Chapter 13

SolutionsSolutions

Overview Solution Process

• energy changes, solution formation, chemical reactions

Concentration• mole fraction, molarity, molality, mass

percent, ppm

Saturated Solutions & Solubility Factors Affecting Interactions

• solute-solvent, pressure, temperature

Colligative Properties

• vapor pressure lowering, boiling point elevation, freezing point depression, osmosis

Colloids

Solutions Solution

• mixture of two or more substances • components are the solute and the solvent

Solvent• component of the mixture present in greater

quantity• often retains its physical characteristics

Solute• component of the mixture present in smaller

quantity

Solution Process

Intermolecular Forces• must be overcome in both the solvent & solute

before the mixture can be formed• forces between the solute & solvent must be

similar in nature and strength

hydration• interaction between water (the solvent) &

solute is termed hydration

solvation• interaction between any solvent & the solute

Energy Relationships

Hsolution = H1 + H2 + H3

• H1 = energy required to separate solute particles

• H2 = energy required to separate solvent particles

• H3 = energy produced by interaction of solute/solvent

Hsolution is exothermic only if

• H3 is larger than H1 + H2

Solubility General Rule -- like dissolves like

• polar substances will dissolve other polar substances

• non-polar substances will dissolve other non-polar substances

• polar substances will not dissolve non-polar substances

Polar/Polar solutions• driven by energy relationships -- H3 is larger

than H1 + H2

Cont’d

Polar/Polar solutions• driven by energy relationships -- H3 is larger

than H1 + H2

Non-polar/Non-polar solutions• driven by disorder -- H3 is about the same as

H1 + H2

Cont’d

True Solution• solute particles remain unchanged

– NaCl(s) + H2O(l) Na+(aq) + Cl-(aq)

• no chemical reaction occurs– Ni(s) + 2HCl(aq) NiCl2(aq) + H2(g)

Concentration

Expresses a ratio between solute andsolvent/solution Mass %

• percent mass (%) = g solute x 100 total g solution

ppm -- parts per million• ppm = mass of solute x 106

tot. mass soln

Mole Fraction• Mole Fraction (X) = moles solute

total moles

Molarity• Molarity (M) = moles solute

1L solution

Molality

• Molality (m) = moles solute 1 kg solvent

Saturated Solutions & Solubility

Process

• solute + solvent solution

solution formation

crystallization

Solubility

• quantity of solute necessary to produce a saturated solution

• generally in grams of solute per 100 grams or mL of water

Saturated Solution

• solution is in equilibrium with undissolved solute

• solution contains the maximum amount of solute possible

Unsaturated Solution• solution contains less than the maximum amount of solute• there is no undissolved solute present

Supersaturated Solution• solution contains more than the maximum amount of solute• there is no undissolved solute present• solution is unstable

Factors Affecting Solubility Solute-Solvent Interactions

• types of solute/solvent -- polar or non-polar• like dissolves like• pairs of liquids which are soluble in all proportions are

miscible • pairs which are not soluble are immiscible

Pressure• solubility of gases increase with

– increasing pressure– increasing mass

Henry’s Law• Cg = kPg Cg is solubility of the gas, Pg is partial

pressure of gas, k is a constant

Temperature• generally, solubility of solids increases with

increasing temperature• solubility of gases decreases with increasing

temperature

Colligative Properties

Properties which depend on the quantity of solute:

Vapor Pressure Lowering• addition of a nonvolatile solute lowers the vapor pressure

of the solvent• extent of lowering depends on concentration of solute,

described by Raoult’s Law

Raoult’s Law• Psolvent = XsolventP°solvent

Cont’d Boiling Point Elevation

• Tb = Kb msolute

• Kb is a constant, m is molality

Freezing Point Depression• Tf = Kf msolute

Osmosis• = (n/V) RT = MRT• M is molarity• R is the gas constant (0.0821 L atm/mol K)

Colloids -dispersed particles which are larger than

molecular in size -size from 10 to 2000Å -may be a clump of particles or one large

particle• hemoglobin has a MM = 64,500 amu and 65 x 55 x 50 Å

-appear cloudy or opaque & scatter light -- Tyndall effect