23
Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Embed Size (px)

Citation preview

Page 1: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Section 13.2 and 13.3 Control of Solubility

Bill ViningSUNY Oneonta

Page 2: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Control of Solubility

In these sections…

Molecular structure control:a.Entropy and thermodynamic controlb.Gas mixturesc. Mixtures of neutral molecules in liquidsd.Mixtures of ionic compounds in water

External (conditions) control:e. pressure f. temperature

Page 3: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Enthalpy and Entropy

Enthalpy: Bond strength- stronger bonds = lower enthalpy = more stable

Entropy: Free motion of atoms- freer mobility = higher entropy = more stable

Page 4: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Example: Enthalpy and Entropy of Evaporation

Page 5: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Enthalpy and Entropy Control of Dissolution

Page 6: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Gas Mixtures

Page 7: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Liquid-Liquid Mixtures

Page 8: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Predicting Miscibility of Two Liquids

General rules: 1. polar solutes dissolve in polar solvents2. nonpolar solutes dissolve in nonpolar solvents

“Like dissolves Like”

Oil and water don’t mix: is oil polar or nonpolar?

For now, we are examining molecular compounds- not ionic compounds.

Page 9: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Hydrophilic groups:

Hydrophobic groups:

–OH and –NH groups

Examples: CH3OH, NH3, H-O-O-H

Long hydrocarbon groups:

CH3CH2CH2CH2CH2CH2

Examples: CH3CH2CH2CH2CH3

CH3CH2CH2CH2Cl

Page 10: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Which of these will not dissolve in water?

1. NH3

2. CH3CH3

3. CH3OH

Page 11: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Which of these is least soluble in water?

1. CH3OH

2. CH3CH2CH2OH

3. CH3CH2CH2CH2OH

Page 12: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Why don’t oil and water mix?

What controls Solubility:

Enthalpy (enthalpy of solution)

Negative if new forces are stronger than original forces

Entropy

Depends on the entropy change of both the water and the solute.

Page 13: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Assume they mix fully

Page 14: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Assume water retains its hydrogen bonds

Page 15: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Which is it?

Experiments show mixing water and oil has:

H close to zero

S highly negative

Page 16: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Control of Solubility of Ionic Compounds

Page 17: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Control of Solubility of Ionic Compounds

Page 18: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Enthalpy Control

Entropy Control

Page 19: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Control of Solubility of Ionic Compounds

Enthalpy: lattice energies and hydration energies follow same trends and mostly offset

Entropy: smaller ions and ions of high charge have larger hydration spheres and are entropy disfavored from dissolving

Page 20: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

Control of Solubility of Ionic Compounds

Page 21: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

External Control of Solubility

Pressure Effects: Solubility of Gases in Liquids

As P of a gas increases, its solubility increases.

Henry’s Law:

What is the solubility of O2 under a pressure of 0.66 atm?

Page 22: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

External Control of Solubility

Temperature Effects

In general,

• if Hdissolution is exothermic, solubility decreases as temperature increases

• if Hdissolution is exothermic, solubility decreases as temperature increases

Page 23: Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

In general, but not always:

• if Hdissolution is exothermic, solubility decreases as temperature increases

• if Hdissolution is endothermic, solubility increases as temperature increases

What do we expect for ammonium nitrate?