Exam 2 Notes

(4/24/20, bes)

Day 1 - Question (30 pts)

1a) (3 pts) Basics of UV-Vis determination of unknown concentration -- Check!

1b) (3 pts) What is the molar absorptivity coefficient (ε) --> this is given = slope with units of 1/(nM cm) <-- units are important!!!

1c) (3 pts) x1, x2, x4, x8 is a serial dilution. All UV-Vis standards should be made via serial dilution, NOT individually. Yes it is true that standards must cover the full range of sample absorbancies, but this does not address the question asked.

2a) (6 pts, 2 each) Dye D --> blue shifted (smaller box), Dye E --> main, Dye F --> red shifter (larger box)

2b) nowhere to be found (errata)

2c) ~69 nm, ~152 nm, ~244 nm; must use the # of π-electrons to determine the n_f and n_i states --> (n_f² - n_i²), math errors can occur if not careful.

Range of scores out of 30 pts: 18 pt --> 30 pts, ave score: 25.2 pts.

Day 2 - Question (30 pts)

Page 1: Essentially copied from notes and book.

Page 2: Essentially copied from notes and book. Often the book does not "show all work", if your response mirrored the example answer (ie with no "work") you may have lost a point of 2.

Page 3: re-writing "Exp" wavefunction into trig...again, details matter, abbreviated answers may have lost a point or two. The last question seemed to be interpreted differently than i intended...i take some credit for this, so i graded this based on effort...blank answers did not receive points.

Range of scores out of 30 pts: 18 pt --> 30 pts, ave score: 24.6 pts.

Day 3 - Question (30 pts)

Page 1: no question asked

Page 2, Q1 (top): We spent significant time doing "reduced mass" calculations in lab...when doing this, we were very precise about using amu for the specific isotopes involved...there was a link in the lab materials showing the mass in amu to MANY sig figs...some of you used average atomic masses from the periodic table...(-2)...must be specific to the isotopes.

Page 2, Q2 (bottom): This is essentially Ex. Prob. 8.2 using 1H19F as opposed to 1H35Cl.

Page 3, This is essentially what we did in lab and it is example problem 8.6..

Range of scores out of 30 pts: 25 pt --> 30 pts, ave score: 28.1 pts.

TOTALS

High score = 100

Low score = 71

Average = 86.9