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Copyright©2000 by Houghton Mifflin Company. All rights reserved.
1
Ch 4: Types of Rxns and Solution Stoik
• Read for comprehension pp 131 - 147
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2
Aqueous Solutions
Water is the dissolving medium, or solvent.
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3
Some Properties of Water
Water is “bent” or V-shaped. The O-H bonds are covalent. Water is a polar molecule. Hydration occurs when salts dissolve in
water.
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4
Figure 4.1 The Water Molecule is Polar
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5
Solute/Solvent
Solute: -- dissolves in water (or other “solvent”) --is present in lesser amount (if the same phase as
the solvent)Solvent: --is present in greater amount (if the same phase as
the solute)
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6
Like Dissolves Like
• Rule of thumb: polar solvents dissolve
polar/ionic solutes
nonpolar solvents dissolve
nonpolar solutes
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7
Figure 4.2Polar Water Molecules Interact with the Positive and Negative Ions of a
Salt
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8
Figure 4.3Polar Bond in ethanol
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9
Figure 4.5BaCl2 Dissolving
Dissociation:
BaCl2(s) --> Ba2+(aq) + 2Cl-(aq)
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10
Electrolytes
Strong - conduct current efficiently Salts: NaCl
Strong acids: HNO3
Strong bases
Weak - conduct only a small current Weak acids/bases:acetic
acid/ammoniaTap water
Non - no current flowspure water, sugar solution
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11
Acids
Strong acids - dissociate completely to produce H+ in solution
hydrochloric and sulfuric acid
Weak acids - dissociate to a slight extent to give H+ in solution
acetic and formic acid
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12
Figure 4.6HCI (aq) is Completely Ionized
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13
Figure 4.8Acetic Acid in Water
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Bases
Strong bases - react completely with water to give OH ions.
sodium hydroxide
Weak bases - react only slightly with water to give OH ions.
ammonia
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15
Figure 4.7An Aqueous Solution of Sodium Hydroxide
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Figure 4.9The Reaction of NH3 in Water
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17
Molarity
Molarity (M) = moles of solute per volume of solution in liters:
M
M
= =
=
molaritymoles of soluteliters of solution
HClmoles of HCl
liters of solution3
62
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18
Common Terms of Solution Concentration
Stock - routinely used solutions prepared in concentrated form.
Concentrated - relatively large ratio of solute to solvent. (5.0 M NaCl)
Dilute - relatively small ratio of solute to solvent. (0.01 M NaCl)
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19
Figure 4.10Preparation of a Standard
Solution
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20
Figure 4.11(a) A Measuring Pipet (b) A
Volumetric (transfer) Pipet
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21
Types of Solution Reactions
Precipitation reactionsAgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
Acid-base reactionsNaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)
Oxidation-reduction reactionsFe2O3(s) + Al(s) Fe(l) + Al2O3(s)
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22
Simple Rules for Solubility
1. Most nitrate (NO3) salts are soluble.
2. Most alkali (group 1A) salts and NH4+ are soluble.
3. Most Cl, Br, and I salts are soluble (NOT Ag+, Pb2+, Hg22+)
4. Most sulfate salts are soluble (NOT BaSO4, PbSO4, HgSO4, CaSO4)
5. Most OH salts are only slightly soluble (NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble)
6. Most S2, CO32, CrO4
2, PO43 salts are only slightly soluble.
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23
Figure 4.14The Reaction of K2CrO4(aq) and
Ba(NO3)2(aq)
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Describing Reactions in Solution
1. Molecular equation (reactants and products as compounds)
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
2. Complete ionic equation (all strong electrolytes shown as ions)
Ag+(aq) + NO3(aq) + Na+(aq) + Cl(aq)
AgCl(s) + Na+(aq) + NO3(aq)
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25
Describing Reactions in Solution (continued)
3. Net ionic equation (show only components that actually react)
Ag+(aq) + Cl(aq) AgCl(s)
Na+ and NO3 are spectator ions.
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26
Figure 4.16The Reaction of KCI(aq) and AgNO3(aq)
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27
Performing Calculations for Acid-Base Reactions
1. List initial species and predict reaction.
2. Write balanced net ionic reaction.
3. Calculate moles of reactants.
4. Determine limiting reactant.
5. Calculate moles of required reactant/product.
6. Convert to grams or volume, as required.
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28
Key Titration Terms
Titrant - solution of known concentration used in titration
Analyte - substance being analyzed
Equivalence point - enough titrant added to react exactly with the analyte
Endpoint - the indicator changes color so you can tell the equivalence point has been reached.
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29
Rules for Assigning Oxidation States
1. Oxidation state of an atom in an element = 0
2. Oxidation state of monatomic element = charge
3. Oxygen = 2 in covalent compounds (except in peroxides where it = 1)
4. H = +1 in covalent compounds
5. Fluorine = 1 in compounds
6. Sum of oxidation states = 0 in compounds Sum of oxidation states = charge of the ion
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30
Balancing by Half-Reaction Method
1. Write separate reduction, oxidation reactions.
2. For each half-reaction:
Balance elements (except H, O)
Balance O using H2O
Balance H using H+
Balance charge using electrons
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31
Balancing by Half-Reaction Method (continued)
3. If necessary, multiply by integer to equalize electron count.
4. Add half-reactions.
5. Check that elements and charges are balanced.
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32
Half-Reaction Method - Balancing in Base
1. Balance as in acid.
2. Add OH that equals H+ ions (both sides!)
3. Form water by combining H+, OH.
4. Check elements and charges for balance.