Reactions in Aqueous Solutions Section 10.3

Objectives Describe aqueous solutions Write complete ionic and net ionic equations for chemical reactions in aqueous solutions Predict whether reactions in aqueous solutions will produce a precipitate, water, or gas.

Key Terms Solute Solvent Aqueous solution Complete ionic equation Spectator ion Net ionic equation

Review of Solutions Solvent- More plentiful substance in solution Solute- The compound dissolved in the solvent Aqueous solution- Solution in which the solvent is water

Aqueous Solutions Many possible solutes: Molecular compounds that exist as molecules Sucrose Ethanol Molecular compounds that exist as ions HCl HCl(g)  H + (aq) = Cl- (aq)

Aqueous Solutions (cont) Ionic compounds that exist as ions NaOH NaOH(aq)  Na + (aq) + OH- (aq)

Aqueous Solutions When two aqueous solutions containing ions react it is always a double replacement reaction. The water does not react There are three possible products when aqueous solutions react: Precipitates Water Gases

Reactions that form Precipitates Double-replacement reaction 2NaOH(aq) + CuCl2 (aq)  2NaCl (aq) + Cu(OH)2(s) Ionic equations are used to show the details of reactions involving ions

Writing Ionic Equations You must show the reactants and the product as ions A complete ionic equation shows all of the particles in the solution as they realistically exist. A net ionic equation only shows particles that participate in the reaction. To write a net ionic equation from a complete ionic equation eliminate all spectators.

Complete Ionic Equations AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) What type of reaction is this? Ag+(aq) + NO3-(aq) + Na+ (aq) + Cl-(aq)  AgCl(s) + Na+ (aq) + NO3-(aq)

Spectator Ions Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)  AgCl(s) + Na+(aq) + NO3-(aq) Ions that are not directly involved in a reaction are called spectator ions They appear on both sides of the arrow exactly the same way

Net Ionic Equation Eliminate spectators and rewrite the equation Ag+(aq) + Cl-(aq)  AgCl(s)

Ionic Equations Make sure that the net charge is balanced. For example… Pb(s) + 2Cl-(aq)  PbCl2(s)

Reactions that Form Water Double-replacement reactions Water molecules increase the number of solvent particles No evidence of reaction is observable (water is colorless and odorless) HBr(aq) + NaOH(aq)  H2O (l) + NaBr(aq)

Practice Write the complete ionic and net ionic equations for the example: HBr(aq) + NaOH(aq)  H2O (l) + NaBr(aq)

Reactions that Form Gases Double-replacement reactions Gas-producing Common gases: Carbon dioxide Hydrogen cyanide Hydrogen sulfide

Practice Write the complete and net ionic equations for this gas-producing reaction: 2HI(aq) + Li2S(aq)  H2S(g) + 2LiI(aq)

Homework 47-51 on page 299