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What is the purpose of adding charcoal during the purification process with low grade benzoic acid?
What is the purpose of adding charcoal during the purification process with low grade benzoic acid?
- To increase the solubility of the benzoic acid
- To remove colored impurities (correct)
- To color the crystals
- To enhance the boiling point of the solvent
Why is the solution containing the charcoal heated to boiling with frequent stirring?
Why is the solution containing the charcoal heated to boiling with frequent stirring?
- To facilitate the removal of insoluble impurities (correct)
- To break down the benzoic acid into smaller components
- To decrease the solubility of benzoic acid
- To speed up the crystallization process
What is the purpose of dividing the filtrate into two Erlenmeyer flasks during the purification process?
What is the purpose of dividing the filtrate into two Erlenmeyer flasks during the purification process?
- To speed up the drying process
- To increase the yield of benzoic acid
- To compare the appearance of crystals under different conditions (correct)
- To enhance the solubility of crystals
Why is it important to wash the crystals with a small amount of cold water?
Why is it important to wash the crystals with a small amount of cold water?
What should be done if drying of crystals is not completed in one lab session?
What should be done if drying of crystals is not completed in one lab session?
Why is it advised to add the solvent in small portions while dissolving the solid in an Erlenmeyer flask?
Why is it advised to add the solvent in small portions while dissolving the solid in an Erlenmeyer flask?
What is the purpose of dividing the filtrate into two Erlenmeyer flasks during the purification process?
What is the purpose of dividing the filtrate into two Erlenmeyer flasks during the purification process?
Why is it advised to add the solvent in small portions while dissolving the solid in an Erlenmeyer flask?
Why is it advised to add the solvent in small portions while dissolving the solid in an Erlenmeyer flask?
What should be done if drying of crystals is not completed in one lab session?
What should be done if drying of crystals is not completed in one lab session?
Why is the solution containing charcoal heated to boiling with frequent stirring?
Why is the solution containing charcoal heated to boiling with frequent stirring?
In recrystallization, what is the purpose of washing the crystals with a small amount of cold water?
In recrystallization, what is the purpose of washing the crystals with a small amount of cold water?
What is the role of adding charcoal during the purification process with low grade benzoic acid?
What is the role of adding charcoal during the purification process with low grade benzoic acid?
Why should the funnel be kept hot during filtration in recrystallization?
Why should the funnel be kept hot during filtration in recrystallization?
What happens when the solution containing charcoal is heated to boiling?
What happens when the solution containing charcoal is heated to boiling?
What does comparing the appearance of crystals in two Erlenmeyer flasks help determine?
What does comparing the appearance of crystals in two Erlenmeyer flasks help determine?
Under what condition should one flask be set aside to cool slowly without disturbance?
Under what condition should one flask be set aside to cool slowly without disturbance?
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Study Notes
Purification of Low Grade Benzoic Acid by Recrystallization
- Recrystallization is a common method for purifying solids, involving several steps.
Steps in Recrystallization
- Dissolve 1.0 gram of low grade benzoic acid in a minimum amount of boiling water (approximately 75 mL) in a 125 mL Erlenmeyer flask.
- Add a small amount of solvent at a time to avoid excess.
- Add charcoal to remove colored impurities, heat to boiling point, and stir frequently.
- Filter the solution while hot through fluted filter paper into a heated Erlenmeyer flask containing 5 mL of water.
- Ensure the funnel is hot to prevent crystallization on the funnel.
Crystallization and Filtration
- Divide the filtrate into two Erlenmeyer flasks.
- Set aside one flask to cool slowly without disturbance to allow crystallization to take place.
- Place the other flask in an ice bath.
- Compare the appearance of the crystals in the two flasks.
- Combine the two solutions and filter the crystals.
- Wash the crystals with a small amount of cold water to remove the adhering mother liquor.
Drying the Crystals
- Spread the crystals on a watch glass and allow to dry.
- If drying is done overnight, cover the crystals with a filter paper and keep in a locker until the next laboratory period.
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