Download Zumdahl`s Chap. 4 - The University of Texas at Dallas

Zumdahl’s
Chapter 4
Chemical Reactions and
Solution Stoichiometry
Chapter Contents
Water
 Aqueous Solutions


Electrolytes


Strong and Weak
Nonelectrolytes
Solution
Composition
 Chemical Reactions


Describing Reactions
 Stoichiometry
 Acid-Base Reactions

Precipitations


Oxidation-Reduction


Titration
Oxidation States
Balancing Redox

Half Reaction Method
Water, H2O, Universal Solvent
Polar (covalent) Molecule ( = 1.4)
 Hydration (high dielectric constant)

Hydration spheres cradle ions
 Electric field dampening reduces ppt


Hydrogen Bonding


( –H•••O– )
O lone pair binds neighbor H (at ~ 15%)
“Like dissolves like.”
Electrolytes

Ions conduct electricity


NaCl, HNO3, Ca(OH)2, MgSO4, soap, etc.
Weak Electrolytes are mostly molecular.


(& mobility)
Strong Electrolytes are fully ionized.


in proportion to their number
Tap water, CH3CO2H, (NH4)OH, etc.
Nonelectrolytes do not ionize.

Pure water, alcohols, sugars, etc.
Solution Composition

Concentration as mol L–1 or Molarity

I.e., moles solute per Liter of final solution


Dilution conserves number of moles


Alt., molality, moles solute per 1 kg solvent.
C1 V1 = C2 V2 solves dilution problems.
Molarity ideal for dispensing solutions.
Controlled volume = controlled moles solute
 Convert to moles by CV, then apply rxn. stoich.

Types of Chemical Reactions

Categorized by motivational factors!

Le Châtlier: “Rxn. favors missing components.”
Gas Evolution (gas leaves the solution )
 Precipitation (solid leaves the solution )
 Weak electrolyte (ions leave the solution)



E.g., acid+base makes water!
Redox
(electrons find happiness)
MEMORIZE THE
SOLUBILITY TABLE
N choice.
Description of Solution
Reactions

Molecular Equations:


Complete Ionic Equations:


HCl + KOH  KCl + H2O
H+ + Cl– + K+ + OH–  K+ + Cl– + H2O
Net Ionic Equation:

H+(aq) + OH–(aq)  H2O(l)
Precipitation Stoichiometry
Write balanced net ionic reaction.
 Determine limiting reactant.


Use Concentration  Volume to get moles.
Calculate product moles.
 If required, calculate leftover reactants.


Use moles divided by Final Volume to get
concentration of leftovers.
Acid – Base Titrations
If at least one is “strong,” neutralization
will be complete because H2O is very
“weak!”
 Choose indicator for strong visual signal
at completion.
 For titrant, CV dispensed gives moles.
 Stoichiometry determines moles sample
 Sample moles / sample vol = original M

Oxidation – Reduction
Reactions: REDOX
Oxidation: loss of electrons (e.g., metals)
 Reduction: gain of electrons (e.g., F2)
 BOTH MUST OCCUR (because electrons conserved)
 Oxidizing Agent gets Reduced (and converse)
 Oxidation States (imagine everything ionic)

Add up to charge on species
 Always zero for neutral elements
 Memrize the algorithm.

Solution Redox Stoichiometry
Determine redox agents
 Use Half Reaction Methods


Balance red- and ox- separately with e–
Balance excess O with H2O
 Balance excess H with H+

Scale each for equal number of e– transfer
 Add & cancel (esp. e–) equally left & right
 “Titrate” equation algebraically if OH–
