Chapter 3.2, Problem 1E

a)

Interpretation Introduction

Interpretation:Solution recrystallization should be defined.

Concept introduction: Sublimation, extraction and chromatography are methods that are used for purification of organic compounds. But recrystallization involves isolation of compounds with extremely high purity. Recrystallization is one of techniques that are employed to purify organic compounds.

Explanation of Solution

Solution recrystallization or simply recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

b)

Interpretation Introduction

Interpretation:Temperature coefficient of solvent should be defined.

Concept introduction:Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Recrystallization solvent should be chosen in such way that compound is insoluble at low temperatures but becomes soluble at high temperatures. This variance in solubility of compound is governed by temperature coefficient of solvent.

c)

Interpretation Introduction

Interpretation:Relationship between dielectric constant and polarity of solvent should be defined.

Concept introduction:Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Most commonly used solvents for recrystallization varies widely in terms of their polarities. These polarities are measured by respective dielectric constants. Solvents with dielectric constants from 2 to 3 are nonpolar while those with values of dielectric constants more than 10 are polar. Solvents with dielectric constant in range of 3 to 10 are considered as intermediate polar. Polar compounds are usually soluble in polar solvents and vice-versa. So polarity of solvent is directly related to dielectric constant.

d)

Interpretation Introduction

Interpretation:Petroleum ether should be defined.

Concept introduction: Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Petroleum ether is generally used as solvent in recrystallization process. It is flammable and highly volatile in nature. It is also known as benzene. Chemical structure for petroleum ether does not contain ether functional group but consists of aliphatic hydrocarbons and has chemical formula of ${\text{C}}_{6-16}{\text{H}}_{12-34}$ .

e)

Interpretation Introduction

Interpretation:Mixed solvents should be defined.

Concept introduction:Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

If more than one solvent exists in mixture, it is termed as mixed solvent. So mixed solvents are usually made up of two or more types of single solvents. For example, isoamyl or banana oil is mixed solvent.

f)

Interpretation Introduction

Interpretation:Solvent selection should be defined.

Concept introduction: Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Criteria mentioned below should be used to select solvent for recrystallization.

1. Solvent should be able to dissolve desired compound in itself at high temperatures but insoluble at low temperatures. In short, solvent with favorable temperature coefficient should be used for particular solute.

2. Solvent should be chosen in such way that impurities are either insoluble in it or remain moderately soluble in it at low temperatures.

3. Boiling point of desired solvent should be low so that it gets separated from crystals easily.

4. Boiling point of solvent should be less than melting point of solid under consideration.

5. There should be no reaction between solvent and substance that needs to be purified.

g)

Interpretation Introduction

Interpretation:Filter-aid should be defined.

Concept introduction:Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Filter aid is substance or agent that is composed of solid particles and is used to improve efficiency of filtration. Its use also controls flow of liquids and removal of solid particles.

h)

Interpretation Introduction

Interpretation:Hot filtration should be defined.

Concept introduction: Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Hot filtration is technique that is used in recrystallization process when insoluble solid impurities are present in solvent. This process is essential to follow when activated charcoal is used to remove colored impurities in recrystallization process.

i)

Interpretation Introduction

Interpretation:Seeding should be defined.

Concept introduction:Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Seeding is method that is used to control supersaturation. Supersaturated solutions are allowed to form crystals by process of seeding. Any of crystals formed are added to solution to induce crystallization that occurs on rapid pace.

j)

Interpretation Introduction

Interpretation:Vacuum filtration should be defined.

Concept introduction: Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Vacuum filtration is technique that is applied to separate solid products from liquids. It is performed with help of Buchner funnel that is attached to vacuum filter flask with aid of rubber stopper or neoprene adapter. Side arm of filter flask is attached to house vacuum line through trap called filter trap. This trap is used for collection of overflowed filtrate from filter flask.

k)

Interpretation Introduction

Interpretation:Mother liquor should be defined.

Concept introduction:Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Mother liquor is nothing but part of solution that remains after crystallization of pure compound. This liquid is generally obtained in filtration process.

l)

Interpretation Introduction

Interpretation:Filtrate should be defined.

Concept introduction: Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Filtration is procedure that is used to remove insoluble impurities, decolorized activated carbon from solution and also for purification of compound. Liquid that has been passed through filter apparatus is called filtrate while solid that cannot pass through filter is known as residue.

m)

Interpretation Introduction

Interpretation: Solute should be defined.

Concept introduction: Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Solution always has two components, one is solute and another is solvent. Solute is that part of solution that is present in small quantity and that dissolves itself into another component called solvent. So solvent is present in larger amount in solution and it dissolves solute in itself.

n)

Interpretation Introduction

Interpretation: Solvent should be defined.

Concept introduction: Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Solution always has two components, one is solute and another is solvent. Solute is that part of solution that is present in small quantity and that dissolves itself into another component called solvent. So solvent is present in larger amount in solution and it dissolves solute in itself.

o)

Interpretation Introduction

Interpretation:Occlusion should be defined.

Concept introduction: Recrystallization is technique that is used for purification of organic compounds. This process includes dissolution of solid in specific solvent at high temperature and then crystals are made again by process of cooling. Temperature of crystals is decreased to allow impurities to remain in solution only.

Explanation of Solution

Occlusion occurs when one substance is included into another one. This process usually occurs if crystallization or precipitation occurs at high speeds.