Section 4: Aqueous Solutions

Chapter 6: Chemical Reactions

Learning Goals

Determine if a compound is soluble.

Aqueous Solutions

A compound is soluble in a particular liquid if it dissolves in that liquid.

A compound is insoluble if it does not dissolve in the liquid.

Aqueous Solutions

An aqueous solution is a homogeneous mixture of a substance with water. When ionic compounds dissolve in water, they usually dissociate into their component ions.

NaCl(s)

NaCl(aq)

Aqueous Solutions

A sodium chloride solution, NaCl(aq), does not contain any NaCl units. Only dissolved Na+ ions and Cl− ions are present.

Substances (such as NaCl) that completely dissociate into ions in solution are called strong electrolytes.

Aqueous Solutions

Pure water does not conduct electricity.

Ions in a sodium chloride solution conduct electricity, causing the bulb to light.

AgNO3(s)

AgNO3(aq)

Aqueous Solutions

AgNO3(aq) is a strong electrolyte solution.

When compounds containing polyatomic ions such as NO3

− dissolve, the polyatomic ions dissolve as intact units.

AgCl(s)AgCl(s)

Aqueous Solutions

Not all ionic compounds dissolve in water. AgCl does not dissolve in water. It does not dissolve into independent ions.

Solubility Rules

A compound is soluble in a particular liquid if it dissolves in that liquid; a compound is insoluble if it does not dissolve in the liquid.

For ionic compounds, empirical rules of solubility have been deduced from observations of many compounds.

Soluble Compounds

Exceptions

NO3-, C2H3O2

-

Li+,Na+, K+, NH4+

Cl-, Br-, I-Except those containing

Ag+, Hg22+, Pb2+

SO42-

Except those containing Ba2+, Ca2+, Pb2+,

Sr2+Will dissolve in water

Will NOT dissolvein water

Solubility Rules

For example: Ca(NO3)2 is soluble

LiBr is soluble

Hg2Cl2 is insoluble

CaSO4 is insoluble

Insoluble Compoun

dsExceptions

S2-

Except those containing Li+, Na+, K+, NH4

+ Ca2+, Ba2+, Sr2+

CO32-, PO4

3-Except those containing Li+, Na+, K+, NH4

+

OH-

Except those containing Li+, Na+, K+, NH4

+

Those containing Ca2+, Sr2+, Ba2+ are slightly soluble

Will dissolve in water

Will NOT dissolve in

water

Solubility Rules

For example: Al2S3 is insoluble

CaCO3 is insoluble

Pb(OH)2 is insoluble

K2S is soluble

Na3PO4 is soluble

NH4OH is soluble

Practice

Use the solubility rules to predict which of the following substances are likely to be soluble in water:

Aluminum nitrate

Magnesium chloride

Rubidium sulfate

Nickel (II) hydroxide

Lead (II) sulfide

Magnesium hydroxide

Iron (III) phosphate

Silver bromide