Solutions Factors that affect solubility intermolecular...

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Solutions Colligative Properties vapor pressure lowering Raoult’s Law: P A = X A P° A boiling point elevation ΔT b = K b m freezing point depression ΔT f = K f m osmotic pressure π = n V RT = M RT Colloids 1 Factors that affect solubility intermolecular interactions (like dissolves like) temperature pressure Mary J. Bojan Chem 110

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  • Solutions

    Colligative Properties vapor pressure lowering

    Raoults Law: PA = XAPA boiling point elevation

    Tb = Kbm freezing point depression

    Tf = Kfm osmotic pressure

    =nV

    RT = M RT

    Colloids 1

    Factors that affect solubility intermolecular interactions

    (like dissolves like) temperature pressure

    Mary J. Bojan Chem 110

  • 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 2 Mary J. Bojan Chem 110

  • How does solubility of ionic solids change with temperature?

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  • How does solubility of gases change with temperature?

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  • 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.

    How do intermolecular forces affect solubility?

    Which one of the following will be most soluble in benzene (C6H6(l))?

    1. H2O(l) 2. CH3OH(l) 3. HCl(l) 4. CH3CH2OH(l) 5. heptane

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  • Like dissolves like Alcohol solubility in water

    at 25C (g/100g of H2O)

    CH3OH total CH3CH2OH total

    CH3CH2CH2OH total

    CH3CH2CH2CH2OH 8.06

    CH3CH2CH2CH2CH2OH 2.82

    CH3CH2CH2CH2CH2CH2OH 0.62

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    As length of hydrocarbon chain increases, solubility of alcohol in water decreases.

    Mary J. Bojan Chem 110

  • Put these in order of increasing solubility in water

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  • Which vitamin is soluble in fat? Which vitamin is water soluble?

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    Fat soluble vitamins can be stored in the body

    Water soluble vitamins are not stored in appreciable amounts

    Mary J. Bojan Chem 110

  • Increase Psolute(gas); increase solubility Decrease Psolute(gas); decrease solubility

    How does solubility of gases change with pressure?

    amount of gas dissolved (Cg) is proportional to the partial pressure of that gas (Pg) above the solution.

    k = Henrys Law constant

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    HENRYS Law Cg = k Pg

    solubility Cg partial pressure Pg

    Mary J. Bojan Chem 110

  • 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.

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  • Ammonia Fountain

    H2O + phenolphthalein (pink in base)

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  • Test yourself To increase the solubility of N2 in water

    1. increase T 2. decrease T 3. increase P 4. 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

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  • COLLIGATIVE PROPERTIES

    Properties that depend on the number of solute particles (collections) in solution but not on the identity of the solute.

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    Examples of Colligative properties vapor pressure lowering boiling point elevation freezing point depression osmotic pressure

  • 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 =

    COLLIGATIVE PROPERTIES

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    What is the total particle concentration 0.2M solution of CH3COOH (acetic acid)? (weak acid, weak electrolyte)

    CH3COOH(aq) H+(aq) + CH3COO(aq)

  • VAPOR PRESSURE LOWERING

    Raoults Law: PA = XAPA

    PA vapor pressure of solution XA mole fraction of solvent PA vapor pressure of pure solvent

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    Vapor pressure lowering is a colligative property It depends on the concentration but not on the nature of the solute.

    rate of evaporation vapor pressure of SOLVENT

  • VAPOR PRESSURE LOWERING

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  • 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

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    Kb and Kf are tabulated for different solvents

    Eg. water Kb= 0.52C/m Kf= 1.86C/m benzene Kb= 2.53C/m Kf= 5.12C/m

  • 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+

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  • Osmosis flow of molecules through a membrane

    Osmotic pressure: Pressure needed to stop the flow of molecules through a membrane

    = nV

    RT = MRT

    units of atm molarity

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  • 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. 20 Mary J. Bojan Chem 110

  • 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.

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  • 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 25C was found to be 1.54 torr.

    Calculate the molar mass of the protein.

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  • COLLOIDS

    true colloidal mixture solution dispersion uniform uniform non-uniform molecules 20-2000 sedimentary

    particles particles

    NaCl milk (fat particles) silt H2O fog (water droplets)

    small large Particle size

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  • Light scattering Tyndall effect: light is scattered when of light particle size

    For colloids (size~ 200nm) is in visible region: Light passes through colloidal suspensions with scattering (milk, fog).

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    For molecules (~5) in X-ray region visible light passes through solutions without scattering Atmosphere scatters small light

    Explains why the sky is blue

  • 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)

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