Chapter 4 Type of Chemical Reactions and Solution Stoichiometric

Chapter 4 Type 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. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

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

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

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

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

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

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

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

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

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

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

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

Practice Example A solution containing Ni2+ is prepared by dissolving g of pure nickel in nitric acid and diluting to 1.00 L. A mL aliquot is then diluted to mL. What is the molarity of the final solution? (Atomic weight: Ni = 58.70). Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

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

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

Describing Reactions in Solution Precipitation
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) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

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

Neutralization Reaction
acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H2O H+ + Cl- + Na+ + OH Na+ + Cl- + H2O H+ + OH H2O Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4.3

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

Oxidation-Reduction Reactions
(electron transfer reactions) 2Mg (s) + O2 (g) MgO (s) 2Mg Mg2+ + 4e- Oxidation half-reaction (lose e-) Reduction half-reaction (gain e-) O2 + 4e O2- 2Mg + O2 + 4e Mg2+ + 2O2- + 4e- 2Mg + O MgO Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

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

Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)
Zn Zn2+ + 2e- Zn is oxidized Zn is the reducing agent Cu2+ + 2e Cu Cu2+ is reduced Cu2+ is the oxidizing agent Copper wire reacts with silver nitrate to form silver metal. What is the oxidizing agent in the reaction? Cu (s) + 2AgNO3 (aq) Cu(NO3)2 (aq) + 2Ag (s) Cu Cu2+ + 2e- Ag+ + 1e Ag Ag+ is reduced Ag+ is the oxidizing agent Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Oxidation numbers of all the elements in the following ? F = -1 7x(-1) + ? = 0 I = +7 K2Cr2O7 NaIO3 Na = +1 O = -2 O = -2 K = +1 3x(-2) ? = 0 7x(-2) + 2x(+1) + 2x(?) = 0 I = +5 Cr = +6 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

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

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

Balancing Redox Equations
Example: Balance the following redox reaction: Cr2O Fe Cr3+ + Fe3+ (acidic soln) 1) Break into half reactions: Cr2O Cr3+ Fe Fe3+ Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

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

2) Balance each half reaction: ClO Cl2 2 ClO Cl2 2 ClO Cl H2O 2 ClO H Cl H2O + 4 OH- + 4 OH- 2 ClO H2O Cl H2O + 4 OH- 2 ClO H2O Cl2 + 4 OH- 2 e- + 2 ClO H2O Cl2 + 4 OH- Copyright©2000 by Houghton Mifflin Company. All rights reserved.

3) Multiply by integer so # e- lost = # e- gained 2 NH OH N2H H2O + 2 e- 2 e- + 2 ClO H2O Cl2 + 4 OH- 4) Add both half reactions 2 NH OH- + 2ClO- + 2 H2O N2H H2O + Cl2 + 4 OH- Copyright©2000 by Houghton Mifflin Company. All rights reserved.

5) Cancel out common species 2 NH OH ClO- + 2 H2O N2H H2O + Cl2 + 4 OH- 2 6) Check final equation: 2 NH ClO N2H4 + Cl2 + 2 OH- 2 N 2 N 6 H 6 H 2 Cl 2 Cl 2 O 2 O -2 -2 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Practice Example In the following the oxidizing agent is: 5H2O2 + 2MnO4- + 6H+  2Mn2+ + 8H2O + 5O2 a. MnO4- b. H2O2 c. H+ d. Mn2+ e. O2 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

ANSWER STUDENT CD: Visualization: Conductivities of Aqueous Solutions HMCLASS PRESENT: Video: Conductivities of Aqueous Solutions HMCLASS PREP: Figure 4.4 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

ANSWER HMCLASS PREP: Figure 4.2 STUDENT CD: Visualization: The Dissolution of a Solid in a Liquid HMCLASS PRESENT: Animation: The Dissolution of a Solid in a Liquid Copyright©2000 by Houghton Mifflin Company. All rights reserved.

ANSWER STUDENT CD: Visualization: Conductivities of Aqueous Solutions HMCLASS PRESENT: Video: Conductivities of Aqueous Solutions HMCLASS PREP: Figure 4.4 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

ANSWER HMCLASS PREP: Figure 4.2 STUDENT CD: Visualization: The Dissolution of a Solid in a Liquid HMCLASS PRESENT: Animation: The Dissolution of a Solid in a Liquid Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Chapter 4 Type of Chemical Reactions and Solution Stoichiometric

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Chapter 4 Type of Chemical Reactions and Solution Stoichiometric

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