Chapter 4 Aqueous Reactions and Solutions Stoichiometry

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Chapter 4 Aqueous Reactions and Solutions
Stoichiometry

• Types of Aqueous Reactions
• Precipitation
• Acid/Base
• Redox
• Solution Stoichiometry
• Concentrations of Solutions

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Definitions

• Solution homogeneous mixture
• Solvent part of above in most amount
• Solute part of above in least amount
• Electrolyte solution that conducts a current,
  showing the presence of ions
• Nonelectrolyte you guessed it
• Try sugar solution vs. salt solution
• animation

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Ionic compounds

• Why do they dissolve in water?
• Called dissociation
• Animation

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Molecular Compounds

• Polar stay in tact but are separated by polar
  water molecules (sugar)
• Nonpolar do not dissolve (oil)

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Strong Electrolytes

• Describes the amount of ions in solution
• Ionic compounds produce strong electrolytes by
  almost 100 dissociation
• Acids react with water to for ions.
• Called ionization
• Strong acids form strong electrolytes because
  they ionize completely
• HCl equation

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Weak Electrolytes

• Weak acids form weak electrolytes because they
  form an equilibrium and ionize very little
• Acetic acid equation
• Animation

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Equations

• Dissociation of ionic compounds must reflect the
  number of ions in the formula
• Try the dissociation of Al2(SO4)3

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Precipitation Reactions

• Result in the formation of an insoluble product
• Demo write the equation
• Pb(NO3)2(aq) 2KI(aq) ? PbI2(s)
• 2KNO3(aq)
• Occurred because certain pairs of oppositely
  charged ions attract each other so strongly that
  they form an insoluble solid
• Need to know rules! Masterson list is easier.

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Rules

• Insoluble means there is less than 0.01 moles
  of the substance dissolved in a liter of solution
• Memorize rules on page 118
• NOTE All compounds of the alkali metal ions and
  NH4 are soluble
• NOTE All nitrates are soluble

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Metathesis or Exchange Reactions

• General term used when ions appear to exchange
  and reform
• Comes from Greek word for transpose
• PE on page 119

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Ionic Equations

• Molecular
• Pb(NO3)2(aq) 2KI(aq) ? PbI2(s)
• 2KNO3(aq)
• Ionic
• Pb2 2NO3- 2K 2I- ? PbI2(s)
  2NO3- 2K
• Net Ionic Show only the ones that react!
• Pb2 2I- ? PbI2(s)
• PE page 121

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Acid Base Reactions

• Important in the body and in the environment
• Aqueous solution

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Acids

• Substances that ionize in water to form H ions
• This is actually a proton
• Acids are called proton donors
• Can be monoprotic (HCl) or diprotic (H2SO4)

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Bases

• Substances that accept protons or H ions.
• Two ways
• dissociate to form OH- (NaOH)
• ionize water to leave OH- (NH3)
• Equations?
• Learn Table 4.2 on page 122

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Determining Strength of Electrolytes

• Ionic? Strong if yes
• Molecular?
• Strong acid strong
• Not a strong acid but contains H weak
• No H and not NH3 nonelectrolyte
• Demo

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Neutralization

• Occurs when an acid and a base are mixed
• Strong acid strong base forms a salt and water
• NaOH HCl ? NaCl H2O
• Salt compound made between an anion from an
  acid and a cation from a base
• Net ionic?

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Reaction of carbonates and sulfides with acids

• Gas formation
• 2HCl(aq) Na2S(aq) ? H2S(g) 2NaCl(aq)
• Net ionic?
• HCl(aq) NaHCO3(aq) ? NaCl(aq)
  H2CO3(aq)
• H2CO3 decomposes rapidly to H2O and CO2
• Net ionic?
• What is the fizz in Alka seltzer?

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Net Ionic Equations for each acid-base combination

• SA SB HCl NaOH
• WA SB CH3COOH NaOH
• SA WB HCl NH3
• Learn these general types.

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Oxidation-Reduction Reactions

• Transfer of electrons
• Oxidation Loss of electrons
• Mg ? Mg2 2e-
• Reduction gain of electrons
• O2 4e- ? 2O2-
• 2Mg(s) O2(g) ? 2MgO(s)
• Leo says grrrrrr!
• You need both in a reaction.

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Bookkeeping

• Oxidation numbers
• 1. All free elements are 0
• 2. Monatomic ions ox is charge
• 3. Oxygen usually -2 except in O22-, which is
  -1.
• 4. Hydrogen is 1 when bonded to nonmetals
  and -1 when bonded to metals.
• 5. Fluorine is -1 in all compounds.
• 6. Sum of all oxidation numbers is 0 for a
  compound or equal to the charge of an ion.
• 7. Practice!

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Types

• Oxidation of metals by an acid or salt called
  single replacement reactions
• Zn(s) 2HBr(aq) ? ZnBr2(aq) H2(g)
• Net ionic?
• What is oxidized? This is called the reducing
  agent.
• What is reduced? This is called the oxidizing
  agent.
• Try for Copper in silver nitrate.

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Activity Series

• Listed as ease of oxidation
• Top is the most easily oxidized, or best reducing
  agents.
• Bottom is most easily reduced, or best oxidizing
  agents.
• Predict if Cu can be oxidized by HCl.

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Molarity

• Symbolized with M
• Defined as
• moles of solute/volume of solution in liters
• 2M is pronounced 2 molar and means 2 moles of
  solute is dissolved in 1 liter of solution
• Try a problem

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Preparation of Solutions

• Volumetric flask is used
• Calculated mass is put in flask
• Water is added to fill line (animation)

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Molar Concentrations of Electrolytes

• Calculate molarity of entire species as before
• To find molarity of each ion, multiply by
  coefficient of each in the balanced equation
• Example, in a 0.1 M solution of Na2O, the
  concentration of the Na ion is 0.2 M (animation)
• Symbolized by
• Na 0.2 M
• Try one

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Interconverting

• Molarity can be used as a conversion factor
• Liters X (mol/liter) moles
• Moles X (liters/mol) liters
• Try a problem

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Dilution Problems

• Calculate number of moles needed by liters X
  (moles/liter)
• Calculate the volume of given solution that will
  yield that number of moles by
• moles X (liters/moles) Animation
• Try one

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Solution Stoichiometry

• Calculate moles by solution calculation
• Look at balanced equation
• Do final calculation by regular stoichiometry
• Complete to volume if necessary
• Try one

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Titration

• Lab procedure for calculating an unknown molarity
  using a solution with a known molarity (standard
  solution)
• Standard solution is added to the unknown
  solution using a buret (animation)
• Equivalence point is reached when stoichiometry
  says quantities are equal
• Indicator changes color at first sign of excess
  of one reagent this is called the end point

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Two Kinds of Titration

• Acid-Base reaction
• Redox Titration
• Try some problems