Chapter 13 Solutions

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  H solution =  H 1 +  H 2 +  H 3  H 1 = energy required to separate solute particles  H 2 = energy required to separate solvent particles  H 3 = energy produced by interaction of solute/solvent  H solution is exothermic only if  H 3 is larger than  H 1 +  H 2

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 --  H 3 is larger than  H 1 +  H 2

Cont’d Polar/Polar solutions driven by energy relationships --  H 3 is larger than  H 1 +  H 2 Non-polar/Non-polar solutions driven by disorder --  H 3 is about the same as  H 1 +  H 2

Cont’d True Solution solute particles remain unchanged –NaCl (s) + H 2 O (l)  Na + (aq) + Cl - (aq) no chemical reaction occurs –Ni (s) + 2HCl (aq)  NiCl 2(aq) + H 2(g)

Concentration Expresses a ratio between solute and solvent/solution Mass % percent mass (%) = g solute x 100 total g solution ppm -- parts per million ppm = mass of solute x 10 6 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 C g = kP g C g is solubility of the gas, P g 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 P solvent = X solvent P° solvent

Cont’d Boiling Point Elevation  T b = K b m solute K b is a constant, m is molality Freezing Point Depression  T f = K f m solute Osmosis  = (n/V) RT = MRT M is molarity R is the gas constant ( 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