Chapter 4 Chemical Reactions

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Chapter 4Chemical Reactions

• Online Homework
• Assignment 2 (Ch 34)
• Note This is the longest of the homework
  assignments you must start early. Due Thurs,
  July 6.

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I. Solubility

• - Many Ionic compounds will dissolve in water and
  produce ions These are soluble and are called
  electrolytes because they conduct electricity.
• - Driving force is that water will be attracted
  to the ions, form weak bonds, and release energy.
• 1) Nonelectrolyte dissolves but does not
  produce ions such as methanol CH3OH or acetone.
• 2) Strong Electrolyte (100 ionization)
• NH4Cl(s) -----) NH4(aq) Cl-(aq)
  (Conducts Well)
• 3) Weak Electrolyte (few ionization in water)
• NH3 H2O (-----) NH4 OH- ( 1
  ionized)
• HC2H3O2 --------) H C2H3O2- (1
  ionized)

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Svante Arrhenius
Nonelectrolyte No Current
Electrolyte Much Current
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I. Solubility Continued

• - Some ionic compounds will not dissolve in water
  - insoluble.
• - Know solubility rules in text (pg 128) below
• 1) All group IA ammonium acetate nitrate
  compounds are soluble No exceptions.
• 2) Halides are soluble except Ag Pb2
  Hg22
• 3) Sulfates are soluble except for Ca2
  Ba2
• Sr2 Ag Pb2 Hg2 2
• 4) Hydroxides are insoluble except for rule 1
  Ca2 Sr 2 Ba 2
• 5) Most carbonates, phosphates, and sulfides
  are insoluble except for rule 1

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II. Writing Reactions

• - Ways to write reactions Example
• Silver(I)nitrate sodium chloride -----)
  silver(I)chloride sodium nitrate
• 1) Molecular Equation (ME) Write all as
  molecules
• AgNO3 NaCl -----) AgCl(s) NaNO3
• 2) Complete Ionic Equation (CIE) Write soluble
• ionic compounds as ions show all ions
  charges.
• Ag NO3- Na Cl- ----) AgCl(s) Na
  NO3-
• 3) Net Ionic Equation (NIE) Eliminate Spectator
  Ions
• Ag Cl- -----) AgCl(s)

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III. Reaction Types A. Precipitation Reactions

• - If reaction produces new insoluble product,
  then can be classified as a precipitation
  reaction.
• - Can predict a product from the solubility
  rules.
• Method Write soluble ionic reactants as ions.
  Check to see if insoluble product can form. If
  can, then this is a product a driving force for
  the reaction.
• Example Predict product when mix K2SO4
• BaCl2 and write CIE and NIE
• 2K SO42- Ba2 2Cl- -----) BaSO4(s) 2K
  2Cl-
• Ba2 SO42- -----) BaSO4(s) (NIE)

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III. Reaction Types B. Acid-Base Rxns

• 1. Definitions
• Arrhenius Acid substance which releases H in
  water.
• Base substance which releases OH- in
  water.
• Examples HCl -----) H Cl-
• NaOH -----) Na OH-
• Bronsted-Lowry Acid Proton Donor
• Base Proton Acceptor
• Example NH3 HCl -----) NH4 Cl-

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III. Reaction Types B. Acid-Base Rxns

• 2. Properties
• Acids Sour taste
• Turn Indicator dyes a specific color
• (Phenolphthalein colorless Litmus red)
• React with bases to yield salt H2O
• Bases Bitter Taste, Feel Slippery
• Turn Indicator dyes a specific color
• (Phenolphthalein red Litmus blue)
• React with acids to yield salt H2O
• Strong Acids/Bases ionize 100 in water
• Weak Acids/Bases ionize lt lt 100 in water

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III. Reaction Types B. Acid-Base Rxns

• 3. Examples
• Strong Acids Bases HCl HBr HI HNO3
  H2SO4
• NaOH KOH Ba(OH)2
• HCl -----) H Cl- 100 to the right
• Weak Acids Bases HF HC2H3O2 HCN
• NH3 (NH4OH) NaHCO3
• NH3 H2O (-----) NH4 OH- 1 to the
  right
• HC2H3O2 (-----) H C2H3O2- 1 to the
  right

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III. Reaction Types B. Acid-Base Rxns

• 4. Acid-Base or Neutralization Reactions
• - Most Acids react with bases to give a salt
  H2O
• - Driving force is to produce very stable H2O and
  sometimes a gas.
• - Examples NaOH HF -----) NaF H2O
• 2KOH H2SO4 ---) K2SO4 2H2O
• - Some Neutralization Rxns produce a gas
  (memorize)
• 2H CO32- or H HCO3- -----) CO2 H2O
  (H2CO3)
• 2H SO32- -----) SO2 H2O (H2SO3)
• 2H S2- -----) H2S
• H CN- -----) HCN Gases are
  in green
• NH4 OH- -----) NH3 H2O

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III. Reaction Types B. Acid-Base Rxns

• 5. ME, CEI and NIE for reaction of potassium
  hydroxide with hydrochloric acid
• ME KOH HCl -----) KCl H2O
• CIE K OH- H Cl- -----) K
  Cl- H2O
• NIE H OH- -----) H2O
• Note 1) The above net ionic equation is common
  for most acid-base reactions. The production of
  stable H2O is a driving force for the reaction.
• 2) H in water better represented by H3O
  (hydronium ion) Memorize this name.

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III. Reaction Types B. Acid-Base Rxns

• 5. ME, CEI and NIE
• - Write the ME, CIE NIE for Rxn of HCl NaHCO3
• ME HCl NaHCO3 -----) NaCl H2O CO2
• CIE H Cl- Na HCO3- ---) Na Cl-
  H2O CO2
• NIE H HCO3- -----) H2O CO2
• 6. Titration - Process of adding known amount of
  known concentration of Base (or Acid) in a
  burette to an unknown concentration of Acid (or
  Base). End point is determined with an indicator
  or a pH meter. Can determine the concentration
  of the unknown (quantitative analysis).

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III. Reaction Types B. Acid-Base Rxns
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III. Reaction Types C. Predicting products

• Driving forces in reactions - production of
• 1) precipitate, 2) gas, 3) a stable molecule.
• Predicting products write ionic reactants as
  ions and look to see if a precipitate can form
  (solubility rules), a gas can form (6 gas
  equations), or if a stable molecule like H2O H
  OH- ---) H2O form. Then write NIE balance.
• Examples 1) BaI2 AgNO3 2) NaCN HCl
• 1) Ba2 I- Ag NO3- -----) AgI(s) Ba2
  NO3-
• Ag I- -----) AgI(s) (NIE)
• 2) Na CN- H Cl- -----) HCN(g) Na
  Cl-
• H CN- -----) HCN(g) (NIE)

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III. Reaction Types D. Redox Rxns

• 1. Definitions Introduction
• - Oxidation Reduction Reaction (Redox Rxn) is
  one in which electrons are transferred.
• - Oxidation Loss of Electrons
• - Reduction Gain of Electrons
• 2. Examples
• 2Mg O2 -----) 2MgO
• 2Mg ---) 2Mg2 4e- Oxidation Half
  Rxn
• O2 4e- -----) 2O2- Reduction
  Half Rxn
• 2Na 2H2O -----) 2NaOH H2
• 2Na -----) 2Na 2e- Oxidation Half
  Rxn
• 2H 2e- -----) H2 Reduction
  Half Rxn

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III. Reaction Types D. Redox Rxns

• Note Oxidizing agent causes oxidation
• Reducing agent causes reduction
• 3. Uses of Redox Rxns a) Create new chemicals
• b) Theoretical Importance (chem 123)
• c) Batteries - force transferred electrons
  through a wire and use them to do work
• 4. Identification (Oxidation Numbers - ON)
• Definition ON the charge that an atom or
  group of atoms would have if they were ionic.
• Uses 1) If a substance changes ON in a rxn,
  then the rxn is redox 2) Nomenclature
  Variable charged metals example FeI2
  Iron(II)Iodide
• Rules Use following rules Order gives
  priority

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III. Reaction Types D. Redox Rxns

• 5. Rules for Determining ON (Different from pg
  147)
• Note When there is a conflict, the first
  rule
• takes priority.
• a) The sum of the ON must add up to give the
  charge
• b) The ON of a neutral element by itself is 0
• c) Group I, II, III ions are 1, 2 3
  respectively
• (H -1 when combined with active metal)
• d) F is -1
• e) O is -2 (O is -1 when found as a
  peroxide, O22-)
• f) Cl, Br, I are -1 (When 2 together, most
  electronegative -1)

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III. Reaction Types D. Redox Rxns

• Examples Determine the ON of single N in each
• N2 Na3N NF3 NO3-1 N2O NO
  NO21-
• 0 -3 3 5 1 2
  3
• - Which of the above forms of N can explosively
  react with organics? Why?
• - Determine ON of each atom in FeSO3
• 2 4 -2
• - Which of the following are redox
• 1) Mg Cl2 -----) MgCl2
• 2) CH4 2 O2 -----) CO2 2 H2O
• 3) HCl NaOH -----) H2O NaCl

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III. Reaction Types D. Redox Rxns

• 6. Reaction Types
• Combination 2Al 3F2 -----) 2AlF3
• Decomposition 2HgO -----) 2Hg O2
• Combustion CH4 2O2 -----) CO2 2H2O
• Displacement Mg 2HCl -----) MgCl2 H2
• Can predict reaction from table 4.6, Pg 151
• The more active metal will replace the cation
• 7. Balancing Can become difficult so, rules
  were generated. Will cover in Chem 123, Chapter
  20.

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IV. Quantitative Aspects of Solutions

• A. Molarity, M
• - Many reactions take place in solution we
  need
• a way to measure concentration M is one way.
• - M moles of Solute/L Solution m/L
• solvent substance present in largest amount
  solute substance(s) dissolved in
  solvent solution solute solvent
• B. Molarity Calculations
• 1) Calculate the M if 4.5 moles of HCl are
  dissolved in a total volume of 0.50 L
• M m/L 4.5 moles / 0.50 L 9.0 m/L HCl
  9.0 M HCl 9.0 molar HCl

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IV. Quantitative Aspects of Solutions

• 2) Calculate M if 20. g of CaCO3 are dissolved in
  4.0 L
• 20. g CaCO3 x 1 mole CaCO3/100. g CaCO3
  0.20 mol CaCO3
• M moles/L 0.20 moles / 4.0 L 0.050 M
  CaCO3
• 3) How many moles of HCl are present in 2.0 L of
  0.30 M HCl?
• M moles/L moles M x L (0.30 m/L) x
  (2.0L) 0.60 moles
• 4) How many L of 12 M HCl are needed to get 1.0
  moles of HCl?
• M m/L L m/M 1.0 moles HCl / (12 mole/L)
  0.083 L

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IV. Quant. Aspects of Solutions C. Dilution
Problems

• - Frequently we are given a concentrated solution
  and we need to dilute it with water to get a more
  dilute solution dilution problem.
• Mi x Vi Mf x Vf Note Initial moles Final
  moles
• Ci x Vi Cf x Vf
• Example How many mL of 12 M HCl are needed to
  make 100. mL of 3.0 M?
• Vi Mf x Vf / Mi (3.0 M x 100.mL)/12 M 25
  mL
• Take 25 mL of 12 M HCl and add enough water to
  make 100 mL.

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IV. Quantitative Aspects of Solutions

• D. Gravimetric Analysis
• - A type of analysis where one converts the
  analyte to an insoluble compound which is then
  purified, dried weighed.
• Example 0.10 L of water containing Ag is mixed
  with NaCl. 0.260 g of dry insoluble AgCl is
  collected on a filter. Calculate the g of Ag
  present in the water.
• NIE 1 Ag 1 Cl- -----) 1 AgCl(s)
• 0.260 g AgCl x 1 mole AgCl x 1 mole Ag
  x 108 g Ag
• 143 g AgCl 1 mole AgCl 1 mole
  Ag
• 0.196 g Ag

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IV. Quantitative Aspects of Solutions

• E. Volumetric Analysis
• - An analysis technique where the M and volume of
  a reagent is used to calculate the amount of an
  unknown.
• Example 0.0250 L of HCl is titrated with 0.0455
  L of 0.433
• M NaOH. Calculate the M of the HCl
• M moles HCl / 0.0250 L
• 1 HCl 1 NaOH -----) 1 NaCl 1 H2O
• (0.433 m/L NaOH) x 0.0455 L 0.0197 m NaOH
  ----) 0.0197 m HCl
• M 0.0197 m HCl / 0.0250 L 0.788 M
  HCl

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V. Suggested Homework 165 - 174

• 1-10 23 25 27 33 37 45
• 49 51 53 55 61 73 (odd)
• 73 79 83 87 99 115
• Online Homework - Assignment 2
• Note This is the longest assignment start
  early. Due Thurs, July 6.