Electrolytes

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• 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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• AP Chemistry
• Wednesday, Febuary 1
• Turn in free response worksheet 1
• Work on Free Response Equation worksheet 2.
  When complete, check your answers on the front
  board. Turn in today if finished, or tomorrow
  beginning of period.
• Video I Came, I Saw, I RedOxd
• Precipitation Demo
• Homework read sections 20.1 and 20.2
• Page 821, do problems 20.2, .4, .6, .8, .10

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Electrolytes
pure water
acetic acid solution
potassium dichromate solution
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• 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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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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Answer a) b) c)
strong electrolyte
nonelectrolyte
weak electrolyte
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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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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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• 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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Soluble Compounds
Exceptions
Almost all salts of Na, K NH4
Salts of NO3-, ClO3-, ClO4-, CH3CO2-
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Exceptions
Insoluble Compounds
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• 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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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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Step 3 Recognize that all soluble ionic
compounds dissociate to form ions in
aqueous solution
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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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Precipitation Reactions

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

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• 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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• 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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Acid-Base Reactions I

• Write the net ionic equation for
• the reaction of HNO3 (strong acid) with KOH
  (strong base).

Overall Reaction
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Acid-Base Reactions II

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

Overall Reaction
2 CH3CO2H(aq) Ca(OH)2(s) Ca(CH3CO2)2(a
q) 2 HOH(l)
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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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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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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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• 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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• 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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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
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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Oxidation-Reduction Reactions

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

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Oxidation-Reduction Reactions
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Redox Reactions and Electron Transfer (oil rig,
leo goes ger)

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

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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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Guidelines For Determining Oxidation Numbers
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Guidelines For Determining Oxidation Numbers
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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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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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Common Oxidizing Agents (species are reduced, i.e
they gain electrons)
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Common Reducing Agents (these species are
oxidized, i.e., they loose electrons)
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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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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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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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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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Some Problems
Question Write the net ionic equation for the
reaction of aqueous solutions of K2CO3 and HClO4.
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Some Problems
Answer Write a balanced equation with
appropriate physical states indicated.
and Remember
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Some Problems
Express the equation in a fully ionic form.
Eliminate spectator ions and reduce to simplest
stoichiometry.
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Some More Problems
Question Write the net ionic equation for the
reaction of Ca with aqueous HCl.
46
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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Some More Problems
Express the equation in a fully ionic form.
Eliminate spectator ions and reduce to simplest
stoichiometry.
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Solubility Rules

• Alkali metals and NH4 compounds are soluble.
• Nitrates(NO3?), acetates (CH3CO2?), chlorates
  (ClO3?), and perchlorates(ClO4?) are soluble.
• Chlorides(Cl?), bromides(Br?), iodides(I?), are
  soluble except for Silver(Ag),mercury(I)(Hg22),
  and lead(II)( Pb2) halides.
• Sulfates(SO4?2) are soluble except for Sr2,
  Ba2, Pb2, and Hg22.
• Hydroxides(OH?) are insoluble except for alkali
  metals and NH4 (see1).
• Sulfides(S?2), carbonates(CO3?2),
  phosphates(PO4?3), and chromates(CrO4?2) are
  insoluble except for alkali metals and NH4
  (see1).

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Classifying Reactions by Type of Chemistry
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Classifying Reactions by Type of Chemistry

• Precipitation AX BZ ?? AZ BX
• Acid Base HX BOH ?? BX H2O
• Gas Evolution
• H2X BCO3 ? H2O CO2(g) BX
• H2X BSO3 ? H2O SO2(g) BX
• NH4X BOH ? H2O NH3(g) BX
• Oxidation Reduction A2 B ?? A B2
• Combustion CxHxOxO2?CO2 H2O

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Classifying Reactions by what Atoms Do
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Classifying Reactions by what Atoms Do

• Combination/Synthesis A Z ?? AZ
• Decomposition AZ ?? A Z
• Single Displacement A BZ ?? AZ B
• Double displacement AX BZ ?? AZ BX
• Neutralization HX BOH ?? BX H2O

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Predicting ReactionsDouble Displacement
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BaCl2 ZnSO4 ?

• Conventional equation
• BaCl2(aq) ZnSO4(aq) ? BaSO4(s) ZnCl2(aq)
• Total ionic equation
• Ba2(aq) 2Cl-1(aq) Zn2(aq) SO4-2(aq) ?
  BaSO4(s) Zn2 (aq) 2Cl-1(aq)
• Net ionic equation
• Ba2(aq) SO4-2(aq) ? BaSO4(s)

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AgNO3 Na2SO4?

• AgNO3 Na2SO4? NR

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(NH4)2CO3 CaCl2 ?

• (NH4)2CO3 CaCl2 ? 2 NH4Cl CaCO3(s)

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Na2S ZnCl2 ?

• Na2S ZnCl2 ?2 NaCl ZnS(s)

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K3PO4 Sr(NO3)2 ?

• 2 K3PO4 3 Sr(NO3)2 ? 6 KNO3 Sr3(PO4)2 (s)

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Mg(NO3)2 NaOH ?

• Mg(NO3)2 2 NaOH ? Mg(OH)2(s) 2 NaNO3

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Ba(OH)2 H3PO4 ?

• 3 Ba(OH)2 2 H3PO4 ? Ba3(PO4)2(s) 6 H2O

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HClO4 NaOH ?

• HClO4 NaOH ? H2O(l) NaClO4

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H3PO3 NH3 ?

• H3PO3 3 NH3 ? (NH4)3PO3

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CH3COOH KOH ?

• CH3COOH KOH ? CH3COO-K H2O

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NH4Cl KOH ?

• NH4Cl KOH ? (NH4OH KCl) ?
• NH3 HOH KCl

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K2CO3 HCl ?

• K2CO3 2 HCl ? (H2CO3 2 KCl)
• ?H2O CO2 2 KCl

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K2SO3 HCl ?

• K2SO3 2 HCl ? (H2SO3 2 KCl)
• ?H2O SO2 2 KCl

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H2CO3 Ca(NO3)2 ?

• H2CO3 Ca(NO3)2 ? CaCO3(s) 2 HNO3

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Fe(NO3)3 NH3 ?

• Fe(NO3)3 3NH3 3H2O? Fe(OH)3(s) 3NH4NO3

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More

• K2S CuSO4 ?
• Na2CrO4 Pb(C2H3O2)2 ?
• ZnBr2 K3PO4 ?
• KOH NH4Cl ?
• NH3 HCN ?

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Predicting Reactions Single Displacement (AKA
Single Replacement)
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(No Transcript)
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Pb Zn(NO3)2 ?
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Fe HCl ?
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Cu AgNO3?
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Cr Zn(NO3)2 ?
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Pb Sn(NO3)2 ?
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H2 NiCl2 ?
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Cr NiCl2 ?
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H2 Au(NO3)2 ?
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• Classifying/Predicting Reactions
• Five types of reactions are possible in the AP
  Exam
• Double Replacement (metathesis) Reactions
• Two binary ionic compounds (including Acids)
• Product is a gas, a precipitate, or a weak
  electrolyte