Understanding Reactions in Aqueous Solutions … 8.1 Understanding Reactions in Aqueous Solutions 1....

Section 8.1

Understanding Reactions in Aqueous Solutions

1. To learn more about some of the results of chemical

reactions

2. To learn to predict the solid that forms in a precipitation

reaction

3. To learn to write molecular, complete ionic, and net ionic

equations

Objectives

Section 8.1

Understanding Reactions in Aqueous Solutions

A. Common Results of a Reaction

• Four common events accompany chemical reactions.

These often occur when a reaction happens

– Formation of a solid

– Formation of water

– Formation of a gas

– Transfer of electrons

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Precipitation Reactions

What Happens When an Ionic Compound Dissolves

in Water?

NaCl (s) H2O NaCl (aq)

But what does NaCl (aq) mean?

NaCl formula

units in water ?

Na and Cl atoms

in water?

Na+ and Cl- ions

in water ?

Section 8.1

Understanding Reactions in Aqueous Solutions

• The ions separate and move around independently –

a strong electrolyte

B. Precipitation Reactions

What Happens When an Ionic Compound Dissolves in

Water?

Section 8.1

Understanding Reactions in Aqueous Solutions

B. A Reaction in Which a Solid Forms

• A reaction in which a solid is formed from a solution is

called a precipitation reaction

– Solid = precipitate = insoluble

When positive and negative ions form a precipitate

the net charge of the precipitate is zero

Pb(NO3)2 (aq) + 2NaI (aq)

PbI2 (s) + 2NaNO3 (aq)

PPT Reactions Video

Section 8.1

Understanding Reactions in Aqueous Solutions

Stalactites in Yosemite

Ca(HCO3)2(aq)

→ CaCO3(s) +

H2O(l) + CO2(aq)

Section 8.1

Understanding Reactions in Aqueous Solutions

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Precipitation Reactions

What Happens When Two Ionic Compounds Dissolve in

Water?

• K2CrO4(aq) + Ba(NO3)2(aq) Products

Section 8.1

Understanding Reactions in Aqueous Solutions

• Determine the possible products from the ions in the

reactants.

• In our example

K2CrO4(aq) + Ba(NO3)2(aq) Products

The possible ion combinations are

B. Precipitation Reactions

How to Decide What Products Form

Section 8.1

Understanding Reactions in Aqueous Solutions

What are the potential products in the reactions

between the following aqueous solutions? – Write

balanced equations for each

• NaOH + CaCl2

• CuBr2 + (NH4)2CO3

• K2SO4 + Fe(NO3)3

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Precipitation Reactions

How Would We Decide What Product Has Formed?

• What is most likely to be the yellow solid formed in the

following reaction?

K2CrO4(aq) + Ba(NO3)2(aq)

• The possible product combinations are KNO3 and BaCrO4

– KNO3 white solid

– BaCrO4 yellow solid

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Precipitation Reactions – Solubility Rules

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Precipitation Reactions

• Predicting Precipitates

Using Solubility Rules

– Soluble solid

– Insoluble solid

– (Slightly soluble solid)

Why are some

compounds

soluble and

others not?

Section 8.1

Understanding Reactions in Aqueous Solutions

Solubility Rules – Are These Compounds Soluble or

Insoluble?

Barium Nitrate

Potassium Carbonate

Sodium Sulfate

Copper (II) Hydroxide

Mercury (I) Chloride

Ammonium Phosphate

Chromium (III) Sulfide

Lead (II) Sulfate

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Precipitation Reactions

Let’s try some predictions: WOC P271 Q10

Section 8.1

Understanding Reactions in Aqueous Solutions

C. Describing Precipitation Reactions in Aqueous Solutions

• Three types of equations:

– Molecular (formula) equation

complete formulas of all reactants and products

– Complete ionic equation

all strong electrolytes are shown as ions

– Net ionic equation

only those components of the solution that undergo a

change

• Spectator ion (those that remain unchanged)

not shown in the net ionic equation

Section 8.1

Understanding Reactions in Aqueous Solutions

C. Describing Precipitation Reactions in Aqueous

Solutions

• Molecular Equation

Pb(NO3)2 (aq) + 2NaI (aq)

PbI2 (s) + 2NaNO3 (aq)

• Complete Ionic Equation

Pb2+(aq) + 2NO3

-(aq) + 2Na+

(aq) + 2I-(aq)

PbI2(s) + 2Na+(aq) + 2NO3

-(aq)

Section 8.1

Understanding Reactions in Aqueous Solutions

C. Describing Precipitation Reactions in Aqueous

Solutions

Pb2+(aq) + 2I-

(aq) PbI2(s)

A solution of magnesium chloride in water reacts with

aqueous silver nitrate to give a precipitate of silver

chloride – write down the three equations that describe

this reaction and identify the spectator ions

• Net Ionic Equation

• What are the spectator ions in this reaction?

(P272 Q14 – all three equations and identify spectators)

Section 8.1

Understanding Reactions in Aqueous Solutions

1. To learn about reactions between strong acids and strong

bases

2. To learn about the reaction between a metal and a

nonmetal

3. To understand how electron transfer produces a chemical

reaction

Objectives

Section 8.1

Understanding Reactions in Aqueous Solutions

A. Reactions Between Acids and Bases

Arrhenius Acids and Bases

• A strong acid is one in which virtually every molecule

dissociates (ionizes) in water to an H+ ion and an anion.

Section 8.1

Understanding Reactions in Aqueous Solutions

• A strong base is a metal hydroxide that is completely

soluble in water, giving separate OH ions and cations.

A. Reactions Between Acids and Bases

Arrhenius Acids and Bases

– Most common NaOH, KOH

Section 8.1

Understanding Reactions in Aqueous Solutions

Properties of Acids and Bases

Acids

Produce Hydrogen ions

pH less than 7

Turn Litmus paper red

Neutralize bases

Corrode Metals

Taste sour

Bases

Produce Hydroxide ions

pH more than 7

Turn Litmus paper blue

Neutralize acids

“Slippery” (proteins)

Taste bitter

Section 8.1

Understanding Reactions in Aqueous Solutions

Acids: Bases:

Section 8.1

Understanding Reactions in Aqueous Solutions

A. Reactions Between Acids and Bases

Reaction Between Arrhenius Acids and Bases

• The products of the reaction of a strong acid and a strong

base are water and a salt (salt = ionic compound)

– “Acid plus base gives salt plus water”

• Example: HCl(aq) + KOH(aq) → H2O(l)+ KCl(aq)

• Net ionic equation:

H+(aq) + OH−

(aq) H2O(l)

(WOC P273 Q22, 23)

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Reactions of Metals with Nonmetals (Oxidation-

Reduction)

• Reactions between metals and nonmetals involve a

transfer of electrons from the metal to the nonmetal.

– oxidation – reduction reaction

What happens to the atoms in this reaction?

2Na + Cl2 → 2NaCl

Sodium Chlorine Reaction

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Reactions of Metals with Nonmetals (Oxidation-

Reduction)

(WOC P273 Q25,26,27)

Oxidation Half-reaction:

Reduction Half-reaction:

Molecular Equation:

Section 8.1

Understanding Reactions in Aqueous Solutions

1. To learn about classification schemes for reactions

Objectives

Section 8.1

Understanding Reactions in Aqueous Solutions

A. Ways to Classify Reactions

– Formation of a precipitate from a solution

AB (aq) + CD (aq) AD (s) + CB (aq)

Double Displacement Reactions

Acid-Base Reactions

− Reaction of acids and bases to give a salt plus water:

HX(aq) + MOH(aq) MX(aq) + H2O(l)

Precipitation Reactions

– Atoms swap partners

Section 8.1

Understanding Reactions in Aqueous Solutions

A. Ways to Classify Reactions

– One atom replaces another in a compound or solution

Thermite Reaction

Single Replacement Reactions

Equation:

Metal Displacement

Reactions Video

Section 8.1

Understanding Reactions in Aqueous Solutions

A. Ways to Classify Reactions

In General: A + BC B + AC

Single Replacement Reactions

Equation:

Section 8.1

Understanding Reactions in Aqueous Solutions

• Involve oxygen and produce energy so rapidly that a flame

results

B. Other Ways to Classify Reactions

Combustion Reactions

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

Special class of oxidation-reduction

reaction

Section 8.1

Understanding Reactions in Aqueous Solutions

• A synthesis reaction is one in which a

compound forms from simpler materials

(often elements)

4Fe (s) + 3O2 (g) 2Fe2O3 (s)

Special class of oxidation-reduction

reactions

B. Other Ways to Classify Reactions

Synthesis (Combination) Reactions

Section 8.1

Understanding Reactions in Aqueous Solutions

• A decomposition reaction occurs when a compound is

broken down into simpler substances.

2H2O(l) 2H2(g) + O2(g)

B. Other Ways to Classify Reactions

Decomposition Reactions

water hydrolysis

Also a special class of oxidation-reduction

reactions

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Other Ways to Classify Reactions

Summary

Section 8.1

Understanding Reactions in Aqueous Solutions

B. Other Ways to Classify Reactions

Summary

Copy the diagram above and write the balanced equation of an

example of each of the six main reaction types (also say if your

example is a single replacement or double displacement reaction)

(WOC P276 Q50, 51)