CHEM173 6 Solutions And Solubility

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Solutions and Solubility
Chapters 4+13

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The Solution Process
• A solution is a homogeneous mixture of solute (present in the smallest amount) and solvent (present in the largest amount)
State of Solution

State of Solvent

State of Solute

Example

Gas

Gas

Gas

Air

Liquid

Liquid

Gas

O2 in water

Liquid

Liquid

Liquid

Alcohol in water

Liquid

Liquid

Solid

Salt in water

Solid

Solid

Gas

H2 in Pd

Solid

Solid

Liquid

Hg in Ag

Solid

Solid

Solid

Ag in Au

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The Solution Process
• Substances that dissolve completely in one another are termed miscible. Immiscible substances do not dissolve completely in one another
• Attractive forces between solute and solvent must be comparable in magnitude to the solute-solute interactions and the solvent-solvent interactions

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The Solution Process
• E.g. NaCl dissolving in water
▫ Water H-bonds need to be broken
▫ NaCl dissociates into Na+ and Cl▫ Ion-dipole forces form:
 Na+···OH2 and Cl–···H2O

▫ Ions become hydrated by water http://catalog.flatworldknowledge.com/bookhub/4309?e=averill_1.0-ch04

http://wps.prenhall.com/wps/media/objects/3312/3391718/blb1301.html

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Factors Affecting Solubility
• Solute- Solvent Interaction: “like dissolves like”

• Polar solutes are soluble in polar solvents
▫ H2O and CH3CH2OH (ethanol) are miscible because the broken H-bonds in both pure liquids are re-established in the mixture
▫ More –OH groups and more polar bonds within a molecule increases the solubility in water
Q. Covalent-network solids are not soluble in polar or non-polar solvents. Why?

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Factors Affecting Solubility
• Non-polar substances are soluble in non-polar solvents
• The number of C atoms in a chain affects solubility
▫ The more hydrophobic C atoms, the less soluble in water
Alcohol

Solubility in Water
(mol alcohol/100 g
H2O) at 20 °C

Solubility in C6H14

CH3OH



0.12

CH3CH2OH









CH3CH2CH2CH2OH

0.11



CH2CH2CH2CH2CH2OH

0.030



CH3CH2CH2CH2CH2CH2OH

0.0058