Exam 2 Preparation for CH302 - Spring 2019

ALL students will check with their specific class webpage (canvas) to determine the time and place (room) for their specific exam. Students are NOT allowed to go to any exam time/place they want. Make sure to confirm with your professor/class announcements page.


What we provide on Exams We will provide all students with:

  • copy of the exam
  • an answer sheet - aka: bubblesheet
  • a Periodic Table Handout sheet
  • scratch paper if needed

Note that the periodic table handout is available on the gchem site in the appendix under "Exam Preparation". Here is a direct link to the Periodic Table Handout for Exam 2 (same as Exam 1). Also, on the back of the Periodic Table handout will be a listing of all necessary ionization constants for weak acids and weak bases. This will be a shorter version of this one on the gchem site.

Coverage: Exam 2 covers all the material that was covered on LE's 09-20 and HW's 04-06. The exam covers all of Chapters 8 and 9 (Chemical Equilibria + Acid/Base Equilibria).

Questions: The exam will have at least 20 multiple choice questions (5 points each) but could go up to 25 questions (4 points each). Point values are included with all questions. We will only grade you by what is bubbled in on the answer sheet. We will not look at your exam copy for answers, nor consider them in any way. Bubble carefully and correctly.

Bring the Following to the Exam

  • a pencil(s) - mechanical or wood
  • scanner only reads pencil - no ink!
  • bring eraser if you are prone to mistakes
  • bring a non-programmable, non-graphing, scientific calculator
  • we provide the rest - see top of page

DO NOT bring...

  • ink pens
  • graphing calculator
  • any type of programmable calculator
  • electronic devices - including earbuds, etc...
  • smart watches - put away that Apple Watch!
  • small creatures - or large... no creatures

Concepts • Equations - 8 Chemical Equilibria

aA   +   bB   ⇌   cC   +   dD

mass action =
activity, K aCc aDd
aAa aBb


mass action =
conc, Kc [C]c [D]d
[A]a [B]b


mass action =
press, Kp PCc PDd
PAa PBb


ΔG = ΔG ° + RT lnQ

ΔG ° = –RT lnK

K = exp(–ΔG °/RT )


Kp = Kc(RT )Δn

Note: remember to use 0.08206 L atm/mol K
for the value of R in this equation

some equilibrium conditions

  1. all concentrations and pressures are NOT changing
  2. kinetics: rateforward = ratereverse
  3. thermo: ΔG = 0
  4. mass action: Q = K
  5. free energy of the system is at a minimum for the stated conditions

Le Chatlier's Principle:
A stress of changing concentration or pressure will change Q. A change in temperature will change K. The system will respond accordingly:

if Q < K    shift right →

if Q > K    ← shift left

if Q = K    no change ⇌

Van't Hoff Equation:

ln K2 K1 = ∆H R 1 T1 1 T2

Concepts • Equations - 9 Acid/Base Equilibria

acid / base theory

(Lowry-Bronsted definition)

acid = a proton donor

base = a proton acceptor


Dr. McCord's
Acid/Base Trainer Page

buffer = a solution that resists pH change

water

Kw = [H+][OH-]

pH = -log[H+]

[H+] = 10-pH

pOH = -log[OH-]

[OH-] = 10-pOH

weak acids / weak bases

acid reaction:
HA(aq) ⇌ H+(aq) + A-(aq)

Ka  =   [H+][A-]
[HA]

base reaction:
B(aq) (+ H2O) ⇌ OH-(aq) + BH+(aq)

Kb  =   [OH-][B+]
[B]

conjugate pairs:   Kw = KaKb

buffer composition

a buffer consists of a weak acid AND its conjugate base, or a weak base AND its conjugate acid. BOTH conjugates must be present. You cannot have a buffer with any strong acid and its conjugate or strong base and its conjugate. Buffers MUST come from weak acids and bases.

Henderson Hasselbalch

pH  = pKa  +  log [base]
[acid]

Note that only outcomes 5-12 for Chemical Equilibrium will be tested on Exam 2. However, you still must know and understand outcomes 1-4 as well.

Learning Outcomes for Chemical Equilibria

Students will be able too...

  1. Know the importance of the activity of a species and how it relates to concentration, pressure, and equilibrium.
  2. Write the mass action expression for homogeneous and heterogeneous equilibria.
  3. Determine new values for K when combining multiple reactions.
  4. Know the difference between Kp and Kc and be able to convert between the two.
  5. Describe the relationship between free energy and equilibrium
  6. Convert ΔG to Q, as well as ΔG° to K and vice versa.
  7. Determine if a system is at equilibrium and if not which direction the reaction will shift to achieve equilibrium.
  8. Set up and solve a RICE table for a multitude of various reaction types.
  9. Calculate the concentration/pressure of all species at equilibrium.
  10. Show a complete understanding of Le Chatelier's principle.
  11. Predict the response of a reaction to an applied stress (concentration, pressure, volume, temperature) both qualitatively and quantitatively.
  12. Calculate the new value of K when the temperature changes to a new value.

Learning Outcomes for Acid/Base Equilibria

Students will be able to...

  1. Understand the strength of an acid (or base) as determined by the percent of ionization in solution.
  2. Identify strong and weak acids and bases.
  3. Identify acid/base conjugate pairs and their relative strengths.
  4. Understand the process of auto-ionization of water and what is meant by acidic, basic, and neutral.
  5. Know the value of Kw at 25°C, and the relationship between Ka and Kb for a conjugate pair.
  6. Convert between hydronium ion concentration, hydroxide ion concentration, pH and pOH for a given solution.
  7. Determine the pH of a strong acid or base solution.
  8. Determine the pH of a weak acid or weak base solution.
  9. Determine the pH of the solution made from the salt of a weak acid or the salt of a weak base.
  10. Recognize and predict the components of a buffer solution.
  11. Calculate the pH of a buffer solution, and a buffer solution after the addition of strong acid or strong base.
  12. Balance a reaction for the neutralization of an acid or base and calculate stoichiometric quantities throughout the reaction (titration).
  13. Determine the majority species for acid/base solutions as well as the pH following neutralization.
  14. Interpret a titration curve plot including calculating the concentration and Ka or Kb for the analyte.
  15. Understand the concept of an acid/base indicator, and determine which indicators are appropriate for a given titration.
  16. Determine the protonation state (or overall charge) for a polyprotic species at a particular pH.
  17. Apply concepts from equilibria to acid/base problems