Chapter 8 Reactions in Aqueous Solution

Will a reaction Occur? Driving Forces in a Chemical Reaction  Formation of a solid  Formation of water  Formation of a gas  Transfer of electrons

Types of Reactions Double Replacement Reactions 1. Precipitation Reactions 2. Acid and Base Reactions Red-ox Reactions 3. Single Replacement Reactions 4. Synthesis Reactions 5. Decomposition Reactions 6. Combustion Reactions

Double Replacement Reactions 1 – Precipitation Reactions 2 – Acid and Base Reactions

Double Replacement Reactions – Reactions involving two compounds in which two elements switch places General Form: AB + CD → AD + CB Double Replacement

Solid Formation: Precipitation Reactions (#1) Precipitation Reaction – a reaction that produces a precipitate K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq) → BaCrO 4 (s) + 2 KNO 3 (aq) In order to know what will form, you need to know what is in solution!

Solid Formation In solution, most compounds break down into their ions Ba(NO 3 ) 2 (aq) → Ba 2+ (aq) + 2 NO 3 1- (aq) Strong Electrolyte – completely dissociates into ions in solution (dissolving.mov)dissolving.mov The reaction is best demonstrated by: 2 K 1+ (aq) + CrO 4 2- (aq) + Ba 2+ (aq) + 2 (NO 3 ) 1- (aq) → BaCrO 4 (s) + 2 K 1+ (aq) + 2 NO 3 1- (aq)

Solid Formation - Solubility Rules Soluble solid – a solid that dissolves in water Insoluble solid – a solid that does not dissolve in water Slightly soluble solid – a small amount of the solid dissolves in water

Solid Formation - Solubility Rules Soluble –  NO 3 - salts  Na+, K+, NH 4 + salts  Cl-, Br-, I- salts, but not when with Ag+, Hg 2 2+, and Pb 2+  SO 4 2- salts, but not when with Ba 2+, Pb 2+, and Ca 2+

Solid Formation - Solubility Rules Insoluble  S 2-  CO 3 2-  PO 4 3-  OH-, but not when with Na +, K +, Ca 2+

Visualizing Solubility

Describing reactions in Aqueous Solutions Molecular Equation – Represents all molecules involved in a reaction Complete Ionic Equation – represents all of the ions in the reacting solution Net Ionic Equation – shows only the ions directly involved in the reaction, spectator ions are not included Spectator Ions – ions that are listed in the complete ionic equation, but not in the net ionic equation. They are not involved in the reaction.

Describing reactions in Aqueous Solutions Molecular Equation Pb(NO 3 ) 2 (aq) + Na 2 SO 4 (aq) → PbSO 4 (s) + 2NaNO 3 (aq) Net Ionic Equation Pb 2+ (aq) + SO 4 2- (aq) → PbSO 4 (s) Complete Ionic Equation Pb 2+ (aq) + 2(NO 3 ) - (aq) + 2Na 1+ (aq) + SO 4 2- (aq) → PbSO 4 (s) + 2Na + (aq) + 2NO 3 - (aq)

Describing reactions in Aqueous Solutions Write the balanced molecular, ionic, and net ionic equations:  Aqueous sodium chloride is added to aqueous silver nitrate to form solid silver chloride plus sodium nitrate

Formation of Water: (#2) Acids & Bases Acid – “acidus” or sour – a substance that produces H+ ions (protons) when it is dissolved in water  Strong acid – completely dissociates in water  HCl(aq) → H 1+ (aq) + Cl 1- (aq)

Base – “alkalis” slippery in feel and sour in taste – a substance that produces hydroxide (OH) ions in solution  Strong base – completely dissociates in water  NaOH(aq) → Na 1+ (aq) + OH 1- (aq) Formation of Water: (#2) Acids & Bases

Formation of Water: Acids & Bases When acids and bases react, they neutralize each other Neutralization – When a strong acid and strong base react to form water and an aqueous salt

Acids & Bases Write the molecular, Complete ionic, and net ionic equation for the reaction of nitric acid and potassium hydroxide

Arrhenius Model  Acids – anything that produces H1+  Bases – anything that produces OH1-  Strong – Completely dissociates Bronsted-Lowrey  Acids – Proton Donor  Bases – Proton Acceptor  Weak – Slightly Soluble, slight dissociation Acids & Bases

Acid + Base → Conjugate Acid + Conjugate Base H 2 SO 4 + NaOH → H 2 O + Na 2 SO 4 To find the conjugate acid – follow the hydrogen To find the conjugate base - follow the anion from the acid Acids & Bases

Concentration – How much material is dissolved in your solution  Concentrated – much material is dissolved  Dilute – little material is dissolved Molarity – Unit of Concentration in Chemistry  The number of MOLES of material per LITER of solution  Unit = M  M = moles / L  Example: 8M HCl = an 8 Molar solution of Hydrochloric Acid, 8 moles of HCl are dissolved in every liter of the solution Acids & Bases

Titration – measuring the exact amount of an acid that reacts with an exact amount of a base.  If you know the concentration of one of the solutions, it can be used to calculate the concentration of the other Equivalence point – the point of neutralization, the amount of acid and base are equal in solution Standard Solutions – solutions of known concentration Acids & Bases

Burette – the tool used to dispense an exact amount of a standard solution in a titration Indicators – substances that change from clear to a color at a specific pH

Acids & Bases Titration Curve – graphing pH of solution versus volume of base added M 1 V 1 = M 2 V 2  Used in Acid/Base  Used in Dilution

Example Problem: A 100.0mL solution of 0.5M HCl(aq) is titrated with 0.10M NaOH. What volume of NaOH do you need to reach equivalence? M 1 V 1 = M 2 V 2 M HCl V HCl = M NaOH V NaOH (100.0mL HCl)(0.50M HCl) = (X mL NaOH)(0.10M NaOH) X = 500.0mL NaOH Acids & Bases

pH – measure of acid strength, equal to the molarity of the H+ ions in solution  1-14 scale  1 = strongest acid  14 = strongest base  7 = neutral  Logarithmic Scale, a change of 1 pH is different in concentration by a factor of 10! pOH – measure of base strength, equal to the molarity of the OH- ions in solution Acids & Bases

Useful pH Equations:  pH = -Log[H+]  pOH = -Log[OH-]  14 = pH + pOH  [H+] = 10 (-pH)  [OH-] = 10 (-pOH)  [OH-] [H+] = 1 x  [ ] = symbol of Molarity

Oxidation – Reduction Reactions 3 – Single Replacement Reactions 4 – Synthesis 5 – Decomposition 6 – Combustion Reactions

Oxidation - Reduction Oxidation/Reduction Reaction – a reaction that involves the transfer of electrons  Usually between a metal and nonmetal to form an ionic compound  Involves 2 half reactions Oxidation – loosing electrons Reduction – gaining electrons Potassium.mov zinc&iodine.mov

Oxidation - Reduction

 2 Mg (s)+O 2 (g) → 2 MgO (s)  Oxidation Mg → Mg e-  Reduction O 2 + 4e- → 2O 2- Oxidation - Reduction

Single Replacement Reaction – Single element combines with a compound, replacing one of the members of the compound. A + BC → AC + B Oxidation – Reduction: (#3) Single Replacement

Activity / Electromotive Series Metals Nonmetals lithium fluorine potassium chlorine calcium bromine sodium iodine magnesium aluminum zinc chromium iron nickel tin lead hydrogen copper silver mercury platinum gold Used to predict if a red-ox reaction will occur Metals replace metals. Nonmetals replace nonmetals. The replacing substance must be more active (higher on the list) than the substance it replaces for a reaction to occur. Oxidation – Reduction

Predict if a chemical reaction will occur in the following redox reactions: iron + copper (II) sufate  chlorine + potassium bromide  copper + zinc chloride  Oxidation - Reduction

Oxidation – Reduction: (#4)Synthesis + (#5)Decomposition Synthesis – Elements combining to make a compound  A + B → AB  Synthesis.MOV Synthesis.MOV Decomposition – Compound separating into its constituent elements  AB → A + B  Decomposition.MOV Decomposition.MOV

Combustion Reactions – any reaction that consumes carbon and oxygen to produce carbon dioxide and water General Form: C x H y + O 2 → CO 2 + H 2 O Example: CH 4 + 2O 2 → CO 2 + 2H 2 O Formation of a Gas: Combustion Reactions

Top 4 Reactions  Single Replacement  Double Displacement  Synthesis  Decomposition  Four Types.mov Four Types.mov  sugar_potassiumchlorate.mov sugar_potassiumchlorate.mov Other Ways to Classify Reactions

Review – Types of Reactions and Driving Forces Double Displacement AB + CD → AD + CB  Acid Base – Formation of water  Multiple - Formation of gas  Precipitation - Formation of a solid Oxidation-Reduction – Driving force for all is transfer of electrons  Single Replacement A + BC → AC + B  Synthesis A + B → AB  Decomposition AB → A + B  Combustion C x H y + O 2 → CO 2 + H 2 O

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