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Section 4: Aqueous Reactions
1. Solution composition2 Electrolytes and nonelectrolytes2. Electrolytes and nonelectrolytes3. Acids, bases, and salts4 N t li ti ti4. Neutralization reactions5. Precipitation reactions6. Oxidation/reduction reactions 7 Molarity7. Molarity
1S. Ensign, aqueous reactions
Water has remarkable chemical and physical propertiesand physical properties
•High melting and boiling points
•Expands when freezes (ice floats)
•Dissolves a wide variety of substances (the•Dissolves a wide variety of substances (the universal solvent)
•Provides an ideal environment in which numerous chemical reactions can occur (aqueous reactions)
•The chemical reactions of life require and•The chemical reactions of life require, and occur in, water 2
S. Ensign, aqueous reactions
S l ti h i t f 2Solutions, solvents, and solutes
• Solution: a homogeneous mixture of 2 or more substances
• Solvent: the substance in the solution present in greatest quantity
• Solutes: other substances that are dissolved in the solvent
• Solution concentration: the amount of solute dissolved in a given quantity of solvent ordissolved in a given quantity of solvent or solution
An aqueous solution is a solutionAn aqueous solution is a solution where water is the solvent 3
S. Ensign, aqueous reactions
Some common aqueous solutions• Solutions of sugars (glucose, fructose,
sucrose, lactose, etc)• Solutions of alcohols (methanol, ethanol, etc)• Solutions of salts (sodium chloride potassiumSolutions of salts (sodium chloride, potassium
chloride, ammonium sulfate, etc)• Solutions of acids• Solutions of acids• Solutions of bases
4S. Ensign, aqueous reactions
The solution process
5S. Ensign, aqueous reactions
The solution process
1. Break intermolecular attractions in pure l t t f i di id l l lsolute to free up individual molecules
(solute)n n solute2. Disrupt water-water intermolecular
attractions to provide room for solute to dissolve
(water)m m water3. Form new solute-water intermolecular
forcesn solute + m H2O (solute)n(water)m
6S. Ensign, aqueous reactions
Electrolytes and nonelectrolytes• Electrolytes: compounds that dissolve in water toElectrolytes: compounds that dissolve in water to
produce ions (soluble ionic compounds, acids and bases in water)– “dissociate” or “ionize” in solution
• Nonelectrolytes: compounds that dissolve in water• Nonelectrolytes: compounds that dissolve in water, and yet do not form ions in solution (soluble molecular compounds in water)p )– “dissolve” but don’t “ionize”
7S. Ensign, aqueous reactions
Sodium chloride dissolves in water to form hydrated sodium and choride ionsy
+
-
8S. Ensign, aqueous reactions
Electrolytes: acids, bases, and salts• Acids:
– Hydrogen-containing compounds that dissociate in water to produce hydrogen ion and a partner anionC d th t i [H+] i l ti– Compounds that increase [H+] in aq. solutions
• Bases:– compounds that react with (accept) hydrogen
ions, producing water– Compounds that increase [OH-] in aq. solutions
• Salts: Ionic compounds that are neither acids or bases
9S. Ensign, aqueous reactions
Acids: Hydrogen-containing compounds that dissociate in water to produce hydrogen ion (H+) and a partner anion
• Strong acids: dissociate (ionize) “completely” in solution
• Weak acids: dissolve completely but only partially ionize• Weak acids: dissolve completely, but only partially ionize in solution
• Polyprotic acids: have more than one “ionizable” proton
10S. Ensign, aqueous reactions
Bases: (1) compounds that react with (accept) hydrogen ions, producing water. (2) Compounds that increase [OH-] in
l tiaq. solutions.• Metal hydroxides
• Ammonia
• Strong bases: dissociate (ionize) “completely” in solution
• Weak bases: Ionize only partially in solution, or dissolve incompletely in solutionincompletely in solution
11S. Ensign, aqueous reactions
Strong acids and basesCommon strong acids
HCl HBr HI (but not HF)
Common strong bases
Group 1A metal hydroxides (LiOHHCl, HBr, HI (but not HF)
HClO4
HNO
Group 1A metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH). These dissociate completely at 1 M and higher
iHNO3
H2SO4 (only the first H+
ionizes completely)
concentrations
The heavier Group 2A metal hydroxides ionizes completely) p ydissociate “completely” but only at low concentrations
12S. Ensign, aqueous reactions
Salts: Compounds that dissociate (ionize) in water but are not acids or bases
13S. Ensign, aqueous reactions
Electrolytes• Strong electrolytes: salts acids and bases that dissolve• Strong electrolytes: salts, acids, and bases that dissolve
completely or nearly completely in water to form ions
W k l t l t C d th t di l i t b t• Weak electrolytes: Compounds that dissolve in water, but produce only a small concentration of ions when dissolved (partial dissociation; partial ionization)( )
14S. Ensign, aqueous reactions
Electrolytes and nonelectrolytes
distilled water: tap water:a nonelectrolyte tap water:a weak electrolyte
15S. Ensign, aqueous reactions
Electrochemistry is a fascinating area
The chemistry going on in this simple demonstration could be the solution to much of of our future energy needsneeds
16S. Ensign, aqueous reactions
Solubility: a term that refers to how h f l t di l i imuch of a solute can dissolve in a given
amount of solvent (grams solute dissolved/100 ml solution)
• Ionic compounds• Molecular compoundsp• Acids and bases
17S. Ensign, aqueous reactions
Degrees of solubility• “soluble” in water: glucose, NaCl, NaOH,
acetic acid, MgSO4 (“soluble” means a significant amount can dissolve)
• “Insoluble” in water: CaCO3, AgCl, C6H14, I23 6 14 2(“insoluble” means a very little amount dissolves)
• “miscible” with water: ethanol, glycerol, formaldehyde (“miscible” means soluble at all y (proportions)
18S. Ensign, aqueous reactions
Solubility of salts
• Most salts are classified as “soluble”• Most salts are classified as soluble• Some salts are “insoluble” (poorly soluble)• The distinction between “soluble” and “insoluble” is• The distinction between soluble and insoluble is
based on whether a “significant amount” dissolves in water (see next slide)
• Don’t memorize which salts are soluble and insoluble at this point, but some being familiar with some general guidelines will be useful for yousome general guidelines will be useful for you
19S. Ensign, aqueous reactions
Salt Solubility (g/100 g water at 25° C
Classification
NaCl 35.9 Largely soluble
NaNO3 91.2 Largely soluble
Ca(CH3COO)2 ~33 Largely soluble( 3 )2 g y
MgSO4 ~25 Largely soluble
CaSO4 ~0.2 Largely insoluble
A Cl 0 000520 L l i l blAgCl 0.000520 Largely insoluble
CaF2 ~0.002 Largely insoluble
NH4F 45 Largely soluble
PbCl2 ~4.5 Slightly soluble
Pb(NO3)2 ~60 Largely soluble
CaCO3 0.0013 Largely insolubleCaCO3 0.0013 Largely insoluble
Na2CO3 ~230 Largely soluble
PbS2 ~2.6 x 10‐9 Largely insoluble
b( ) l l blPb(CH3COO)2 ~50 Largely soluble
20S. Ensign, aqueous reactions
Solubility of some commonly encountered salts in water• All ionic compounds with nitrate (NO -) group 1A metal ions• All ionic compounds with nitrate (NO3 ), group 1A metal ions,
and ammonium ion (NH4+) are soluble
• All binary salts of Cl-, Br-, I- are soluble, except with Ag+, Hg+, Pb2+Pb2+
• Nearly all acetate (CH3COO-) salts are soluble• Most sulfate (SO4
2-) salts are soluble (exceptions: BaSO4, ( 4 ) ( p 4,CaSO4, PbSO4, SrSO4
• Most hydroxide (OH-) salts are insoluble (ex. w/group 1A metal ions or NH + heavier group 2A hydroxides are slightly soluble)ions or NH4 , heavier group 2A hydroxides are slightly soluble)
• Most oxide (O2-) and sulfide (S2-)salts are insoluble (ex. w/group 1A metal ions or NH4
+)• Most phosphate and carbonate salts are insoluble (ex. w/group
1A metal ions or NH4+)
• Many F- salts are insoluble (ex. w/group 1A metal ions or NH4+ y ( g p 4and some others)
• Blah, blah, blah………….. That’s enough for now 21S. Ensign, aqueous reactions
Summary….• Many salts are “soluble” and hence “strong• Many salts are soluble and hence strong
electrolytes”• Most acids are weak acids and hence “weakMost acids are weak acids and hence weak
electrolytes”• Group 1A and the heavier group 2A metalGroup 1A and the heavier group 2A metal
hydroxides are strong bases and hence “strong electrolytes”
• Ammonia is a weak base and hence a “weak electrolyte”
• Soluble molecular compounds that don’t ionize in solution are nonelectrolytes
22S. Ensign, aqueous reactions
Common reactions in aqueous l isolutions
• PrecipitationPrecipitation• Neutralization
G ti• Gas generation• Metals: oxidation/reduction
23S. Ensign, aqueous reactions
Precipitation Reactions: Formation of an insoluble salt from the mixing of aqueous solutions of soluble saltsthe mixing of aqueous solutions of soluble salts
Example: Silver nitrate (AgNO3)is soluble in water Sodiumis soluble in water. Sodium chloride (NaCl) is soluble in water. Silver chloride (AgCl) iswater. Silver chloride (AgCl) is insoluble in water. •What will happen if solutions ofWhat will happen if solutions of AgNO3 and NaCl are mixed together?g
•Write a balanced chemical equation for the reaction.equation for the reaction.
24S. Ensign, aqueous reactions
Precipitation Reactions: Formation of an insoluble salt from the mixing of aqueous solutions of soluble saltsthe mixing of aqueous solutions of soluble saltsExample: Silver nitrate (AgNO3) is soluble in water. Sodium chloride (NaCl) is soluble in water. Silver chloride (AgCl) is insoluble in water.
•What will happen if solutions of AgNO3 and NaCl are mixed together?
•Write a balanced chemical equation for the reaction.
25S. Ensign, aqueous reactions
More solution chemistry terms•Molecular equation: shows the complete chemical formulas of reactants and products, not necessarily as they actually exist in solution
•Complete ionic equation: all soluble salts are shown as ions- i.e. in the form they actually exist in solutions
•Net ionic equation: includes only ions and molecules that are directly involved in a chemical reaction occurring in solution
•Spectator ions: ions in solution that are not involved in a chemical reaction, and appear in identical forms on both sides of the chemical equationequation
26S. Ensign, aqueous reactions
Write molecular, complete ionic, and net ionic equations for the formation of a precipitate of PbI after mixing solutions of precipitate of PbI2 after mixing solutions of Pb(NO3)2 and KI
Lead (II) iodide precipitates when potassium iodide is mixed with lead (II) nitrate.Author PRHaneylicensed under the Creative Commonslicensed under the Creative CommonsAttribution-Share Alike 3.0 Unported license.
27S. Ensign, aqueous reactions
Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte y ( ) y
is formed
• A reactant may be soluble or insoluble to begin with
• Sometimes a product is a gas, or reacts further to produce a gasproduce a gas
• Reactions can be represented by molecular complete• Reactions can be represented by molecular, complete ionic, or net ionic equations
28S. Ensign, aqueous reactions
Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte is formedy ( ) y• Reactions can be represented by molecular, complete ionic, or
net ionic equationsH d hl i id di h d id– Hydrochloric acid + sodium hydroxide
– Sulfuric acid + potassium hydroxide
29S. Ensign, aqueous reactions
Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte is formedy ( ) y• A reactant may be insoluble to begin with
– Insoluble hydroxide plus strong acid:
– Insoluble metal oxide + strong acid:
30S. Ensign, aqueous reactions
Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte is formedy ( ) y• Sometimes a product is a gas, or the product reacts further to
produce a gas– Strong acid + sodium sulfide or sodium cyanideStrong acid + sodium sulfide or sodium cyanide
– Strong acid + carbonate or sulfite salt
31S. Ensign, aqueous reactions
Neutralization reactions of acids and bases• A nonelectrolyte (water) and a salt or weak electrolyte is formedy ( ) y• Sometimes a product is a gas, or the product reacts further to
produce a gas– Alka seltzerAlka seltzer
– Baking powder
32S. Ensign, aqueous reactions
Common reactions in aqueous l isolutions
• PrecipitationPrecipitation• Neutralization
G ti• Gas generation• Oxidation/reduction
33S. Ensign, aqueous reactions
Oxidation/reduction reactions: chemical ti h l t t f dreactions where electrons are transferred
from one reactant to another
34S. Ensign, aqueous reactions
Oxidation/reduction reactions: chemical reactions where electrons are transferred from one reactant to another
Na: 1s2 2s22p6 3s1 Cl: 1s2 2s22p6 3s23p5
1
n = 2
n = 3
11p+ 1
n = 2
n = 3
17 p+n = 111p+ n = 117 p+
35S. Ensign, aqueous reactions
Oxidation/reduction reactions: chemical reactions where electrons are transferred from one reactant to another
Na+: 1s2 2s22p6 Cl-: 1s2 2s22p6 3s23p6
+ -
1
n = 211p+ 1
n = 2
n = 3
17 p+n = 111p+ n = 117 p+
36S. Ensign, aqueous reactions
Oxidation/reduction reactions• Oxidation: lose electrons
– Metals lose electrons to obtain a Noble gas e- configuration g g(Li Li+ + e-)
• Reduction: gain electrons– nonmetals often gain electrons to obtain a Noble gas
electron configuration (Cl2 + 2e- 2Cl-)Some cations will gain electrons to form a stable “reduced”– Some cations will gain electrons to form a stable reduced product (2H+ + 2e- H2)
• An oxidation reaction must be linked to a reductionAn oxidation reaction must be linked to a reduction reaction
• “Oxidation numbers” assigned to atoms and ions in gcompounds are used to keep track of electrons gained or lost during oxidation/reduction reactions 37
S. Ensign, aqueous reactions
Oxidation numbers• An atom in its elemental state has an oxidation number of
zero, meaning it has neither gained nor lost electrons– Oxidation numbers of H, N, O, C, and S in H2, N2, O2, C(graphite), and S8
are all zero
• For monatomic ions, the oxidation number is the same as the ion charge
Monatomic metal cation Oxidation number
Monatomicnonmetal anion Oxidation number
Li+ Na+ K+ Cu+ “plus one” (+1) F- Cl- Br- I- “minus one” ( 1)Li+ Na+, K+, Cu+ plus one (+1) F- Cl-, Br-, I- minus one (-1)
Mg2+, Ca2+, Sr2+, Fe2+ “plus two” (+2) O2-, S2- Se2-, Te2- “minus two” (-2)
Al3+, Fe3+, Cr3+, Ni3+ “plus three” (+3) N3-, P3- “minus three” (-3)
• Note H, a nonmetal, can have an oxidation number of +1 in the hydrogen ion (H+) or -1 in the hydride ion (H-)
• The oxidation numbers of atoms in molecular compounds and polyatomic ions are assigned by rules we will discuss later 38
S. Ensign, aqueous reactions
Metals lose electrons to obtain a Noble gas e- configuration (Li Li+ + e-)
Nonmetals gain electrons to obtain a Noble gas electron configuration (Cl2 + 2e- 2Cl-)
Some cations will gain electrons to form a stable “reduced” product (2H+ + 2e- H )
Alkali metal plus halogen gas:
Some cations will gain electrons to form a stable reduced” product (2H+ + 2e- H2)
Alkali metal plus water:
Metal plus strong acid:
39S. Ensign, aqueous reactions
Solution concentration• The amount of solute dissolved in a given
quantity of solvent or solution
1 00 L1.00 L
50 particles/liter25 particles/liter10 particles/liter40
S. Ensign, aqueous reactions
MolarityMolarity
Molarit M Moles soluteMolarity = M = Volume of solution (liters)
molsL
# of particlesDefined volumeL Defined volume
[sol te][solute]
41S. Ensign, aqueous reactions
(1) Add proper mass f l t t
(2) Mix to (3) Add more (4) Solution ofof solute to prepare defined volume of solution, add some water
dissolve solute(3) Add more water to reach final desired volume
(4) Solution of defined molarity
42S. Ensign, aqueous reactions
Preparing a 1 M solution of sodium chloride1711 17Cl
35.45
11Na
22.99
FWNaCl = 58.44 amu = 58.44 g/mol
43S. Ensign, aqueous reactions
Preparing a 1 M solution of sodium chlorideFWNaCl = 58.44 g/molNaCl
58.44 gNaCl
1 mol/LNaCl
1.00 L
NaCl
44S. Ensign, aqueous reactions
Interconversion of mass, mols, and b f ti lnumber of particles
Molar Avogadro’sbmass moles moleculesmass number
Interconversion of mass, mols, and concentration of particlesconcentration of particles
Molar mass
Volume of solution molsmass moles molaritymass solution mols
L
45S. Ensign, aqueous reactions
Potassium permanganate (KMnO4), a common lab chemical, is a purple-black solid that dissolves in water to give a is a purple black solid that dissolves in water to give a deep purple solution. If you dissolve 0.435 g of KMnO4 in enough water to give 250 ml of solution, what is [KMnO4] i l /L?
FW O = 158 0 g/mol
in mols/L?
FWKMnO4= 158.0 g/mol
46S. Ensign, aqueous reactions
If you dissolve 0.435 g of KMnO4 in enough water to give 250 ml of solution, what is [KMnO4] in mols/L?g [ 4]
mass moles molarity
Molar mass
Volume of solution y
FWKMnO4= 158.0 g/mol V = 0.25 l
47S. Ensign, aqueous reactions
Molarity as a conversion factorMolarity as a conversion factor
Molar Volume of
mass moles molarity
Molar mass
Volume of solution
Molar mass
Molarity of solutionmass moles volumemass solution
gmol
moll
48S. Ensign, aqueous reactions
How many mols of HCl are present in 250 ml of 12 M HCl?
Molar Molarity of
mass moles volumemass solutiong
molmol
l
49S. Ensign, aqueous reactions
You need 5.0 mols of HCl. What volume of 12 M HCl would provide these 5.0 mols?
mass moles volume
Molar mass
Molarity of solution
g molgmol l
50S. Ensign, aqueous reactions
For a certain experiment, you need 250 mlp , yof 1.50 M sodium carbonate (Na2CO3). How do you prepare this solution?y p p
Molar mass
Molarity of solutionmass moles volumemass solution
mass moles molarity
Molar mass
Volume of solution y
51S. Ensign, aqueous reactions
For a certain experiment, you need 250 ml of 1.50 M sodium carbonate (Na2CO3). How do you prepare this solution?
Molar Molarity of
mass moles volume
Molar mass
Molarity of solution
52S. Ensign, aqueous reactions
Changing solution concentration byconcentration by
dilution
20 particles/100 ml 20 particles/200 ml53
S. Ensign, aqueous reactions
DilutionWhat is the concentration of an NaOH solution prepared by diluting 0.25 L of 6.0 M NaOH to a final volume of 1.25 L by addition of water?
⎟⎞
⎜⎛
⎟⎟⎞
⎜⎜⎛
⎟⎞
⎜⎛ L 0.25NaOH mol 6.0
⎟⎠
⎜⎝⋅⎟⎟⎠
⎜⎜⎝⋅⎟⎠
⎜⎝ L 1.25L 1.0
·V ÷VM1 M2
·V1 moles÷V2
54S. Ensign, aqueous reactions
Wh t l f 6 0 M N OH d tDilution
What volumes of 6.0 M NaOH and water are required to prepare 0.50 liters of 1 M NaOH?
⎟⎞
⎜⎛
⎟⎞
⎜⎛
⎟⎟⎞
⎜⎜⎛ L 1.0NaOH mol 1.0L 0.50
⎟⎠
⎜⎝⋅⎟⎠
⎜⎝⋅⎟⎟⎠
⎜⎜⎝ NaOH mol 6.0L 1.0
V1 V2·M1 moles ÷M2
55S. Ensign, aqueous reactions
DilutionV V·V1M1 M2moles÷V1
÷V2
· V2
V V·M1 l ÷M2
M x V = moles
V1 V21 moles
÷M1 ·M2
M2
M1 x V1 = moles
M2 x V2 = moles2 2
moles = moles
So:
M1 x V1 = M2 x V2 56S. Ensign, aqueous reactions
Review some solution termsM l l ti h th l t h i l f l•Molecular equation: shows the complete chemical formulas
of reactants and products, not necessarily as they actually exist in solutionexist in solution
•Complete ionic equation: all soluble salts are shown as ions i e in the form they actually exist in solutionsions- i.e. in the form they actually exist in solutions
•Net ionic equation: includes only ions and molecules that di l i l d i h i l i i iare directly involved in a chemical reaction occurring in
solution
•Spectator ions: ions in solution that are not involved in a chemical reaction, and appear in identical forms on both id f th h i l tisides of the chemical equation
57S. Ensign, aqueous reactions
What concentrations of species are present in solutions of strong electrolytes?in solutions of strong electrolytes?
• Molecular equation: shows the complete chemical formulas of reactants and products, not necessarily as they actually
0.025 M NaCl0 025 M Na SO necessarily as they actually
exist in solution• Complete ionic equation: all
soluble salts are shown as ions- i.e. in the form they
0.025 M Na2SO4
ions i.e. in the form they actually exist in solutions
• Net ionic equation: includes only ions and molecules that are directly involved in a ychemical reaction occurring in solution
• Spectator ions: ions in solution that are not involved in a h i l ti dchemical reaction, and appear
in identical forms on both sides of the chemical equation
58S. Ensign, aqueous reactions
Useful problem solving strategies for chemical reactions occurring in aqueous solutionsInterconverting moles, molarity, and volume:g , y,
M V·Vmoles
÷V
÷M
· M
Dilution problems:·V1M1 M2moles÷V1
÷V2
· V21
V1 V2·M1 moles÷M1 ·M2
÷M2
massa molesa Ma or VaMolar massa
Ma or Va
Interconverting mass, moles, and volume in aqueous chemical reactions:
Stoichiometric relationship in a reaction
59S. Ensign, aqueous reactions
massb molesb Mb or VbMolar massb Mb or Vb
Problem solving strategy for chemical ti i i l tireactions occurring in aqueous solutions
Molar mass Ma or Vamassa molesa Ma or VaMolar massa a a
Stoichiometric relationship in arelationship in a reaction
massb molesb Mb or VbMolar massb Mb or Vbmassb molesb Mb or Vb
60S. Ensign, aqueous reactions
Sodium bicarbonate (NaHCO3) is often used to neutralize spills of acids such as sulfuricto neutralize spills of acids such as sulfuric acid (H2SO4).
2NaHCO3(s) + H2SO4(aq) Na2SO4(aq) + 2H2O(l) + 2CO2(g)
What mass of NaHCO3 would be required to
M V
3 qneutralize 25 ml of 6.0 M H2SO4?
massa molesa Ma or VaMolar massa
Ma or Va
Stoichiometric Start here…
relationship in a reaction
l M VMolar massb Mb or Vbmassb molesb Mb or Vbb b b
End here61
S. Ensign, aqueous reactions
2NaHCO3(s) + H2SO4(aq) Na2SO4(aq) + 2H2O(l) + 2CO2(g)
What mass of NaHCO3 would be required to neutralize 25 ml of 3 q6.0 M H2SO4? massa molesa Ma or Va
Molar massaMa or Va
Stoichiometric relationship in a
Start here…
preaction
massb molesb Mb or VbMolar massb Mb or Vb
End here
62S. Ensign, aqueous reactions
What volume of 0.105 M HClO4 would be required to neutralize 50.0 ml of 0.0875 M
mass moles M or VMolar massaMa or Va
NaOH?
massa molesa Ma or Va
Stoichiometric relationship in a
Start here…
reaction
massb molesb Mb or VbMolar massb Mb or Vb
End here
63S. Ensign, aqueous reactions
What volume of 0.105 M HClO4 would be required to neutralize 50.0 ml of 0.0875 M NaOH?
64S. Ensign, aqueous reactions
What volume of 0.158 M HCl would be required to neutralize 2.87 g of Mg(OH)2?
65S. Ensign, aqueous reactions
What is the total concentration of all solute species present in a solution prepared by mixing 50.0 ml of 0.20 M KClO3 with 25.0 ml of 0 20 M Na SO ??ml of 0.20 M Na2SO4??
66S. Ensign, aqueous reactions