Solubility Factors

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Solubility Factors

Solubility Factors

Warm Up:

What factors influence the

solubility of a substance?


Solubility Factors

Read Chapter 15


What is a solution?

A solution is defined as

a homogeneous mixture of two or more substances in

a single phase.

Homogeneous means that

the mixture appears uniform

because the particles of both

substances are evenly

interspersed.

The phase of a solution may be

solid, liquid, or gas.

Evenly interspersed particles in a

saltwater solution.


Components of a solution

Solute: The substance

being dissolved.

Solvent: The dissolving

medium, usually present in

greater amount.

To keep these terms straight, remember the phrase,

“The solute dissolves in the solvent.”


The Process of Dissolving

The process of dissolving is called solvation, or when

water is the solvent, hydration.

STEP 1: Solvent is attracted to the solute.

STEP 2: Solvent particles surround the solute

particles and pull them into solution.


Endothermic vs. Exothermic

Reactions

All chemical reactions involve bond breaking and bond

making.

Solute-solute intermolecular bond breaking is

endothermic (energy is absorbed from surroundings)

Solute-solvent intermolecular bond forming is exothermic

(energy is released into the surroundings)


Dissociation vs. Decomposition

Dissociation is the separation of ions that occurs when

an ionic compound dissolves in water. It is a physical

change.

NaCl(s)


O


H 2

Na

(aq)

(aq)

Note that this is not the same thing as decomposition,

which occurs when a compound chemically breaks down

into simpler substances.


Cl

electricity

NaCl(l)

Na(l)

Cl2

(g)


What is Solubility?

Solubility is defined as

The maximum amount of solute that can dissolve in a

specific amount of solvent at a specific temperature.

(grams of solute/100 grams of solvent)

Example: 85 grams of KNO 3 will dissolve in 100 grams

of water at 50°C.


Miscible vs. Immicible

Miscible

Describes two liquids that are soluble in each other.

Ex: Kool-aid and water

Immiscible

Describes two liquids that cannot be dissolved in a

given solvent.

Ex: oil and water


Degree of Saturation

A saturated solution contains the maximum amount of

solute. Additional solute won’t dissolve.

An unsaturated solution contains less than the

maximum amount of solute. Additional solute will

dissolve.

A supersaturated solution contains more

than the maximum amount of solute and is

unstable. Additional solute causes rapid

crystallization.


What is the

solubility

of KNO 3 at

30°C?


Factors Affecting Solubility

TEMPERATURE

Solubility curves show how the

solubility of a solute changes

with temperature.

a) At high temperatures

solids are more soluble

gases are less soluble

b) Example

Warm sodas fizz more than cold

sodas when you open them

because CO 2 gas is less soluble

at higher temperatures.


Factors Affecting Solubility

PRESSURE

Henry’s Law - Gases become more soluble as the

pressure above the solution increases.

Everyday Example

Opening a bottle of soda

decreases the pressure

inside the bottle. This

decreases the solubility

of CO 2 in the soda and

results in the formation

of bubbles, or fizz.

At higher pressures, more gas

molecules are forced into solution.


Factors Affecting Solubility

NATURE OF SOLUTE AND SOLVENT

Polar solutes dissolve well in polar solvents.

Nonpolar solutes dissolve well in nonpolar solvents.

Polar solutes do not dissolve well in nonpolar solvents

and vice versa.

This relationship is often expressed as, “Like dissolves

like.” The solute and solvent must be alike in terms of

polarity.


Like Dissolves Like

“Like dissolves like,” but why?

Polar molecules have positive and negative regions.

Solute and solvent are both polar - The opposite charges

help attract the particles to each other and solvation occurs.

One polar, one nonpolar - There is no attraction between the

particles and solvation does not occur. These substances

are described as insoluble or immiscible.


A polar water molecule.

Both substances are polar.

Opposite charges attract.

One polar, one nonpolar.

No attraction.


“Like Dissolves Like”

Everyday Example

Water and grease are

insoluble because water

is polar and grease is

nonpolar.

Soap helps dissolve

greasy stains because

it contains a polar head

and a long, nonpolar tail.

The nonpolar tail mixes with the grease while the polar

head mixes with the water. Goodbye greasy stain!


Factors Affecting

Rate of Dissolution

Just as different factors affect the amount of solute that

dissolves, there are also various factors that influence

how quickly a solute dissolves.

The factors affecting the rate of dissolution are

Temperature

Agitation

Surface area


TEMPERATURE

Factors Affecting

Rate of Dissolution

Solutes dissolve faster at high temperatures.

At high temperatures, solvent particles move faster and

solvation occurs more quickly.

Everyday Example

When making sweetened iced tea,

it is much easier to add the sugar

while the tea is still hot. The hot

temperature helps the sugar

dissolve more quickly.


AGITATION

Factors Affecting

Rate of Dissolution

Solutes dissolve faster when the solution

is agitated by stirring or shaking.

The solvent immediately surrounding the

solute can quickly become saturated.

Agitation helps bring fresh solvent into

contact with the surface of the solute so

that more solute can dissolve.

Everyday Example

When adding sugar to coffee, stirring

helps the sugar dissolve faster.


SURFACE AREA

Factors Affecting

Rate of Dissolution

Solutes dissolve faster when the surface area of the

solute is increased by crushing it into smaller pieces.

Solvation occurs at the surface of the solute. The greater

the surface area, the more opportunities there are for the

solvent to attack the solute.

Everyday Example

A sugar cube takes longer

to dissolve in a cup of tea

than an equal amount of

granulated sugar.


Image Credits

Solubility Curve

"Solubility Curve" North Carolina Department of Public Instruction. 20 Jan.

2003

Henry’s Law Diagram, Soap Dissolving Grease

Brucat, PJ. "CHM2041 Fall '97, Lecture 9, Solutions" University of Florida.

20 Jan. 2003

Saltwater Solution, Hydration of LiCl, Water Molecule, Soluble,

Insoluble, Surface Area

Davis, Raymond E., H. Clark Metcalfe, John E. Williams, and Joseph F.

Castka. Modern Chemistry: Annotated Teacher's Edition. Austin: Holt,

Reinhart and Winston, 2002.

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