# Reactions in Aqueous Solution - PowerPoint

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```					Bell Work

Why is it important to understand
limiting and excess reactants?
Reactions in
Aqueous Solution
Chapter 4
Reactions in Aqueous Solution

 Most of the reactions considered in
Chapter 3 involved pure substances
reacting with each other.
 Most of the reactions that occur in the
world involve ions or molecules dissolved
in water (aqueous solution).
Review

 Solution – homogeneous mixture

 Solute – what is being dissolved

 Solvent – what is doing the dissolving
Molarity
 The concentration of a solute in solution can be
expressed in terms of molarity.

molarity (M) =    moles of solute
Liter of solution

 The symbol [ ] is commonly used to represent
the molarity of a substance in solution.
Molarity

 For a solution containing 1.20 moles of
substance A in 2.50 L of solution,

 [A] = 1.20 mole = 0.480 mole/L or .480 M
2.50L
What do we use it for?

 Conversions:
 What mass of K3PO4 is required to prepare
4.00 Liters of 1.50 M solution?

4.00 L     1.50 mol
-------- x ------------- x --------
1        1 L             1 mol
Molarity

 How would you prepare 0.125 M NaOH
Solution?

   molarity = moles
Liter
   mole =            mass (g)
molecular mass (g/mole)
Molarity

0.125 moles NaOH    40 g NaOH
1 L solution   1 mole NaOH

5 g of NaOH dissolved in 1 L of Water
Molality

 Similar to molarity – except mols per kg

 Abbreviated as m
Science Bell Work

 Tell me if the following problems are
molarity or molality problems, then solve
for the unknown.
 What mass of water is required to dissolve
100 g NaCl to prepare 1.50 m solution?
 What volume of 0.750 M solution can be
prepared using 90.0 g of NH4Cl?
Molarity (cont)

 When an ionic solid dissolves in water, the
cations and anions separate from one another.
 This process can be represented by a chemical
equation in which the reactant is the solid and
the products are the positive and negative ions
in water solution.
 Ionic solids are commonly described as strong
electrolytes
 The ions they contain are good conductors of
electricity in aqueous solutions.
Electrolytes

 Strong electrolytes – soluble ionic
compounds (those containing metals,
nonmetals, and the ammonium ion)
 Weak electrolytes – partially soluble ionic
compounds, ionizable molecular
compounds (acetic acid)
 Nonelectrolytes – solids (insoluble ionic
compounds), molecular compounds
Review with molarity and
molality
Precipitation Reactions
 A precipitation reaction is a reaction which
results in the formation of an insoluble product,
or precipitate.

 A precipitation is an insoluble solid that
separates form the solution.

 Precipitations reactions usually involve ionic
compounds. They result from double
displacement reactions.

Solubility Rules
 Group 1 ions and Ammonium form soluble
salts
 Na NO3, NaF , K3PO4
 NH4F, (NH4)CO3

 CH3COO- All acetates are soluble.
 Na CH3COO, NH4 CH3COO , Ca(CH3COO)2

 NO3-    All nitrates are soluble.
 Na NO3, NH4 NO3 , Ca(NO3)2

 CH3COO- All acetates are soluble.
 Na CH3COO, NH4 CH3COO , Ca(CH3COO)2
Solubility Rules

 Cl- All chlorides are soluble
except AgCl, Hg2Cl2,
PbCl2.
 CaCl2, NH4 Cl , Al Cl3
 Other Halides generally follow like Chloride
except Fluoride
 CaI2 yes           CaF2 not
More Solubility Rules
 SO42- Most sulfates
are soluble;
exceptions include
SrSO4, BaSO4,
PbSO4

 CuSO4, CaSO4, Na2SO4
More Solubility Rules
 CO32-       All carbonates are
insoluble except those
with Group 1 elements
or NH4+.

 Na2CO3 , (NH4)2CO3 , K2CO3   soluble
 CaCO3 , Hg2CO3 , Al2(CO3)3   insoluble
More Solubility Rules
 OH-   All hydroxides are insoluble
except those of the Group 1
elements, Sr(OH)2 , Ba(OH)2 ,
and Ca(OH)2 somewhat

 KOH, Sr(OH) 2         soluble
 Al(OH)3 and Fe(OH)3   insoluble
More Solubility Rules
 S2-   All sulfides are insoluble
except those with Group
1 & 2 elements and NH4+.

 Na2S, (NH4)2S, and CaS   soluble
 Fe2S3, Al2S3, and CuS    insoluble
Precipitation Reactions

 Example
 When lead (II) nitrate reacts with sodium iodide

 Molecular equation
 Pb(NO3)2 (aq) + 2 NaI (aq) → PbI2 (s) + 2 NaNO3 (aq)

 PbI2 is insoluble therefore forms a solid precipitate.
Practice

 Decide if the products produced are
soluble or insoluble. If soluble, then no
precipitate forms:

 CuSO4 and NaNO3
 Na2CO3 and CaCl2
Practice with precipitation
reactions
Reactions in Aqueous Solution

 Since the chemical equations for these
reactions involve ions in solution they are
referred to as a net ionic equation.
Net Ionic Equation

 A chemical equation for a reaction
involving ions in which only those species
that actually react are included.

 Atom balance- There must be the same
number of atoms on both sides.
 Charge balance- There must be the same
total charge on both sides.
Net Ionic Equation

 Molecular Equation
Pb(NO3)2 (aq) + 2 NaI (aq) → PbI2 (s) + 2 NaNO3 (aq)

 Ionic Equation
Pb+2 (aq) + 2 NO3- (aq) + 2 Na+ (aq) + 2 I- (aq) →
PbI2 (s) + 2 Na+ (aq) + 2 NO3- (aq)
Net Ionic Equation

 Ionic Equation
Pb+2 (aq) + 2 NO3- (aq) + 2 Na+ (aq) + 2 I- (aq) →
PbI2 (s) + 2 Na+ (aq) + 2 NO3- (aq)

 Net ionic equation
Pb+2 (aq) + 2 I- (aq) → PbI2   (s)
Practice
1. Write a balanced molecular equation for each
of the following pairs of substances.
BaCl2 with Na2SO4
K3PO4 with Ca(NO3)2
Cr(NO3)3 with NaOH
NaCl with Mg(NO3)2
2. Using your solubility chart predict if a
precipitate will form or not.
3. Write the balanced ionic equation.
4. Cancel out spectator ions.
5. Write the net ionic equation.
Acid-Base Reactions
 Acids
 Acidic solutions have a sour taste.
 Vinegar, lemon juice, and soda are acidic.
 An acid is a species that produces H+ ions in water
solution.
 Bases
 Basic solutions have a slippery feeling
 Ammonia, most detergents and cleaning agents are
basic.
 A base is a species that produces OH- ions in water
solution.
Acid-Base Reactions (cont)

 Strong acids ionize completely, forming
H+ ions and anions.
 HCl (aq)         H+ (aq) + Cl - (aq)

 A weak acid is only partially ionized to
H+ ions in water.
 HF (aq)          H+ (aq) + F - (aq)
Acid-Base Reactions (cont)

 Strong bases ionize completely, forming OH -
ions and cations.
 NaOH (s)          Na+ (aq) + OH- (aq)

 A weak base produces OH - ions in a different
way. They react with H2O molecules, acquiring
H+ ions and leaving OH – ions behind.
 NH3 (aq) + H2O          NH4+ (aq) + OH - (aq)
Common Strong Acids And Bases

Acid   Name of Acid         Base     Name of Base
HCl         Hydrochloric acid   LiOH      Lithium hydroxide

HBr         Hydrobromic acid    NaOH      Sodium hydroxide

HI          Hydroiodic acid     KOH       Potassium hydroxide

HNO3        Nitric acid         Ca(OH)2   Calcium hydroxide

HClO4       Perchloric acid     Sr(OH)2   Strontium hydroxide

H2SO4       Sulfuric acid       Ba(OH)2   Barium hydroxide
Equations for Acid-Base Reactions

 When an acidic water solution is mixed
with a basic water solution, an acid-base
reaction occurs.
 The nature of the reaction and the
equation depend on whether the acid and
base involved are strong or weak.
Equations for Acid-Base Reactions

   Strong acid – strong base
(neutralization reaction)
   Net ionic equation:

   H+ (aq) + OH – (aq)   H2O
Equations for Acid-Base Reactions

       Weak acid – strong base (2-step process)
     Net ionic equation:

   HB (aq)             H+ (aq) + B – (aq)

   H+ (aq) OH – (aq)          H 2O
     Overall equation:

   HB (aq) + OH – (aq)        B – (aq) + H2O
Equations for Acid-Base Reactions

       Strong acid – weak base (2-step process)
     Net ionic equation:

   NH3 (aq) + H2O       NH4+ (aq) + OH – (aq)

   H+ (aq) OH – (aq)    H 2O
     Overall equation

   H+ (aq) + NH3 (aq)          NH4+ (aq)

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