BCHEM 142A   General Chemistry I

Winter 2013                  General Assignment #11                March 17 , 2013

Reading Assignments and prep work for class in week 11 (Mar 17 – Mar 19):

• For Tuesday, Mar 19

• Read and thoroughly study the assigned sections of Chapters 6-8 of Zumdahl for the exam. Note that we have skipped sections 6.9, 7.9, 7.10, and 8.3. We have not gone beyond 8.4. We also skipped parts of 7.7. See GA 7-11 for details. Study only the sections assigned in the General Assignments for those weeks.
• Complete all of the exercises and problems in the Hanson activities that we have done in this section: 15-1, 15-2, 15-4, 16-1, 16-2, 16-3, and 17-1. Note we did only some sections of 16-2.
• Complete all of the OWL mastery problems by 11 AM on Mar 18..
• Complete as many as possible of the OWL extra-credit, End of Chapter Problems for chapters 6-8 by 11 AM on Mar 19. These count as extra credit in the homework category.
• Prepare a 4 x 6 “ card including whatever you will need (student number, unit conversions, nomenclature of difficult-to-name compounds, important constants such as Avogadro’s number, Gas Constant, K_w value, value of the amu in grams, and solubility rules.) You may want the quadratic equation formula here. Some students did not have the table of polyatomic ions and needed it on the last exam.
• I will provide tables of K_a and K_b values.
• Bring your calculator – no cell phones allowed – only ordinary calculators .
• Bring pencils or blue/black pens – no red pens on the exam.
• The second page of this GA11 lists topics within the scope of the exam that may be there.

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Homework : See OWL for details and due dates. The summary of assignments is:

· Required Assignments due Mar 18, 11:00 AM: sections of chapters 7 and 8

· Extra Credit due March 19, 11 AM: 6-EOC

· Extra Credit due March 19, 11 AM: 7-EOC and 8-EOC

Final Exam. The exam will be taken from the material covered in Chapters. A list of study topics follows on the next page.

Topics to review for Exam 3

· Understand the nature of dynamic equilibrium. What it does mean for it to be “dynamic”?

· Understand the relationship between the rates of forward and reverse reactions when a chemical system is at equilibrium.

· Know how to construct the equilibrium constant (or mass action quotient) from a balanced chemical reaction.

· Be familiar with the use of either molarity or pressure in the equilibrium constant expression and be able to relate K to K_p... You might want this relationship on your card.

· Understand how to express equilibrium constant expressions when the reactants or products include pure liquids or pure solids.

· Know how to calculate K from the measured equilibrium concentrations of reactants and products

· Know how to find unknown equilibrium concentrations from the value of an equilibrium constant, the balanced chemical reaction and a subset of the equilibrium concentrations.

· Be able to apply the RICE process to equilibrium problems. This is particularly useful where initial concentrations are stated and equilibrium concentrations must be calculated.

· Be able to determine whether a reaction will proceed toward products (to the right) or reactants (to the left) given the value of K and the current value of Q.

· Be able to make reasonable approximations when changes are small relative to initial concentrations and how to check their validity after solving the problem (the 5% rule).

· Understand Le Chatlier’s principle and how to determine the shift in equilibrium when concentrations, volumes, pressures, or temperatures are perturbed.

· Know the definitions of exothermic and endothermic reactions and how the equilibrium of each will respond to changes in temperature.

· Understand the Bronsted-Lowry definition of acids and bases and how to identify the acids and bases in a chemical reaction.

· Be able to define the conjugate acid-base pairs. (extremely important!)

· What are strong acids, strong bases, weak acids, and weak bases and be able to identify them based on the chemical reaction and on the values of K_a and K_b.

· It might be prudent to place the list of common strong acids/bases on your card.

· Understand the relationship between K_a for a weak acid, K_b for its conjugate base, and K_w, the dissociation constant of water.

· Be able to calculate pH, pOH, or pK from values of [H⁺], [OH^-], or K. i.e. know that the operator p represents – log() and how to find the value with your calculator. \

· Also know how to convert a pH, pOH, or pK value to the actual number and how to use your calculator to do that.

· Be able to calculate the pH and pOH for a strong acid or strong base solution. This is straightforward.

· Given the acid/base dissociation constants, be able to calculate the pH and pOH of solutions of weak acids or weak bases.

· Be able to relate pH and pOH values to each other rapidly.

· Be able to relate a list of acids in order of strength to an ordered list of their conjugate bases. That is, which acids have the stronger conjugate bases and vice versa.

· Understand how pK_a is related to K_a

· Be familiar with calculating the percent dissociation of a weak acid or base.

· Understand how a polyprotic acid like sulfuric acid gives rise to a strong acid and a weak one successively.

· Understand how salts like NaCN may have acid/base properties in solution.

· Be able to use the quadratic equation to solve 2^nd order equations that may arise in equilibrium problems.

· Be familiar with logarithms of products and ratios.

· When you encounter two acid equilibria with very different magnitude K_a’s, be familiar with how you choose the dominant one to solve the problem and then check to make sure that the secondary one is truly unimportant in determining pH.

· Given a list including strong acids, weak acids, weak bases, strong bases and neutral compounds, be able to order their solutions in increasing or decreasing pH value. (We did this in class on March 14.)

· Given a compound that may contain weak acids or bases be able to indicate if its solution is acidic, basic, or neutral. (We did this in class on March 14.)

· Given a compound that contains both a weak acid and weak base, such as NH₄F, be able to determine if its solution is acidic, basic, or neutral. (We did this in class on March 14.)

· Understand the nature of a buffer: what does it consist of, why does it work, and how do you determine its pH.

· Be able to relate a weak acid’s pK_a value and the ratio of its concentration to that of its conjugate base to the pH of the buffer. Be able to work with the weak acid equilibrium constant equation directly or in its logarithmic form (Eq 8.2). Notice that the acid/base concentration ratio is inverted as you pass from one to the other. Also note that it is easy to derive Eq 8.2 from the usual equation for K_a

· Know how to create a buffer by either directly adding the weak acid and its conjugate base to solution, or by reacting some of the weak acid or base by addition of a strong base or acid.

· Understand buffer capacity. Be able to calculate how much the pH of a buffer changes when a certain amount of strong acid or base is added to it. That is, how much does it change as opposed to the same addition to an unbuffered solution (see Activity 17-1 and section 8.4)

· Do not go beyond section 8.4.