CHAPTER 7: Solutions & Colloids Predict the relative solubility of materials on the basis of polarity Describe solution formation in terms of solutesolvent interactions Calculate solution concentrations in terms of molarity and percentages Apply solution concentrations in stoichiometric calculations Understand the effect of concentration on colligative properties Describe the characteristics of colloids 7.1 PHYSICAL STATES of S Homogeneous mixture of of at at least 2 components: the (in (in lesser quantity) and the SOLVENT (in (in greater quantity) SALINE CLUB SODA 14karat GOLD GOLD AMALGAM AIR STATE SOLVENT H 2 O NaCl H 2 O CO 2 Au Au Cu Hg N 2 O 2 more sugar! 7.2 SOLUBILITY SUGAR HOMOGENEOUS CORN OIL NONHOMOGENEOUS 2 phases more alcohol! ALCOHOL HOMOGENEOUS SOLUBLE Dissolves to to a significant extent in in a solvent INSOLUBLE Does not dissolve to to a significant extent in in a solvent MISCIBLE Liquids soluble in in all all proportions Opposite: IMMISCIBLE NONHOMOGENEOUS 2 phases HOMOGENEOUS Sodium Chloride Potassium Chloride Calcium Carbonate Ascorbic Acid Ethyl Alcohol Sucrose = miscible NaCl 36 KCl 29 CaCO 3 0.0012 C 6 H 8 O 6 33 C 2 H 5 OH SOLUBILITY g/100 g H 2 O C 12 H 22 O 11 179 Degrees of Solution A solution is UNSATURATED if it contains less than the maximum amount of solute that can be dissolved under existing conditions A solution is SATURATED it contains the maximum amount of solute that can be dissolved... A solution is SUPERSATURATED if it temporarily contains excess dissolved solute Excess solute that comes out of solution is a PRECIPITATE Page 71
Solubility Environmental Effects A measure of how much of solute can be dissolved in a solvent (g/ml) Factors affecting solubility: Temperature Pressure Polarity PHASE SOLID LIQUID EFFECT on SOLUBILITY T > 0 P > 0 increases no change varies no change LIKE DISSOLVES LIKE GAS decreases increases 7.3 THE PROCESS Attraction of of solute particles (ions or molecules) and solvent where solute and solvent phases come into contact Reduction of interparticle attraction between solvated particle and rest of solute Separation of SOLVATED particles into solvent phase, with increasing solvation as separation proceeds SOLVATION Solvent molecules surround a solute ion or or molecule Dissolving Ionic Compounds When an ionic dissolves in water, the polar solvent removes ions from the crystal lattice Solvated ion Dissolving Covalent Compounds Covalent compounds do not dissociate: HEATS of Heat is usually absorbed or released when a solute dissolves in a solvent The type of energy transfer tells something about the solution process: weaker interaction Na OH H 2 O Na (solvated) OH (solvated) HEAT stronger interaction stronger interaction weaker interaction NH 4 NO 3 H 2 O HEAT NH 4 (solvated) NO 3 (solvated) Page 72
7.4 CONCENTRATIONS MOLARITY When describing chemical reactions that take place in solution, we need a way to tell how much solute (reactant) is in a solution We can refer to the solute s CONCENTRATION Concentrations may be described in terms of Molarity (mol/l) Weight/weight percent (w/w) Weight/volume percent (w/v) Volume/volume percent (v/v) Mass of of solute (mol) M = Volume of of solution (L) Accounts for differences in formula weights: A 1M ( 1 molar ) solution of glucose contains the same number of molecules as an equal volume of 1M ethyl alcohol [X] read as as the concentration of of X X Concentrations Expressed as Percents TYPE WEIGHT/WEIGHT PERCENT WEIGHT/VOLUME PERCENT VOLUME/VOLUME PERCENT UNITS Weight, g Weight, g Volume, ml SOLVENT UNITS Weight, g Volume, ml Volume, ml W solute 100 W solution W solute 100 V solution V solute 100 V solution Saline is is a 0.9% (w/v) solution of of NaCl in in water 7.5 PREPARATION You can prepare different volumes of specific concentrations by using proportional amounts (weight, volume). Remember, for the same concentration: C = n 1 /V 1 = n 2 /V 2 Once you have a solution, it can be diluted by adding more solvent. Remember: C conc V conc = C dil dil V dil dil Where n = number of moles, C = concentration 7.6 STOICHIOMETRY Describing chemical reactions that take place in solution requires BALANCED CHEMICAL EQUATIONS Give molar relationships among reactants and between reactants and products Weight A WEIGHT Moles EQUATION Moles A B COEFFICIENT WEIGHT MOLARITY MOLARITY Weight B CONCENTRATIONS of REACTANT S Give the relationships between moles of solute and volumes of solutions Volume Volume Solution A Volume Volume Solution B Page 73
7.7 PROPERTIES Blood Serum Electrolytes ELECTROLYTE Ionic solute in polar solvent Solute dissociated to ions in solution Solution conducts electricity NONELECTROLYTE Covalent solute in polar or nonpolar solvent Solute dispersed but not dissociated in solution Solution does not conduct electricity HCO 3 ION Na K Ca 2 Mg 2 Cl venous arterial meq/l 135145 3.55.0 4.55.5 1.52.5 95105 19025 2226 n equivalents = n mol ion charge mm 135145 3.55.0 2.252.75 0.751.25 95105 19025 2226 COLLIGATIVE PROPERTIES Ionic vs Covalent Compounds in Solution Properties that depend on on the number of of solute particles Depends on how much solute, but not what type of solute Effect of ionic materials is based on the number of ions produced VAPOR PRESSURE LOWERING BOILING POINT ELEVATION FREEZING POINT DEPRESSION OSMOTIC PRESSURE 1 mol NaCl 1 mol of Na 1 mol of Cl 2 mol of PARTICLES 1 mol glucose 1 mol of PARTICLES Molality Moles of of solute particles (mol) m = Mass of of solvent (kg) 1 mole glucose / L solution = 1 M 1 mole glucose / kg solvent = 1 m 1 molecule/mol 1 mole CaCl 2 / L solution = 1 M 1 mole CaCl 2 / kg solvent = 3 m 3 ions/mol Vapor Pressure Lowering All colligative properties are based on Raoult s Law: Solution vapor pressure decreases in proportion to the concentration of solute. mole fraction P solution = χ solvent P solvent P solution =(1 χ solute ) P solvent Ionic substances have a greater effect / mol than do covalent substances Molality is temperature independent Page 74
Boiling Point Elevation Freezing Point Depression The magnitude of boiling point elevation increases with increasing solute concentration: T b = K b m n K b M EXAMPLES: Making maple syrup Antifreeze The magnitude of freezing point depression increases with increasing solute concentration: T f = f K f f m EXAMPLES: Salting roads in winter Making ice cream Osmosis Diffusion of of a solvent through a semipermeable membrane from a more dilute solution to to a more concentrated one Semipermeable Membrane Na Cl SEMIPERMEABLE MEMBRANE Small molecules (such as solvent) go through, large molecules (such as hydrated ions) do not RESULT: PRESSURE due to oneway solvent flow Cell walls are semipermeable membranes Na Cl Na Cl SEMIPERMEABLE MEMBRANE Osmotic Pressure Pressure required to to stop osmosis Π = nmrt PURE ELECTROLYTE SOLVENT Water flows uphill until pressure equalized n M = OSMOLARITY (mol particles/l) T = Temperature (K) R = Gas law constant Page 75
Transport Across Cell Membranes Blood Cell in an Isotonic Solution Three conditions can exist across a cell membrane: The osmolarity is the same on both sides (ISOTONIC): no flow through membrane The osmolarity is greater on the outside (HYPERTONIC): H 2 O flows out of the cell The osmolarity is greater on the inside (HYPOTONIC): H 2 O flows into the cell A red blood cell and plasma have the same osmotic pressure Blood Cell in a Hypertonic Solution Blood Cell in a Hypotonic Solution Salt in the plasma is too high, the cell collapses CRENATION: water is drawn out of the cell Salt in the plasma is too low, the cell swells and ruptures HEMOLYSIS: water is drawn into the cell 7.10 DIALYSIS Diffusion of of solvent, small molecules, and hydrated ions through a semipermeable membrane from a more dilute solution to to a more concentrated one Process used in the kidneys: 7.87.9 COLLOIDS A stable, uniform dispersion of of one or or more substances (DISPERSED PHASE) in in another substance (DISPERSING MEDIUM or or CONTINUOUS PHASE) Na Na PROTEIN Na Na Na Na Na Particle Size, cm Homogeneity Particle Charges Light Scattering <<10 7 10 7 10 5 varies no COLLOID Many physiological fluids are colloids because of the large protein molecules they contain Page 76
Light Scattering: THE TYNDALL EFFECT DISPERSING MEDIUM DISPERSED PHASE NAME EXAMPLE(S) COLLOID aerosol foam emulsion sol aerogel gel fog smoke whipped cream milk latex paint marshmallow gelatin stained glass Page 77