Reactions in Aqueous Solutions

Ms. Mack

Chapter 10, Section 3

Chemistry I- 3/24/09

Introduction

• Many reactions involve substances dissolved in water.

• When this happens, solutions form– Solutions (homogeneous substances)

• Two parts:– SOLUTES- substances dissolved in water– SOLVENTS- the most plentiful substance in a solution

Water, the universal solvent (H2O)

• Examples of Solutes:– Molecular compounds that exist as molecules– Molecular compounds that form ions when

they dissolve in water (H+ ions=acids)– Ionic compounds

• When dissolved in water, the ions can separate

The Products

• When 2 aqueous solutions that contain ions are combined, the ions may react with one another in a DOUBLE-REPLACEMENT reaction producing:A.A. Precipitate (s)Precipitate (s)

B. B. Water (l)Water (l)

C. C. Gas (g)Gas (g)

A. Precipitate

• Use ionic equations to show the details of reactions that involve ions in aqueous solutions

• Substances are written as ions

• Complete ionic equations- show all particles involved in a chemical reaction

NaCl (aq) + AgNO3 (aq) NaNO3 (aq) + AgCl (s)AgCl (s)

Complete:

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

Na+ (aq) + NO3- (aq) + AgCl (s)

Spectator Ions

• Notice, that there are ions that appear on both sides of the equation

• These ions do not participate in the formation of the solid product

• These ions are called spectator ions. – What were the spectator ions in the previous

slide?

Net Ionic Equations

• Equations that show only the ions involved- omitting the spectator ions are called complete ionic equations!

From the previous example:

Cl- + Ag+ AgCl (s)

Practice!

• Write the chemical, balanced, complete ionic and net ionic equation for the following:

Aqueous solutions of potassium iodide and silver nitrate are mixed, forming

the precipitate silver iodide.

See white board for solution!

B. Water

• Some reactions form water

• No evidence of the chemical reaction can be observed. Why?

• Example:

HCl (aq) + KOH (aq) H2O (l) + KCl (aq)

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

Practice!

Sulfuric acid (H2SO4) and aqueous potassium hydroxide

react to produce water and potassium sulfate.

C. Gas

• Common gases produced: carbon dioxide, hydrogen cyanide, and hydrogen sulfide

Example:

Na2S (aq) + HCl (aq) NaCl (aq) + HH22S S (g)(g)

Practice!

Sulfuric acid and aqueous rubidium sulfide with

production of hydrogen sulfide gas