Aqueous%20Reactions%20and%20Solution%20Stoichiometry

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Aqueous Reactions and Solution Stoichiometry

• What is aqueous?
• What is an aqueous reaction?
• What are some types of aqueous reactions?
• Why might these be important? Give examples.
• Aqueous reactions cannot take place without
  water. What do you already know about water that
  will help us understand aqueous reactions?

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Solutions

• Homogeneous mixtures of two or more pure
  substances.
• The solvent is present in greatest abundance.
• All other substances are solutes.

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Dissociation

• When an ionic substance dissolves in water, the
  solvent pulls the individual ions from the
  crystal and solvates them.
• This process is called dissociation.

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Electrolytes

• Substances that dissociate into ions when
  dissolved in water. Example NaCl
• A nonelectrolyte may dissolve in water, but it
  does not dissociate into ions when it does so.
  Example C12H22O11

Notice, solubility does not imply that something
is or is not an electrolyte.
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Electrolytes and Nonelectrolytes

• Soluble ionic compounds tend to be electrolytes.

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Electrolytes and Nonelectrolytes

• Molecular compounds tend to be nonelectrolytes,
  except for acids and bases.

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Solution   Analyze We are asked to associate
the charged spheres in the diagram with ions
present in a solution of an ionic
substance. Plan We examine the ionic substances
given in the problem to determine the relative
numbers and charges of the ions that each
contains. We then correlate these charged ionic
species with the ones shown in the
diagram. Solve The diagram shows twice as many
cations as anions, consistent with the
formulation K2SO4. Check Notice that the total
net charge in the diagram is zero, as it must be
if it is to represent an ionic substance.
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Electrolytes

• A strong electrolyte dissociates completely when
  dissolved in water.
• A weak electrolyte only dissociates partially
  when dissolved in water.

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Strong Electrolytes Are

• Strong acids

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Strong Electrolytes Are

• Strong acids
• Strong bases

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Strong Electrolytes Are

• Strong acids
• Strong bases
• Soluble ionic salts

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Precipitation Reactions

• When one mixes ions that form compounds that are
  insoluble (as could be predicted by the
  solubility guidelines), a precipitate is formed.

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Metathesis (Exchange) Reactionsa.k.a. Double
Replacement Rxns

• Metathesis comes from a Greek word that means to
  transpose

• AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)

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Metathesis (Exchange) Reactions a.k.a. Double
Replacement Rxns

• Metathesis comes from a Greek word that means to
  transpose
• It appears the ions in the reactant compounds
  exchange, or transpose, ions

• AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)

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Metathesis (Exchange) Reactions

• Metathesis comes from a Greek word that means to
  transpose
• It appears the ions in the reactant compounds
  exchange, or transpose, ions

• AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)

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AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)
How did we know that silver chloride was a
solid??? We checked the solubility table.
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Predict the products of the following reactions

• BaCl2 (aq) K2SO4 (aq)
• Fe2(SO4)3 (aq) LiOH (aq)
• Mg(NO3)2 (aq) CaS (aq)
• NaCl (aq) KNO3 (aq)

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Predict the products of the following reactions

• BaCl2 (aq) K2SO4 (aq)
• ? BaSO4 (s) 2KCl (aq)
• Fe2(SO4)3 (aq) 6LiOH (aq)
• ? 2Fe(OH)3 (s) 3Li2SO4 (aq)
• Mg(NO3)2 (aq) CaS (aq)
• ? MgS (s) Ca(NO3)2 (aq)
• NaCl (aq) KNO3 (aq)
• ? NaNO3 (aq) KCl (aq) or NR

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Solution Chemistry

• It is helpful to pay attention to exactly what
  species are present in a reaction mixture (i.e.,
  solid, liquid, gas, aqueous solution).
• If we are to understand reactivity, we must be
  aware of just what is changing during the course
  of a reaction.

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Molecular Equation

• The molecular equation lists the reactants and
  products in their molecular form.

• AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)

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Ionic Equation

• In the ionic equation all strong electrolytes
  (strong acids, strong bases, and soluble ionic
  salts) are dissociated into their ions.
• This more accurately reflects the species that
  are found in the reaction mixture.

• Ag (aq) NO3- (aq) K (aq) Cl- (aq) ??
• AgCl (s) K (aq) NO3- (aq)

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Net Ionic Equation

• To form the net ionic equation, cross out
  anything that does not change from the left side
  of the equation to the right.

• Ag(aq) NO3-(aq) K(aq) Cl-(aq) ??
• AgCl (s) K(aq) NO3-(aq)

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Net Ionic Equation

• To form the net ionic equation, cross out
  anything that does not change from the left side
  of the equation to the right.
• The only things left in the equation are those
  things that change (i.e., react) during the
  course of the reaction.

• Ag(aq) Cl-(aq) ?? AgCl (s)

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Net Ionic Equation

• To form the net ionic equation, cross out
  anything that does not change from the left side
  of the equation to the right.
• The only things left in the equation are those
  things that change (i.e., react) during the
  course of the reaction.
• Those things that didnt change (and were deleted
  from the net ionic equation) are called spectator
  ions.

• Ag(aq) NO3-(aq) K(aq) Cl-(aq) ??
• AgCl (s) K(aq) NO3-(aq)

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Writing Net Ionic Equations

1. Write a balanced molecular equation.
2. Dissociate all strong electrolytes.
3. Cross out anything that remains unchanged from
   the left side to the right side of the equation.
4. Write the net ionic equation with the species
   that remain.

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Writing Net Ionic Equations Write the net ionic
equation for each reaction

• Pb(NO3)2 (aq) KI (aq)
• Li2S (aq) BaBr2 (aq)
• NH4Cl (aq) Sr(OH)2 (aq)

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Writing Net Ionic Equations Write the net ionic
equation for each reaction

• Pb(NO3)2 (aq) 2KI (aq)
• ? PbI2 (s) 2K(NO3) (aq)
• Pb2 2I- ? PbI2 (s)
• Li2S (aq) BaBr2 (aq)
• ? LiBr (aq) BaS (aq)
• 2Li (aq) S-2 (aq) Ba2 (aq) 2Br- (aq) ?
  2Li (aq) 2Br- (aq) Ba2 (aq) S-2 (aq)
• Notice .all spectator ions. They all cancel and
  therefore, no reaction occurs.
• 2NH4Cl (aq) Sr(OH)2 (aq)
• ? SrCl2 (aq) 2NH4OH (aq)
• 2NH4 (aq) 2Cl- (aq) Sr2 (aq) 2OH- (aq) ?
  Sr2 (aq) 2Cl- (aq) 2NH4 (aq) 2OH- (aq)
• Notice .all spectator ions. They all cancel and
  therefore, no reaction occurs.

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Acids

• Substances that increase the concentration of H
  when dissolved in water (Arrhenius).
• Proton donors (BrønstedLowry).

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Acids

• There are only seven strong acids
• Hydrochloric (HCl)
• Hydrobromic (HBr)
• Hydroiodic (HI)
• Nitric (HNO3)
• Sulfuric (H2SO4)
• Chloric (HClO3)
• Perchloric (HClO4)

These substances are consider strong acids
because they do not just dissolve in water, they
will completely dissociate.
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Bases

• Substances that increase the concentration of OH-
  when dissolved in water (Arrhenius).
• Proton acceptors (BrønstedLowry).

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Bases

• The strong bases are the soluble salts of
  hydroxide ion
• Alkali metals
• Calcium
• Strontium
• Barium

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Acid-Base Reactions

• In an acid-base reaction, the acid donates a
  proton (H) to the base.

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Neutralization Reactions

• Generally, when solutions of an acid and a base
  are combined, the products are a salt and water.

• HCl (aq) NaOH (aq) ?? NaCl (aq) H2O (l)

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Neutralization Reactions

• When a strong acid reacts with a strong base, the
  net ionic equation is

• HCl (aq) NaOH (aq) ?? NaCl (aq) H2O (l)
• H (aq) Cl- (aq) Na (aq) OH-(aq) ??
• Na (aq) Cl- (aq) H2O (l)

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Neutralization Reactions

• When a strong acid reacts with a strong base, the
  net ionic equation is

• HCl (aq) NaOH (aq) ?? NaCl (aq) H2O (l)
• H (aq) Cl- (aq) Na (aq) OH-(aq) ??
• Na (aq) Cl- (aq) H2O (l)
• H (aq) Cl- (aq) Na (aq) OH- (aq) ??
• Na (aq) Cl- (aq) H2O (l)

H (aq) OH- (aq) ? H2O (l)
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Neutralization ReactionsWhat does this have to
do with you???

• What happens when you have a stomach ache?
• What do you do about it?
• Why?

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Neutralization ReactionsWhat does this have to
do with you???

• Many antacids contain magnesium hydroxide. It
  undergoes a neutralization reaction with stomach
  acid.
• What acid constitutes the largest quantity of
  stomach acid?
• Write a net ionic equation for the neutralization
  reaction between magnesium hydroxide and
  hydrochloric acid.
• Mg(OH)2 (s) H (aq) ? Mg2 (aq) H2O (l)

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Neutralization Reactions

• Observe the reaction between Milk of Magnesia,
  Mg(OH)2, and HCl.
• Can you overdoes on antacid?? What do you think
  would happen?

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Gas-Forming Reactions

• These metathesis reactions do not give the
  product expected.
• The expected product decomposes to give a gaseous
  product (CO2 or SO2).

• CaCO3 (s) HCl (aq) ??CaCl2 (aq) CO2 (g)
  H2O (l)
• NaHCO3 (aq) HBr (aq) ??NaBr (aq) CO2 (g)
  H2O (l)
• SrSO3 (s) 2 HI (aq) ??SrI2 (aq) SO2 (g) H2O
  (l)

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Gas-Forming Reactions

• This reaction gives the predicted product, but
  you had better carry it out in the hood, or you
  will be very unpopular!
• Just as in the previous examples, a gas is formed
  as a product of this reaction

• Na2S (aq) H2SO4 (aq) ?? Na2SO4 (aq) H2S (g)

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A Carbonated Beverage is Another Example

• How is a beverage carbonated?
• What happens to the dissolved gas?
• H2O (l) CO2 (g) ? H2CO3 (aq)
• H2O (l) CO2 (g) ? 2H (aq) CO3-2 (aq)

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Oxidation-Reduction Reactions

• An oxidation occurs when an atom or ion loses
  electrons. (It becomes more positive)
• A reduction occurs when an atom or ion gains
  electrons. (It becomes more negative)

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Oxidation-Reduction Reactions

• One cannot occur without the other.

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Oxidation Numbers

• To determine if an oxidation-reduction reaction
  has occurred, we assign an oxidation number to
  each element in a neutral compound or charged
  entity.

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Oxidation Numbers

• Elements in their elemental form have an
  oxidation number of 0.
• The oxidation number of a monatomic ion is the
  same as its charge.

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Oxidation Numbers

• Nonmetals tend to have negative oxidation
  numbers, although some are positive in certain
  compounds or ions.
• Oxygen has an oxidation number of -2, except in
  the peroxide ion in which it has an oxidation
  number of -1.
• Hydrogen is -1 when bonded to a metal, 1 when
  bonded to a nonmetal.

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Oxidation Numbers

• Nonmetals tend to have negative oxidation
  numbers, although some are positive in certain
  compounds or ions.
• Fluorine always has an oxidation number of -1.
• The other halogens have an oxidation number of -1
  when they are negative they can have positive
  oxidation numbers, however, most notably in
  oxyanions.

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Oxidation Numbers

• The sum of the oxidation numbers in a neutral
  compound is 0.
• The sum of the oxidation numbers in a polyatomic
  ion is the charge on the ion.

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Oxidation NumbersFind the oxidation numbers for
each of the following species.

• CO32-
• H2S
• S8
• SCl2
• SO42-
• Cr2O72-

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• CO32-
• C 4 and O -2
• H2S
• H 1 and S -2
• S8
• S 0
• SCl2
• S 2 and Cl -1
• SO42-
• S 6 and O -2
• Cr2O72-
• Cr 6 and O -2

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Examine each Reaction below and Identify the
oxidized and reduced reagents

• 2K (s) 2H2O (l) ? 2KOH (aq) H2 (g)
• Fe2O3 (s) 2Al (s) ? 2Fe (l) Al2O3 (s)
• Si (s) 2Cl2 (g) ? SiCl4 (l)

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Examine each Reaction below and Identify the
oxidized and reduced agents

• 2K (s) 2H2O (l) ? 2KOH (aq) H2 (g)
• K (s) ? K (aq), it was oxidized Hydrogen was
  reduced in water to form hydrogen gas.
• Fe2O3 (s) 2Al (s) ? 2Fe (l) Al2O3 (s)
• Aluminum metal is oxidized iron is reduced
• Si (s) 2Cl2 (g) ? SiCl4 (l)
• Si is oxidized while Cl is reduced

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Which three of the following reactions are
Red-Ox? What is oxidized and what is reduced?

• Zn (s) 2NO3- (aq) 4H (aq) ? Zn2 (aq) 2NO2
  (g) 2H2O (l)
• Zn(OH)2 (s) H2SO4 (aq) ? ZnSO4 (aq) 2H2O (l)
• Ca (s) 2H2O (l) ? Ca(OH)2 (s) H2 (g)
• 4Fe(OH)2 (s) 2H2O (l) O2 (g) ? 4Fe(OH)3 (aq)

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Which three of the following reactions are
Red-Ox? What is oxidized and what is reduced?

• Zn (s) 2NO3- (aq) 4H (aq) ? Zn2 (aq) 2NO2
  (g) 2H2O (l)
• Red-ox zinc is oxidized, nitrogen is reduced
• Zn(OH)2 (s) H2SO4 (aq) ? ZnSO4 (aq) 2H2O (l)
• Not Red-ox
• Ca (s) 2H2O (l) ? Ca(OH)2 (s) H2 (g)
• Red-ox calcium is oxidized, hydrogen is reduced
• 4Fe(OH)2 (s) 2H2O (l) O2 (g) ? 4Fe(OH)3 (aq)
• Red-ox Iron is oxdized, oxygen is reduced

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Displacement Reactionsa.k.a. Single Replacement
Reactions

• In displacement reactions, ions oxidize an
  element.
• The ions, then, are reduced.

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Displacement Reactions

• In this reaction,
• silver ions oxidize
• copper metal.
• Cu (s) 2 Ag (aq) ?? Cu2 (aq) 2 Ag (s)

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Displacement Reactions

• The reverse reaction,
• however, does not
• occur.
• Cu2 (aq) 2 Ag (s) ?? Cu (s) 2 Ag (aq)

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Activity Series
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Use the Activity Series to predict the products
of the following reactions. If the reactions
does take place, write the net ionic equation for
the reaction. Lastly, identify the species being
oxidized and reduced.

• Al (s) HBr (aq)
• Fe(s) KI (aq)
• Zn (s) Ni(NO3)2 (aq)

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• 2Al (s) 6HBr (aq)
• ? 2AlBr3 (aq) 3H2 (g)
• 2Al (s) 6H (aq) ? 2Al3 (aq) 3H2(g)
• Aluminum is oxidized and Hydrogen is reduced.
• Fe(s) KI (aq)
• No Reaction
• Zn (s) Ni(NO3)2 (aq)
• ? Zn(NO3)2 (aq) Ni (s)
• Zn (s) Ni2 (aq) ? Zn2 (aq) Ni (s)
• Zinc is oxidized and Nickel is reduced.

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Molarity

• Two solutions can contain the same compounds but
  be quite different because the proportions of
  those compounds are different.
• (For example, it would be much more dangerous to
  spill a high concentration of hydrochloric acid
  on your hand than a low concentration)
• Molarity is one way to measure the concentration
  of a solution.

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Mixing a Solution

• How many grams of silver nitrate are required to
  make 100 mL of a 0.5 M solution?
• How many grams of NaOH are required to make 50
  mL of an 8.2 M solution?

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Mixing a Solution

• How many grams of silver nitrate are required to
  make 100 mL of a 0.5 M solution?
• 9 grams
• How many grams of NaOH are required to make 50.0
  mL of an 8.2 M solution?
• 16 grams

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Dilution
M1V1 M2V2
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Dilution

• You have 1L of a 1.00 M stock solution of
  hydrochloric acid. You need to make 500 mL of a
  0.20M solution. How much of the stock solution
  is needed?
• You need to make 100 mL of 0.50 M nitric acid.
  The storage bottle reads 6.0M. How much of the
  6.0M nitric acid will you need?

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Dilution

• You have 1L of a 1.00 M stock solution of
  hydrochloric acid. You need to make 500 mL of a
  0.20M solution. How much of the stock solution
  is needed?
• 100. mL or 0.100 L
• You need to make 100 mL of 0.50 M nitric acid.
  The storage bottle reads 6.0M. How much of the
  6.0M nitric acid will you need?
• 8.3 mL

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Using Molarities inStoichiometric Calculations

• How many grams of Ca(OH)2 are needed to
  neutralize 20.0 mL of a 0.150 M H2SO4 solution?
• 0.222 g

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Using Molarities inStoichiometric Calculations

• How many liters of 0.500 M HCl are needed to
  react completely with 0.100 mol Pb(NO3)2, forming
  the precipitate PbCl2?
• 0.400L

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Titration

• The analytical technique in which one can
  calculate the concentration of a solute in a
  solution.

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Titration
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Titration Example

• A 1.034-g sample of impure oxalic acid (H2C2O4)
  is dissolved in water and an acid-base indicator
  is added. The sample required 34.47 mL of 0.485
  M NaOH to reach the equivalence point. What is
  the mass of oxalic acid and what is its mass
  percent in the sample?
• 0.752 g H2C2O4 and 72.7 H2C2O4

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Titration

• A 0.263-g sample of sodium carbonate requires
  28.35 mL of aqueous HCl for titration to the
  equivalence point. What is the molarity of the
  HCl?
• 0.175 M HCl

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