home   /   exams   /   exam 3

3 Ex exam 3    3/27

We now have an official Exam Procedure page. Check it out and know what to expect on Tuesday.

Coverage for Exam 3: Exam 3 covers all the material that was covered on LE's 18-23 and HW05 and HW06. The exam covers the rest of Chapter 10 (buffers, titration curves, and indicators) PLUS Chapter 8 on solubility equilibria. Remember to check out extra practice assignments (5 and 6) on canvas as well.

Length / Time for Exam 3: You should expect 25 multiple choice questions. The questions will have a range of point values from 2 points to 5 points. Remember that the point values are included with all questions. The exam is given during class time (9:30-10:45, 11-12:15) which is 75 minutes total which includes the handout time.

Concepts • Equations - 10 Acid/Base Equilibria

acid / base theory

acid = a proton donor

base = a proton acceptor

(Lowry-Bronsted definition)

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-][BH+]
[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]

Concepts • Equations - 8 Solubility Equilibria

For a saturated solution of the salt MxAy :

MxAy(s)   =   xM+y(aq)   +   yA-x(aq)

Ksp   =   [M+y]x · [A-x]y

The most common x : y ratios...
1 : 1    1 : 2    1 : 3    2 : 3

Solubility Product

None of this will be printed on the exam. You need to KNOW this on your own.

salt
ratio		salt
formula		 aqueous
cation		 aqueous
anion		 equilibrium
formula		 Ksp(x) molar
solubility
1:1 MX(s) ⇌ M+(aq) + X–(aq) Ksp = [M+][X–] \(K_{\rm sp} = x^2\) \(x = \sqrt{K_{\rm sp}}\)
1:2 MX2(s) ⇌ M2+(aq) + 2 X–(aq) Ksp = [M2+][X–]2 \(K_{\rm sp} = 4x^3\) \(x = \root 3 \of {K_{\rm sp}\over 4}\)
1:3 MX3(s) ⇌ M3+(aq) + 3 X–(aq) Ksp = [M3+][X–]3 \(K_{\rm sp} = 27x^4\) \(x = \root 4 \of {K_{\rm sp}\over 27}\)
2:3 M2X3(s) ⇌ 2 M3+(aq) + 3 X2–(aq) Ksp = [M3+]2[X2–]3 \(K_{\rm sp} = 108x^5\) \(x = \root 5 \of {K_{\rm sp}\over 108}\)

Reaction Quotient vs Equilibrium Constant

   forward\(\rightarrow\)     \(Q < K\) which means more solid will dissolve if there is any or nothing happens because the solution is undersaturated.

equil\(\rightleftharpoons\)ibrium     \(Q = K\) which means the solution concentrations will hold constant and there is no net change.

   \(\leftarrow\)reverse     \(Q > K\) means the solution is oversaturatured and a precipitation will occur until the concentrations drop to saturation level.

Note that mainly outcomes 10-16 will be on the exam for the Acid/Base chapter. However, you still need to know many of the concepts and definitions from outcomes 1-9.

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

Learning Outcomes for Solubility Equilibria

Students will be able to...

  1. Understand the concept of saturation and how it relates to the solubility product, Ksp.
  2. Write total and net ionic equations to identify spectator ions.
  3. Quantitatively determine molar solubility from Ksp.
  4. Quantitatively determine Ksp from molar solubility.
  5. Convert general (common) solubility terms to molar solubility.
  6. Understand and apply the "common ion effect" on solubility.
  7. Given concentrations of specific ions, predict if a precipitate will form (amount or concentration) using Qsp vs Ksp.