal Pressure Sublimation
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Vacuum Sublimation
Vacuum Sublimation
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What is Recovery percentage?
What is Recovery percentage?
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Recovery % vs. Yield %
Recovery % vs. Yield %
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Study Notes
- Sublimation and recrystallization are methods for purifying solid organic compounds.
Sublimation
- A solid compound transitions directly to the gas phase without becoming a liquid.
- Solid becomes gas directly.
- Purification of solids with significant vapor pressure, which is equal to or higher than atmospheric pressure, can be achieved through sublimation.
- Sublimation happens when the total atmospheric pressure is less than the solid's vapor pressure.
- Sublimation occurs at temperatures and pressures below the triple point.
- Organic compounds with high vapor pressure and impurities with low vapor pressure can be purified using sublimation.
- Organic compounds sublime while impurities do not.
- This process results in pure organic compounds
Sublimation Process
- The sample is heated and evaporates, transitioning from solid to gas (S → G).
- The vapor then condenses on a cold surface, forming new, pure crystals, which is deposition (G → S).
Advantages of Sublimation
- No solvent use makes it a clean method, preferred over recrystallization where solvent is an impurity.
- Sublimation is a simple and fast method.
Disadvantages of Sublimation
- Only a small fraction of organic compounds can be purified this way.
- The recovery percentage is low.
Recovery Percentage Formula
- Recovery % = (mass of compound recovered / mass of crude) * 100 %
Types of Sublimation
- Normal Pressure Sublimation
- Vacuum Sublimation
Vacuum Sublimation
- Occurs at lower temperatures.
- Used for compounds with low vapor pressure or those that decompose at high temperatures.
Examples of Organic Compounds Purified by Sublimation
- 1,4-dichlorobenzene
- Naphthalene
- Salicylic acid
- Anthracene
- 1-naphthole
- Acetamide
- Benzoic acid
- Caffeine
- Camphor
Procedure Notes
- Place 1 gram of the organic compound sample on a watch glass.
- Record the exact mass of the crude sample.
- Use a weight funnel with cotton.
- Heat at a very low temperature.
- Use a weight funnel with cotton to deposit the sample.
Recovery Calculation
- Recovery % = (mass of compound recovered / mass of crude) * 100 %
- Can also be expressed as Recovery % = (m2 - m1 / mass of crude) * 100%, where m1 is the weight of the funnel with cotton and m2 is the weight of the funnel with cotton and the deposited sample.
- Recovery% is for purified and separated samples, while Yield% is for chemical reaction products.
Important Notes
- Very low heating is important to prevent sample melting.
- A beaker can be added to prevent high temperature from reaching the sample.
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