****TEST # 2 ***** ***During Regularly Scheduled Class***
Answers for Exam 2: ExamView – Test2, 2009
Announcements:
1)The material covered for this exam was more difficult than that of the first exam – it is normal for the scores to be a little lower. Average = 64, as calculated below. I will post a histogram tomorrow.
2) The exam scores were calculated as follows: (# correct)x(4) + 4 = score.
3) one question was worded poorly, so I gave everybody 4 points for that question (see above)
4) the exam answer key had a mistake on each exam form: The correct answer to ion radius is Br- (Form A, #14; varies from form to form). This mistake was corrected prior to calculating the scores above.
5) In order to help normalize scores, I will do the following: Your percentage score on the final exam will replace that of your lowest midterm, provided that this will improve your score. (eg: MT = 62/100, final = 90/120. Your MT score would get dropped, and replaced by a “75”.)
Does anyone know when elements are ferromagnetic? And are all elements that have unpaired electrons paramagnetic?
any idea which demos might be on the exam that Prof. Knapp was talking about?
to Alyssa’s question I believe the interchapter Prof. Knapp was talking about is the one right after chapter 7 it talks about all the experiments that Knapp talked about a couple classes ago
It’s on the useful information page:
delta E = -Rhc(1/nf^2 – 1/ni^2)
I know that there is an equation for the change in energies of an atom between orbitals, but I can’t for the life of me find it! I know it has something to do with N(larger)-N(smaller)?
Somebody help me please! It’s killing me, cause its right on the tip of my tongue!
where are the interchapters?
what equations do we have to know and which ones are we given?
Every point counts. Please give me my bonus point.
Oksana,
for #1, the way you can eliminate (A is by thinking that if HNO2 reacted with NaOH then that would be an acid-base reaction that doesnt produce a precipitate. so that only leaves answer (D.
for #10 i did a calorimetry equation. so (m*deltaT*Cp)=(m*deltaT*Cp). you know both Ms both Cp (water is 4.184) and the initial temps. so the only variable is final temp and its the same on both sides so thats what you solve for. when i did it out i didnt get the exact answer but close the answer closest to what i got and it was the right one.
for #11, its a Hess’s law problem. The trick is to reverse reaction (b) and double it to get it to match. so once you do that then you add the two reactionns together and you get the desired reaction. but when you reverse and double (b), you have to change the sign of the energy and double it. then you just add the two energies of (a) and (b) and you get the answer.
Finally, to be product favored means that the energy level of the product is lower than the reactants therefore its more stable and the reaction is product favored. so on a graph the energy would start at a high point and slope downward to a lower point.
he gives us the constants that we need to know.
I hope all of that is helpful,
Tommy
Hi everyone, I was going over the practice exam today and had some questions..5 actually 🙂
Practice exam
Number 1) Which correctly describes nitrous acid, HNO2?
Well, I know that b) and c) are wrong. I said a) reacts with NaOH to produce a precipitate, but it was wrong. The answer is d) in ionic equation, it would be written in its molecular form. Why so? Doesn’t it react w/ NaOH?
Number 10) Please, please explain this one 🙁
Number 11) I think we did something like that in class, but I do not remember and my notes are not helpful at all! I need help, please!
What is product favored?
Do we have to know any constants or equations for the exam?
Thanks 🙂
Thanx Mike! that really cleared it up!
I have another question about getting to the final answer on finding the final temperature in calorimeter problems….I just get a little lost with working out what Tf is? If anyone has a way to simplify it let me know!!!
For Laura Risch:
(Psi)^2 is used to determine the probability of finding an electron in a given area. For example, it would be 0 at nodes, and it would decrease as you move further from the nucleus (for certain orbitals). It has to be squared because there are negative and positive phases for a wave function, so squaring it will make all of the answers positive. So that’s where the shape comes from- the probability that it will be found in a given area. Hope this helps, and good luck on the exam tomorrow!
-Patrick
Haley-
someone may correct me if im wrong but when l=2 then the M sub L of magnetic quantum numbers can either be -2,-1,0,12. Which would be equal to 5 or answer D.
Hope this helps
Mike
opps sorry not danielle, and apparently someone answered that.. scratch
For more info on that, page 286 has a good chart.
@ Danielle,
I’m not exactly sure as to why, but from owl’s I know that L equals 0,1,2,or 3 based on the subshell level, s,p,d, or f (respectively) then ml can equal a range from -L to +L.. so for #23, L=2 so ml can equal -2,-1,0,1,2.. therefore there are 5 possibilities. maybe this helps?
For #25…
Only one orbital at all times can have a specific set of numbers to describe it. No other orbitals can have the same exact sequence of numbers.
For #23…
When l = 2 just think like this…
all negative values and positive values including 0 are included in the range
so…
-2, -1, 0, +1, +2 will all be values…therefore the answer is 5.
Can anyone tell me if Psi ^2 and an orbital represent the same thing?
Thanks!
Do we need to know the exception in the periodic trends for tomorrow’s exam?
Kieran the noble gas notations are as follows Cr = [Ar] 3d5 4s1 and Cu = [Ar] 3d10 4s1. These elements are exceptions to the general rules of sdpf notation.
What are the noble gas notations for Chromium and Copper?
On the practice exam, can someone help me with question 12?
How many questions are on the test again for tomorrow?
How many problems will be on the test again?
I guess i will leave a comment to get an extra point. Can’t hurt but good luck to everyone on the exam tomorrow
Andy Ng,
correct me if I’m wrong, but Hess’s Law is basically used to figure out the total change in energy of a reaction. the equation states that the total change in energy of the reaction equals the sum of the energy of the products minus the sum of the energies of the reactants.
To sum it up, its products – reactants.
Hope this helps,
D
Graham the temperature and the energy both change during a phase change
On the practice exam #23. Can someone explain how to understand this concept?
posting for those puntos!
to answer the question about the oil drop experiment—B the answer is Milikan
Can someone please explain Hess’s Law to me?
Can someone please explain Hess’s Law to me
the answer to Graham Gaspar’s question is….During a phase change the temperature does not change, but the internal energy is increased.
The answer to Jonathan Aprile’s question is b.) Milikan. Final answer.
Does the temperature actually change during a phase change? Or just the energy in the system.
Prof. Knapp,
On this test, will it be cumulative or strictly on what we have covered after the first test?
Thank You
question for 2 bonus points on exam 2:
Which scientist is responsible for creating the Oil Drop Experiment?
a) Rutherford
b) Milikan
c) Hess
d) Einstein
Just leaving a comment for the bonus point on the exam.
Everybody remember to get there early!
bonus point!
Hey does anyone know if we should we be focusing on specific redox reactions like Mg and HCl and Zn and Cu. These are the examples that were used in Owls.
Prof Knapp,
Base on the practice exam, I’ve noticed that there are some materials from the first exam (strong base, strong acid, etc). I was wondering if there are any other materials from the first exam that we would need to know.
Thank you!
I really do not understand question 25 on the practice exam. any help would be much appreciated, thanks!
Could someone please explain question number 15 from the practice test. This question states- The reaction energy profile for a chemical reaction in which the products are less stable than the reactants is: …and it gives 4 graphs.
Thanks so much.
Prof Knapp,
Will we be required to know the exceptions for the Aufbau Rule? (Such as Cr, Mo, W, Cu, Ag, and Au)
Thanks so much!
Hi everyone,
Will we have to know the equation for work under constant pressure, w = negative pressure multipled by change in volume, for the exam? If so then why is pressure negative in the equation? Is it possible to even have negative of something like pressure?
Many thanks.
Oh shoot, sorry, ignore the part I said about speed since they travel at same speed…And just think of something like a heartbeat monitor moving along at constant speed..And if a wave is shorter (less wavelength) then its tip (or whichever part of it) will pass by some fixed point many more times (more frequent) than a wave with a longer wavelength; it’ll almost appear “faster” but it’s not the case..Just more frequent b/c its small size thus more ‘oscillations.’
Here is my answer to Edmund’s question…(Alex gave you an equation but not a real reason)…so, wavelength is the literal length of one full wave, and if you think of its speed being proportional to its energy (like atoms speeding up when you put heat energy into them)…where its speed is how many times the tip of the wave appears while traveling at light speed (a less wavelength would mean a greater frequency of waves since they travel at same speed…like it you had a pendulum with a short string – shorter wavelength – vs. a pendulum with a long string – longer wavelength – and the shorter one would have many more oscillations due to a shorter length, the same works for waves.) So, with a large wavelength and less oscillations/less frequent passing of the wave, comes a less frequency (b/c frequency just means #). Thus frequency and wavelength are inversely proportional; hope I helped!!
Well the answer has to do with the equation needed for the energy of a particular wave. Another way to think of it is the “velocity” of a wave expressed by the equation v=fλ. by this equation wavelength and frequency are inversely proportional. That’s the best i can really show this, but I’m sure there is a better answer.
Could someone explain why as wavelength increases does frequency and energy decrease among the electromagnetic spectrum?