Types of Chemical Reactions

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Chapter 4

• Types of Chemical Reactions
• And Solution Stoichiometry

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Section 4.1 Water, The Common Solvent
Hydration of an ionic compound will occur when
the partial positive end of a water becomes
attracted to the anions in the compound likewise
for the partial negative center of the water and
the cations.
Solubility depends on the strength of the
intermolecular attractions between the ions and
water, as well as the intramolecular attractions
of the cations and anions of the compound.
NH4NO3(s) ? NH4(aq) NO3-(aq)
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What can dissolve?

• Soluble
• Alcohols
• ex C2H5OH
• Sugars
• ex C6H12O6
• Ionic compounds
• ex NaCl, KOH, LiBr

• Insoluble
• Fats
• ex bacon grease
• Oils
• ex cooking oil
• Non-Polar Substances
• ex turpentine

WHY?
Because of intermolecular forces the OH group on
the sugars and alcohols is particularly
attractive to a water molecule. Generally
speaking Like Dissolves Like
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Section 4.2 Strong and Weak Electrolytes

• Solute Solvent Solution
• Strong electrolytes conduct electricity
• Weak electrolytes barely conduct electricity
• Conductivity depends upon ionization

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• Strong Electrolytes
• Soluble salts
• Strong acids
• Strong bases
• All of these dissociate completely in water.

• Weak Electrolytes
• Weak acids
• Weak bases
• All of these partially dissociate in water

HCl ? H Cl- NaOH ? Na OH-
HC2H3O2 H C2H3O2
Non-Electrolytes are completely molecular
substances in water (not even a little
dissociation) Non polar substances.
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Section 4.3 Composition of Solutions

• Concentration is measured in molarity, molality,
  and many others.
• Concentration DOES NOT directly express the
  number of ions present in a solution.

M moles solute liters solution
MgCl2 ? Mg2 2Cl- 1.0 M 1.0 M
2.0 M
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Sample Problems

• Calculate the number of moles of Cl- ions in 1.75
  L of 1 x 10-3 M ZnCl2.
• A chemist needs 1.0 L of 0.20 M K2Cr2O7 solution.
  How much solid K2Cr2O7 must be weighed out to
  make this solution?

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• Standard Solution a solution whose concentration
  is accurately known.
• Example 0.1022 M HCl 1.003 M NaOH
• Creating dilutions
• Chemical analysis of a compound
• Theoretical Calculations

What would you do to prepare a standard solution?
In your answer, include specific pieces of
glassware, techniques, or equipment you should
use.
ANSWER NOW
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Dilutions

• Dilution is the process used to make the solution
  less concentrated.
• moles before dilution moles after dilution
• Because M mol/L,
• V1(M1) V2(M2)
• Lab Technique Use a pipet to deliver the correct
  amount of original solution to a volumetric
  flask. Add some water, swirl. Fill to line,
  invert.

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Section 4.4 Types of Chemical Reactions

• There are more than just these few types, but in
  this chapter we will cover
• Precipitation
• Acid-base
• Oxidation-Reduction

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Section 4.5 Precipitation Reactions

• Precipitation Reactions (double displacement)
• Forms a solid precipitate from aqueous reactants.
• Color of precipitate can help in identification
• Solubility rules help BUNCHES

MORE
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Solubility RULES

• All compounds containing alkali metal cations and
  the ammonium ion are soluble.
• All compounds containing NO3-, ClO4-, ClO3-, and
  C2H3O2- anions are soluble.
• All chlorides, bromides, and iodides are soluble
  except those containing Ag, Pb2, and Hg2.
• All sulfates are soluble except those containing
  Hg2, Pb2, Sr2, Ca2, and Ba2.
• All hydroxides are only slightly soluble, except
  those containing an alkali metal, Ca2, Ba2,and
  Sr2. NaOH and KOH are the most soluble
  hydroxides.
• All compounds containing PO43-, S2-, CO32-, and
  SO32- are only slightly soluble except for those
  containing alkali metals or the ammonium ion.

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Practice Predicting

• Potassium nitrate and barium chloride
• Sodium sulfate and lead (II) nitrate
• Potassium hydroxide and iron (III) nitrate

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• ALL REACTIONS SHOULD BE WRITTEN IN NET IONIC FORM

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Section 4.7 Stoichiometry of Precipitation
Reactions

• Stoichiometry in a precipitation reaction is
  performed just like stoichiometry for a molecular
  reaction.
• You need to know which ion comes from which
  molecular formula.

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Sample problem

• Calculate the mass of solid NaCl needed to add to
  1.5 L of 0.1 M silver nitrate solution to
  precipitate all Ag ions in the form of AgCl.

Net Ionic Eq Ag Cl- ? AgCl
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General Format

• Write the Net Ionic Equation
• Calculate the moles present
• Identify the Limiting Reactant
• Use Mole Ratio(s)
• Fancy-fy your answer (put in correct units)

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Try Me!

• What mass of precipitate will be produced when
  50.0 mL of 0.200M aluminum nitrate is added to
  200.0 mL of 0.100 M potassium hydroxide?

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Section 4.8 Acid-Base Reactions
Acids yield H Bases yield OH -

• Definitions of acid and base vary.
• Arrhenius and Bronsted/Lowry are common theories.
• Acid-Base rxns are called NEUTRALIZATIONS

Bases are proton acceptors
Acids are proton donors
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• Strong Acid-Strong Base
• (HCl) (NaOH)
• Both dissociate completely
• H OH- ? H2O
• Na and Cl- are spectators.

Weak Acid - Strong Base (HC2H3O2)
(KOH) Acetic acid will not dissociate KOH will
completely HC2H3O2 OH- ? H2O C2H3O2- K is a
spectator.
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Stoichiometry sample

• What volume of 0.100 M HCl is needed to
  neutralize 25 mL of 0.35 M NaOH?

H OH- ? H2O
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Titrationsdefine me!

• Volumetric analysis
• Titration
• Titrant
• Analyte
• Equivalence point
• Indicator
• Endpoint

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To complete a successful titration

• The reaction between the titrant and the analyte
  should be known (you should know WHAT substances
  you have)
• The equivalence point should be marked accurately
  (you should use the right indicator)
• Volume of the titrant needed to reach the
  equivalence point should be recorded accurately
  (you should use a buret!)

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Effective Indicator Ranges
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Titration Try Me Calc 1

• A 50.0 mL sample of a sodium hydroxide solution
  is to be standardized. 1.3009 M of KHP
  (potassium hydrogen phthalate, KHC8H4O4) is used
  as the titrant. KHP has one acidic hydrogen.
  41.20 mL of the KHP solution is used to titrate
  the sodium hydroxide solution to the endpoint.
  What is the resulting concentration of the
  analyte?

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Titration Try Me Calc 2

• How many milliliters of a 0.610 M sodium
  hydroxide solution are needed to neutralize 20.0
  mL of a 0.245 M sulfuric acid solution?

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Norton Tutorial

• Go to the website www2.wwnorton.com/college/c
  hemistry/gilbert/tutorials/ch16.htm
• Find the tutorial on Acid/Base ionization.
• Complete the tutorial question form.

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Section 4.9 Redox Reactions

• What is it??
• -A reaction that occurs in conjunction with a
  transfer of electrons.
• We assign oxidation states to individual atoms in
  a reaction to observe the change in electrons.

• Oxidation states
• are written with
• the /- sign
• before the quantity.

Ion charges are written with the /- sign
behind the quantity.
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Assigning Oxidation States
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• Oxidation an increase in the oxidation state
• Reduction a decrease in the oxidation state

oxidation
2Na(s) Cl2(g) ? 2NaCl(s)
reduction
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Metal Atom

• Oxidized Substance
• Loss of electrons
• Oxidation state increases
• Gets Smaller
• Called the Reducing Agent

Other Atom
e-
Other Ion
Metal Ion

• Reduced Substance
• Gain of electrons
• Oxidation state decreases
• Gets Bigger
• Called the Oxidizing Agent

• The metal is oxidized and the other substance
  is reduced.

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Section 4.10 Balancing Redox
How To, in Acid

• Write the ½ reactions
• Balance the non-H and non-O atoms
• Balance O by adding H2O where needed
• Balance H by adding H where needed
• Balance charge using e-
• Multiply by coefficients until both e- are equal
  for each ½ reaction
• Add the ½ reactions together (cancel stuff)

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Redox Sample Problem

• Balance
• MnO4- Fe2 ? Fe3 Mn2

2
3
2
3
Check Charges!
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1-
2
0
7
2
x5!
x5!
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Redox Try Me Problem

• As2O3(s) NO3- ? H3AsO4 NO(g)

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How To, in Base

• Repeat steps from old procedure
• Cancel out H by adding OH- ions
• Re-write H and OH- as water
• Add ½ reactions together (and cancel stuff)

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Redox Try Me Problem 2

• Balance, in base
• Ag(s) CN- O2 ? Ag(CN)2-