RecrystallizationA purification Technique for Solids

Objectives

bull To understand the concept behind recrystallization and its usefulness in organic synthesisbull Learn how to choose the correct solvent for recrystallization

Introduction

Crystallization may be defined as the process in which a solid compound precipitates from a saturated solution in the form of crystals Saturation is usually effected through cooling or evaporation

- Purification by recrystallization depends on the following facts1 Different solids have different solubilities in a given solvent2 Most solids are more soluble in hot than in cold solvents

Figure 1 a crystallized compound

When the impure solid is dissolved in a minimum volume of a suitable hot solvent and the resulting solution is gradually cooled saturation and eventual crystallization of the pure compound occurs Impurities in a solid are of two kinds soluble and insoluble and recrystallization involves the removal of both to purify a solid Insoluble impurities are first removed by gravity filtration of the hot solution while the soluble impurities remain dissolved in the cold saturated solution (mother liquor) after precipitation of the desired compound The pure crystals are separated from the supernatant liquid by suction filtration

Generalized Experimental Procedure

Recrystallization involves the following sequence of steps1 Selection of a suitable solvent2 Preparation of the solution3 Hot Filtration (Gravity Filtration)4 Cooling5 Collecting and Drying of Crystals

11

Each step will now be discussed more fully

1 Selection of a suitable solvent

A suitable solvent for recrystallization should possess the following important properties1 Dissolve a large amount of the solid to be purified at high temperature2 Dissolve impurities readily at low temperatures (= soluble impurities) or not at all even at the boiling point (= insoluble impurities)

Experimentally the suitable solvent is determined through solubility testsThis is done by shaking about 01 g of the powdered solid with ~2 mL of the given solvent in a dry test tube If the entire solid has nearly dissolved in the cold solvent the solvent considered unsuitable If not the mixture is heated gently to the boiling point with stirring If most of the solid did not dissolve the solvent is also unsuitable

If a substance is found to be too soluble in one solvent and insoluble in another then a mixture of both solvents (solvent pair) may be used In such cases the solvents must be completely miscible The compound to be recrystallized is dissolved in the solvent in which it is very soluble and then the other solvent is added gradually at the boiling point until a slight turbidity occurs The solution is then allowed to stand at room temperature to effect slow crystallization before chilling in ice

Table 1 Common solvents for Recrystallization

Solvent bp C Particulars of Solvents

Water 100 To be used whenever suitableMethanol 65 Flammable toxicEthanol 78 FlammableAcetone 56 Flammable

Chloroform 61 Non-flammable vapor toxicCyclohexane 81 FlammableEthyl acetate 78 Flammable

2 Preparation of the solution

To prepare the hot solution the finely divided solid is placed in an Erlenmeyer (conical) flask and the selected solvent is added in small portions The mixture is stirred and heated to boiling after each addition until the solid dissolves completely A slight excess of the solvent is usually added to compensate for any losses (through evaporation) during hot filtration

12

NOTE Decolorizing charcoal may added at this stage if the solution is colored due to colored impuritiesThe flask should be removed from the heat source before adding charcoal to it otherwise bumping will occur

3 Hot Filtration (Gravity Filtration)

Filtration of the hot solution is necessary to remove insoluble impurities Upon addition to the funnel the solution will cool rapidly and this can cause unwanted precipitation This can be minimized or avoided by using a fluted filter paper and a stemless funnel placed on top of a beaker on a hotplate containing a few milliliters of the recrystallization solvent

4 Cooling

Cooling the filtered solution will allow crystals to form The rate of cooling plays a role in determining the size of the crystals that form fast cooling will tend to generate more crystals of small size slow cooling can allow largest crystals to form The best compromise of speed convenience and crystal quality is simply to let the solution cool to room temperature on the lab bench To ensure maximum recovery of material the solution should be cooled in an ice-water bath after the solution has reached room temperatureNOTE Scratching of the inner surface of the glass can help in crystal formation

5 Collecting and Drying of Crystals

When the crystallization is complete the crystals need to be collected by suction filtration using a Buchner funnel to ensure rapid and complete removal of the solvent Transfer the crystalline material as a suspension to the filter being careful to never fill the funnel over half full Most of the time it will be difficult to completely transfer all of the crystals to the funnel quantitatively so it will be necessary to add a small amount of ice-cold solvent to the flask to help facilitate the transfer of all of the crystals The crystals are then washed with a little more ice-cold solvent to remove any final impurities that may remain on the surface of the crystals This solvent should be as cold as possible to keep the crystals from redissolvingThe crystals are finally dried in an oven or allowed to air-dry in case the melting point is low by spreading them over a sheet of paper

13

Experimental

1048774 Selection of SolventPerform solubility tests on anthracene salicylic acid benzoic acid and sodium benzoate in water alcohol and ligroin as followsWith a spatula take about 01 g of the powdered solid and place in a dry test tube Start by dissolving it in about 2 mL of solvent with stirring If insoluble heat the mixture to boiling (in water bath) and observe the solubility The results should allow the selection of a suitable solvent for each compound

1048774 Recrystallization of an impure unknown Weigh about 1 g of the impure unknown and recrystallize it from the solvent you have selected(By making a solubility tests on pure unknown to choose the suitable solvent)Make sure you use the minimum volume of solvent otherwise the amount of recovered product will be small Determine the weight and melting point of the purified compound

14

RecrystallizationReport Sheet

1048774 Selection of Recrystallization Solvent

Compound

SolubilitySuitable

SolventWater Alcohol Ligroin

Cold Hot Cold Hot Cold Hot

Sodium benzoate

Salicylic acid

Anthracene

Benzoic Acid

1048774 Recrystallization of an Impure unknown

-Unknown letter- Suitable recrystallizing solvent

- Mass of crude sample

- Mass of purified sample

- yield

- Melting point of crude sample

- Melting point of pure sample

-What is the effect of the presence of impurities on the mp

-Did you find insoluble impurities in the crude unknown How can you remove it

15

Name---------------------

1048774 Questions

1 What is the purpose of recrystallization

2 What properties should ideally be possessed by a recrystallization solvent

3 How might the melting point of a material differ before and after recrystallization

4 Why should the crystals be washed with extra solvent when collected using suction filtration Why cold solvent

5 Why it is preferable to allow the hot solution to cool gradually instead of chilling immediately in an ice-bath

6 For what purpose is charcoal used in recrystallization

16

7 Results of solubility tests for compound A are shown in the following table (gmL) Which solvent will you choose for recrystallization

Solvent Water Ethanol Diethyl etherCold 20 3 5 Hot 30 25 5

___________________________

Procedure for Crystallization

The photos below illustrate the process of crystallization

Heat some solvent to boiling Place the solid to be recrystallized in an Erlenmeyer flask

Pour a small amount of the hot solvent into the flask containing the solid

Swirl the flask to dissolve the solid

Place the flask on the steam bath to keep the solution warm

If the solid is still not dissolved add a tiny amount more solvent and swirl again

When the solid is all in solution set it on the bench top Do not disturb it

17

After a while crystals should appear in the flask

You can now place the flask in an ice bath to finish the crystallization process

You are now ready to filter the solution to isolate the crystals Please see the section on vacuum filtration After your crystals are filtered from the solution put them on a watch glass as shown below

Here is the filter paper with crystals on it

Carefully scrape the crystals onto the watch glass

Let the crystal finish drying on the watch glass

You may Go to httporgchemcoloradoeduhndbksupportcrystcrystprochtml

18

Each step will now be discussed more fully

1 Selection of a suitable solvent

A suitable solvent for recrystallization should possess the following important properties1 Dissolve a large amount of the solid to be purified at high temperature2 Dissolve impurities readily at low temperatures (= soluble impurities) or not at all even at the boiling point (= insoluble impurities)

Experimentally the suitable solvent is determined through solubility testsThis is done by shaking about 01 g of the powdered solid with ~2 mL of the given solvent in a dry test tube If the entire solid has nearly dissolved in the cold solvent the solvent considered unsuitable If not the mixture is heated gently to the boiling point with stirring If most of the solid did not dissolve the solvent is also unsuitable

If a substance is found to be too soluble in one solvent and insoluble in another then a mixture of both solvents (solvent pair) may be used In such cases the solvents must be completely miscible The compound to be recrystallized is dissolved in the solvent in which it is very soluble and then the other solvent is added gradually at the boiling point until a slight turbidity occurs The solution is then allowed to stand at room temperature to effect slow crystallization before chilling in ice

Table 1 Common solvents for Recrystallization

Solvent bp C Particulars of Solvents

Water 100 To be used whenever suitableMethanol 65 Flammable toxicEthanol 78 FlammableAcetone 56 Flammable

Chloroform 61 Non-flammable vapor toxicCyclohexane 81 FlammableEthyl acetate 78 Flammable

2 Preparation of the solution

To prepare the hot solution the finely divided solid is placed in an Erlenmeyer (conical) flask and the selected solvent is added in small portions The mixture is stirred and heated to boiling after each addition until the solid dissolves completely A slight excess of the solvent is usually added to compensate for any losses (through evaporation) during hot filtration

12

NOTE Decolorizing charcoal may added at this stage if the solution is colored due to colored impuritiesThe flask should be removed from the heat source before adding charcoal to it otherwise bumping will occur

3 Hot Filtration (Gravity Filtration)

Filtration of the hot solution is necessary to remove insoluble impurities Upon addition to the funnel the solution will cool rapidly and this can cause unwanted precipitation This can be minimized or avoided by using a fluted filter paper and a stemless funnel placed on top of a beaker on a hotplate containing a few milliliters of the recrystallization solvent

4 Cooling

Cooling the filtered solution will allow crystals to form The rate of cooling plays a role in determining the size of the crystals that form fast cooling will tend to generate more crystals of small size slow cooling can allow largest crystals to form The best compromise of speed convenience and crystal quality is simply to let the solution cool to room temperature on the lab bench To ensure maximum recovery of material the solution should be cooled in an ice-water bath after the solution has reached room temperatureNOTE Scratching of the inner surface of the glass can help in crystal formation

5 Collecting and Drying of Crystals

When the crystallization is complete the crystals need to be collected by suction filtration using a Buchner funnel to ensure rapid and complete removal of the solvent Transfer the crystalline material as a suspension to the filter being careful to never fill the funnel over half full Most of the time it will be difficult to completely transfer all of the crystals to the funnel quantitatively so it will be necessary to add a small amount of ice-cold solvent to the flask to help facilitate the transfer of all of the crystals The crystals are then washed with a little more ice-cold solvent to remove any final impurities that may remain on the surface of the crystals This solvent should be as cold as possible to keep the crystals from redissolvingThe crystals are finally dried in an oven or allowed to air-dry in case the melting point is low by spreading them over a sheet of paper

13

Experimental

1048774 Selection of SolventPerform solubility tests on anthracene salicylic acid benzoic acid and sodium benzoate in water alcohol and ligroin as followsWith a spatula take about 01 g of the powdered solid and place in a dry test tube Start by dissolving it in about 2 mL of solvent with stirring If insoluble heat the mixture to boiling (in water bath) and observe the solubility The results should allow the selection of a suitable solvent for each compound

1048774 Recrystallization of an impure unknown Weigh about 1 g of the impure unknown and recrystallize it from the solvent you have selected(By making a solubility tests on pure unknown to choose the suitable solvent)Make sure you use the minimum volume of solvent otherwise the amount of recovered product will be small Determine the weight and melting point of the purified compound

14

RecrystallizationReport Sheet

1048774 Selection of Recrystallization Solvent

Compound

SolubilitySuitable

SolventWater Alcohol Ligroin

Cold Hot Cold Hot Cold Hot

Sodium benzoate

Salicylic acid

Anthracene

Benzoic Acid

1048774 Recrystallization of an Impure unknown

-Unknown letter- Suitable recrystallizing solvent

- Mass of crude sample

- Mass of purified sample

- yield

- Melting point of crude sample

- Melting point of pure sample

-What is the effect of the presence of impurities on the mp

-Did you find insoluble impurities in the crude unknown How can you remove it

15

Name---------------------

1048774 Questions

1 What is the purpose of recrystallization

2 What properties should ideally be possessed by a recrystallization solvent

3 How might the melting point of a material differ before and after recrystallization

4 Why should the crystals be washed with extra solvent when collected using suction filtration Why cold solvent

5 Why it is preferable to allow the hot solution to cool gradually instead of chilling immediately in an ice-bath

6 For what purpose is charcoal used in recrystallization

16

7 Results of solubility tests for compound A are shown in the following table (gmL) Which solvent will you choose for recrystallization

Solvent Water Ethanol Diethyl etherCold 20 3 5 Hot 30 25 5

___________________________

Procedure for Crystallization

The photos below illustrate the process of crystallization

Heat some solvent to boiling Place the solid to be recrystallized in an Erlenmeyer flask

Pour a small amount of the hot solvent into the flask containing the solid

Swirl the flask to dissolve the solid

Place the flask on the steam bath to keep the solution warm

If the solid is still not dissolved add a tiny amount more solvent and swirl again

When the solid is all in solution set it on the bench top Do not disturb it

17

After a while crystals should appear in the flask

You can now place the flask in an ice bath to finish the crystallization process

You are now ready to filter the solution to isolate the crystals Please see the section on vacuum filtration After your crystals are filtered from the solution put them on a watch glass as shown below

Here is the filter paper with crystals on it

Carefully scrape the crystals onto the watch glass

Let the crystal finish drying on the watch glass

You may Go to httporgchemcoloradoeduhndbksupportcrystcrystprochtml

18

NOTE Decolorizing charcoal may added at this stage if the solution is colored due to colored impuritiesThe flask should be removed from the heat source before adding charcoal to it otherwise bumping will occur

3 Hot Filtration (Gravity Filtration)

Filtration of the hot solution is necessary to remove insoluble impurities Upon addition to the funnel the solution will cool rapidly and this can cause unwanted precipitation This can be minimized or avoided by using a fluted filter paper and a stemless funnel placed on top of a beaker on a hotplate containing a few milliliters of the recrystallization solvent

4 Cooling

Cooling the filtered solution will allow crystals to form The rate of cooling plays a role in determining the size of the crystals that form fast cooling will tend to generate more crystals of small size slow cooling can allow largest crystals to form The best compromise of speed convenience and crystal quality is simply to let the solution cool to room temperature on the lab bench To ensure maximum recovery of material the solution should be cooled in an ice-water bath after the solution has reached room temperatureNOTE Scratching of the inner surface of the glass can help in crystal formation

5 Collecting and Drying of Crystals

When the crystallization is complete the crystals need to be collected by suction filtration using a Buchner funnel to ensure rapid and complete removal of the solvent Transfer the crystalline material as a suspension to the filter being careful to never fill the funnel over half full Most of the time it will be difficult to completely transfer all of the crystals to the funnel quantitatively so it will be necessary to add a small amount of ice-cold solvent to the flask to help facilitate the transfer of all of the crystals The crystals are then washed with a little more ice-cold solvent to remove any final impurities that may remain on the surface of the crystals This solvent should be as cold as possible to keep the crystals from redissolvingThe crystals are finally dried in an oven or allowed to air-dry in case the melting point is low by spreading them over a sheet of paper

13

Experimental

1048774 Selection of SolventPerform solubility tests on anthracene salicylic acid benzoic acid and sodium benzoate in water alcohol and ligroin as followsWith a spatula take about 01 g of the powdered solid and place in a dry test tube Start by dissolving it in about 2 mL of solvent with stirring If insoluble heat the mixture to boiling (in water bath) and observe the solubility The results should allow the selection of a suitable solvent for each compound

1048774 Recrystallization of an impure unknown Weigh about 1 g of the impure unknown and recrystallize it from the solvent you have selected(By making a solubility tests on pure unknown to choose the suitable solvent)Make sure you use the minimum volume of solvent otherwise the amount of recovered product will be small Determine the weight and melting point of the purified compound

14

RecrystallizationReport Sheet

1048774 Selection of Recrystallization Solvent

Compound

SolubilitySuitable

SolventWater Alcohol Ligroin

Cold Hot Cold Hot Cold Hot

Sodium benzoate

Salicylic acid

Anthracene

Benzoic Acid

1048774 Recrystallization of an Impure unknown

-Unknown letter- Suitable recrystallizing solvent

- Mass of crude sample

- Mass of purified sample

- yield

- Melting point of crude sample

- Melting point of pure sample

-What is the effect of the presence of impurities on the mp

-Did you find insoluble impurities in the crude unknown How can you remove it

15

Name---------------------

1048774 Questions

1 What is the purpose of recrystallization

2 What properties should ideally be possessed by a recrystallization solvent

3 How might the melting point of a material differ before and after recrystallization

4 Why should the crystals be washed with extra solvent when collected using suction filtration Why cold solvent

5 Why it is preferable to allow the hot solution to cool gradually instead of chilling immediately in an ice-bath

6 For what purpose is charcoal used in recrystallization

16

7 Results of solubility tests for compound A are shown in the following table (gmL) Which solvent will you choose for recrystallization

Solvent Water Ethanol Diethyl etherCold 20 3 5 Hot 30 25 5

___________________________

Procedure for Crystallization

The photos below illustrate the process of crystallization

Heat some solvent to boiling Place the solid to be recrystallized in an Erlenmeyer flask

Pour a small amount of the hot solvent into the flask containing the solid

Swirl the flask to dissolve the solid

Place the flask on the steam bath to keep the solution warm

If the solid is still not dissolved add a tiny amount more solvent and swirl again

When the solid is all in solution set it on the bench top Do not disturb it

17

After a while crystals should appear in the flask

You can now place the flask in an ice bath to finish the crystallization process

You are now ready to filter the solution to isolate the crystals Please see the section on vacuum filtration After your crystals are filtered from the solution put them on a watch glass as shown below

Here is the filter paper with crystals on it

Carefully scrape the crystals onto the watch glass

Let the crystal finish drying on the watch glass

You may Go to httporgchemcoloradoeduhndbksupportcrystcrystprochtml

18

Experimental

1048774 Selection of SolventPerform solubility tests on anthracene salicylic acid benzoic acid and sodium benzoate in water alcohol and ligroin as followsWith a spatula take about 01 g of the powdered solid and place in a dry test tube Start by dissolving it in about 2 mL of solvent with stirring If insoluble heat the mixture to boiling (in water bath) and observe the solubility The results should allow the selection of a suitable solvent for each compound

1048774 Recrystallization of an impure unknown Weigh about 1 g of the impure unknown and recrystallize it from the solvent you have selected(By making a solubility tests on pure unknown to choose the suitable solvent)Make sure you use the minimum volume of solvent otherwise the amount of recovered product will be small Determine the weight and melting point of the purified compound

14

RecrystallizationReport Sheet

1048774 Selection of Recrystallization Solvent

Compound

SolubilitySuitable

SolventWater Alcohol Ligroin

Cold Hot Cold Hot Cold Hot

Sodium benzoate

Salicylic acid

Anthracene

Benzoic Acid

1048774 Recrystallization of an Impure unknown

-Unknown letter- Suitable recrystallizing solvent

- Mass of crude sample

- Mass of purified sample

- yield

- Melting point of crude sample

- Melting point of pure sample

-What is the effect of the presence of impurities on the mp

-Did you find insoluble impurities in the crude unknown How can you remove it

15

Name---------------------

1048774 Questions

1 What is the purpose of recrystallization

2 What properties should ideally be possessed by a recrystallization solvent

3 How might the melting point of a material differ before and after recrystallization

4 Why should the crystals be washed with extra solvent when collected using suction filtration Why cold solvent

5 Why it is preferable to allow the hot solution to cool gradually instead of chilling immediately in an ice-bath

6 For what purpose is charcoal used in recrystallization

16

7 Results of solubility tests for compound A are shown in the following table (gmL) Which solvent will you choose for recrystallization

Solvent Water Ethanol Diethyl etherCold 20 3 5 Hot 30 25 5

___________________________

Procedure for Crystallization

The photos below illustrate the process of crystallization

Heat some solvent to boiling Place the solid to be recrystallized in an Erlenmeyer flask

Pour a small amount of the hot solvent into the flask containing the solid

Swirl the flask to dissolve the solid

Place the flask on the steam bath to keep the solution warm

If the solid is still not dissolved add a tiny amount more solvent and swirl again

When the solid is all in solution set it on the bench top Do not disturb it

17

After a while crystals should appear in the flask

You can now place the flask in an ice bath to finish the crystallization process

You are now ready to filter the solution to isolate the crystals Please see the section on vacuum filtration After your crystals are filtered from the solution put them on a watch glass as shown below

Here is the filter paper with crystals on it

Carefully scrape the crystals onto the watch glass

Let the crystal finish drying on the watch glass

You may Go to httporgchemcoloradoeduhndbksupportcrystcrystprochtml

18

RecrystallizationReport Sheet

1048774 Selection of Recrystallization Solvent

Compound

SolubilitySuitable

SolventWater Alcohol Ligroin

Cold Hot Cold Hot Cold Hot

Sodium benzoate

Salicylic acid

Anthracene

Benzoic Acid

1048774 Recrystallization of an Impure unknown

-Unknown letter- Suitable recrystallizing solvent

- Mass of crude sample

- Mass of purified sample

- yield

- Melting point of crude sample

- Melting point of pure sample

-What is the effect of the presence of impurities on the mp

-Did you find insoluble impurities in the crude unknown How can you remove it

15

Name---------------------

1048774 Questions

1 What is the purpose of recrystallization

2 What properties should ideally be possessed by a recrystallization solvent

3 How might the melting point of a material differ before and after recrystallization

4 Why should the crystals be washed with extra solvent when collected using suction filtration Why cold solvent

5 Why it is preferable to allow the hot solution to cool gradually instead of chilling immediately in an ice-bath

6 For what purpose is charcoal used in recrystallization

16

7 Results of solubility tests for compound A are shown in the following table (gmL) Which solvent will you choose for recrystallization

Solvent Water Ethanol Diethyl etherCold 20 3 5 Hot 30 25 5

___________________________

Procedure for Crystallization

The photos below illustrate the process of crystallization

Heat some solvent to boiling Place the solid to be recrystallized in an Erlenmeyer flask

Pour a small amount of the hot solvent into the flask containing the solid

Swirl the flask to dissolve the solid

Place the flask on the steam bath to keep the solution warm

If the solid is still not dissolved add a tiny amount more solvent and swirl again

When the solid is all in solution set it on the bench top Do not disturb it

17

After a while crystals should appear in the flask

You can now place the flask in an ice bath to finish the crystallization process

You are now ready to filter the solution to isolate the crystals Please see the section on vacuum filtration After your crystals are filtered from the solution put them on a watch glass as shown below

Here is the filter paper with crystals on it

Carefully scrape the crystals onto the watch glass

Let the crystal finish drying on the watch glass

You may Go to httporgchemcoloradoeduhndbksupportcrystcrystprochtml

18

1048774 Questions

1 What is the purpose of recrystallization

2 What properties should ideally be possessed by a recrystallization solvent

3 How might the melting point of a material differ before and after recrystallization

4 Why should the crystals be washed with extra solvent when collected using suction filtration Why cold solvent

5 Why it is preferable to allow the hot solution to cool gradually instead of chilling immediately in an ice-bath

6 For what purpose is charcoal used in recrystallization

16

7 Results of solubility tests for compound A are shown in the following table (gmL) Which solvent will you choose for recrystallization

Solvent Water Ethanol Diethyl etherCold 20 3 5 Hot 30 25 5

___________________________

Procedure for Crystallization

The photos below illustrate the process of crystallization

Heat some solvent to boiling Place the solid to be recrystallized in an Erlenmeyer flask

Pour a small amount of the hot solvent into the flask containing the solid

Swirl the flask to dissolve the solid

Place the flask on the steam bath to keep the solution warm

If the solid is still not dissolved add a tiny amount more solvent and swirl again

When the solid is all in solution set it on the bench top Do not disturb it

17

After a while crystals should appear in the flask

You can now place the flask in an ice bath to finish the crystallization process

You are now ready to filter the solution to isolate the crystals Please see the section on vacuum filtration After your crystals are filtered from the solution put them on a watch glass as shown below

Here is the filter paper with crystals on it

Carefully scrape the crystals onto the watch glass

Let the crystal finish drying on the watch glass

You may Go to httporgchemcoloradoeduhndbksupportcrystcrystprochtml

18

7 Results of solubility tests for compound A are shown in the following table (gmL) Which solvent will you choose for recrystallization

Solvent Water Ethanol Diethyl etherCold 20 3 5 Hot 30 25 5

___________________________

Procedure for Crystallization

The photos below illustrate the process of crystallization

Heat some solvent to boiling Place the solid to be recrystallized in an Erlenmeyer flask

Pour a small amount of the hot solvent into the flask containing the solid

Swirl the flask to dissolve the solid

Place the flask on the steam bath to keep the solution warm

If the solid is still not dissolved add a tiny amount more solvent and swirl again

When the solid is all in solution set it on the bench top Do not disturb it

17

After a while crystals should appear in the flask

You can now place the flask in an ice bath to finish the crystallization process

You are now ready to filter the solution to isolate the crystals Please see the section on vacuum filtration After your crystals are filtered from the solution put them on a watch glass as shown below

Here is the filter paper with crystals on it

Carefully scrape the crystals onto the watch glass

Let the crystal finish drying on the watch glass

You may Go to httporgchemcoloradoeduhndbksupportcrystcrystprochtml

18

After a while crystals should appear in the flask

You can now place the flask in an ice bath to finish the crystallization process

You are now ready to filter the solution to isolate the crystals Please see the section on vacuum filtration After your crystals are filtered from the solution put them on a watch glass as shown below

Here is the filter paper with crystals on it

Carefully scrape the crystals onto the watch glass

Let the crystal finish drying on the watch glass

You may Go to httporgchemcoloradoeduhndbksupportcrystcrystprochtml

18