Solutions, Colloids and Suspensions. Solutions Solutions are homogeneous mixtures of two or more pure substances. In a solution, the solute is dispersed.

Solutions, Colloids and Suspensions

Solutions• Solutions are homogeneous mixtures of two or

more pure substances.• In a solution, the solute is dispersed uniformly

throughout the solvent.

Solutions

Have small particles (ions or molecules)

Are transparent

Do not separate

Cannot be filtered

Do not scatter light.

Types of Solutions

• Saturated:Solvent holds as much solute as is possible at that

temperature.• Unsaturated:

Less than the maximum amount of solute for that temperature is dissolved in the solvent.

• Supersaturated:Solvent holds more solute than is normally possible at

that temperature.

Ways of Expressing Concentrations of Solutions

Mass Percentage

Mass % of A =mass of A in solutiontotal mass of solution 100100

Percent (by mass) =g solute

g solutionx 100

g solute

g solute + g solvent

x 100=

• % (w/w) =

• % (w/v) =

• % (v/v) =

% Concentration

100xsolutionmasssolutemass

100xsolutionvolumesolutemass

100xsolutionvolumesolutevolume

Parts per Million andParts per Billion

ppm = mass of A in solutiontotal mass of solution 101066

Parts per Million (ppm) ((g/g, mg/L)g/g, mg/L)

Parts per Billion (ppb) (ng/g, (ng/g, g/L)g/L)

ppb =ppb = mass of A in solutiontotal mass of solution

101099

The units ppm or ppb are used to express trace concentrations.

These are weigh or volume based, rather than mole based.

The units ppm or ppb are used to express trace concentrations.

These are weigh or volume based, rather than mole based.

Colloids

Have medium size particles

Cannot be filtered

Separated with semipermeable

membranes

Scatter light (Tyndall effect)

The scattering of visible light by colloidal particles is called the Tyndall effect.

Colloids in Biological Systems

Some molecules have a polar, hydrophilic (water-loving) end and a nonpolar, hydrophobic (water-hating) end.

Colloids in Biological Systems• Sodium stearate is one example of

such a molecule.

• These molecules can aid in the emulsification of fats and oils in aqueous solutions.

Suspensions

Have very large particles

Settle out

Can be filtered

Must stir to stay suspended

Examples of Suspensions

Blood platelets

Muddy water

Calamine lotion

Osmosis and Dialysis

Osmosis and Osmotic Pressure

►Osmosis: The passage of solvent through a semipermeable membrane separating two solutions of different concentration.

►Osmotic pressure: The amount of external pressure applied to the more concentrated solution to halt the passage of solvent molecules across a semipermeable membrane.

Osmosis

semipermeable membrane

4% starch 10% starch

H2O

Equilibrium is reached.

water flow becomes equal

7% starch

7% starch

H2OO

Osmotic Pressure

Produced by the number of solute particles

dissolved in a solution

Equal to the pressure that would prevent

the flow of additional water into the more

concentrated solution

Increases as the number of dissolved

particles increase.

Osmotic Pressure of the Blood

Cell walls are semipermeable membranes

The osmotic pressure of blood cells

cannot change or damage occurs.

The flow of water between a red blood

cell and its surrounding environment

must be equal.

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Isotonic solutions

• Exert the same osmotic pressure as red blood cells.

• Medically 5% glucose and 0.9% NaCl are used their solute concentrations provide an osmotic pressure equal to that of red blood cells

H2O

Hypotonic Solutions

Lower osmotic pressure than red blood cells

Lower concentration of particles than RBCs

In a hypotonic solution, water flows into the

RBC

The RBC undergoes hemolysis; it swells and

may burst.

H2O

Hypertonic Solutions

Has higher osmotic pressure than RBCHas a higher particle concentration In hypertonic solutions, water flows out

of the RBCThe RBC shrinks in size (crenation)

H2O

Dialysis

Occurs when solvent and small solute

particles pass through a semipermeable

membrane

Large particles retained inside

Hemodialysis is used medically (artificial

kidney) to remove waste particles such as

urea from blood.

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