Advanced Reaction Topics

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Advanced Reaction Topics
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Advanced Reaction Topics

• Reaction Rates
• Equilibrium
• Acids and Bases
• Redox Chemistry

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Reaction Rates
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Reaction Rates

• Things that affect the rate of a reaction
• Temperature
• Increasing the temperature 10C doubles the
  reaction rate typically
• Concentration
• Surface Area
• Catalyst
• Every reaction is different and has a different
  reaction rate.

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Collision Theory

• Reactions happen when molecules collide with each
  other
• The reaction only happens IF
• They collide with enough energy
• They collide with the right orientation.

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How Do They Relate?

• Things that affect the rate of a reaction
• Temperature
• Increasing Temperature increases the energy in a
  collision.
• Concentration
• Increases the number of particles in the same
  volume and therefore the number of collisions
• Surface Area
• Increases the accessible area for collisions

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Equilibrium
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Fishbowl Demo

• What are the characteristics once it reaches
  equilibrium?
• The amount of reactants and products is not
  changing
• Reactions are still occurring in both the
  forward and reverse direction.
• The rate of the reactions is the same at
  equilibrium

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Characteristics of Equilibrium

• The amounts of the reactants and products do not
  change while the system is at equilibrium.
• Consider N2 3H2 ? 2NH3

Notice the double half arrows
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Characteristics of Equilibrium

• The forward and reverse reactions still both
  occur but at the same rate.
• For this reason, equilibrium can also be called
  dynamic equilibrium

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Acids and Bases
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Hydrochloric Acid

• HCl(aq)
• What type of compound is it?
• What type of electrolyte is hydrochloric acid?

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Hydrochloric Acid

• Why does it light up?
• What must be present in solution?
• Is hydrochloric acid an ionic compound?
• No. It is in a small subset of covalent compounds.

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Hydrochloric Acid

• It must be making some ions in solution
• What are the ions?
• HCl H2O ? H3O(aq) Cl-(aq)

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Hydrochloric Acid

• H3O is called the hydronium ion
• Things that make hydronium ions in water are
  called acids.

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A Word About Hydronium

• Depending on how you look at it acids make
• H - hydrogen ion
• H3O - hydronium ion
• The two are interchangable
• H H2O ? H3O
• Anytime you see one it can mean the other.

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Common Acids

• Hydrochloric acid (HCl)
• Muriatic acid
• Sulfuric acid (H2SO4)
• Battery acid
• Nitric acid (HNO3)
• Acetic acid (HC2H3O2)
• Vinegar
• Phosphoric acid (H3PO4)

• Citric Acid
• Lactic Acid
• Ascorbic Acid
• Vitamin C
• Acetylsalicylic Acid
• Aspirin
• Stearic Acid

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Common Bases

• Sodium hydroxide
• Lye, Caustic Soda
• Calcium hydroxide
• Lime
• Magnesium hydroxide
• Milk of magnesia

• Ammonia
• Sodium hypochlorite
• Bleach
• Sodium hydrogen carbonate
• Baking Soda
• Calcium carbonate
• Chalk
• Tums

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Acids and Bases

• Arrhenius Definitions
• Arrhenius Acid a substance that dissociates and
  produces hydronium ions in water
• Arrhenius Base a substance that dissociates and
  produces hydroxide ions in water
• Brønsted-Lowry Definitions
• Brønsted-Lowry Acid a substance that donates a
  hydrogen ion (H) (a proton)
• Brønsted-Lowry Base a substance that accepts a
  hydrogen ion (H) (a proton)

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Acid and Base Definitions

• There is quite a bit of overlap between the
  definitions
• HCl H2O ? Cl- H3O
• HCl dissociates and produces hydronium ions
• Arrhenius Acid
• HCl donates an H to water
• Brønsted-Lowry Acid
• All Arrhenius Acids are Brønsted-Lowry Acids and
  vice versa.

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Acid and Base Definitions

• Relations between the base definitions are not as
  simple.
• NaOH dissolves in water to form Na and OH-
• Arrhenius Base
• NaOH H ? Na H2O
• Brønsted-Lowry Base
• Hydroxides are both Arrhenius and Brønsted-Lowry
  Bases.
• Non-hydroxide bases cant be Arrhenius bases
• No hydroxide obviously
• Non-hydroxide bases will be Brønsted-Lowry bases
• CO32- H ? HCO3-
• NH3 H ? NH4

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Acid and Base Definitions

• Arrhenius acids and bases are tied to water
• Brønsted-Lowry acids and bases are not.
• Brønsted-Lowry can be used to describe reactions
  in the gas phase or in other solvents besides
  water.

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Acid-Base Definitions

• Monoprotic acid an acid that has one ionizable
  hydrogen
• HCl, HNO3
• Diprotic acid an acid that has two ionizable
  hydrogens
• H2SO4
• Triprotic acid an acid that has three ionizable
  hydrogens
• H3PO4
• What kind of acid is acetic acid, HC2H3O2?
• Monoprotic
• Typically only hydrogens written first are
  ionizable.

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Autolysis of Water

• Water spontaneously splits itself
• 2H2O ? H3O OH
• An equilibrium system.
• Makes equal parts hydronium and hydroxide
• Equal parts acid and base
• Water is neutral.

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Autolysis of Water

• We will use brackets to represent molarity
• H3O is the molarity of the hydronium ion.
• When acids and bases are dissolved in water
  H3OOH Kw 1x10-14

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Acid Base Reactions

• Acid Base Neutralization Reaction
• HA B ? A HB
• Transfer of hydrogen ions (H)
• Hydrochloric acid and sodium hydroxide solutions
  are mixed

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Acid Base Reactions

• Acid Base Neutralization Reaction
• HA B ? A HB
• Transfer of hydrogen ions (H)
• Acetic acid and barium hydroxide solutions are
  mixed.

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Acid Base Reactions

• Acid Base Neutralization Reaction
• HA B ? A HB
• Transfer of hydrogen ions (H)
• Ammonia and sulfuric acid solutions are mixed

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Acid Base Reactions

• Acid Base Neutralization Reaction
• HA B ? A HB
• Transfer of hydrogen ions (H)
• Hydrochloric acid and sodium sulfide solutions
  are mixed.

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Acids

• Hydrochloric acid
• Is it an electrolyte?
• Why is it an electrolyte?
• Acetic acid
• Is it an electrolyte?
• Why is it an electrolyte?
• Why doesnt it light up as much as hydrochloric
  acid?

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Strength of Acids and Bases

• Hydrochloric acid completely dissociates
• HCl H2O ? H3O Cl-
• Acetic acid doesnt make as many ions
• Acetic acid partially dissociates
• HC2H3O2 H2O ? H3O C2H3O2
• Around 0.5 of acetic acid molecules make
  hydronium ions
• Reactant side is very favored.

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Strength of Acids and Bases

• Strong acid or base an acid or base that
  completely reacts with water to form hydronium
  ions or hydroxide ions.
• Strong acids hydrochloric, sulfuric, nitric
• Strong bases LiOH, NaOH, KOH, RbOH, CsOH,
  Ca(OH)2, Sr(OH)2, Ba(OH)2
• Weak acid or base an acid or base that
  partially reacts with water to form hydronium
  ions or hydroxide ions.
• Weak acids everything except the above
• Weak bases everything except the above

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Strong Acid
Weak Acid
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Strength of Acids and Bases

• Strength does not describe concentration
• Consider
• A bottle of glacial acetic acid (99)
• A bottle of concentrated sulfuric acid (98)
• Both have (nearly) the same concentration
• Acetic acid will not ionize as much in water as
  sulfuric acid will
• Acetic acid is a weak acid

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Concentration of Acids

• If not all acids completely dissociate in water
• The concentration of the acid molecules is
  different for every acid
• The concentration of the hydronium ion in
  different acids is different
• Need a system that describes the concentration of
  acids.

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pH

• pH -log H3O
• Also define a relationship for the amount of base
• pOH -log OH
• How do you reverse a log?
• 10-pH H3O
• 10-pOH OH

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How are pH and pOH related?

• Kw H3OOH
• log Kw log (H3OOH)
• log Kw log H3O log OH
• log 1x10-14 log H3O log OH
• -14 log H3O log OH
• 14 -log H3O -log OH
• 14 pH pOH

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pH Scale

• Take 7 minutes to fill in this pH scale using the
  chemical formulas you know.

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Practice Problems

• What is the pH of a solution with H of
  1.0x10-3 M?

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Practice Problems

• What is the pOH of a solution with H of
  1.0x10-3 M?

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Practice Problems

• What is the OH- of a solution with a pH of 9.00?

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Practice Problems

• What is the OH- of a solution with an H3O
  concentration of 1.0x10-5 M?

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Practice Problems

• What is the pH of a solution with a hydronium ion
  concentration of 2.55x10-4M?

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Practice Problems

• What is the pOH of a solution that has a
  hydronium ion concentration of 5.50x10-8 M?

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Indicators

• Colored compounds that are sensitive to changes
  in pH
• Indicators will change color based on how acidic
  or basic the conditions around it are
• Chemical reaction with the acids or bases

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Universal Indicator

• Universal Indicator is a mixture of different
  indicators.
• Resulting color depends on each of the four
  indicators states

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Redox Chemistry
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Electrolysis

• Run a current through water.
• Splits water into hydrogen and oxygen
• 2H2O ? 2H2 O2

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Oxidation Numbers

• Describes the relative amount of electrons
  associated with a particular atom
• Has no actual physical meaning (for the most
  part)
• Only an electron bookkeeping method.

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Oxidation Numbers

• Every uncombined element in its natural state has
  an oxidation number of zero.
• The oxidation number of a monatomic ion is its
  charge.
• Remember the following
• Fluorine in a compound is always -1
• Hydrogen is a 1 normally in a compound. It is
  -1 when a hydride.
• Oxygen is almost always -2 in a compound unless
  it is a peroxide (-1)
• The sum of the individual oxidation numbers on
  every atom in a species is equal to the overall
  charge on that species.

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Oxidation Numbers Practice

• Give the oxidation number of every element in the
  following compounds.
• CHF3

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Oxidation Numbers Practice

• Give the oxidation number of every element in the
  following compounds.
• BaCl2

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Oxidation Numbers Practice

• Give the oxidation number of every element in the
  following compounds.
• KNO3

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Oxidation Numbers Practice

• Give the oxidation number of every element in the
  following compounds.
• S2O32-

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Oxidation Numbers Practice

• Give the oxidation number of every element in the
  following compounds.
• P4

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Oxidation Numbers Practice

• Give the oxidation number of every element in the
  following compounds.
• (NH4)2C2O4

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Oxidation and Reduction

• Oxidation - chemical process involving the loss
  of electrons.
• Reduction chemical process involving gaining
  electrons.
• LEO the lion goes GER
• OIL RIG

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Oxidation and Reduction

• Consider
• MnO4- C2O42- H ? Mn2 CO2 H2O
• What element has been reduced?
• What element has been oxidized?
• What species reacted with the element that was
  reduced?
• This is the reducing agent.
• What species reacted with the element that was
  oxidized?
• This is the oxidizing agent.

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Vanadium Oxidation States

• Vanadium oxidation states.mov

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Practice

• Identify the element oxidized, the element
  reduced, the species that is the oxidizing agent,
  and the species that is the reducing agent in
• I- ClO- H ? I3- Cl- H2O

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Practice

• Identify the element oxidized, the element
  reduced, the species that is the oxidizing agent,
  and the species that is the reducing agent in
• H Cr2O72- C2H5OH ? Cr3 CO2 H2O

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Half Reaction

• Different Parts of redox reactions are
  interchangable
• We split redox reactions into two parts
• Oxidation half reaction
• Reduction half reaction
• Write the compounds or ions involved and show
  which ones are losing and gaining electrons

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Practice Problems

• Cu Ag ? Cu2 Ag

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Practice Problems

• Al H ? Al3 H2

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Practice Problems

• F2 Cl- ? F- Cl2

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Practice Problems

• Sn2 Fe3 ? Fe2 Sn4

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Balancing Redox Reactions

• This gets ugly.
• Must follow the process.

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The Rules Copy the Rest

• Split the overall reaction into two half
  reactions, one for oxidation and one for
  reduction.
• Balance each half reaction separately
• Balance everything but O and H
• Balance O by adding H2O where necessary
• Balance H by adding H where necessary
• Balance the charge by adding electrons.

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The Rules Copy the Rest

• Make the number of electrons in the two half
  reactions agree by multiplying the entire half
  reaction by coefficients.
• Add the two half reactions and cancel identical
  species
• Double check to make sure everything (elements
  and charge) is balanced!!!!!!!!
• These rules apply to reactions occurring under
  acidic conditions thats all we need for this
  class

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Practice Problems

• Dichromate and iodide ions react in acidic
  solution to form chromium(III) and iodate ions.

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Practice Problems

• Permanganate ions and methanol (CH3OH) react to
  form manganese(II) ions and formic acid (HCO2H)
  in acidic solution.

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Practice Problems

• Arsenic metal and chlorate ions react in acidic
  solution to form arsenous acid (H3AsO3) and
  hypochlorous acid (HClO)

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Practice Problems

• Solid iodine reacts with hypochlorite ions to
  form iodate ions and chloride ions in acidic
  conditions.

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Practice Problems

• Arsenic metal and chlorate ions react in acidic
  solution to form arsenous acid (H3AsO3) and
  hypochlorous acid (HClO)
• Solid iodine reacts with hypochlorite ions to
  form iodate ions and chloride ions in acidic
  conditions.
• Oxalate ions (C2O42-) and permanganate ions react
  in acidic conditions to form manganese(II) ions
  and carbon dioxide.
• Dichromate ions react with hydrogen peroxide to
  produce chromium(III) ions and oxygen gas in
  acidic conditions
• Aluminum metal reacts with iodate ions in acidic
  solution to form aluminum ions and solid iodine.

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Uses of Redox Chemistry

• Batteries
• Harnessed flow of electrons driven by redox
  reaction.
• Car battery

PbO2(s) Pb(s) 2H2SO4 ? 2PbSO4(s) 2H2O
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Alkaline Batteries
Zn 2MnO2 ? ZnO Mn2O3
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Fuel Cells

• 2H2 O2 ? 2H2O

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Electroplating
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Corrosion