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Solubility behavior of organic

compounds

Dotsha J. Raheem

Muslih S. Hamasharif 

College of Science

Department of Chemistry

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1. Solubility (definition)2. Information obtained from solubility

3. Types of solubility

4. Factors affecting solubility5. Water soluble compounds

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The amount of solute needed to form a

solution in a given quantity of solvent.

Soluble if it dissolves to the extent of 

(3.3g/ 100 ml ) of solvent

Solubility ( definition)

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Information obtained from solubility

i. Presence of a functional group.

Because hydrocarbons are insoluble in water, observing thatan unknown is partially soluble in water indicates that a polar

functional group is present.

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ii. Solubility in certain solvents often leads to

more specific information about functional

group.

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iii. Certain conclusions about molecular size and

composition may sometimes be made from

solubility tests.

CH3(CH2)nCH2OH If ( n) higher than 5 is water insoluble

If ( n) fewer than 5 is water solublemonofunctional

compounds

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types of solubilityThe solubility of organic compounds can be divided into two

categories:

e.g. benzoic aciddissolves in 5% NaOH but

not in H2O

e.g. CHCl3 in C2H5-O-C2H5

Utilized for identi-

fication of functional

groups

To determine

solvents for chemical

reactions and

purification (as in

recrystallization)7

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Factors affecting solubility1-Temperature:

A-if the solution process absorbs energy then

the solubility will be increase with increasing

temperature.B-if the solution process releases energy then

the solubility will decrease with increasing

temperature.

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Factors affecting solubility2-Polarity:

“Like dissolves like”

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• Polar compounds dissolve in polar solvents

• Ionic compounds dissolve in polar solvents.

H

H

N

OH

H

CH3

H

H

N

OH

H

CH3

Hydrogen

bonding

CH3NH2 + H2O

methyl

amine

water

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• non polar compounds dissolve in non polar

solvents

e.g. Iodine(I2)is a (non polar) and soluble in nonpolar solvents like carbon tetrachloride(CCl4).

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Factors affecting solubility3-Molecular Size:

In general, an increases in molecular weight leads an increase inintermolecular forces and decreased solubility.

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Q//What are the intermolecularforces?

Q//What is the relation

between melting point andsolubility

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Factors affecting solubility4-Effect of chain branching on solubility.

1-Compounds having a branched chain are more

soluble than the corresponding straight-chain

compound (branching lowers intermolecular

forces and decreases intermolecular

attraction).

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2-The position of the functional group in the

carbon chain also affects solubility.

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Water soluble compounds

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Solubility in H2OWhen a compound dissolves in water, it’s

expected to be:

- Low M. wt. compound- Polar

- ionic

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A compound soluble in H2O and in

etherSA: Acids (carboxylic)

SB: Bases (amines)S1: Neutral compounds (alcohols, aldehydes,

ketones, esters)

General characteristics:

- Polar (non ionic)

- Contain 5 or less C atoms- Has a functional group that is polar and capable

of forming H-bonds

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A compound soluble in H2O but not in

etherS2: Salts of organic acids (RCO2Na, RSO3Na), amine

hydrochlorides (RNH3Cl), amino acids,carbohydrates, polyhydroxy compounds andpolybasic acids.

General characteristics:

- Ionic ( a salt)

- Contain two or more polar groups but not morethan 4C atoms per functional group

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