Chemistry-140 Lecture 10

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Chemistry-140 Lecture 10

• Chapter 5 Reactions in Aqueous Solution

• Chapter Highlights
• definitions of electrolytes nonelectrolytes
• recognize acids bases
• predict solubility of ionic compounds in water
• determine net ionic equations
• learn four basic reactions types predict
  products
• acid base
• precipitation
• gas-forming
• oxidation -reduction

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Chemistry-140 Lecture 10

• Electrolytes

Definition a substance whose aqueous solution
conducts electricity is called an electrolyte

• a substance can be a strong electrolyte, a weak
  electrolyte or a nonelectrolyte depending on the
  degree of dissociation (ionization) in solution

• Example
• For sodium chloride, the ionic solid
  dissociates 100 in water forming exclusively
  Na and Cl- ions in solution
• 100 dissociation strong electrolyte

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Chemistry-140 Lecture 10
Electrolytes
pure water
acetic acid solution
potassium dichromate solution
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Chemistry-140 Lecture 10

• Identifying Electrolytes

• Strong electrolytes Substances that dissociate
  completely in water. Simple salts like NaCl
  that are combination of a metal and a
  nonmetal
• Weak electrolytes Substances that do not
  dissociate fully in water but do form some
  ions. Usually molecular compounds like
  acetic acid (CH3COOH) with ionizable groups
  (H)
• Nonelectrolytes Substances that do not
  dissociate in water to form ions. Molecular
  compounds which are soluble but which
  remain intact as the molecule in solution

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Chemistry-140 Lecture 10
Question What type of electrolytes are these
compounds? a) Epsoms salt MgSO4 . 7
H2O b) Methanol CH3OH c) Acetic acid
CH3COOH
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Chemistry-140 Lecture 10
Answer a) b) c)
strong electrolyte
nonelectrolyte
weak electrolyte
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Chemistry-140 Lecture 10
Understanding Predicting Reactions in Solution

• Driving Force a property of the reaction that
  can be identified as the reason for product
  formation

• Examples

solid formation
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Chemistry-140 Lecture 10
Types of Reactions

• the reaction type depends on the driving force of
  the reaction. There are four basic types

• Formation of an insoluble compound
• Formation of a nonelectrolyte
• Formation of a gas
• Transfer of electrons

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Chemistry-140 Lecture 10

• Solubility

• certain combinations of cations and anions are
  soluble that is they dissolve in water..
• if a compound will not dissolve in water it is
  insoluble
• if a combination of anion and cation results in
  the formation of an insoluble solid, this is a
  precipitate

• Example

precipitate
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Chemistry-140 Lecture 10
Soluble Compounds
Exceptions
Almost all salts of Na, K NH4
Salts of NO3-, ClO3-, ClO4-, CH3CO2-
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Chemistry-140 Lecture 10
Exceptions
Insoluble Compounds
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Chemistry-140 Lecture 10

• Net Ionic Equations

• the balanced equation that results from the
  omission of all spectator ions is the net ionic
  equation
• spectator ions are the ions which do not
  participate in the reaction

Example Write a balanced net ionic equation for
the reaction of AgNO3 with CaCl2 to produce AgCl
and Ca(NO3)2.
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Chemistry-140 Lecture 10
Step 1 Write the complete balanced equation
with appropriate stoichiometry
Step 2 Decide on the physical state (eg
solubility) of each compound.
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Chemistry-140 Lecture 10
Step 3 Recognize that all soluble ionic
compounds dissociate to form ions in
aqueous solution
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Chemistry-140 Lecture 10
Step 4 Identify the spectator ions and remove
them from the complete ionic equation
to give the net ionic equation. Simplify
the resulting equation in terms of
stoichiometric coefficients.

• The sum of ion charges is the same on
• both sides of the net ionic equation

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Chemistry-140 Lecture 10
Precipitation Reactions

• Write the net ionic equation for
• the reaction of Pb(NO3)2 with KI.

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Chemistry-140 Lecture 10

• Acids Bases

• Acid any substance that , when dissolved in
  water, increases the concentration of hydrogen
  ions, H, in the water
• Base any substance that, when dissolved in
  water, increases the concentration of hydroxide
  ions, OH-, in the water

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Chemistry-140 Lecture 10

• Strong Vs. Weak

• A strong acid or strong base an acid or base
  which ionizes completely in water a strong
  electrolyte
• A weak acid or base an acid or base which does
  not ionize completely in water a weak
  electrolyte

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Chemistry-140 Lecture 10
Acid-Base Reactions I

• Write the net ionic equation for
• the reaction of HNO3 with KOH.

Overall Reaction
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Chemistry-140 Lecture 10
Acid-Base Reactions II

• Write the net ionic equation for
• the reaction of CH3CO2H with Ca(OH)2.

Overall Reaction
2 CH3CO2H(aq) Ca(OH)2(s) Ca(CH3CO2)2(a
q) 2 HOH(l)
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Chemistry-140 Lecture 10
Some Common Acids Bases
Strong Acids
Strong Bases
HCl, HBr, HI, HNO3, H2SO4, HClO4
NaOH, KOH, Ca(OH)2
Weak Acids
Weak Bases
CH3CO2H, H3PO4, HF, H2CO3
NH3
H2SO4(l) H(aq) HSO4-(aq)
Note
HSO4-(aq) H(aq) SO42-(aq)
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Chemistry-140 Lecture 10
Gas-Forming Reactions

• The acids of some nonmetal ions are gases and a
  small number of aqueous acids easily decompose to
  form a gaseous product.

Examples
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Chemistry-140 Lecture 10
Gas-Forming Reactions

• Write the net ionic equation for
• the reaction of HNO3 with NiCO3.

Overall Reaction
2 HNO3(aq) NiCO3(s)
Ni(NO3)2(aq) H2CO3(aq)
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Chemistry-140 Lecture 10

• Properties of Compounds in Aqueous Solution

• Aqueous solution a solution of any substance or
  substances dissolved in water

• Example
• Solid sodium chloride dissolves in water to
  give an aqueous solution of sodium cations and
  chloride anions

aqueous solution of sodium chloride
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Chemistry-140 Lecture 10

• Oxides of Metals Nonmetals

• If a nonmetal oxide is dissolved in water an
  acidic solution results. This compounds is known
  as an acidic oxide
• If a metal oxide is dissolved in water a basic
  solution results. This compounds is known as a
  basic oxide

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Chemistry-140 Lecture 10
Summary Types of Reactions

• the reaction type depends on the driving force of
  the reaction. There are four basic types

Reaction Type Driving
Force Precipitation Reaction Formation of an
insoluble compound Acid-Base Neutralization Forma
tion of a nonelectrolyte (water) Gas-Forming Ev
olution of a water insoluble gas Oxidation
-reduction Transfer of electrons
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Chemistry-140 Lecture 10

• Textbook Questions From Chapter 5
• Solubility 21, 22, 24
• Precipitation Reactions 32
• Net Ionic Equations 36, 37
• Reaction Types 42, 49, 52, 57
• Concentration/Stoichiometry 70, 75, 76
• Titration 84, 86, 90

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Chemistry-140 Lecture 11

• Chapter 5 Chemical Reactions

• Chapter Highlights
• definitions of electrolytes nonelectrolytes
• recognize acids bases
• predict solubility of ionic compounds in water
• determine net ionic equations
• learn four basic reactions types predict
  products
• acid base
• precipitation
• gas-forming
• oxidation -reduction

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Chemistry-140 Lecture 11
Types of Reactions

• the reaction type depends on the driving force of
  the reaction. There are four basic types

Reaction Type Driving
Force Precipitation Reaction Formation of an
insoluble compound Acid-Base Neutralization Forma
tion of a nonelectrolyte (water) Gas-Forming Ev
olution of a water insoluble gas Oxidation
-reduction Transfer of electrons
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Chemistry-140 Lecture 11
Oxidation-Reduction Reactions

• Write the net ionic equation for
• the reaction of Cu with AgNO3.

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Chemistry-140 Lecture 11
Oxidation-Reduction Reactions
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Chemistry-140 Lecture 11
Redox Reactions and Electron Transfer

• All oxidation-reduction reactions involve the
  transfer of electrons between substances

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Chemistry-140 Lecture 11
Oxidation Numbers
Question How can you tell an
oxidation-reduction reaction when you see one ?
Answer Look for a change in oxidation number
for an element(s)
Example
silver is reduced from oxidation state 1 to
oxidation state 0
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Chemistry-140 Lecture 11
Guidelines For Determining Oxidation Numbers
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Chemistry-140 Lecture 11
Guidelines For Determining Oxidation Numbers
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Chemistry-140 Lecture 11
Guidelines For Determining Oxidation Numbers

• The oxidation number of H is 1 and of O is -2 in
  most compounds.

• Exceptions are very few BUT. binary compounds
  between metals and hydrogen are hydrides (H-) and
  H has oxidation state -1.
• Exceptions are very few BUT peroxide O22- has
  oxygen in oxidation state -1.

• The algebraic sum of the oxidation numbers in
  neutral compounds must be 0 in a polyatomic ion,
  the sum must be equal to the ion charge.

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Chemistry-140 Lecture 11
Assigning Oxidation Numbers
Question What are the oxidation numbers
of a) Lithium and oxygen in
Li2O b) Manganese and oxygen in MnO4-
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Chemistry-140 Lecture 11
Assigning Oxidation Numbers
Answers a) Rule 1 states that the Li ion
will have the 1 oxidation state. This gives
O2- an oxidation state of -2 which is
consistent with Rule 5. Total is 0, correct for
a neutral compound b) Rule 5 states O
should have oxidation state -2, for a
contribution of -8. To have a total oxidation
state sum of -1 for a monoanion Mn must be 7.
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Chemistry-140 Lecture 11
Common Oxidizing Agents
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Chemistry-140 Lecture 11
Common Reducing Agents
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Chemistry-140 Lecture 11
Products of Simple Redox Reactions

• Write the net ionic equation for the
• reaction of Na with Cl2

• Na is a good reducing agent

• Cl2 is a good oxidizing agent

• the overall redox equation would then be

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Chemistry-140 Lecture 11
Products of Simple Redox Reactions

• Write the net ionic equation for the
• reaction of K with H2O

• K is a good reducing agent

• H can be reduced to molecular hydrogen

• the overall redox equation would then be

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Chemistry-140 Lecture 11
Products of Simple Redox Reactions

• Write the net ionic equation for the
• reaction of Fe2O3 with Al

• Al is a good reducing agent

• a metal oxide (Fe2O3) can be reduced back to the
  metal

• the overall redox equation would then be

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Chemistry-140 Lecture 11
Summary Types of Reactions

• the reaction type depends on the driving force of
  the reaction. There are four basic types

Reaction Type Driving
Force Precipitation Reaction Formation of an
insoluble compound Acid-Base Neutralization Forma
tion of a nonelectrolyte (water) Gas-Forming Ev
olution of a water insoluble gas Oxidation
-reduction Transfer of electrons
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Chemistry-140 Lecture 11
Some Problems
Question Write the net ionic equation for the
reaction of aqueous solutions of K2CO3 and HClO4.
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Chemistry-140 Lecture 11
Some Problems
Answer Write a balanced equation with
appropriate physical states indicated.
and Remember
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Chemistry-140 Lecture 11
Some Problems
Express the equation in a fully ionic form.
Eliminate spectator ions and reduce to simplest
stoichiometry.
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Chemistry-140 Lecture 11
Some More Problems
Question Write the net ionic equation for the
reaction of Ca with aqueous HCl.
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Chemistry-140 Lecture 11
Some More Problems
Answer Write a balanced equation with
appropriate physical states indicated.
because

• H can be reduced to molecular hydrogen

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Chemistry-140 Lecture 11
Some More Problems
Express the equation in a fully ionic form.
Eliminate spectator ions and reduce to simplest
stoichiometry.
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Chemistry-140 Lecture 12

• Chapter 5 Chemical Reactions

• Chapter Highlights
• mass calculations related to stoichiometric
  reactions
• limiting reagents percent yields
• empirical formula from analytical data
• molarity
• calculations from titration standardization data

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Chemistry-140 Lecture 12

• Solution Stoichiometry

• Molarity, M An expression of concentration -
  the moles of solute per litre of solution

• For example
• Suppose 0.435 g of KMnO4 is dissolved in enough
  water to make a 250 mL solution. What is the
  concentration of the KMnO4(aq) solution ?

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Chemistry-140 Lecture 12
Making a Solution
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Chemistry-140 Lecture 12
Molarity of a Solution
Step 1 Calculate the number of moles of KMnO4.
Step 2 Calculate the molarity of the KMnO4
solution.
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Chemistry-140 Lecture 12
(molarity of A) x (volume A)
(molarity of B) x (volume B)
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Chemistry-140 Lecture 12

• Textbook Questions From Chapter 5
• General Stoichiometry 7
• Limiting Reagents 15, 17
• Percent Yields 21, 23
• Chemical Analysis 25, 27
• Empirical Formula 31, 33
• Solution Stoichiometry 45, 51
• Titrations 59, 61, 65
• General Review 69, 73, 79, 85, 87