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Osmosis• osmosis is the flow of solvent through a semi-

permeable membrane from solution of low concentration to solution of high concentration

• the amount of pressure needed to keep osmotic flow from taking place is called the osmotic pressure

• the osmotic pressure, , is directly proportional to the molarity of the solute particlesR = 0.08206 (atm∙L)/(mol∙K)

= MRT

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Ex 12.10 – What is the molar mass of a protein if 5.87 mg per 10 mL gives an osmotic pressure of 2.45 torr at 25°C?

Solve:

MRT, T(K)=T(°C)+273.15, R= 0.08206atm∙L/mol∙KM = mol/L, 1 mL = 0.001 L, MM = g/mol, 1 atm = 760 torr

Concept Plan:

Relationships:

5.87 mg/10 mL, P = 2.45 torr, T = 25°C

molar mass, g/mol

Given:

Find:

T MMRT

mL L mol proteinmL 1

L 0.001LM mol

g/mol 1045.4mol 10318.1

g1087.5 36

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MM

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Colligative Properties• colligative properties are properties whose value

depends only on the number of solute particles, and not on what they areVapor Pressure Depression, Freezing Point Depression,

Boiling Point Elevation, Osmotic Pressure

• the van’t Hoff factor, i, is the ratio of moles of solute particles to moles of formula units dissolved

• measured van’t Hoff factors are often lower than you might expect due to ion pairing in solution

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An isosmotic solution has the same osmotic pressure as the solution inside the cell – as a result there is no net the flow of water into or out of the cell.

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Colloids

• a colloidal suspension is a heterogeneous mixture in which one substance is dispersed through anothermost colloids are made of finely divided particles

suspended in a medium

• the difference between colloids and regular suspensions is generally particle size – colloidal particles are from 1 to 100 nm in size

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Properties of Colloids

• the particles in a colloid exhibit Brownian motion

• colloids exhibit the Tyndall Effectscattering of light as it passes through a suspensioncolloids scatter short wavelength (blue) light more

effectively than long wavelength (red) light

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Tro, Chemistry: A Molecular Approach 10

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Soap and Micelles

• soap molecules have both a hydrophilic (polar/ionic) “head” and a hydrophobic (nonpolar) “tail”

• part of the molecule is attracted to water, but the majority of it isn’t

• the nonpolar tail tends to coagulate together to form a spherical structure called a micelle

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Soap Action

• most dirt and grease is made of nonpolar molecules – making it hard for water to remove it from the surface

• soap molecules form micelles around the small oil particles with the polar/ionic heads pointing out

• this allows the micelle to be attracted to water and stay suspended

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The polar heads of the micelles attract them to the water, and simultaneously repel other micelles so they will not coalesce and settle out.

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