The Chemistry Of Recrystallization Theory Quiz

1. How are crude solid compounds isolated from a chemical synthesis or extraction purified?

By sublimation, which involves the transition of a solid directly to a gas.

By chromatography, which separates compounds based on their affinity to a stationary phase.

By distillation, which involves the separation of compounds based on differences in volatility.

By recrystalization. Which is based on the difference of solubility of solids in a given solvent system

Crude solid compounds can be isolated and purified through recrystallization, using the difference in solubility of solids in a solvent system to separate impurities. The incorrect answers do not describe the process of purifying solid compounds through recrystallization.

Explanation

Crude solid compounds can be isolated and purified through recrystallization, using the difference in solubility of solids in a solvent system to separate impurities. The incorrect answers do not describe the process of purifying solid compounds through recrystallization.

2. How does the solubility change in recrystallization process?

The solubility of a compound increases with temperature so that a saturated solution of compound is made at an elevated

The solubility of a compound decreases with temperature during recrystallization process.

The solubility of a compound is not a factor in the recrystallization process.

The solubility of a compound remains constant regardless of temperature during recrystallization process.

In recrystallization, the solubility of a compound typically increases with temperature to ensure a saturated solution is formed for the purification process.

Explanation

In recrystallization, the solubility of a compound typically increases with temperature to ensure a saturated solution is formed for the purification process.

3. How does temperature affect solubility in recrystallization?

The solubility of a compound increases as the solution cools.

Increasing the stirring speed decreases the solubility of the compound.

The addition of impurities increases the solubility of the compound.

Temperature, the same compound can be recovered in solid form by simply allowing the solution to cool

During recrystallization, controlling the temperature is crucial as it affects the solubility of the compound in the solution. When the solution cools, the solubility of the compound decreases, causing it to crystallize out of the solution.

Explanation

During recrystallization, controlling the temperature is crucial as it affects the solubility of the compound in the solution. When the solution cools, the solubility of the compound decreases, causing it to crystallize out of the solution.

4. What does it mean for a solution to be saturated?

Being the most concentrated solution possible at a given temperature; unable to dissolve still more of a substance

Being able to dissolve an unlimited amount of a substance

Having a perfect balance of solutes and solvents in a solution

Being the least concentrated solution possible at a given temperature

5. How does purification result?

Because the soluble impurities contaminating the main component are in much smaller concentration

As a result of increasing the concentration of impurities in the main component.

Due to the addition of more impurities to balance out the composition.

Because the insoluble impurities contaminating the main component are easy to remove.

Purification results when the soluble impurities contaminating the main component are in much smaller concentration, allowing for separation and removal from the main component.

Explanation

Purification results when the soluble impurities contaminating the main component are in much smaller concentration, allowing for separation and removal from the main component.

6. How does purification result?

Purification results when impurities are added to a substance.

And hence will remain in solution under both hot and cold conditions.

Purification results when impurities evaporate from a substance.

Purification results when impurities change color in a substance.

Purification is the process of removing impurities from a substance to ensure that it remains in solution under various conditions.

Explanation

Purification is the process of removing impurities from a substance to ensure that it remains in solution under various conditions.

7. How does purification result?

Purification happens when impurities are intentionally added to the solution.

Purification is achieved by heating the solution to a high temperature until impurities evaporate.

Purification occurs by mixing different solvents together.

Even if there are many impurities in solution, the growing crystals of the chief component often reject them in recrystalization process

Purification through crystallization involves the selective rejection of impurities by the growing crystals of the main component. This process results in obtaining a purified compound through recrystallization.

Explanation

Purification through crystallization involves the selective rejection of impurities by the growing crystals of the main component. This process results in obtaining a purified compound through recrystallization.

8. How does purification result?

By increasing the impurity concentration in the crystal lattice.

Due to the fact that the impurities do not meet the required geometry of the already forming crystal lattice

Through a chemical reaction that eliminates impurities.

By reducing the temperature of the system to remove impurities.

Purification occurs when impurities are unable to integrate into the crystal lattice, leading to their removal during crystal formation.

Explanation

Purification occurs when impurities are unable to integrate into the crystal lattice, leading to their removal during crystal formation.

9. How can insoluble impurities be effectively removed from a solution?

By adding more insoluble impurities to the solution

By shaking the solution vigorously

These are removed while solution is at elevated temp (hot gravity filtration)

By freezing the solution and then filtering it

10. How are the purified solid crystals separated from surrounding liquid (mother liquid)?

By using a magnet to attract the crystals.

By a procedure called suction / vaccum filtration

By adding more liquid to dissolve the crystals.

By heating the mixture until the liquid evaporates.

Suction/vacuum filtration is the correct answer, as it involves using a vacuum to separate the solid crystals from the liquid. The other incorrect answers do not involve this specific separation method.

Explanation

Suction/vacuum filtration is the correct answer, as it involves using a vacuum to separate the solid crystals from the liquid. The other incorrect answers do not involve this specific separation method.

11. What are the 4 basic requirements of a good solvent for recrystallization?

4) It must have a strong odor for easy identification.

1) It must dissolve the compound only sparingly or not at all at room temperature, but readily at its boiling point.

3) It must be inexpensive and easily accessible.

2) It must dissolve the compound completely at all temperatures.

The correct answer is focused on the solubility properties of the solvent, specifically highlighting the need for sparing solubility at room temperature and high solubility at boiling point. The incorrect answers do not meet the criteria for a good recrystallization solvent as they do not address the necessary solubility characteristics.

Explanation

The correct answer is focused on the solubility properties of the solvent, specifically highlighting the need for sparing solubility at room temperature and high solubility at boiling point. The incorrect answers do not meet the criteria for a good recrystallization solvent as they do not address the necessary solubility characteristics.

12. What are the 4 basic requirements of a good solvent for recrystallization?

3) Should have a lower boiling point than the compound

2) Should have the same physical state as the compound

4) Should be non-volatile at room temperature

1) Should also dissolve compound in reasonable volume

The correct answer highlights the importance of dissolving the compound, while the incorrect answers focus on physical state, boiling point, and volatility which are not essential requirements for a good solvent for recrystallization.

Explanation

The correct answer highlights the importance of dissolving the compound, while the incorrect answers focus on physical state, boiling point, and volatility which are not essential requirements for a good solvent for recrystallization.

13. What are the 4 basic requirements of a good solvent for recrystallization?

2) It cannot react chemically with the compound to be purified

4) It should be easily available at low cost.

1) It must form a eutectic mixture with the compound to be purified.

3) It should have a high boiling point to ensure efficient recrystallization.

In recrystallization, the solvent must not react chemically with the compound to be purified to avoid contamination of the final product.

Explanation

In recrystallization, the solvent must not react chemically with the compound to be purified to avoid contamination of the final product.

14. What are the 4 basic requirements of a good solvent for recrystallization?

2) It should be a colorless liquid for easy visualization of crystal formation

1) It should have a high boiling point to ensure quick evaporation

4) It should have a low solubility in water to prevent excessive dilution of the desired compound

3) It should either dissolve impurities exceedingly well (so that they remain in solution even when cooled)

The correct answer highlights the importance of dissolving impurities well, while the incorrect answers provide misleading criteria for a good recrystallization solvent.

Explanation

The correct answer highlights the importance of dissolving impurities well, while the incorrect answers provide misleading criteria for a good recrystallization solvent.

15. What are the 4 basic requirements of a good solvent for recrystallization?

Solubility in cold solvent

High boiling point

Chemically reactive with the compound of interest

Or not at all (so that they can be mechanically removed from the hot solution

In recrystallization, it is important for the solvent to have a high boiling point, low solubility in cold solvent, and should not be chemically reactive with the compound being purified. This ensures optimal crystallization and separation of impurities.

Explanation

In recrystallization, it is important for the solvent to have a high boiling point, low solubility in cold solvent, and should not be chemically reactive with the compound being purified. This ensures optimal crystallization and separation of impurities.

16. What are the 4 basic requirements of a good solvent for recrystallization?

1) It should have a boiling point higher than the melting point of the solid to be purified for efficient recrystallization.

2) It should have a similar melting point to the solid to be purified to ensure maximum purity during recrystallization.

3) It should have a strong odor to indicate its effectiveness in dissolving impurities during the recrystallization process.

4) Ideally it should have a boiling point lower than melting point of solid to be purified in order to avoid a situation

The correct answer is 4) because having a solvent with a boiling point lower than the melting point of the solid helps prevent the situation where the solid re-crystallizes before impurities are removed.

Explanation

The correct answer is 4) because having a solvent with a boiling point lower than the melting point of the solid helps prevent the situation where the solid re-crystallizes before impurities are removed.

17. What are the 4 basic requirements of a good solvent for recrystallization?

2) Solvent that has a high boiling point to speed up the recrystallization process.

1) Solvent that instantly dissolves the solid at room temperature.

4) In which the solid merely oils out "melts but does not dissolve". Hard to distinguish melting and dissolving

3) Solvent that forms a cloudy solution when mixed with the solid.

The correct answer highlights the importance of the solid merely 'oiling out' instead of dissolving completely in the solvent, making it hard to distinguish between melting and dissolving.

Explanation

The correct answer highlights the importance of the solid merely 'oiling out' instead of dissolving completely in the solvent, making it hard to distinguish between melting and dissolving.

18. If one solvent does not have all the above requirements, what should be done?

Mix the solvent with any other liquid available to compensate for the missing requirements.

Increase the temperature of the solvent to enhance its properties.

Discard the entire solvent mixture and start over.

We use a second solvent, miscible with the first and it is added to form a solvent pair

When one solvent does not meet all the requirements, it is ideal to add a second solvent that complements the first to form a solvent pair. This helps in achieving the desired properties for the solvent mixture.

Explanation

When one solvent does not meet all the requirements, it is ideal to add a second solvent that complements the first to form a solvent pair. This helps in achieving the desired properties for the solvent mixture.

19. What is the purpose of the solvent pair?

The second solvent modifies or intensifies properties of 1st solvent and make the system suitable for recrystalllization

To reduce the boiling point of the solvent for faster evaporation.

To dilute the solute for easier handling.

To completely dissolve the solute without any modifications.

The purpose of the solvent pair is to have the second solvent modify or intensify properties of the first solvent to make the system suitable for recrystallization.

Explanation

The purpose of the solvent pair is to have the second solvent modify or intensify properties of the first solvent to make the system suitable for recrystallization.

20. What are the properties of a solvent pair?

Both solvents dissolve the compound equally well.

Both solvents dissolve the compound poorly.

One solvent dissolves the compound well, while the other solvent dissolves the compound poorly

One solvent dissolves the compound quickly, while the other solvent dissolves it slowly.

One solvent dissolves the compound well, while the other solvent does not dissolve the compound at all.

A solvent pair consists of two solvents where one solvent has a high solubility towards the compound being dissolved, while the other solvent has low solubility towards the same compound. This creates a selective dissolution process.

Explanation

A solvent pair consists of two solvents where one solvent has a high solubility towards the compound being dissolved, while the other solvent has low solubility towards the same compound. This creates a selective dissolution process.