Chapter 8

Reactions in Aqueous Solution

Will a reaction Occur?

Driving Forces in a Chemical ReactionFormation of a solidFormation of waterFormation of a gasTransfer 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

K2CrO4 (aq) + Ba(NO3)2 (aq) →

BaCrO4 (s) + 2 KNO3 (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(NO3)2 (aq) → Ba2+

(aq) + 2 NO3

1- (aq)

Strong Electrolyte – completely dissociates into ions in solution (dissolving.mov)

The reaction is best demonstrated by:

2 K1+ (aq) + CrO42-

(aq) + Ba2+(aq) + 2 (NO3)1- (aq) → BaCrO4 (s) + 2 K1+ (aq) + 2 NO3

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 –NO3

- salts

Na+, K+, NH4+ salts

Cl-, Br-, I- salts, but not when with Ag+, Hg2

2+, and Pb2+

SO42- salts, but not when with Ba2+ , Pb2+,

and Ca2+

Solid Formation - Solubility Rules

InsolubleS2-

CO32-

PO43-

OH-, but not when with Na+, K+, Ca2+

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(NO3)2 (aq) + Na2SO4 (aq) → PbSO4 (s) + 2NaNO3 (aq)

Net Ionic Equation Pb2+ (aq) + SO4

2-(aq) → PbSO4 (s)

Complete Ionic Equation Pb2+ (aq) + 2(NO3)- (aq) + 2Na1+ (aq) + SO4

2-(aq) → PbSO4 (s) + 2Na+ (aq) + 2NO3

- (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 waterStrong acid – completely dissociates in waterHCl(aq) → H1+ (aq) + Cl1- (aq)

Base – “alkalis” slippery in feel and sour in taste – a substance that produces hydroxide (OH) ions in solutionStrong base – completely dissociates in waterNaOH(aq) → Na1+ (aq) + OH1- (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 ModelAcids – anything that produces H1+Bases – anything that produces OH1-Strong – Completely dissociates

Bronsted-LowreyAcids – Proton DonorBases – Proton AcceptorWeak – Slightly Soluble, slight dissociation

Acids & Bases

Acid + Base → Conjugate Acid + Conjugate Base

H2SO4 + NaOH → H2O + Na2SO4

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

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

M1V1 = M2V2

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

MHClVHCl = MNaOHVNaOH

(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

Acids & Bases

Useful pH Equations: pH = -Log[H+] pOH = -Log[OH-] 14 = pH + pOH [H+] = 10(-pH)

[OH-] = 10(-pOH)

[OH-] [H+] = 1 x 10-14

[ ] = symbol of Molarity

Oxidation – Reduction Reactions

3 – Single Replacement Reactions4 – Synthesis5 – Decomposition6 – 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)+O2 (g) → 2 MgO (s)

OxidationMg → Mg 2+ + 2e-

ReductionO2 + 4e- → 2O2-

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

Decomposition – Compound separating into its constituent elements AB → A + B Decomposition.MOV

Combustion Reactions – any reaction that consumes carbon and oxygen to produce carbon dioxide and water

• General Form: CxHy + O2 → CO2 + H2O

• Example: CH4 + 2O2 → CO2 + 2H2O

Formation of a Gas: Combustion Reactions

Top 4 ReactionsSingle ReplacementDouble DisplacementSynthesisDecomposition

Four Types.movsugar_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 CxHy + O2 → CO2 + H2O

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