Aqueous

Reactions1

Aqueous

Reactions

Chapter 4

Aqueous Reactions and

Solution Stoichiometry

Aqueous

Reactions

4.1 General Properties of Aqueous

Solutions

• Solutions are homogeneous

mixtures of two or more pure

substances.

• The substance present in the

greatest quantity is the solvent.

• The other substances present are

called solutes. They are said to be

dissolved in the solvent.

• Solute + solvent = solution

• Ex: salt dissolved in water3

Aqueous

Reactions

Electrolytes

• An electrolyte is a substance

that dissociates into ions

when dissolved in water.

• Electrolyte solutions conduct

electricity.

• A nonelectrolyte (sugar, for

example) may dissolve in

water, but it does not

dissociate into ions when it

does so.

• Nonelectrolyte solutions do

not conduct electricity.

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Aqueous

Reactions

Ionic Compounds in Water

• When an ionic substance dissolves in

water it undergoes dissociation.

• The water molecules pull individual ions

from the crystal and surrounds them in

a process called solvation.

• Water is a polar

molecule, so the

negatively charged side

is attracted to cations

(+) and the positively

charged side is

attracted to anions (-).

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Aqueous

Reactions

Electrolytes and Nonelectrolytes

Soluble ionic

compounds tend to

be electrolytes.

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Aqueous

Reactions

Electrolytes and Nonelectrolytes

Molecular compounds

tend to be

nonelectrolytes, except

for acids and bases.

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Aqueous

Reactions

Electrolytes

• A strong electrolyte

dissociates completely

when dissolved in water.

• Essentially all soluble

ionic compounds and a

few molecular compounds

are strong electrolytes.

• A weak electrolyte only

dissociates partially when

dissolved in water.

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Aqueous

Reactions

Strong Electrolytes Are…

• Strong acids

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Aqueous

Reactions

Strong Electrolytes Are…

• Strong acids

• Strong bases

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Aqueous

Reactions

Strong Electrolytes Are…

• Strong acids

• Strong bases

• Soluble ionic salts

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Aqueous

Reactions

4.2 Precipitation Reactions

When one mixes ions

that form compounds that

are insoluble (as could

be predicted by the

solubility guidelines), a

precipitate is formed.

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Aqueous

Reactions

Metathesis (Exchange) Reactions

• Metathesis comes from a Greek word that

means “to transpose”

• It appears the ions in the reactant

compounds exchange, or transpose, ions

AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq)

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Aqueous

Reactions

Solution Chemistry

• It is helpful to pay attention to exactly what

species are present in a reaction mixture (i.e.,

solid, liquid, gas, aqueous solution).

• If we are to understand reactivity, we must be

aware of just what is changing during the

course of a reaction.

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