Factors that affect solubility intermolecular interactions like dissolves like temperature pressure Solutions Colligative Properties vapor pressure lowering Raoult s Law PA XAP A boiling point elevation Tb Kbm freezing point depression Tf Kfm osmotic pressure n RT M RT V Colloids Mary J Bojan Chem 110 1 SOLUBILITY FACTORS THAT AFFECT SOLUBILITY Temperature Effect of Temperature on solubility of ionic solids Effect of temperature on solubility of gases Type of intermolecular interactions and their strengths LIKE DISSOLVES LIKE Pressure Mary J Bojan Chem 110 2 How does solubility of ionic solids change with temperature Mary J Bojan Chem 110 3 How does solubility of gases change with temperature Mary J Bojan Chem 110 4 How do intermolecular forces affect solubility In general like dissolves like polar solvents dissolve polar and ionic solutes nonpolar solvents dissolve non polar solutes If intermolecular forces broken and formed are the same dissolution is probable Which one of the following will be most soluble in benzene C6H6 l 1 2 3 4 5 Mary J Bojan H2O l CH3OH l HCl l CH3CH2OH l heptane Chem 110 5 Like dissolves like Alcohol solubility in water at 25 C g 100g of H2O CH3OH total CH3CH2OH total CH3CH2CH2OH total CH3CH2CH2CH2OH 8 06 CH3CH2CH2CH2CH2OH 2 82 CH3CH2CH2CH2CH2CH2OH 0 62 As length of hydrocarbon chain increases solubility of alcohol in water decreases Mary J Bojan Chem 110 6 Put these in order of increasing solubility in water Mary J Bojan Chem 110 7 Which vitamin is soluble in fat Which vitamin is water soluble Fat soluble vitamins can be stored in the body Water soluble vitamins are not stored in appreciable amounts Mary J Bojan Chem 110 8 How does solubility of gases change with pressure Increase Psolute gas increase solubility Decrease Psolute gas decrease solubility HENRY S Law C g k Pg solubility partial pressure Cg Pg amount of gas dissolved Cg is proportional to the partial pressure of that gas Pg above the solution k Henry s Law constant Mary J Bojan Chem 110 9 Deep Sea Diving Solubility increases with increasing P amount of N2 in blood increases as depth increases As divers rise N2 bubbles out of blood causing painful bends Solution use He O2 mixture when diving deep He is not as soluble in blood Mary J Bojan Chem 110 10 Ammonia Fountain H2O phenolphthalein pink in base Mary J Bojan Chem 110 11 Test yourself To increase the solubility of N2 in water 1 2 3 4 increase T decrease T increase P decrease P How will the solubility of KClO3 be effected by an increase in pressure 1 increase solubility 2 decrease solubility 3 no effect on solubility Mary J Bojan Chem 110 12 COLLIGATIVE PROPERTIES Properties that depend on the number of solute particles collections in solution but not on the identity of the solute Examples of Colligative properties vapor pressure lowering boiling point elevation freezing point depression osmotic pressure Mary J Bojan Chem 110 13 COLLIGATIVE PROPERTIES Example What is the total particle concentration in a 0 2M solution of Pb NO3 2 salt strong electrolyte Pb 2 NO3 total concentration of particles What is the total particle concentration 0 2M solution of CH3COOH acetic acid weak acid weak electrolyte CH3COOH aq H aq CH3COO aq Mary J Bojan Chem 110 14 VAPOR PRESSURE LOWERING rate of evaporation vapor pressure of SOLVENT Raoult s Law PA XAP A PA XA P A vapor pressure of solution mole fraction of solvent vapor pressure of pure solvent Vapor pressure lowering is a colligative property It depends on the concentration but not on the nature of the solute Mary J Bojan Chem 110 15 VAPOR PRESSURE LOWERING Mary J Bojan Chem 110 16 BOILING POINT ELEVATION FREEZING POINT DEPRESSION Tb Kbm Kb molal boiling point elevation constant Tf Kfm Kf molal freezing point depression constant m molality of the solution Kb and Kf are tabulated for different solvents Eg water benzene Mary J Bojan Kb 0 52 C m Kf 1 86 C m Kb 2 53 C m Kf 5 12 C m Chem 110 17 Example What is the freezing point of seawater assuming all of the salinity is due to NaCl MW of NaCl 58 5 g mol ocean salinity is ca 35 g salt 1 kg seawater mainly Cl Na SO42 Mg2 Ca2 K Mary J Bojan Chem 110 18 Osmosis flow of molecules through a membrane Osmotic pressure Pressure needed to stop the flow of molecules through a membrane n RT MRT V units of atm Mary J Bojan molarity Chem 110 19 Osmosis through a membrane Hypertonic solution water moves out of cell Hypotonic solution water moves into cell can cause cell to rupture Isotonic solution that has same osmotic pressure as cell Mary J Bojan Chem 110 20 Reverse Osmosis exert pressure on a concentrated solution forcing solvent molecules through a membrane Solute molecules are trapped in concentrated portion Used to purify water Mary J Bojan Chem 110 21 An aqueous solution contains 3 50 mg of protein dissolved in sufficient water to form 5 00 mL of solution The osmotic pressure of the solution at 25 C was found to be 1 54 torr Calculate the molar mass of the protein Mary J Bojan Chem 110 22 COLLOIDS Particle size small large true solution colloidal dispersion uniform molecules uniform 20 2000 particles NaCl H 2O milk fat particles fog water droplets Mary J Bojan mixture non uniform sedimentary particles Chem 110 silt 23 Light scattering Tyndall effect light is scattered when of light particle size For molecules 5 in X ray region visible light passes through solutions without scattering Atmosphere scatters small light Explains why the sky is blue For colloids size 200nm is in visible region Light passes through colloidal suspensions with scattering milk fog Mary J Bojan Chem 110 24 Test Question Which of the following aqueous solutions has the greatest total concentration of ions 1 0 2M NH4NO3 2 0 2M Pb NO3 2 3 0 2M Na2SO4 4 0 2M AlPO4 5 0 2M AlBr3 6 0 2M CH3COOH acetic acid Mary J Bojan Chem 110 25
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