Chapter #7Reactions in Aqueous Media

Aqueous Ionic CompoundsMost ionic compounds dissolve in water to produce solutions that conduct electricity. The degree to which a solution will conduct electricity is used to determine if a solute is a strong or weak electrolyte. Solutions that do not conduct electricity are called nonelectrolytes. Molecular compounds that dissolve in water to that conduct electricity, are acids. Strong acids are referred to as strong electrolytes since there ae solutions are good conductors of electricity. Weak acid solutions do not conduct electricity well and are called weak electrolytes

Aqueous Ionic CompoundsMost ionic compounds dissolve in water to produce solutions that conduct electricity. The degree to which a solution will conduct electricity is used to determine if a solute is a strong or weak electrolyte. Solutions that do not conduct electricity are called nonelectrolytes. Molecular compounds that dissolve in water to that conduct electricity, are acids. Strong acids are referred to as strong electrolytes since there are solutions are good conductors of electricity. Weak acid solutions do not conduct electricity well and are called weak electrolytes.

How do we tell if a solution conducts electricity?

Solution Conductivity

Strong electrolyte Weak electrolyte Nonelectrolyte

The Solution ProcessEarlier in the quarter we defined a solution as a homogeneous mixture; a random combination of two or more things. The part of the solution we have the most of is the solvent and the minor components of a solution are referred to as the solutes. Water is the most common solvent and a good one for ionic solutes. Half of a water molecule is slightly positive and the other half is slightly negative and because of this is called polar. When forming a solution between an ionic compound and water, the positive region of the water attracts to an anion in the solute crystal while the negative region of another water molecule attracts to the cation in the crystal lattice

Types of Aqueous SolutionsSolutions are homogeneous mixtures of a solute and a solvent.

• The solute is the solution component in the smallest amount while the solvent is the larger component of a solution.

• Solutes whose solutions conduct electricity are called electrolytes

• Solutes whose solutions do not conduct electricity are called nonelectrolytes

• Electrolytes are solutes that form ions when they dissolve. Ionic solutes or acids usually form solutions that conduct electricity.

Solution FormationWater is one of the best solvents known. It is able to dissolve ionic solutes, such as sodium chloride, to produce solutions that conduct electricity. Molecules, containing a positive and negative regions, are called polar. Water is an example of a polar molecule and can dissolve ionic solutes by the positive region of water attracting to the negative ion of an ionic solute thus separating the crystal lattice in to a solution of solvated ions.

Sodium Chloride Crystal Lattice

The Solvation ProcessIf the attractive force between the surface ion and the solvent is greater than the forces between the ion and the solid then the ion will enter the solution phase.

K+

H2O The ion that has left the solid and becomes completed surrounded by water molecules. It has become solvated or hydrated.

+

+

--

++

+

+

+

+

--

--

The process continues as new water molecules approach the crystal until the crystal has been fully dissolved.

Note the different orientation of water molecules around the oppositely charged ions.

Solvated Ions

+--

-

-

+

+

++ +

-

Reaction Driving ForcesFive Driving Forces Favor Chemical Change

1. Formation of a solid 2. Formation of water 3. Transfer of electrons 4. Formation of a gas5. Formation of a weak electrolyte

PrecipitationPrecipitation is the formation of a solid when two solutions are combined.

Solubility RulesHow do we determine if an ionic solute will dissolve in water?

Solubility RulesHow do we determine if an ionic solute will dissolve in water? Use the solubility rules

Writing Ionic EquationsIonic compounds that are water soluble are indicated with and (aq) after the symbol, and if insoluble then (s) goes after the symbol.Consider the following equation.AgNO3 (aq) + NaCl (aq) What are the products?

Writing Ionic EquationsIonic compounds that are water soluble are indicated with and (aq) after the symbol, and if insoluble then (s) goes after the symbol.Consider the following equation.AgNO3 (aq) + NaCl (aq) NaNO3 (aq) + AgCl (s)

Called a formula equation

Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq) Na+(aq) + NO3

-(aq) + AgCl (s) Called an ionic equation

Writing Ionic EquationsIonic compounds that are water soluble are indicated with and (aq) after the symbol, and if insoluble then (s) goes after the symbol.Consider the following equation.AgNO3 (aq) + NaCl (aq) NaNO3 (aq) + AgCl (s)

Called a formula equation

Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq) Na+(aq) + NO3

-(aq) + AgCl (s) Called an ionic equation

Spectator Ions

Writing Ionic EquationsIonic compounds that are water soluble are indicated with and (aq) after the symbol, and if insoluble then (s) goes after the symbol.Consider the following equation.AgNO3 (aq) + NaCl (aq) NaNO3 (aq) + AgCl (s)

Called a formula equation

Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq) Na+(aq) + NO3

-(aq) + AgCl (s) Called an ionic equation

Spectator Ions

Ag+ (aq) + Cl-(aq) AgCl (s) Called the net ionic equation

Writing Ionic EquationsIonic compounds that are water soluble are indicated with and (aq) after the symbol, and if insoluble then (s) goes after the symbol.Consider the following equation.AgNO3 (aq) + NaCl (aq) NaNO3 (aq) + AgCl (s)

Called a formula equation

Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq) Na+(aq) + NO3

-(aq) + AgCl (s) Called an ionic equation

Spectator Ions

Ag+ (aq) + Cl-(aq) AgCl (s) Called the net ionic equation

This reaction goes to completion because the solid silver chloride is formed. It is called a precipitate.

Ionic Equations

It is possible for all of the reactants and products to be water soluble and thus produce all spectator ions. If this is the case then all of the ions cancel out and there is no net ionic equation. When this occurs we say that there is No Reaction, and give the label NR. This makes sense, since in order for reactions to go to completion a solid, water, gas, or electron transfer must occur in order for a reaction to go to completion.

Reaction Driving ForcesFive Driving Forces Favor Chemical Change

1. Formation of a solid 2. Formation of water 3. Transfer of electrons 4. Formation of a gas5. Formation of a weak electrolyte

Water FormationFormation of water is a normal product between acids and bases. Since acids and bases dissolve in water to make solutions that are electrolytes, then we conclude that acids and bases have some ionic character. Since water does not ionize, then when water is formed, we will also have a net ionic equation and then a chemical reaction.

Acids as ElectrolytesStrong acids and bases ionize 100%!Memorized Strong acids and bases:

Acids BasesHCl (aq)HI (aq)HBr (aq)HNO3

H2SO4

HClO4

Hydroxides of group I and II metals, except Be and Mg

Acids undergo characteristic double replacement reactions with oxides, hydroxides, carbonates and bicarbonates.

2HCl (aq) + CuO (s) CuCl2 (aq) + H2O (l)

2HCl (aq) + Ca(OH)2 (aq) CaCl2 (aq) + 2H2O (l)

2HCl (aq) + CaCO3 (aq) CaCl2 (aq) + H2O (l) + CO2 (g)

2HC l (aq) + Sr(HCO3)2 (aq) SrCl2 (aq) + 2H2O (l) + 2CO2 (g)

Acid-Base Reactions

Acids undergo characteristic double replacement reactions with oxides, hydroxides, carbonates and bicarbonates.

2HCl (aq) + CuO (s) CuCl2 (aq) + H2O (l)

2HCl (aq) + Ca(OH)2 (aq) CaCl2 (aq) + 2H2O (l)

2HCl (aq) + CaCO3 (aq) CaCl2 (aq) + H2O (l) + CO2 (g)

2HC l (aq) + Sr(HCO3)2 (aq) SrCl2 (aq) + 2H2O (l) + 2CO2 (g)

Acid-Base Reactions

Bases undergo a double replacement reaction with acids called neutralization:

NaOH (aq) + HCl (aq) H2O (l) + NaC l (aq)

In words this well known reaction is often described as: “acid plus base = salt plus water”

We previously discussed this reaction when describing types of reactions.

Acid-Base Reactions

We have discussed the double replacement reactions and ionic equations before. Since the acids and bases undergo double replacement reactions called neutralization reactions, then they can have ionic equations too.Formula equation:

HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)

Total ionic equation:

H+ (aq) + Cl- (aq) + Na+ (aq) + OH- (aq) Na+ (aq) + Cl- (aq) + H2O (l)

Net ionic equation:

H+ (aq) + OH- (aq) H2O (l)

Acid-Base Reactions

Another property of acids is their reaction with certain metals to produce hydrogen gas, H2 (g).

Zn (s) + 2HC l (aq) H2 (g) + ZnCl2 (aq)

This is an example of a single replacement reaction and is a redox reaction.

Total ionic equation:

Zn (s) + 2H+ (aq) + 2Cl- (aq) H2 (g) + Zn2+ (aq) + 2Cl- (aq)

Net ionic equation:

Zn (s) + 2H+ (aq) H2 (g) + Zn2+ (aq)

Acid-Base Reactions

Reaction Driving ForcesFive Driving Forces Favor Chemical Change

1. Formation of a solid 2. Formation of water 3. Transfer of electrons 4. Formation of a gas5. Formation of a weak electrolyte

The End