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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)
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