Aqueous Reactions and Solution Stoichiometry

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Aqueous Reactions and Solution Stoichiometry
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• Aqueous Solutions a solution which water is the
  solvent
• Solution Solute Solvent
• Solute smaller part being dissolved
• Solute larger fraction doing the dissolving
• Molarity is used to express conc.

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Molarity

• M moles of solute/ liters of solution
• A 0.38g sample of sodium nitrate is placed in a
  50.0 ml volumetric flask and is filled with water
  to the mark. What is the molarity of the solution?

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Molarity

• How many grams of potassium permanganate are
  needed to prepare 2.0 liters of a 0.2 molar
  solution of the salt?

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Dilution Problems

• M1V1 M2V2
• How many liters of 12 molar sulfuric acid is
  necessary to make 2 liters of a 6 molar conc. of
  the acid?

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Specific Gravity or Density Problems

• Commercially available conc. HCl is in a aq sol
  cont 38 HCl by mass. D 1.19g/ml a) what is the
  molarity of the solution? b) how many ml of conc
  HCl are required to make 1.00 l of a 0.10 molar
  solution?

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Electrolytes

• Solutes that separate into tow or more ions when
  dissolved in water are called electrolytes.
• Solutes that remain uncharged molecules are
  called non-electrolytes.
• Either may be soluble in water.

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Electrolytes

• NaCl(s) ? Na Cl- ionic solids dissociate
  into ions.
• Electrical Conductivity
• Strong electrolytes conduct electricity very
• well because ions totally dissociate
• Weak electrolytes only weakly conduct
• because ions only partially dissociate
• Nearly all ionic cmps are strong and molecular
  cmps are usually non-electrolytes

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Acids, Bases, And Salts

• Acids are solutes that can ionize to produce
  hydrogen ions
• H(aq)
• Strong acids dissociate and exist almost totally
  as ions
• Ex HCl(aq) ? H Cl-

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Weak Acids

• HC2H3O2 ?H C2H3O2-
• ?
• Weak acids only partially
• dissociate the double arrows indicate that the
  reaction occurs in significant amounts in both
  directions
• Acedic Acid or Vinegar is the classic example.

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Acids Cont.

• H is simply a proton acids are often called
  proton donors
• Monoprotic acids contribute one H per molecule
  of acid ex. HCl or HNO3.
• Diprotic acids contribute two H per moleclue ex.
  H2SO4
• Polyprotic acids contribute greater than one H
  ex. H2SO4 or H3PO4.

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Bases

• Are substances that accept H ions or a proton.
• Ex H(aq) OH-(aq) ? H2O(l)
• Ex H(aq) NH3-((aq) ? NH4(aq)
• OH- NH3- are the bases. OH- is the most common
  base in aqueous solution. Sometimes bases are
  defined as substances with increased OH- ions in
  solution.

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Note

• Acids and bases are electrolytes if a strong
  acid or base they are strong electrolytes if a
  weak acid or base a weak electrolyte.
• Strong Acids
• HCl (aq) Hydrochloric H2SO4 Sulfuric
• HNO3 (aq) Nitric HBr
  Hydrobromic
• HClO4 (aq) Prechloric HI Hyrooiodic
• HClO3 (aq) chloric

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• Weak Acids
• HF Hydrofluoric
• H2C2H3O2 Acedic
• Strong bases
• Grp I Hydroxides
• LiOH, NaOH, KOH, RbOH, and CsOH
• Grp II Hydroxides
• Ca(OH)2, Sr(OH)2, Ba(OH)2
• Weak Base NH3 Ammonia

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Salts

• Are ionic compounds formed from acids by the
  replacement of one or more H ions with some
  other cation.
• For example replacing the H ion in HCl(aq) with
  Na ion yields NaCl.

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Identifying strong and weak electrolytes

• most salts are strong electrolytes
• most acids are weak electrolytes except for the
  strong acids
• most strong bases hydroxides of metals are
  strong electrolytes except NH3 which is a weak
  base and electrolyte

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• Neutralization reactions are those between an
  acid and a base they yield salt and water
• Ionic Equations
• a. varying amounts of detail can be included in
  chem eq depending on what information is relevant
  to the problem at hand
• b. molecular equations - have all the species
  written as associated molecules even though they
  may be disassociated
• c. complete ionic eq strong electrolytes are
  written as dissociated ions molecules, solids,
  and weak electrolytes are written as associated
  ions

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• d. net ionic equations an ionic eq in which
  the spectator ions have been cancelled.
• Rules for Converting Molecular eq to Ionic
• 1. Ionic Sub indicated as dissolved in solution
  such as NaCl(aq) are normally written as ions
• 2. Ionic substances that are insoluble (do not
  dissolve readily) either as reactants or products
  (precipitates) are rep as formulas of the
  compounds

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• d. Molecular substances that are strong
  electrolytes such as strong acids are written as
  ions.
• e. Molecular substances that are weak
  electrolytes are represented as their molecular
  formulas
• f. Spectator ions ions in an equation that do
  not take part in the equation are cancelled from
  both sides of the equation

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Examples

• Ba(C2H3O2)2 K2CrO4 ?
• Ba(C2H3O2)2 K2CrO4 ? BaCrO4 2KC2H3O2
• Ba 2C2H3O2 2K CrO4 ? BaCrO4 2K
• 
  2 C2H3O2
• Ba CrO4 ? BaCrO4

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Examples

• Ca(C2H3O2)2 H2C2O4 ?
• Ca(C2H3O2)2 H2C2O4 ? CaC2O4 HC2H3O2
• Ca 2C2H3O2 H2C2O4 ? CaC2O4 HC2H3O2
• Weak acids do not split

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Examples

• NH4NO3 NaOH ?
• NH4NO3 NaOH ? NH4OH Na NO3
• NH4 NO3 Na OH ? NH3 H2O Na
• 
  NO3
• NH4 OH ? NH3 H2O

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Metathesis Reactions

• Reactions in which two ionic reactants exchange
  ion partners
• AX BY ? AY BX
• Precipitation reactions are those metathesis
  reactions in which an insoluble solid product or
  precipitate forms
• A. Precipitate insoluble solid product
• B. Solubility the amount of a substance that
  can dissolve in a given amount of solvent

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• (expressed in g/100 ml or in liters/mol) A
  substance is considered insoluble if its
  solubility is less that 0.01 mol/l.
• Predicting solubility is a matter of know the
  solubility rules (Table 4.3 or what I should know
  for AP list)
• Some metathesis reactions from water or another
  weak electrolyte or non-electrolyte in ionic and
  net ionic equations (appear as associated
  species)
• Some methesis reactions form gases these are
  usually binary compounds of non-metals exam ples
  H2S, CO2, HCN.

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Redox Its electro-magic

• I. Oxidization Numbers
• A. Oxidization loss of
• electrons. LEO
• B. Reduction gain of electrons GER
• C. When one reactant loses es another reactant
  must gain them

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Intro to electrochemistry

• D. reactions in which electrons are trans are
  called oxidization reduction or redox reactions
• E. oxidization number (ON) rules
• 1. atoms in the elemental form oxidization
  0

• 2. monatomic ions the oxidization the
  charge of the ion
• ex Na 1 S-2 -2
• 3. non-metals usually have neg ON although they
  can sometimes be positive
• agt Oxygen usually
• -2 except peroxides
• O2-2 each O -1

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• b) hygrogen usually 1 when bonded to
  non-metals -1 when bonded to metals
• c) Fluorine -1 in all cmps halogens -1 in
  most binary cmps but when combine with oxygen as
  in oxyanions they have a number
• 4. The sum of oxidizations s
• a) in a neutral cmp 0
• b) in a polyatomic ion charge of ion
• Work sample exercise 4.6

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