10.3 Reactions in Aqueous Solutions

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10.3 Reactions in Aqueous Solutions Powered By Docstoc
					10.3 Reactions in
Aqueous Solutions
Objectives:
Describe aqueous solutions
Write complete ionic and net ionic
equations for chemical reactions in
aqueous solutions
Predict whether reactions in aqueous
solutions produce water precipitate or
gas
Introduction
   When a substances dissolves in water a
    solution forms.
   We previously learned, solutions are
    homogeneous mixtures.
   A solution contains one or more substances
    dissolved in water called solutes.
   In this case, water is the solvent, the most
    plentiful substance in the solution .
   An aqueous solution is a solution in which the
    solvent is water.
Aqueous Solutions

   Although water is always the solvent in
    aqueous solution; there are many
    possible solutes.
    – Example: Sucrose (Table sugar),
                Ethanol (grain alcohol)
    – Most are molecular compounds that form
      ions when dissolved into water
Molecular Compound

   Hydrogen Chloride (referred to as
    hydrochloric acid) forms hydrogen ions
    and chloride ions when it dissolves in
    water
Ionic Compounds

 Ionic compounds may be solutes in
  aqueous solution
 Remember Ionic Compound contain
  positive ions and negative ions held
  together by ionic bonds
 The ions will separate when dissolved
  in water
Example (Aqueous Solution of ionic
compound Sodium Hydroxide )



   When two aqueous solutions contain
    ions as solutes are combined, ions may
    react with each other
    – Always Double Replacement
Three types of products can form
from Double Replacement
 Precipitate
 Water
 Gas
Reactions that form Precipitate

   Aqueous Solutions of Sodium hydroxide
    and Copper (II) Chloride are mixed, a
    double replacement reaction occurs in
    which the precipitate copper (II)
    hydroxide forms.
Some Notes….

 Sodium hydroxide and copper (II)
  chloride are ionic compounds
 In aqueous solutions they exist as
  Na+, OH- Cu 2+ , and Cl- ions
 Solutions combine copper and
  hydroxide join to form the precipitate
  Copper (II) hydroxide and Na+ and Cl-
  ions remain dissolved in solution
Ionic Equations

 Chemists use ionic equations to show
  details of reactions that involve ions in
  aqueous solutions.
 Difference between ionic equations and
  chemical equations is that substances
  and written as ions.
Ionic Equations
   Complete Ionic Equation
    – Ionic equation that shows all of the particles in a
      solution as they realistically exist
   Spectator ions
    – Ions that do not participate in a reaction
    – Previous example: Na+ and Cl- are spectator ions
   Net Ionic Equations
    – Ionic equation that only includes the particles that
      participate in the reaction
       • Net ionic equations are taken from complete ionic
         equations and spectator ions are crossed out
Example

   Write the chemical, complete ionic, and
    net ionic equations for the reaction
    between aqueous solutions of barium
    nitrate and sodium carbonate that forms
    the precipitate barium carbonate.
Reactions That Form Water

 Another type of double replacement
  reaction occurs in aqueous solutions
  produces water molecules.
 The water molecules produced will
  increase the number of solvent
  particles.
 There is no evidence of this occurring
  because it is colorless and odorless.
Example

   When you mix hydrobromic acid with a
    sodium hydroxide solution a double
    replacement reaction occurs and water
    is formed.
Continued
 In this case, the reactants and the product
  sodium bromide exist as ions .
 The complete ionic equation looks like this:




   If you look closely at the complete ionic
    equation. The reacting solute ions are the
    hydrogen and hydroxide ions because the
    sodium and bromine ions are both spectator
    ions.
Net Ionic Equation
Example

   Write the chemical, complete ionic, and
    net ionic equations for the reaction
    between hydrochloric acid and aqueous
    lithium hydroxide which produces water.
Reactions That Form Gases

   A third type of double replacement
    reaction occurs in aqueous solutions
    results in the formation of a gas
    – Example: CO2, HCN, H2S
Continued

 A gas producing reaction occurs when
  you mix hydroiodic acid (HI) with an
  aqueous solution of lithium sulfide.
 Bubbles of hydrogen sulfide gas form in
  the container during the reaction. Also,
  Lithium Iodine is produced and remains
  dissolved in the solution.
Chemical Reaction

 2HI(aq) + Li2S(aq) -> H2S(g) + 2LiI(aq)
 The reactants hydroiodic acid and lithium
  sulfide exist as ions in aqueous solution.
  Therefore, you can write an ionic equation for
  this reaction. The complete ionic equation
  includes all the substances in the solution.
 2H+(aq)+ 2I-(aq) + 2Li+(aq) + S 2-(aq)->
   H2S(g) + 2Li+(aq)+ 2I-(aq)
Net ionic Equation left

 Note, there are many spectator ions in
  the equation.
 When the spectator ions are crossed
  out, only the substances involved in the
  reaction remain in the equation.
2H+(aq)+   2I-(aq) +2Li+(aq) + S 2-(aq)->
    H2S(g) + 2Li+(aq)+ 2I-(aq)
The net ionic equation is….

2H+ (aq) + S 2- (aq) -> H2S (g)
Example
   Baking soda and vinegar produces a carbon
    dioxide gas when they are mixed.
   Vinegar is an aqueous solution of acetic acid
    and water
   Baking soda consists of sodium hydrogen
    carbonate.
   A similar reaction can occur when you
    combine any acidic solution and sodium
    hydrogen carbonate to any solution.
   These two reactions occur at the same time,
    which one is a decomposition and single
    replacement
The reactions are:
 The two reactions can then be
  combined and represented by one
  chemical equation in a process similar
  to adding mathematical equations.
 An equation that combines two
  equations is called the overall equation.
Overall Equation

   To write an overall equation, the
    reactants in the two reaction are written
    on the reactant side of the combined
    reaction, and the products of the two
    equations are on the product side.
Example

   Reaction 1

   Reaction 2

   Combined Equation



   Overall Equation
The explanation

 The ions exist in an aqueous solution,
  therefore, a complete ionic equation can be
  written.
 Sodium and chloride are spectator ions.
  When you cross them out the only
  substances that take part in the reaction
  remain.
 The net ionic reaction shows that water and
  carbon dioxide are produced in this reaction.