Reactions in Aqueous Solution - Wikispaces4_APStudent... · Compounds in Aqueous Solution Since...
Transcript of Reactions in Aqueous Solution - Wikispaces4_APStudent... · Compounds in Aqueous Solution Since...
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Reactions in Aqueous
Solution
Chapter 4
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Compounds in Aqueous Solution
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
This is a reaction in which reactants are in solution
Solution – homogeneous mixture composed of two
parts:
solute – the medium which is __________
solvent – the medium which dissolves the solute.
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Compounds in Water
Some compounds conduct electricity when dissolved in
water –_____________
Those compounds which do not conduct electricity when
dissolved in water are called – nonelectrolytes
Compounds in Aqueous Solution
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Ionic Compounds in Water (Electrolytes)
The conductivity of the solution is due to the formation
of ions when the compound dissolves in water
These ions are not the result of a chemical reaction, they
are the result of a dissociation of the molecule into ions
that compose the solid.
)()()( 2 aqClaqNasNaCl OH
Compounds in Aqueous Solution
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Molecular Compounds in Water(Nonelectrolytes)
In this case no ions are formed, the molecules just
disperse throughout the solvent.
)()( 2 aqsugarssugar OH
Compounds in Aqueous Solution
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Molecular Compounds in Water(Nonelectrolytes)
There are exceptions to this, some molecules are strongly
attracted to water and will react with it.
ClOHOHHCl
OHNHOHNH
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Compounds in Aqueous Solution
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Strong and Weak Electrolytes Strong electrolytes – A substance which completely
ionizes in water.
For example:
ClOHOHHCl 32
Compounds in Aqueous Solution
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Strong and Weak Electrolytes
Weak electrolyte: A substance which partially ionizes
when dissolved in water.
For example:
OHCOCHOHHCOCH 323223
Compounds in Aqueous Solution
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Strong and Weak Electrolytes
OHCOCHOHHCOCH 323223
Compounds in Aqueous Solution
Notice that the arrow in this reaction has two heads,
this indicates that two opposing reactions are
occurring simultaneously.
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Strong and Weak Electrolytes
OHHCOCHOHCOCH
and
OHCOCHOHHCOCH
223323
323223
Compounds in Aqueous Solution
Since both reactions occur at the same time,
this is called a chemical equilibrium.
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- A reaction which forms a solid (precipitate)
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
- AgCl is classified as an insoluble substance
Precipitation Reaction
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Net Ionic Equation
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
- AgNO3 and NaNO3 are electrolytes in solution so they
actually occur as free ions.
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)
AgCl(s) + Na+(aq) + NO3-(aq)
Precipitation Reaction
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Net Ionic Equation
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)
AgCl(s) + Na+(aq) + NO3-(aq)
- Notice that NO3-(aq) and Na+(aq) occur in both the left
and right side of the equation.
-These are called _________________.
Precipitation Reaction
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Net Ionic Equation
Ag+(aq) + Cl-(aq) AgCl(s)
- With the spectator ions removed, the resulting
equation shows only the ions involved in the reaction
remain.
- This is a net ionic equation.
Precipitation Reaction
Practice
Write the net ionic reaction for the neutralization
of HF by NaOH.
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Solubility Guidelines for Ionic Compounds 1. Most nitrates (NO3
-) and acetates (CH3CO2-) are
soluble in water.
2. All chlorides are soluble except: Hg+, Ag+, Pb2+, Cu+
3. All sulfates are soluble except: Sr2+, Ba2+, Pb2+
4. Carbonates (CO32-), Phosphates (PO4
3-), Borates
(BO33-),Arsenates (AsO4
3-), and Arsenites (AsO33-)
are insoluble.
5. Hydroxides (OH-) of group Ia and Ba2+ and Sr2+ are
soluble.
6. Most sulfides (S2-) are insoluble.
Compounds in Aqueous Solution
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Solubility Guidelines for Ionic Compounds
Predict the solubility of the following compounds:
PbSO4
AgCH3CO2
(NH4)3PO4
KClO4
Compounds in Aqueous Solution
Practice
Which one of the following substances is
predicted to be soluble in water?
AgCl Mg(OH)2 FeS PbSO4 Mo(NO3)2
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Acid - substance which ionizes to form hydrogen cations
(H+) in solution
Examples:
Hydrochloric Acid HCl
Nitric Acid HNO3
Acetic Acid CH3CO2H
Sulfuric Acid H2SO4
Sulfuric acid can provide two H+’s - Diprotic acid,
The other acids can provide only one H+
- Monoprotic acid.
Acids and Bases
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Diprotic acid
H2SO4 H+ + HSO4-
HSO4- H+ + SO4
2-
Acids and Bases
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Base - substance which reacts with H+ ions.
Examples:
ammonia NH3
sodium hydroxide NaOH
Acids and Bases
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Acid-Base Reaction
H+ + OH- H2O
- It is clear that the metal hydroxides (NaOH for
example) provide OH- by disassociation.
- Bases like ammonia make OH- by reacting with water
(ionization)
NH3 + H2O NH4+ + OH-
Acids and Bases
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Strong and Weak Acids and Bases
Strong acids and bases are ________electrolytes.
Weak acids and bases are ______electrolytes.
Acids and Bases
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Strong Acids
- The strength of acids and bases are concerned with
the ionization (or dissociation) of the substance, not its
chemical reactivity.
Example:
Hydrofluoric acid (HF) is a weak acid, but it is very
chemically reactive.
- this substance can’t be stored in glass bottles
because it reacts with glass (silicon dioxide).
Acids and Bases
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Common Strong Acids and Bases
Common Strong Acids
Hydrochloric Acid HCl
Hydrobromic Acid HBr
Hydroiodic acid HI
Nitric Acid HNO3
Perchloric Acid HClO4
Sulfuric Acid H2SO4
Acids and Bases
KNOW ALL OF THEM
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Common Strong Acids and Bases
Common Strong Bases
Lithium Hydroxide LiOH
Sodium Hydroxide NaOH
Potassium Hydroxide KOH
Acids and Bases
KNOW ALL OF THEM
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Neutralization Reaction - Reaction between an acid and a base.
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
“The neutralization between acid and metal hydroxide
produces__________________”
Salt – an ionic compound whose cation comes from a
base and anion from an acid.
Acids, Bases, and Salts
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Neutralization Reaction
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
- despite the appearance of the equation, the reaction
actually takes place between the ions.
Acids, Bases, and Salts
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Neutralization Reaction
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
Total Ionic Equation
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)
H2O(l) + Na+(aq) + Cl-(aq)
Acids, Bases, and Salts
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Metal Carbonates and Acid
Gas-Forming Reactions
2 HCl(aq) + Na2CO3(aq) 2 NaCl(aq) + H2O(l) +
CO2(g)
- Metal carbonates (or bicarbonates) always form a salt,
water and carbon dioxide
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Metal Sulfide and Acid
Gas-Forming Reactions
2 HCl(aq) + Na2S(s) H2S(g) + 2 NaCl(aq)
- Metal sulfides form a salt and hydrogen sulfide.
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Metal Sulfite and Acid
Gas-Forming Reactions
2 HCl(aq) + Na2SO3(s) SO2(g) + 2 NaCl(aq) +
H2O(l)
- Metal sulfites form a salt, sulfur dioxide and water.
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Ammonium Salt and Strong Base
Gas-Forming Reactions
NH4Cl(s) + NaOH(aq) NH3(g) + NaCl(aq) + H2O(l)
- This reaction forms ammonia, salt and water
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Oxidation-Reduction Reactions
- Reaction where electrons are exchanged.
2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g)
Na(s) Na+(aq) + 1 e-
oxidation- _______________
2 H+(g) + 2 e- H2(g)
reduction – _______________
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Oxidation-Reduction Reactions
- Reaction where electrons are exchanged.
2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g)
- An alternate approach is to describe how one reagent
effects another.
- Reducing Agent, a substance that causes another substance
to be reduced.
Na(s) Na+(aq) + 1 e-
- Oxidizing Agent, a substance that causes another substnace
to be oxidized.
2 H+(g) + 2 e- H2(g)
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Oxidation-Reduction Reactions
Oxidation Numbers 1. Each atom of a pure element has an oxidation number of
zero(0).
2. For monatomic ions, the oxidation number equals the
charge on the ion.
3. Fluorine always has an oxidation state of -1 in compounds.
4. Cl, Br, and I always have oxidation numbers of -1, except
when combined with oxygen or fluorine.
5. The oxidation number of H is +1 and O is -2 in most
compounds.
6. The sum of the oxidation numbers must equal the charge
on the molecule or ion.
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Oxidation-Reduction Reactions
Oxidation Numbers
Examples
PCl5
P 1( ) =
Cl 5( ) = ________
0
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Oxidation-Reduction Reactions
Oxidation Numbers
Example
CO32-
C 1( ) =
O 3( ) = _____
-2
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Oxidation-Reduction Reactions
Oxidation Numbers
Example
K2CrO4
K 2( ) =
O 4( ) =
Cr 1( ) = ________
0
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Molarity(M) Unit of concentration, moles of solute per liter of solution.
solutionofLiters
soluteofMolesMolarity
Solutions
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Example: What is the molarity(M) of a solution which
contains 17.51g of NaCl in 751mL of solution?
F.W. (NaCl): 58.45g/mol
Solutions
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Solutions Molarity
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Dilution
MdiluteVdilute = MconcentratedVconcentrated
Solutions
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If 200. mL of a 2.50 M NaOH
solution is diluted to 500. mL,
what is the new concentration of
NaOH?
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Dilution
Example: What volume of 6.00M NaOH is required to
make 500mL of 0.100M NaOH?
Mconcentrated = 6.00M Mdilute = 0.100M
Vconcentrated = ? Vdilute = 500mL
0.100M(500mL) = 6.00M(Vconcentrated)
Vconcentrated = 8.33mL
Solutions
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pH Scale
Concentration scale for acids and bases.
]log[ HpH
• The square brackets around the H+ indicate that
the concentration of H+ is in molarity.
• So, a change of 1 pH unit indicates a 10X change in
H+ concentration.
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Solution Stoichiometry
- We can now use molarity to determine stoichiometric
quantities.
Example
How many grams of hydrogen gas are produced when
20.0 mL of 1.75M HCl is allowed to react with 15.0g of
sodium metal?
2 HCl(aq) + 2 Na(s) H2(g) + 2 NaCl(aq)
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Solution Stoichiometry
Titrations