types of chemical reactions and solution

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Chapter 4Type of Chemical Reactions and Solution Stoichiometric : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chapter 4Type of Chemical Reactions and Solution Stoichiometric Water, Nature of aqueous solutions, types of electrolytes, dilution. Types of chemical reactions: precipitation, acid-base and oxidation reactions. Stoichiometry of reactions and balancing the chemical equations.

Aqueous Solutions : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Aqueous Solutions Water is the dissolving medium, or solvent.

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Figure 4.1: (Left) The water molecule is polar. (Right) A space-filling model of the water molecule.

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Figure 4.2: Polar water molecules interact with the positive and negative ions of a salt assisting in the dissolving process. Cl- Na+ Cl- Na+ H2O

Some Properties of Water : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 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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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Figure 4.3: (a) The ethanol molecule contains a polar O—H bond similar to those in the water molecule. (b) The polar water molecule interacts strongly with the polar O—H bond in ethanol. This is a case of "like dissolving like."

A Solute : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 A Solute dissolves in water (or other “solvent”) changes phase (if different from the solvent) is present in lesser amount (if the same phase as the solvent)

A Solvent : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 A Solvent retains its phase (if different from the solute) is present in greater amount (if the same phase as the solute)

General Rule for dissolution : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 General Rule for dissolution Like dissolve like Polar dissolve polar (water dissolve ethanol) Non-polar dissolve nonpolar (benzene dissolve fat)

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure 4.5: When solid NaCl dissolves, the Na+ and Cl- ions are randomly dispersed in the water.

Electrolytes : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Electrolytes Strong - conduct current efficiently NaCl, HNO3 Weak - conduct only a small current vinegar, tap water Non - no current flows pure water, sugar solution

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure 4.4: Electrical conductivity of aqueous solutions.

Acids : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Acids Strong acids - dissociate completely to produce H+ in solution hydrochloric and sulfuric acid HCl , H2SO4 Weak acids - dissociate to a slight extent to give H+ in solution acetic and formic acid CH3COOH, CH2O

Bases : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 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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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure 4.6: HCl(aq) is completely ionized.

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Figure 4.7: An aqueous solution of sodium hydroxide.

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Figure 4.8: Acetic acid (HC2H3O2) exists in water mostly as undissociated molecules. Only a small percentage of the molecules are ionized.

Molarity : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Molarity Molarity (M) = moles of solute per volume of solution in liters:

Common Terms of Solution Concentration : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 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): (MV)initial=(MV)Final

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Figure 4.10: Steps involved in the preparation of a standard aqueous solution.

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Figure 4.12: Dilution Procedure (a) A measuring pipet is used to transfer 28.7mL of 17.4 M acetic acid solution to a volumetric flask. (b) Water is added to the flask to the calibration mark. (c) The resulting solution is 1.00 M acetic acid.

Types of Solution Reactions : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Types of Solution Reactions Precipitation reactions AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) Acid-base reactions NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l) Oxidation-reduction reactions Fe2O3(s) + Al(s)  Fe(l) + Al2O3(s)

Simple Rules for Solubility : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 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, CrO42, PO43 salts are only slightly soluble.

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Figure 4.13: When yellow aqueous potassium chromate is added to a colorless barium nitrate solution, yellow barium chromate precipitates.

Describing Reactions in SolutionPrecipitation : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Describing Reactions in SolutionPrecipitation 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)

Describing Reactions in Solution (continued) : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Describing Reactions in Solution (continued) 3. Net ionic equation (show only components that actually reacts) Ag+(aq) + Cl(aq)  AgCl(s) Na+ and NO3 are spectator ions.

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Acid-Base Reactions An acid produces H+ ions in water A base produces OH- ions in water An acid is a proton donor A base is a proton acceptor Arrhenius’s concept Bronsted & Lowrys’ concept

Performing Calculations for Acid-Base Reactions : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 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. Remember: n H+ = n OH- (MV) H+ = (MV) OH-

Neutralization Reaction : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 Neutralization Reaction 4.3

Key Titration Terms : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 30 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. movie

Oxidation-Reduction Reactions : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 31 Oxidation-Reduction Reactions (electron transfer reactions) Oxidation half-reaction (lose e-) Reduction half-reaction (gain e-)

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 32

Redox Reactions : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 33 Redox Reactions Many practical or everyday examples of redox reactions: Corrosion of iron (rust formation) Forest fire Charcoal grill Natural gas burning Batteries Production of Al metal from Al2O3 (alumina) Metabolic processes combustion

Rules for Assigning Oxidation States : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 34 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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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 35

Slide 36: 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 36 Zn is oxidized Cu2+ is reduced Zn is the reducing agent Cu2+ is the oxidizing agent 4.4 Ag+ is reduced Ag+ is the oxidizing agent

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 37 NaIO3 Na = +1 O = -2 3x(-2) + 1 + ? = 0 I = +5 IF7 F = -1 7x(-1) + ? = 0 I = +7 K2Cr2O7 O = -2 K = +1 7x(-2) + 2x(+1) + 2x(?) = 0 Cr = +6 4.4

Balancing by Half-Reaction Method : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 38 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

Balancing by Half-Reaction Method (continued) : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 39 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.

Half-Reaction Method - Balancing in Base : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 40 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.

Balancing Redox Equations : 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 41 Balancing Redox Equations Example: Balance the following redox reaction: Cr2O72- + Fe2+ Cr3+ + Fe3+ (acidic soln) 1) Break into half reactions: Cr2O72- Cr3+ Fe2+ Fe3+

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 42 Balancing Redox Equations

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 43 Balancing Redox Equations 2) Balance each half reaction (cont)

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 44 Balancing Redox Reactions 3) Multiply by integer so e- lost = e- gained

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 45 Balancing Redox Reactions 3) Multiply by integer so e- lost = e- gained 6 Fe2+ 6 Fe3+ + 6 e- 6 e- + Cr2O72- + 14 H+ 2 Cr3+ + 7 H2O 4) Add both half reactions Cr2O72- + 6 Fe2+ + 14 H+ 2 Cr3+ + 6 Fe3+ + 7 H2O

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 46 Balancing Redox Reactions Cr2O72- + 6 Fe2+ + 14 H+ 2 Cr3+ + 6 Fe3+ + 7 H2O 5) Check the equation 2 Cr 2 Cr 7 O 7 O 6 Fe 6 Fe 14 H 14 H +24 + 24

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 47 Balancing Redox Reactions Procedure for Basic Solutions: Divide the equation into 2 incomplete half reactions one for oxidation one for reduction

Slide 48: 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 48 Balancing Redox Reactions Balance each half-reaction: balance elements except H and O balance O atoms by adding H2O balance H atoms by adding H+ add 1 OH- to both sides for every H+ added combine H+ and OH- on same side to make H2O cancel the same # of H2O from each side balance charge by adding e- to side with greater overall + charge different

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 49 Balancing Redox Equations Multiply each half reaction by an integer so that # e- lost = # e- gained Add the half reactions together. Simply where possible by canceling species appearing on both sides of equation Check the equation # of atoms total charge on each side

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 50 Balancing Redox Reactions Example: Balance the following redox reaction. NH3 + ClO- Cl2 + N2H4 (basic soln) NH3 N2H4 ClO- Cl2 1) Break into half reactions:

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 51 Balancing Redox Reactions 2) Balance each half reaction: + 2 OH- + 2 OH-

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 52 Balancing Redox Reactions 2) Balance each half reaction:

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 53 Balancing Redox Reactions 3) Multiply by integer so # e- lost = # e- gained 2 NH3 + 2 OH- N2H4 + 2 H2O + 2 e- 2 e- + 2 ClO- + 2 H2O Cl2 + 4 OH- 4) Add both half reactions 2 NH3 + 2 OH- + 2ClO- + 2 H2O N2H4 + 2 H2O + Cl2 + 4 OH-

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 54 Balancing Redox Reactions 5) Cancel out common species 2 NH3 + 2 OH- + 2 ClO- + 2 H2O N2H4 + 2 H2O + Cl2 + 4 OH- 2 6) Check final equation: 2 N 2 N 6 H 6 H 2 Cl 2 Cl 2 O 2 O -2 -2

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 55

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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 56