TemperatureTemperature

• Solubility curves have temperature on the Solubility curves have temperature on the X-axis.X-axis.

• Depends on the system, but we have a Depends on the system, but we have a couple of general rules:couple of general rules:

– Solubility of all gases Solubility of all gases as temperature as temperature ..

– Solubility of most solids Solubility of most solids as as temperature temperature ..

Solubility of GasesSolubility of Gases

1.1. Depends on temperature. Gases Depends on temperature. Gases are more soluble in colder solvents.are more soluble in colder solvents.

2.2. Depends on pressure.Depends on pressure.

Pressure & Solubility of GasesPressure & Solubility of Gases

• Henry’s Law: Henry’s Law:

• At a given temperature, the solubility of a At a given temperature, the solubility of a gas in a liquid is directly proportional to the gas in a liquid is directly proportional to the pressure of the gas above the liquid.pressure of the gas above the liquid.

• Solubility = k·PSolubility = k·Pgasgas

• Many bottling plants use pressures of 5 to Many bottling plants use pressures of 5 to 7 atmospheres to carbonate beverages 7 atmospheres to carbonate beverages (i.e., dissolve CO(i.e., dissolve CO22 in them). in them).

Effect of Pressure on Solubility of a Gas

Effect of Gas Pressure on SolubilityEffect of Gas Pressure on Solubility

What kind of relationship does the graph show & how do you know?

Do pressure changes affect other Do pressure changes affect other systems?systems?

• Solubility of liquids & solids is Solubility of liquids & solids is notnot influenced by pressure influenced by pressure changes.changes.

Which system is most affected by pressure changes?

a) NaCl(s) Na+(aq) + Cl-(aq)

b) C6H12O6(s) C6H12O6(aq)

c) NH3(g) NH3(aq)

It’s the only one involving a gas!!!

Nature of the solute & the solventNature of the solute & the solvent

• Another factor that determines solubility.Another factor that determines solubility.

• NATURE:NATURE:– IonicIonic– Nonpolar covalentNonpolar covalent– Polar covalentPolar covalent

• Rule is “Rule is “Like Dissolves LikeLike Dissolves Like” ”

CCA, Volume 2

Possibilites are:Possibilites are:

• SolventSolvent: Nonpolar covalent or polar : Nonpolar covalent or polar covalentcovalent

• SoluteSolute: Ionic, nonpolar covalent, : Ionic, nonpolar covalent, polar covalentpolar covalent

Possibilites are:Possibilites are:

• Nonpolar solute in nonpolar solvent.Nonpolar solute in nonpolar solvent.

• Polar solute in polar solvent.Polar solute in polar solvent.

• Ionic solute in polar solvent.Ionic solute in polar solvent.

Identify the nature of each of the following as PC, NPC, or ionic.

• CH4

• NaCl• H2O• CCl4• CH3OH• H2S• CaBr2

• C6H14

• NH3

• NH4OH• C4H10

• PH3

• CH3CH2OH

Nonpolar Cov.Ionic

Polar CovalentNonpolar Cov.

Polar Cov.

Polar Cov.IonicNonpolar Cov.

Polar Cov.

Ionic

Nonpolar Cov.Polar Cov.

Polar Cov.

IONIC vs. COVALENTIONIC vs. COVALENT

• IonicIonic: Substance is composed : Substance is composed of positive & negative ions of positive & negative ions (usually metal + nonmetal).(usually metal + nonmetal).

• CovalentCovalent: Substance is : Substance is composed of neutral molecules composed of neutral molecules (all nonmetal elements).(all nonmetal elements).

NONPOLAR COVALENTNONPOLAR COVALENT

• Have a symmetrical electron cloud.Have a symmetrical electron cloud.

• Have no separation of charge.Have no separation of charge.

• Have weak van der Waals forces.Have weak van der Waals forces.

• Are easy to pull apart.Are easy to pull apart.

• Have low melting points, low boiling Have low melting points, low boiling points, low heats of fusion.points, low heats of fusion.

• Have high vapor pressures.Have high vapor pressures.

Easy categories of nonpolar covalent substances

• Noble gases

• Homonuclear diatomics

• Molecules that are extremely symmetric (CO2, SiH4, CCl4, CF4)

• Anything that’s just C and H

POLAR COVALENTPOLAR COVALENT

• Have a lopsided electron cloud.Have a lopsided electron cloud.• Have a separation of charge.Have a separation of charge.• Have dipole-dipole interactions.Have dipole-dipole interactions.• Are harder to pull apart.Are harder to pull apart.• Have higher melting points, boiling Have higher melting points, boiling

points, and heats of fusion than points, and heats of fusion than nonpolar molecules.nonpolar molecules.

• Have lower vapor pressures than Have lower vapor pressures than nonpolar molecules.nonpolar molecules.

Nature of Nature of SoluteSolute

Nonpolar Nonpolar SolventSolvent

Polar Polar SolventSolvent

NonpolarNonpolar SolubleSoluble InsolubleInsoluble

PolarPolar InsolubleInsoluble SolubleSoluble

IonicIonic InsolubleInsoluble SolubleSoluble

Solvation in different systems.

Ionic-polarPolar-polar

Ionic-nonpolar Nonpolar-NPPolar-nonpolar

What kind of solvent is HWhat kind of solvent is H22O?O?

• Water is polar covalent.Water is polar covalent.

• The oxygen end: The oxygen end: -.-.

• The hydrogens: The hydrogens: +.+.

• Ionic & Polar solutes dissolve well in HIonic & Polar solutes dissolve well in H22O. O.

• Nonpolar solutes do not dissolve in HNonpolar solutes do not dissolve in H22O.O.

Dissolving NaCl in waterDissolving NaCl in water• Water is a polarpolar molecule. The O has a -

charge and the H’s have a + charge. NaCl is ionicionic. The Na ion has a full +1 charge & the Cl ion has a full -1 charge.

• The Na+ is attracted to the - of the O’s. This beats out the attraction to the Cl-.

• The Cl- is attracted to the + of the H’s. This beats out the attraction to the Na.

Dissolving Polar substances in Dissolving Polar substances in water.water.

• PolarPolar substances have a separation of charge. One side of the molecules is - and one side +.

• The + of the solute interacts with the - or oxygen end of the water molecule and vice versa.

Dissolving a sugar cube in water.

Dissolving nonpolar substances in Dissolving nonpolar substances in waterwater

• Symmetrical molecules are nonpolar.

• Many organic molecules (C,H) are nonpolar.

• NonpolarNonpolar molecules do not dissolve in water because the attractive forces between the polar water molecules and the nonpolar molecules are too weak.

Why soap worksWhy soap works

• Grease won’t dissolve easily in water.

• Grease is nonpolar & water is polar.

• Soaps – very long molecules.

– One end is polar & dissolves in water.

– The other end is nonpolar, & grease will dissolve in it.

Nonpolar end is hydrophobic

Ionic end is hydrophilic or attracted to water

Hydrophobic means attracted to substances that are NOT water-soluble, like grease.

Summary: Factors Affecting Summary: Factors Affecting SolubilitySolubility

• Nature of the solvent and the solute:Nature of the solvent and the solute:

LIKE DISSOLVES LIKELIKE DISSOLVES LIKE

• Temperature Temperature

• Pressure (for systems with gases)Pressure (for systems with gases)