SOLUBILITY AND COLLIGATIVE PROPERTIES OF SOLUTION

FOOD PHYSICAL CHEMISTRY

Widya Dwi Rukmi Putri

TERMS - MIXTURE

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SOLUTIONa homogeneous

mixture containing particles with the size

of a typical ion or covalent molecule.

(0.1–2.0 nm)

COLLOIDa homogeneous

mixture containing particles with

diameters in the range 2–500 nm

SUSPENSIONare mixtures with even

larger particles, but they are not considered true solutions because they separate upon standing

SOLUTION

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SOLUTEthe dissolved substance in a

solution

SOLVENTthe major

component in a solution

MiscibilityMiscible – liquids that completely

dissolved together (Think mixable)Immiscible – two liquids that form

layers when mixed together

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How well something dissolves in a solvent is a solubility

Like dissolves likePolar solutes will dissolve in polar

solventsNon polar solutes will dissolve in non

polar solventsSolubility is affected by temperature.

Increase in temperature will increase the solubility of most of the substances.

Most gases become less soluble in water as the temperature increases.

SOLUBILITY

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A solution is saturated when no additional solute can be dissolved at a particular temperature

A supersaturated solution can form when more than the equilibrium amount of solute is dissolved at an elevated temperature, and then the supersaturated solution is slowly cooled.

An unsaturated solution is formed when more of the solute can dissolve in it at a particular temperature.

SOLUBILITY

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTION

more solute dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

increasing concentration

SOLUBILITY

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The maximum amount of solute that can dissolve in a specific amount of solvent (usually 100 g.

g of solute 100 g water

SOLUBILITY

LecturePLUS Timberlake 9

Learning Check

At 40C, the solubility of KBr is 80

g/100 g H2O. Indicate if the

following solutions are

(1) saturated or (2) unsaturated

A. ___60 g KBr in 100 g of water at 40C

B. ___200 g KBr in 200 g of water at 40C

C. ___25 KBr in 50 g of water at 40C

Temperature and Solubility Solid solubility and temperature

solubility increases with increasing temperature

solubility decreases with increasing temperature

Temperature and Solubility

Gas solubility and temperature

solubility usually decreases with increasing temperature

12.4

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SOLUBILITY GRAPH OF SALTS IN WATER

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SOLUBILITY GRAPH OF GASES IN WATER

Pressure has little effect on the solubility of liquids and solids. The solubility of gases is strongly influenced by pressure. Gases dissolve more at high pressure.

COLLIGATIVE PROPERTIES OF SOLUTION

COLLIGATIVE PROPERTIES OF SOLUTIONS

Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.

Vapor Pressure Lowering

Boiling Point Elevation

Freezing Point Depression

Osmotic Pressure

VAPOR PRESSURE LOWERING

Vapor pressure : is the pressure exerted by a vapor in equilibrium with its liquid state.

Liquid molecules at the surface escape into the gas phase

These gas particles create pressure above the liquid in a closed container

BOILING POINT ELEVATION

When a solute is dissolved in a solvent, the boiling point of that solvent is raised.

The temperature difference between a solution’s boiling point and a pure solvent is called the boiling point elevation

Boiling Point Elevation Equation

ΔTb = Kbm

ΔTb = boiling point elevation

Kb = molal boiling point elevation constant (these values change depending on the solvent)

m = molality

FREEZING POINT DEPRESSIONWhen a solute dissolves into

a solvent, the freezing point of that solvent can decline.

The decline is referred to as a freezing point depression.

The freezing point depression is the difference between the solution’s freezing point and the normal freezing point of the solvent.

FREEZING POINT DEPRESSION

Freezing-Point Depression of Solutions

DTf = T f – Tf0

T f > Tf0 DTf > 0

T f is the freezing point of the pure solvent

0

T f is the freezing point of the solution

DTf = Kf m

m is the molality of the solution

Kf is the molal freezing-point depression constant (0C/m)

12.6

OSMOTIC PRESSURE OF SOLUTIONSOsmotic pressure is the

minimum pressure  which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane  

the tendency of a pure solvent to move through a semi-permeable membrane and into a solution containing a solute

OSMOTIC PRESSURE OF SOLUTIONS

ProblemWhat is the boiling point and freezing point of

a 0.058 m aqueous solution of sodium chloride (NaCl)? Kb = 0.512 °C/m

Kf = 1.86 °C/m

What is the solvent?

Solubility CurvesGraphical method of showing solubility of compounds

Used to figure out the amount of solute that will dissolve at any temperature given on the graph, and comparing solubility of compounds.

For example:

At 60 degrees, you can dissolve 100 grams of KNO3. You can only dissolve 55 grams of NH4Cl.

How much of Ce2(SO4)3 can dissolve at 60 degrees?