CHEMISTRY COMMUNITY

Cooper_Geralds_3B

I still cannot see my midterm 2 grade on CCLE, is this happening for anyone else??

Cooper_Geralds_3B

I believe you must earn 200/400 total points to end with a final passing grade of C-.

Cooper_Geralds_3B

You use the Nernst equation E=E∘−RTnFln(Q)=E∘−0.0592 Vnlog(Q)

Cooper_Geralds_3B

My #3 was a bit different "ClO−2 is oxidized to ClO−4 and Ag+ is reduced to Ag", but for this I used the half reactions: Ag++e−⟶Ag and ClO−2+2H2O⟶ClO−4+4H++4e− and in order to put these two half reactions together in an overall reaction, we then multiply the silver reaction by a factor of ...

Cooper_Geralds_3B

I believe concentration cells consist of anode and cathode compartments that are identical except for the concentrations of the reactant. Because ΔG = 0 at equilibrium, the measured potential of a concentration cell is zero at equilibrium (the concentrations are equal).

Cooper_Geralds_3B

Here are some rules that might help! I believe the oxidation number of an atom is the charge the atom would have if it was composed of ions. The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element, and the oxidation number of simple ions is equal to the...

Cooper_Geralds_3B

I would start by looking at if you can multiply one of the half reactions by a common factor to balance the electron transfer. Then after you combine the equations by adding them, convert from acidic solution (H+) to basic solution (OH−) . Add enough OH− ions to both sides so that all H+ ions can co...

Cooper_Geralds_3B

Look at your oxygens, I believe I noticed 6 oxygens on the left and 5 on the right.

Cooper_Geralds_3B

I emailed the professor and the department and they both said that at this current time they are not planning to expand class sizes and they do not offer PTE. I have to take a quarter off from chemistry which is not ideal, but definitely look at other pre health requirements that you can take in the...

Cooper_Geralds_3B

Hi, I am not sure if this is exactly what you are asking, but from sapling I found: The standard potential for a cell, E∘, is a constant and does not depend on the reaction coefficients. Therefore, it will not change when the coefficients are for example doubled.

Cooper_Geralds_3B

Hi! I usually try to distract myself and focus on getting ahead in the class or dedicating time to other classes. At the end of the day, once you submit an exam, the numerical value is out of your control but the best thing to do is to stay up to date on the upcoming materials in order to definitely...

Cooper_Geralds_3B

a salt bridge, also known as an ion bridge is used to connect the oxidation and reduction half-cells of a galvanic/ voltaic cell, and its purpose is to act as source of spectator ions that can migrate into each of the half cells to preserve neutrality.

Cooper_Geralds_3B

From Friday's lecture 2/19, I believe he will either give us the numbers in the problem or it will be linked to a table in the sapling textbook similar to the previous extra homework problems. Worst case scenario we should be able to look the values up!

Cooper_Geralds_3B

The final will definitely be cummulative and the weight of each topic will likely depend on how long we focused on the topic in class, but Dr. Lavelle will send out a few emails closer to the final going into the specifics that will be covered on the final.

Cooper_Geralds_3B

Specifically for the questions that Dr. Lavelle gives us I would just stick with the anode on the left and cathode on the right unless he specifies otherwise in the problem!

Cooper_Geralds_3B

Hi,

I was wondering if the department head plans on opening more spots for 14C and 14CL during the spring? I am going to be behind and not able to start upper divisions if I cannot complete 14D in the fall.

Cooper_Geralds_3B

Hi,

I was wondering if anyone knows the specific extra textbook homework problems for midterm 2 or where I can a list of which problems are helpful for preparing for midterm 2?

Cooper_Geralds_3B

Hi! Here is my work for the following problem. Please feel free to ask any follow up questions.

Cooper_Geralds_3B

Hi, 1) add 273 degrees to each temperature given to convert the values to kelvin 2)use the equation deltaS= given molar heat capacity * ln(Tf/Ti) 3)use the equation above 3 times to calculate for phase changes --> S1= molar heat capacity of liquid *ln(Tf/Ti) --> S2= standard molar entropy given --> ...

Cooper_Geralds_3B

Hi! I used the equation deltaS=nCv,mln(Tf/Ti) + nRln(Vf/Vi)
n= given noles of neon gas
Cv,m= given Cv,m
Tf= final temperature
Ti= initial temperature
R= gas constant of 8.314
Vf= final volume
Vi= initial volume

Cooper_Geralds_3B

Hi! I struggled with this problem and reading explanations because I am such a visual learner, so I included an image of my work below! Hopefully this helps you out, let me know if you have any questions about my work:)

Cooper_Geralds_3B

Hi, can someone please help walk me through this problem?

Cooper_Geralds_3B

for isothermal reactions, -temperature of system stays constant -transfer of heat in or out of system occurs slow enough that thermal equilibrium is maintained -a helpful example to further understand isothermal reactions is a refrigerator because changes take place but the temperature inside remain...

Cooper_Geralds_3B

Reversible reactions are those with infinite number of changes throughout the process and are categorized by the fact that the system and its surroundings can return to original states through reverse path.

Cooper_Geralds_3B

Depending on the system, phase changes may occur at either changes in temperature or changes in pressure!

I attached an image for reference below.

Cooper_Geralds_3B

Here is a video that defines the differences between open, closed, and isolated systems: https://www.youtube.com/watch?v=TFP6SvWPOQc As for the specifics for a closed system: -energy can be exchanged with its surroundings but not matter -mass of the system is constant -boundaries are completely closed

Cooper_Geralds_3B

Here are two helpful videos to help you understand entropy!

https://www.youtube.com/watch?v=YM-uykVfq_E

https://www.khanacademy.org/science/ap-chemistry/thermodynamics-ap/entropy-tutorial-ap/v/introduction-to-entropy

Cooper_Geralds_3B

Dr. Lavelle defined entropy as an extensive property (depends on the # of particles) and denoted by the "S". S= KblnW1W2 (Kb is boltmann constant) A helpful definition of entropy, S, that I found online is: Entropy is a measure of the degree of randomness of particles in a system. In addit...

Cooper_Geralds_3B

Hi! I was a bit confused on this as well, but this is what I found after doing further research: -a reversible process is one in which both the system and its surroundings can return to their original states by following the reverse path; whereas a irreversible process is one in which the system and...

Cooper_Geralds_3B

Here are two super helpful video links that explain the differences of endothermic and exothermic reactions

https://www.youtube.com/watch?v=eJXL0IrbtqE

https://www.youtube.com/watch?v=0cUK4jcAEaU

Cooper_Geralds_3B

I am taking BL right now with 14B and am thinking about doing 14C and CL next quarter!

Cooper_Geralds_3B

Yes, definitely take care of yourself during midterm weeks and cut yourself some slack after the exams. Remember that there is nothing that you can do after the fact so it is not worth your energy to stress over something that is out of your control! Now that the first midterm is out of the way, is ...

Cooper_Geralds_3B

Hi can someone help me with the following problem: An ice cube with a mass of 46.4 g at 0.0 ∘C is added to a glass containing 428 g of water at 45.0 ∘C . Determine the final temperature of the system at equilibrium. The specific heat capacity of water, Cs , is 4.184 J/g⋅∘C , and the standard enthalp...

Cooper_Geralds_3B

Such a great idea, accountability helps so much in classes like this where the grade is broken down into components on different platforms.

Cooper_Geralds_3B

I took 14A with Dr. Lavelle and I would say that the best way to study is to complete all of the sapling homework before the due date to stay up to date on the current topics and then complete the extra homework problems listed on the syllabus before each test. I would say that forming study groups ...

Cooper_Geralds_3B

Thank you so much! It is so nice to have notes outlined on a computer where you can command F and search the topics that you need to review the most!

Cooper_Geralds_3B

Jack Johnson is good for doing work while listening to music!

Cooper_Geralds_3B

Hi, I think that you can copy and paste an image the same way you would text using command c (to copy) and then command v (to paste) or use the attachments button listed below the save draft, preview, and submit buttons after you clicked post reply!

Cooper_Geralds_3B

Does Dr. Lavelle use chem mod for answering chemistry community questions real time in class or the discussions he hosts?

Cooper_Geralds_3B

Hi! I hope this helps

pKa= -log(Ka) and pH= -log (H3O+)
and pKa + pKb = 14

Cooper_Geralds_3B

Hi! I believe it depends when your specific TA plans on checking for your posts but I would just try your best to do 5 posts/week so that you can use chem community as a resource for homework, study, concept help throughout the course rather than just cramming in random posts for points towards the ...

Cooper_Geralds_3B

Hi! The exam format will likely be multiple choice including concepts and calculations depending on the units covered. We will likely have lockdown browser and have to zoom our TAs with an external device such as a phone so that they can monitor our hand movement. You should print out the equation s...

Cooper_Geralds_3B

I haven't been able to register until now, could I make up the points by posting more this week? Hi! You should be able to, last quarter in 14a, the TAs generally only calculated the total mid quarter and at the end, but if you contact your TA and let them know your technological circumstances I am...

Cooper_Geralds_3B

Pretty sure that Sapling is mandatory, and will actually be collected midnight of the following Sunday, however, is this the only "homework" due?? Yes sapling is the only homework that is taken for a grade, but the extra homework problems that Dr. Lavelle lists on the syllabus and chapter...

Cooper_Geralds_3B

Juwan_Madaki_3K wrote:When using the ideal gas law, which units should the temperature be in? Kelvins or Celsius?

I believe most of the time in 14B we will be using Kelvin for temperature unless a specific problem indicates otherwise!

Cooper_Geralds_3B

Did you hear the one about cobalt, radon, and yttrium?

It was ~CoRnY~

Cooper_Geralds_3B

Where can we find all the answers to the textbook practice problems? I believe it might be on Lavelle's website but I cannot recall under what tab. Given that this concept requires all sorts of equation solving back and forth it might be a good idea to gain a better grasp by literally applying it i...

Cooper_Geralds_3B

I was wondering why when we calculate partial pressure the answer could be either in bars or moles per liter. Is there any unit out of the two that is preferred? Usually the units preferred are given in the question or you can deduce the best units from the units given! Sometimes on tests as well D...

Cooper_Geralds_3B

Thank you so much! It is so nice to have everything organized into one neat simple document with hyperlinks, this really helped decrease my stress in regards to organizing all of the topics!

Cooper_Geralds_3B

I am wondering if anyone has found a good way to study conceptual topics? I always find myself second guessing myself on the exam questions that are more concept based rather than numerical or calculation based.

Cooper_Geralds_3B

Hi, I noticed the -OH in today's lecture as well and am used to seeing OH- in both his lectures and the homework, but I am pretty certain that they are the same!

Cooper_Geralds_3B

Hi! I found this from sapling textbook which is a helpful list of strong acids and bases, and essentially every other acid or base not listed is considered weak.

Cooper_Geralds_3B

Hi,

I am currently trying to watch today's uploaded lecture #28, but there is an error coming up saying "this video file cannot be played. Error:232001". I was wondering if anyone else is running into this issue or if this might be an issue on my end with my computer.

Thank you.

Cooper_Geralds_3B

Hi! I find the extra textbook problems and sapling to be the best as far as simulating test questions, and then I try to find khan academy videos for concepts that I do not understand fully.

Cooper_Geralds_3B

I feel like the hardest part for me is grasping the conceptual material for the exams, I feel like there are always questions that surprise me when it comes to the concepts. Do you guys have any good ways or sources to review the conceptual material for the final?

Cooper_Geralds_3B

If we complete the sapling assignments by the due dates are we guaranteed the full 50 points for that portion of our grades?

Cooper_Geralds_3B

I was really stressed that I would not end up getting the classes that I need for winter quarter, but I ended up getting them which is such a relief! I am curious, how do you guys plan on reviewing for the final? I want to start reviewing soon so that I avoid the stress of cramming a few days in adv...

Cooper_Geralds_3B

Hi, here is a helpful definition that I found on coordination numbers: "Coordination number, also called Ligancy, the number of atoms, ions, or molecules that a central atom or ion holds as its nearest neighbors in a complex or coordination compound or in a crystal" (Britannica). Hope this...

Cooper_Geralds_3B

Hi! In discussion yesterday, I learned that cations (+) come before and anions (-) come after!

Cooper_Geralds_3B

Hi! I think that the electron pairs look like this because they drew the lewis structure to resemble the molecular structure, but I do not think this is required. Also, it is linear because there are two regions of electron density, the hybridization is sp and therefore the bond angels are 180 degre...

Cooper_Geralds_3B

I believe that trigonal planar has 3 regions of electron density and the bond angels are 120 degrees whereas trigonal pyramidal has 4 regions of electron density and has bond angels of 109.5 degrees.

Cooper_Geralds_3B

Here is a helpful summary of the molecular structures that we have done so far and their corresponding bond angles. Please feel free to add to this list! -linear 180 degrees -trigonal planar 120 degrees, -trigonal pyramidal 109.5 degrees -trigonal bipyramidal 90 degrees, 120 degrees -octahedral 90 d...

Cooper_Geralds_3B

I also felt like the second midterm was a bit more challenging, not necessarily because of harder concepts but because for me it is hard to think through the number of problems we had in 50 minutes especially not being able to mark up a paper and do the process of elimination by crossing things out....

Cooper_Geralds_3B

Hi, when looking on the periodic table, the number of the element group is at the very top. You can follow these numbers in order with groups 1, 2, skip to 13 (and then look at the second # in double digits for example 3 in 13), 14, 15, 16, 17, 18 to figure out the number of valence electrons in eac...

Cooper_Geralds_3B

Hi! I have these notes written down that summarize hydrogen bonding that is repetitive but might help you: -N,O, or F shares a lone pair of e- with positively polarized (electron-deficient) H -partially positive H is bonded to a partially negative N, O, or F -There must be one of these three bonds: ...

Cooper_Geralds_3B

Thank you! Also, would it be okay to take the Chem 14BL Lab section from 11am-1:30pm on Friday even though it goes into Chem 14B's friday lecture at 1pm, since the lecture is recorded? Yes! When enrolling, you might get an error notification due to the overlap but you can quickly bypass it by click...

Cooper_Geralds_3B

This is the most stable structure. If Cl were to have two bonds and then two lone pairs, its formal charge would be 7-(4+4/2) which equals +1. so when drawing structures, we should always just go with what gives us the most stable configuration regardless of the atom's electronegativity? yes! Also ...

Cooper_Geralds_3B

Hi! Generally the resonance structure with a formal charge closest to zero is the most stable structure! Try to see if the charges on each atom cancel each other out, and if they do, this is a good indicator that the formal charge is zero and the structure is stable!

Cooper_Geralds_3B

"Select which intermolecular forces of attraction are present between CH3CHO molecules" How do you determine what intermolecular forces of attraction are present just by given the molecular formula?

Cooper_Geralds_3B

I attached a screenshot from the textbook of a helpful list of oxidation rules for calculating oxidation numbers! hope it helps!

Cooper_Geralds_3B

Hi,
I was wondering if there will be any audio-visual modules for MD2 topics? Right now, the last module is on the Heisenberg Uncertainty Principle.

Cooper_Geralds_3B

Hi, Please feel free to add on to this if I leave anything out, but it was helpful to me to make a bullet point list of all of the things that strength of induced dipole-induced dipole interactions depends on to understand the concept. -polarizability of molecule 1 and 2 (a1a2), distance between 2 m...

Cooper_Geralds_3B

In discussion section today, we were asked what element has the electron [Ar]3d^7 and were given that it is M^2+. Can anyone explain why the answer is cobalt? I thought that if we were given ^2+ we would move two to the left on the periodic table because it is two less electrons but cobalt is two to...

Cooper_Geralds_3B

For example, would Br^-2 be two to the right on the periodic table or two to the left of the normal Br?

Cooper_Geralds_3B

Hi, I might be the only one but I was struggling to understand electron configurations in the lecture but I found a couple of helpful youtube videos that I will paste below if anyone wants a quick review or summary on how to do electron configurations! I hope this is helpful. https://www.youtube.com...

Cooper_Geralds_3B

Hi, Dr. Lavelle mentioned in week 4 lecture 3 that you should arrange the lewis structures by choosing the atom with the lowest ionization energy as the central atom and arrange atoms symmetrically around the central atom. It is important to remember that Hydrogen is never a central atom and as far ...

Cooper_Geralds_3B

Hi, ionization energy is the energy required to remove an electron from an atom whereas electron affinity is the energy released when an electron is added to an atom. On a periodic table, both ionization energy and electron affinity decreases down a group and increases across a period.

Cooper_Geralds_3B

Hi, going off of your question, I am wondering if anyone has a trick or anything on how they remember how to do electron configurations for different compounds?

Cooper_Geralds_3B

Hi, I believe that ionization energy increases that means it is increasingly more difficult to remove an electron. As you move across a period, ionization energy increases, this is because as you move across the period- the atomic radius decreases. As the atomic radius decreases, the atom is essenti...

Cooper_Geralds_3B

Hi, I am wondering how you went about getting in all the classes that you needed for your undergraduate major at UCLA while also making sure to get in extra classes needed for pre-reqs of med school. Furthermore, how should I go about making sure I am meeting all the course requirements at various m...

Cooper_Geralds_3B

Hi, yesterday in Office Hours, Dr. Lavelle said that scores should be out this Thursday!

Cooper_Geralds_3B

Hi, in office hours yesterday Dr. Lavelle said that scores for midterm 1 should be out this week Thursday 11/5!

Cooper_Geralds_3B

For the value of Ms, is there an arrow always given to indicate whether it is spin up or spin down or is there another way to determine whether the value is + or -1/2?

Cooper_Geralds_3B

I am wondering if sapling is not in the same order for everyone because some of my questions 1-19 do cover material we have not yet learned such as quantum numbers and some questions past 19 cover material that we have learned such as DeBroglie. Is there anyway that a list of the specific questions ...

Cooper_Geralds_3B

Calculate the wavelength, in nanometers, of the spectral line produced when an electron in a hydrogen atom undergoes the transition from the energy level n=3 to the level n=2. I am getting 12.66 nm as the answer after doing Rydberg's equation, but sampling is saying this answer is incorrect. Is anyo...

Cooper_Geralds_3B

Hi, In discussion today, my TA suggested that we know all the elements that are diatomic, so I thought it would be helpful for me to put them all here if anyone needs them. Hydrogen (H2) Nitrogen (N2) Fluorine (F2) Oxygen (O2) Iodine (I2) Chlorine (Cl2) Bromine (Br2) A sentence I found online said t...

Cooper_Geralds_3B

Hi, I was wondering if anyone could tell me how Dr. Lavelle found the mass of 9.1 x 10^-31 kg when he was calculating the change in velocity in the following problem: For H-atom the electron is then confined to its nuclear diameter, 1.7 x 10^-15 m (which would be the electron's uncertainty in positi...

Cooper_Geralds_3B

Hi, Does anyone know when we should make sure to calculate elements in their diatomic forms? For example, when finding calculating for empirical and molecular formulas, is there ever a time that we would not double the mass of nitrogen, oxygen, or any of the other elements that only exist in diatomi...

Cooper_Geralds_3B

Hi, Dr. Lavelle said that anything shorter than 10^-15 m is not detectable. I also researched further and found that the longest detectable wavelengths is generally from 10^6 to 10^11 m, but also make sure to pay attention to your units!

Cooper_Geralds_3B

Hi,

I must have missed this in lecture, but does anyone know the numerical value of Planck's constant?

Cooper_Geralds_3B

Hi is there a groupme for discussion 2E yet?

Cooper_Geralds_3B

194 g/mol of 0.376 g of caffeine burned, 0.682 g CO2, 0.174 g H2O, 0.110 g N2 formed. Determine empirical and molecular formula, write equation for combustion. I started by finding the grams of H and got 0.0196 through dimensional analysis, but I am wondering how to go about finding grams for carbon...

Cooper_Geralds_3B

Hi, we did this problem in discussion today but I missed the answers. For part a) I ended up getting 0.0423 moles and I was wondering why I got a different answer than posted above? I multiplied 8.61 g * (1 mol/ 202.484 g/mol). I got 202.484 g/mol by adding up the molar mass.

Cooper_Geralds_3B

Hi, we did this problem in discussion today but I missed the answers. For part a) I ended up getting 0.0423 moles and I was wondering why I got a different answer than posted above? I multiplied 8.61 g * (1 mol/ 202.484 g/mol). I got 202.484 g/mol by adding up the molar mass.

Cooper_Geralds_3B

Hi, I am wondering where I can find or gain access to the solutions manual for the textbook? I am working through the extra problems right now and want to double check my answers.

Cooper_Geralds_3B

Hi, the general rule for rounding is wait until the very end of the problem to round and follow sig figs unless it is given specifically in the question.

Cooper_Geralds_3B

Hi, a great starting point for this problem is to start by forming the molecular formula by counting the number of each element seen in the structure! I had to do research to figure that out, but once you have the molecular formula, you can proceed as you would following the normal steps for determi...

Cooper_Geralds_3B

As far as balancing equations, I recommend always starting with the element that is least abundant and then moving to the next least abundant element, and if it ever comes down to needing for example 6.5 as the coefficient to balance one side, use the fractional form of 6.5 --> 13/2 and then multipl...

Cooper_Geralds_3B

The significant figure depends on what the specific question is asking for, if the question specifically asks about moles then you would refer to the sig fig of the moles given and used throughout the problem.

Cooper_Geralds_3B

Correct! Sapling is the only graded homework assignment that needs to be turned in according to the end of the section covered in class. The current due dates are the end of week 1 and the end of week 3. All other textbook problems are optional but will likely help in review for midterms and final.

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