Properties of Solutions or Colligative Properties Properties of pure substances are based on...
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Properties of Solutions or Colligative Properties • Properties of pure substances are based on strength of IMF • Properties of solutions are based on # solute particles in solution # solute particles ~ i x concentration These solution properties include: I. Vapor Pressure II. Boiling Point III.Freezing and Melting Points IV. Osmotic Pressure
Properties of Solutions or Colligative Properties Properties of pure substances are based on strength of IMF Properties of solutions are based on # solute
Properties of Solutions or Colligative Properties Properties of
pure substances are based on strength of IMF Properties of
solutions are based on # solute particles in solution # solute
particles ~ i x concentration These solution properties include:
I.Vapor Pressure II.Boiling Point III.Freezing and Melting Points
IV.Osmotic Pressure
Slide 3
I. Vapor Pressure Vapor Pressure Lowering Presence of a solute
decreases the vapor pressure of a solvent More Solute = lower vapor
pressure v.p. solution < v.p. solvent P solution = solvent P
solvent Where: P solution = vapor pressure of the solution P
solvent = vapor pressure of the pure solvent solvent = mole
fraction of solvent molecular solute: solvent = mol solv. / (mol
solute + mol solv.) ionic solute: solvent = mol solv. / (mol cation
+ mol anion + mol solv.)
Slide 4
II. Boiling Points Boiling Point Elevation Presence of a solute
increases the boiling point of a solvent More Solute = higher b.p.
b.p. solution > b.p. solvent (typo corrected) b.p. solution =
b.p. solvent + T b T b = i k b m Where: i = vant hoff (# solute
particles formed when dissolved) k b = boiling pt elevation
constant (based on solvent, C/m) m = molality of solute (moles
solute / Kg solvent)
Slide 5
III. Freezing/Melting Points Freezing Point Depression Presence
of a solute lowers the freezing/melting point of a solvent More
Solute = lower f.p./m.p. f.p./m.p. solution < f.p./m.p. solvent
f.p./m.p. solution = f.p./m.p. solvent T f T f = i k f m Where: i =
vant hoff (# solute particles formed when dissolved) k f = freezing
pt depression constant (based on solvent, C/m) m = molality of
solute (moles solute / Kg solvent)
Slide 6
IV. Osmotic Pressure Presence of a solute creates osmotic
pressure More Solute = higher osmotic pressure o.p. solution >
o.p. solvent = i R T M Where: = osmotic pressure in atm (1 atm =
760 torr) i = vant hoff (# solute particles formed when dissolved)
R = gas constant, 0.08206 (L ATM) / (mol K) T = temperature in
Kelvin ( T K = T C + 273.15) M = molarity of solute (moles solute /
L solution)
Slide 7
Osmosis is the flow of solvent from a solution of low solute
concentration into a solution of high solute concentration. The
solutions may be separated by a semipermeable membrane. A
semipermeable membrane allows solvent, but not solute, to flow
through it. Osmosis occurs because of the difference in vapor
pressure on the two sides (lower v.p. for solution) Osmosis
Slide 8
An isosmotic or isotonic solution has the same osmotic pressure
as the solution inside the cell; as a result, there is no net flow
of water into or out of the cell. Osmotic Pressure and Cells
Slide 9
A hyperosmotic or hyper tonic solution has a higher osmotic
pressure than the solution inside the cell There is a net flow of
water out of the cell, causing it to shrivel. Osmotic Pressure and
Cells
Slide 10
A hyposmotic or hypotonic solution has a lower osmotic pressure
than the solution inside the cell There is a net flow of water into
the cell, causing it to swell. Osmotic Pressure and Cells
Slide 11
Calculations involving Solution Properties Two primary types of
calculations A.Given concentration: Determine the solution property
B.Given a solution property: Determine the molar mass of the
solute
Slide 12
A. Determine the Solution Property i.Identify the solvent and
solute ii.Identify the solution property needed (v.p. / b.p. / m.p.
/ f.p. / o.p.) iii.Write the equation for the property iv.Convert
the concentration unit as needed v.Plug in numbers with correct
units vi.Calculate
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B. Determine the Molar Mass of Solute i.Identify the solvent
and solute ii.Identify the solution property given to you (v.p. /
b.p. / m.p. / f.p. / o.p.) iii.Write the equation for the solution
property iv.Plug in numbers with correct units v.Solve for the
concentration (m or M) vi.Use concentration definition to find
moles solute (M = moles / L soln) or (m = moles / Kg solv) vii.
Molar Mass = g solute / moles solute (note that g solute will be
given)