AP Chemistry Super Saturday Review I tried to include as much review material as possible in this session. Work on practice tests and review the Bozeman videos for other material.
AP Chemistry Super Saturday Review 5 Essentials Know the basics – writing formulas, writing and balancing equations, dimensional analysis, atomic theory, acid-base theories (Arrhenius and Bronsted Lowry), VSEPR, kinetic molecular theory, and collision theory.
5 Essentials 2. Atomic and Molecular Structures Atomic structures (like electron configurations) will help explain relationships on the periodic table which explains many physical and chemical properties. Molecular structures involves Lewis structures and VSEPR to determine shapes which describes polarities thus describing intermolecular forces which describes many physical properties.
5 Essentials 3. Stoichiometric Calculations Basic stoichiometry, limiting reactants, titration calculations, and empirical formulas. 4. Principles of chemical kinetics, equilibrium, And thermodynamics Kinetics- describes the speed in which substances react Equilibrium – used to determine the extent of a reaction or the composition at equilibrium Thermodynamics – explains why chemical reactions happen in terms of kinetic and potential energies
5 Essentials Representation and Interpretation Be able to draw what is happening at the molecular level and read and interpret graphs and data tables
Net Ionic Equations Graphic: Wikimedia Commons User Tubifex
Solubility Rules – AP Chemistry All sodium, potassium, ammonium, and nitrate salts are soluble in water. Memorization of other “solubility rules” is beyond the scope of this course and the AP Exam. • What dissociates (“breaks apart”) – Aqueous solutions of the following: • All strong acids (HCl, HBr, HI, HNO3, H2SO4, and HClO4) • Strong bases (group I and II hydroxides) • Soluble salts
Write the net ionic for the following:1. Solutions of lead nitrate and potassium chloride are mixed2. Solutions of sulfuric acid and potassium hydroxide are mixed.3. Solid sodium hydroxide is mixed with acetic acid
Big Idea #6:Chemical Equilibrium 2NO2(g) 2NO(g) + O2(g) Sketch a graph of change in concentration vs. Time for the reaction above
2NO2(g) 2NO(g) + O2(g) Be able to explain the variance in slope
Law of Mass Action For the reaction: jA + kB lC + mD WhereKis the equilibrium constant, and is unitless
Product Favored Equilibrium Large values for K signify the reaction is “product favored” When equilibrium is achieved, most reactant has been converted to product
Reactant Favored Equilibrium Small values for K signify the reaction is “reactant favored” When equilibrium is achieved, very little reactant has been converted to product
Writing an Equilibrium Expression Write the equilibrium expression for the reaction: 2NO2(g) 2NO(g) + O2(g) K =???
Conclusions about Equilibrium Expressions • The equilibrium expression for a reaction is the reciprocal for a reaction written in reverse 2NO2(g) 2NO(g) + O2(g) 2NO(g) + O2(g) 2NO2(g)
Conclusions about Equilibrium Expressions • When the balanced equation for a reaction is multiplied by a factor n, the equilibrium expression for the new reaction is the original expression, raised to the nth power. 2NO2(g) 2NO(g) + O2(g) NO2(g) NO(g) + ½O2(g)
If the equilibrium constant for A+B C is 0.208 then the equilibrium constant for 2C 2A + 2B is Answer: D
Equilibrium Expressions Involving Pressure For the gas phase reaction: 3H2(g) + N2(g) 2NH3(g)
Heterogeneous Equilibria • The position of a heterogeneous equilibrium does not depend on the amounts of pure solids or liquids present Write the equilibrium expression for the reaction: PCl5(s) PCl3(l) + Cl2(g) Pure solid Pure liquid
The Reaction Quotient For some time, t, when the system is not at equilibrium, the reaction quotient, Q takes the place of K, the equilibrium constant, in the law of mass action. jA + kB lC + mD
Significance of the Reaction Quotient • If Q = K, the system is at equilibrium • If Q > K, the system shifts to the left, consuming products and forming reactants until equilibrium is achieved • If Q < K, the system shifts to the right, consuming reactants and forming products until equilibrium is achieved
If you mixed 5.0 mol B, 0.10 mol C, and 0.0010 mol A in a one-liter container, which direction would the reaction initially proceed?
LeChatelier’s Principle Henry Le Chatelier When a system at equilibrium is placed under stress, the system will undergo a change in such a way as to relieve that stress and restore a state of equilibrium.
Le Chatelier Translated: When you take something away from a system at equilibrium, the system shifts in such a way as to replace some of what you’ve taken away. When you add something to a system at equilibrium, the system shiftsin such a way as touse up some of what you’ve added.
Acid Equilibrium and pH SørenSørensen
Acid/Base Definitions • Arrhenius Model • Acids produce hydrogen ions in aqueous solutions • Bases produce hydroxide ions in aqueous solutions • Bronsted-Lowry Model • Acids are proton donors • Bases are proton acceptors
Acid Dissociation HA H+ + A- AcidProtonConjugate base Alternately, H+ may be written in its hydrated form, H3O+ (hydronium ion)
Reaction of Weak Bases with Water The base reacts with water, producing its conjugate acid and hydroxide ion: CH3NH2 + H2O CH3NH3+ + OH- Kb = 4.38 x 10-4
Kb for Some Common Weak Bases Many students struggle with identifying weak bases and their conjugate acids.What patterns do you see that may help you?
Reaction of Weak Bases with Water The generic reaction for a base reacting with water, producing its conjugate acid and hydroxide ion: B + H2O BH+ + OH- (Yes, all weak bases do this – DO NOT try to make this complicated!) Ex. Write the reaction of ammonia with water
Self-Ionization of Water H2O + H2O H3O+ + OH- At 25, [H3O+] = [OH-] = 1 x 10-7 Kw is a constant at 25 C: Kw = [H3O+][OH-] Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-14
Calculating pH, pOH pH = -log10(H3O+) pOH = -log10(OH-) Relationship between pH and pOH pH + pOH = 14 Finding [H3O+], [OH-] from pH, pOH [H3O+] = 10-pH [OH-] = 10-pOH
A Weak Acid Equilibrium Problem What is the pH of a 0.50 M solution of acetic acid, HC2H3O2, Ka = 1.8 x 10-5 ? (answer=4.52)
A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH3, Kb= 1.8 x 10-5 ? (answer=9.48)
Acid-Base Properties of Salts To determine if a salt is acidic or basic, determine the stronger parent. Examples: KCl NH4Cl NaC2H3O2 NaCl KNO3
Acid-Base Properties of SaltsIf both parents are weak: • IF Ka for the acidic ion is greater than Kb for the basic ion, the solution is acidic • IF Kb for the basic ion is greater than Ka for the acidic ion, the solution is basic • IF Kb for the basic ion is equal to Ka for the acidic ion, the solution is neutral
Buffered Solutions A solution that resists a change in pH when either hydroxide ions or protons are added. Buffered solutions contain either: A weak acid and its salt A weak base and its salt
Acid/Salt Buffering Pairs The salt will contain the anion of the acid, and the cation of a strong base (NaOH, KOH)
Base/Salt Buffering Pairs The salt will contain the cation of the base, and the anion of a strong acid (HCl, HNO3)
Titration of an Unbuffered Solution A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH
Titration of a Buffered Solution A solution that is 0.10 M CH3COOH and 0.10 M NaCH3COO is titrated with 0.10 M NaOH
Comparing Results Buffered Unbuffered
Henderson-Hasselbalch Equation This is an exceptionally powerful tool that can be used in your problem solving.
Title: A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH Endpoint is above pH 7
Title: Endpoint is at pH 7 A solution that is 0.10 M HCl is titrated with 0.10 M NaOH
Title: A solution that is 0.10 M NaOH is titrated with 0.10 M HCl Endpoint is at pH 7 It is important to recognize that titration curves are not always increasing from left to right.