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Schedule to Exam 2

Date Day Topics
2/9MonTalked about Exam 1. 26 questions all equally weighted. Gave out some "always" solubility rules: ALL group IA metal cation salts are soluble. ALL nitrate and acetate salts are soluble. AND.. ammonium salts are soluble. Tried to start up on chemical equilibrium. Tried to get you to see the differences in different ΔG's - when its negative or positive, big number vs little number. Drew free energy curves that showed free energy vs composition of the mixture. READ pages 436-439 in your book... that's chapter 10 section 10 and 11. Finished with what a mass action expression looks like... will start there on Wednesday. from 6-7 PM in WEL 2.246
2/11WedMore on the mass action expression and the reaction quotient, Q. WHEN (what conditions) does K equal Q? What happens when Q > K? when Q < K? Also showed the relationship of ΔG and K from Chapter 10: &DeltaG;° = -RTlnK
Also had 3 chemical demonstrations today: the blue bottle, an oscillating rxn, and the very exothermic rxn of Mg metal with CO2 (dry ice).
2/13FriDiscussed the various forms of K... Kc, Kp, Kw, Ka, etc... Derived the relationship between Kp and Kc. Showed HOW K's value will change when change the way the reaction is balanced: flipping = inverting K or getting 1/K or better, K-1. Doubling a reaction you change K to K2. Then I went over heterogeneous equilibria. Pure solids and pure liquids do not belong in the mass action expression and therefore NOT a part of the equilibrium equation. You DO have to have them in the reaction mixture but the AMOUNTS absolutely don't matter and don't affect the equilibrium mix.
2/16MonShowed the details of solving equilibrium problems. Showed how you create an "ICE" table and fill it out. Did various problems where different amounts of information was given. Easyiest: ALL equilibrium conc are given - plug in and get K. Still Easy: Initial concentrations are given, and ONE final concentration is given: we ask what are all the other final concentrations and what is the value of K? HARDEST (but not really that hard): You're given initial concentrations and the value of K. You calculate the final concentration of all species.
2/18WedLe Chatelier's Principle. Had numerous clicker questions about reactions shifting to the left or right or no change. Learned how stress affects the equilibrium and how the reaction responds. Studied conc changes and temperature changes. On Friday we'll study overall pressure changes. Also had 3 demos: elephant toothpaste, ethanol cannon, and the big methanol bottle blast.
2/19ThurH05 due by 12 noon
2/20FriHad a verbal overview of Chapter 6 material. Discussed "global pressure" changes and how the equilibrium shifts. The answer? Any global pressure increase (think volume is decreasing) will result in the reaction shifting to the side with the FEWEST gas moles. Starting talking about Chapter 7 and aqueous equilibria. I harped on the term "weak" electrolyte and what "weak" means. Unfortunately, "weak" means pretty much any dissociation/ionization of less than 100% (which is "strong"). "We need more adjectives", I said and TRIED to point this out. We will see more of this as chapter 7 plays out. Defined what an acid is and what a base is (proton donor or acceptor). Water IS a very very weak electrolyte itself and it ionizes into protons (H+) and hydroxide ions (OH-). Wrote the equilibria and the equilibrium constant for this. Told you to MEMORIZE this one. 1.0 x 10-14 is the value of Kw.
2/23MonMore on Kw and H+ and OH-. Defined what pH is and lots of other pX's: pOH, pKa, pKb, pKw. Also defined what an acid/base conjugate pair is. Also looked at and commented on the pH scale and the pOH scale. Start using the Acid/Base Help Sheets here on this website. H07 is available now.
2/24TueH06 due by 12 noon
2/25WedWent over the dissociations of weak acids and weak bases. Showed how ALL the "ice" tables will look when doing this type of problems from Chapter 7. Defined what I call a "Type 1" problem: only ONE species put into solution. Pointed out the 4 acid/base help sheets on our web site for Type 1 problems.
2/27FriWorked a strong acid + strong base problem (HCl + NaOH). Pointed out that this is really just Chapter 4 (section 9) stuff (fundamentals). It's a limiting reactant problem and some H+ was left over thus SETTING the pH. Also worked a weak acid problem where the percent ionization and conc is given and we calculate the Ka. Calculated the OH- concentration for a conjugate weak base solution (NaA or NaX).
3/2MonStarted analyzing polyprotic acids. Pointed out how the acid loses one proton at a time and you have a Ka expression for each dissociation. You number the Ka's as 1, 2, 3, etc... as the protons come off. You have a similar thing going with bases except you have Kb's that are numbered 1, 2, 3, etc... as you put protons ON the base. You must be able to match up appropriate Ka's and Kb's for polyprotic acids and their conjugate bases.
3/3TueH07 due by 12 noon
3/4WedShowed how to calculate and plot a fraction of species diagram for polyprotic acids. Also described the material balance for a given species set.
3/6FriMore on fraction of species. Told you to MEMORIZE the way in which the polynomial is written for the fraction of species. Each term in the polynomial will represent a species in the series. The question on H08 about the lake and the the total alkalinity can easily be answered via the fraction of species equation for HA-. HA- here would represent bicarbonate, HCO3-.
3/8SunH08 due by 3 PM
3/9MonTalked a bit about Exam 2 - 29 questions. Then I covered a bit about acid strengths in certain series. Trends: the more electronegative the atom is that the acidic hydrogen is attached to, the weaker the bond, and therefore the stronger the acid. Also, for oxy-acids in a series, the more oxygens on the central atom, the strong the acid. I then started on Chapter 8 - Type 2 problems. I showed the basic set up on the ICE table, then I switched over to the web site and showed the help sheet for Type 2 - a weak acid and its salt. I finished by showing a fraction of species diagram and pointed out the RATIOS of the conjugates throughout the diagram. Only in the CROSSOVER region (pKa±1) are the ratios such that both components must be considered reasonable.
3/10TueEXAM 2, 7-9 PM