CHEMISTRY COMMUNITY

Alex Mele 2A

Ka is for acid dissociation, and Kb is for base dissociation.

Alex Mele 2A

Dr. Lavelle said that Chemistry Community will be available up to the day of the final exam. Because of this, I think our posts might be due by saturday at midnight, but I'm not totally sure.

Alex Mele 2A

Percent ionization and dissociation are the same thing. Percent deprotonation is the same if a compound ionizes to release an H+!

Alex Mele 2A

I always hand-write my notes. It helps me remember the material!

Alex Mele 2A

I don't think we will ever just be given two equations and have to figure out which is slower. We will either be told which is the slow step or we will be given enough rate law information to figure it out.

Alex Mele 2A

You can use E0(red)cathode - E0(red)anode or E0(red)cathode + E0(ox)anode!

Alex Mele 2A

To add on to the previous comment, you can look at the slow step of the reaction to determine the rate law but still have to eliminate intermediates from the final rate law. You can do this by looking at another step of the reaction to substitute out for an equal concentration.

Alex Mele 2A

The overall order of a reaction is just defined as the sum of the individual orders. In general, it measures the how sensitive a reaction rate is to changes in reactant concentrations.

Alex Mele 2A

I did the same thing as the previous response. In general, I don't think we'd need to include the exponent 1 or the concentration of C as it doesn't affect the reaction rate at all.

Alex Mele 2A

Aww this is such a fun idea!

Alex Mele 2A

I liked chemical equilibrium. I agree with the response that says ICE tables are satisfying!

Alex Mele 2A

I love our campus! I can't wait to walk around and see campus busy again

Alex Mele 2A

I'm going home to see my family! I'm excited to sleep in and drive around back home.

Alex Mele 2A

I'm part of greek life and PUMP, the premed undergrad mentorship program! I met someone who is involved with PUMP, would u say it is a good thing to do for premed students? also, I've never been on campus so idk but is greek life a good thing to get into at UCLA? PUMP has helped me connect with a l...

Alex Mele 2A

I'm part of greek life and PUMP, the premed undergrad mentorship program!

Alex Mele 2A

I think you can look at it the same way and check for the presence of OH- in a basic solution and H+ in an acidic solution! If you look at the sapling problems, you'll see that the basic solution equations have OH- in their final equations.

Alex Mele 2A

You get a point for every post on chemistry community, but we are assigned 5 posts per week for 10 weeks so the max is 50 points!

Alex Mele 2A

I think the same as the other responses. I've heard that Dr. Lavelle rounds some grades, especially those that are close to failing, but I don't think he curves the class as a whole.

Alex Mele 2A

I don't know if there is a way to see the distribution on CCLE, but maybe your TA could tell you more. We know that the average is 85% though!

Alex Mele 2A

I'm taking chem 30A, ls7A, and the '60s cluster!

Alex Mele 2A

You can get the ln out by raising e to the power of both sides of the equation! For example, if ln K = X, then K = e^x

Alex Mele 2A

It might be good to look at what you'll need to memorize for ochem early if you think you'll be really busy next quarter. Organic chemistry tutor on youtube is really helpful! I'm also planning on reviewing my ap chem notes

Alex Mele 2A

I don't think it's possible for a real system to be truly isolated. There is always some energy exchange.

Alex Mele 2A

I reviewed sapling and textbook questions, the outlines, my notes, and new questions on chemistry community. I also found the review sessions helpful!

Alex Mele 2A

Boiling points do occur at delta G = 0 because there is no change in temperature. Energy is going toward the phase transition and not toward heating up the substance.

Alex Mele 2A

I think the final will be cumulative. There will likely be review sessions and an email from Dr. Lavelle as we approach week 10 though!

Alex Mele 2A

Total entropy is the sum of entropy (system) and entropy (surroundings). Delta S (univ) is positive for a spontaneous reaction according to the second law of thermodynamics. In general, I like to remember that the universe likes to create more disorder.

Alex Mele 2A

Yes, we should be receiving an email about the final as we approach week 10, but it will more than likely be proctored in the same way as the previous exams.

Alex Mele 2A

I think of positive entropy as more disordered molecules, for example going from solid to liquid phase or liquid to gas phase. Negative entropy is the opposite, like going from gas to solid.

Alex Mele 2A

I solved this one by using the equation entropy = nRln(v2/v1). You don't need to know the number of moles of gas because the answer is per mole. You do know the gas constant R and the ratio V2/V1, so you can use these to get your delta S value!

Alex Mele 2A

Like others have said, it might be best to start by breaking this question up into three parts. I used the equation entropy = (Cv)ln(T2/T1) to account for each temperature change and the given value for entropy of vaporization to solve for the middle step. Every number that you need to use in this p...

Alex Mele 2A

I think there is a place where you can look up how fast classes at UCLA have filled up in the past! I've personally used my first pass to enroll in chem 14A and 14B, but I know lots of people have used their second pass too, and not everyone in 14B will go on to take 14C.

Alex Mele 2A

I'm not totally sure, but I think we have used ºC + 273.15 to get kelvin before.

Alex Mele 2A

Last quarter, I found the final harder than the midterms, in part because it covered material from the whole quarter. However, there were lots of review opportunities that helped!

Alex Mele 2A

I've been reading midnight sun when I've wanted to relax by myself. Takes me back to middle school for sure.

Alex Mele 2A

Going over the outlines can be really helpful for me. I also like to reread my notes right after lectures to make sure I understand and can remember all of the new material.

Alex Mele 2A

I always make a list of specific things that I have to do, and I start feeling very productive when I can cross things off. I'll even include things like taking a shower and making breakfast. For some reason, it always makes me feel like I have less work to do because each step that I write down is ...

Alex Mele 2A

This is just like the amount of energy that is added to the system. When a system does work on its surroundings, it uses energy, which gives the negative value. When the surroundings do work on the system, there is a positive value. I hope this makes sense.

Alex Mele 2A

I understand how frustrating it can be to not do as well as you expected on a test you really prepared for. However, there is still time to make up for your score on the second midterm and the final! I would recommend going to your TA's office hours to look over your exam and see where you can impro...

Alex Mele 2A

He also played Numb by Portishead a lot in the fall! I really like that song and it always reminds me of this class now haha

Alex Mele 2A

The assignment is due sunday at midnight. I found the textbook and the last lecture are helpful for learning the topics!

Alex Mele 2A

You can flip the reactions around (and change the enthalpy value appropriately) so that the compounds you don't want cancel each other out! So, if you have N2 on the reactants side and you combine it with a reaction that has the same amount N2 on the products side, you can eliminated N2 from your fi...

Alex Mele 2A

I believe the midterm will be all multiple choice like 14a was last quarter!

Alex Mele 2A

I love 60s-80s rock music. I'm listening right now to the smithereens, but I also really like eagles, queen, hall and oates, the rolling stones, etc!

Alex Mele 2A

Thank you so much for sharing! I also find reviewing the textbook helpful for studying

Alex Mele 2A

Since qp measures a change in energy at constant pressure, a different change in temperature would give a different qp = ∆H!

Alex Mele 2A

I was wondering the same thing, and also, will anything from Week 4 be on the first midterm or is it only covering everything up to the lecture on 1/22 (end of Week 3)? I think he will probably tell us during lectures where the midterm material ends. I think during 14A he also sent an email making ...

Alex Mele 2A

I think we'll take them during the lecture that we are enrolled in! I believe Dr. Lavelle told us at the beginning of the quarter that we shouldn't enroll in another class during our lecture for this reason.

Alex Mele 2A

Like others have said, studying the outlines and textbook problems is really helpful! I did this for both midterms and the final in chem 14a. I also reviewed sapling problems and some of my lecture notes.

Alex Mele 2A

I think the material is just similar to those sections in the textbook, so any of the problems from those sections would probably be good to review!

Alex Mele 2A

If the Ka of a monoprotic weak acid is 8.6×10−6, what is the pH of a 0.33 M solution of this acid? How would I do this problem? I would start by writing out the Ka equation. Ka = [H3O+][A-]/[HA] and this can be set equal to 8.6 x 10^(-6). You know that the initial HA concentration is 0.33M, so the ...

Alex Mele 2A

If something is amphoteric, it can act as an (arrhenius) acid or a base (e.g. water, Al(OH)3, Be(OH)2). If something is amphiprotic, it can either donate or accept a proton (water, HCO3-, HSO4-). Everything that is amphiprotic is also amphoteric.

Alex Mele 2A

Yes! You use the other compound in the conjugate acid/base pair in these types of problems just to find the Ka or Kb that you need to use.

Alex Mele 2A

I started by making an ice table from the initial partial pressures. Then, I plugged the equilibrium values into the Kp expression and solved for x. To find the total pressure at equilibrium, I added all of the partial pressures that I found together. Hope this helps!

Alex Mele 2A

The constant pKa measures dissociation with the negative log of [A-][H30+]/[HA]. pH is just the negative log of [H30+]. Both are affected by temperature and both pKa and pH are lower for stronger acids, but they are not necessarily equal to each other.

Alex Mele 2A

The constant pKa measures dissociation with the negative log of [A-][H30+]/[HA]. pH is just the negative log of [H30+]. Both are affected by temperature and both pKa and pH are lower for stronger acids, but they are not necessarily equal to each other.

Alex Mele 2A

idella 1D wrote:
idella 1D wrote:What is one of the worst compounds to use for chemistry?

Uranium Scandium

(USc)

proud to say that prof. Lavelle used this joke in today's lecture :D

Haha I loved this one!

Alex Mele 2A

This one is a pickup line that I told my friend during a titration lab in AP Chem back in the day: hey girl, I must be phenophthalein because you make me turn bright pink ;)

Alex Mele 2A

I think it's really helpful to have a designated study area! As opposed to doing homework on your bed. That helps me focus on what I'm doing and makes me feel more like I'm in a classroom.

Alex Mele 2A

K does not depend on starting concentrations. The ratio will end up the same if only starting concentrations are changed. If temperature is changed, on the other hand, K will also change.

Alex Mele 2A

The ideal gas law works best at low pressures and high temperatures. It doesn't take into account intermolecular forces and molecular size like Van Der Waal's equation does, so that is also a limitation. PV=nRT won't provide a very accurate response if these conditions aren't met.

Alex Mele 2A

You should get access to the solutions manual with sapling! That's how it worked for 14A last quarter.

Alex Mele 2A

^^ So this will change the concentrations of reactants and products at equilibrium, thus changing the ratio K.

Alex Mele 2A

Temperature will shift the equilibrium. If the reaction in exothermic, so heat is a product, increasing heat will increase the rate of the reverse reaction and shift equilibrium to the left. Decreasing temperature will shift equilibrium to the right. The opposite is true for an endothermic reaction,...

Alex Mele 2A

I don't know if those specific groupmes exist, but if they're made they'll probably be sent in the general 14B groupme: https://groupme.com/join_group/62288203/dSSkobMS

Alex Mele 2A

Temperature does matter, but 25ºC is a standard temperature where everything we have learned applies. I think you may have just made a calculator error here, because 10^(-2.44) is around 3.6 x 10^(-3).

Alex Mele 2A

Kb is the base dissociation constant. A large Kb value indicates a strong base. Table 6C.2 shows that Kb of morphine is 1.6x10^-6, and pKb (-log[Kb]) is 5.79. From 6C.1, pKa of HBrO is 8.69, so pKb of BrO- is 14-8.69= 5.31. pKa + pKb for conjugate acid/base pairs = 14. The hypobromite ion (conjugate...

Alex Mele 2A

I'm pretty sure our exams will be proctored by TAs like the midterms have been. It's possible that we will join our TA's regular zoom link, or maybe they will post or email us new links. I'm not certain about that, but I'm sure we will learn more when we get closer to sunday.

Alex Mele 2A

I don't think course evaluations in this class are for credit. However, Dr. Lavelle asked us to fill them out because they provide important feedback.

Alex Mele 2A

I think you determine this based on electron configuration. Mn normally has 7 valence electrons ([Ar]4s²3d⁵) so Mn4+ has only 3. The reason both 4s and 3d electrons can act as valence electrons is because these orbitals have a small energy difference.

Alex Mele 2A

Strong acids dissociate completely in a solution. This means that they lose H+ more easily than weak acids do. Weak acids, because they don't give up protons as easily, do not completely ionize in a solution.

Alex Mele 2A

You can draw or write out a normal valence shell electron configuration, then only use hybridization when necessary. If something is has sp3 hybridization, you will move one electron from s to p without changing any other orbital. I don't think you will usually need to draw non-valence orbitals at a...

Alex Mele 2A

I'm planning on going through the old outlines, lecture notes and sapling questions. I also like reviewing chemistry community before tests to see if I know how to answer questions that I might not have thought of myself.

Alex Mele 2A

I believe that the ligand is always written after the metal atom or ion. However, I am not positive, so I would be interesting in seeing another student's response too!

Alex Mele 2A

I've heard that Organic Chemistry Tutor on youtube is really helpful for reviewing specific topics!

Alex Mele 2A

This is tetrahedral because there are four bonding groups and no lone pairs (i.e. AX4). Single, double, and triple bonds can all be treated the same when determining VSEPR molecular shape.

Alex Mele 2A

I'm doing well! Happy to be home with everyone here for the holidays. The cold weather makes it easier for me to focus on school, too.

Alex Mele 2A

Hybridization allows for the forming of more bonds. For example, C has electron configuration 1s2 2s2 2p2, meaning it has only two unpaired valence electrons and can form two bonds. However, we know that carbon likes to form four bonds. This is explained by sp3 hybridization, when a 2s electron jump...

Alex Mele 2A

The easiest way for me to think about shapes is just to draw a lewis diagram and picture the molecule in my head. Then I can see if it's a plane, pyramid, seesaw, etc. and think of the name that matches my mental image. Charts can also be helpful for memorizing what these possible names are!

Alex Mele 2A

I don't remember my TA saying when scores would come out, but I also heard from other student's that they might come out sometime today.

Alex Mele 2A

I don't think it's been addressed either, but I don't think there's any reason why we wouldn't have a lecture. At least if we learned new material on that Friday it would be fresh in our minds for the final.

Alex Mele 2A

I think this question is asking you to look a the O-S-Cl bond angles and see if their measures are different from each other. In this trigonal pyramidal molecule, there is only one angle measure because every OSCl has equally spacing.

Alex Mele 2A

Joel Meza 2E wrote:Is there no prerequisite for 20L that is a 20 series class? Or in other words, we don't have to previously taken a specific 20 series class to enroll in 20L?

Nope! 14A, 20A, and 20AH can each fulfill the prerequisite, and 14B, 20B, and 20BH can fulfill the corequisite.

Alex Mele 2A

You can take them together or you can take 14BL after 14B. I don't think you can enroll in BL before enrolling in B.

Alex Mele 2A

Hi all! I recently looked at UCLA's recommended courses for medical school, and I noticed that lots of med schools require a year of English (or 3 quarters). I think any W class can count, so does anyone know if we need to take 2 more English/W classes after taking a cluster? Or does the cluster cou...

Alex Mele 2A

Mo does have 4d5 and 5s1. The half-filled d-orbital + half-filled s orbital is still a more stable combination than 4d4 5s2. This is the same rule that Cr follows even though Mo is one row down!

Alex Mele 2A

Yes! As far as I know, any molecule with the same number of bonding and lone pairs will have the same VSEPR shape. Molecular geometry tables based one the VSEPR model assign shapes just based on those two factors.

Alex Mele 2A

I recommend looking at the Chemical Bonds outline on Dr. Lavelle's website. It says we should understand ionic vs. covalent bonds, bond lengths, coordinate covalent bonds, dissociation energy, LD forces, dipole-dipole interactions, Hydrogen bonding, etc.

Alex Mele 2A

I like to go for a walk in the morning to pick up a cup of coffee before class or to jog some hills on the weekends. I also participated in virtual yoga with my sorority on Saturday and it felt really good. :)

Alex Mele 2A

Your TA might let you attend another of their discussions for the week if you couldn't make the one you're enrolled in. That way you could still practice with the material.

Alex Mele 2A

Hi all! I was wondering if anyone else was planning on taking chem 14B and chem 20L together next quarter? Or if anyone has heard whether or not that's recommended?

Alex Mele 2A

According to Dr. Lavelle's website, "Step-Up sessions go through step-by-step fundamentals working through prepared topics and worksheets for students who want step-by-step assistance. Drop-In sessions are for all students to ask questions and get involved in discussion. Workshops involve worki...

Alex Mele 2A

Thank you for answering all of these questions! I always hear about how medical school is so hard to get into and it makes me feel good to hear from people who have done it. Do you know if a lot of your UCLA classmates got into programs too?

Alex Mele 2A

Adjusting to the quarter system has been different. I feel like with all of my classes I'm always getting ready for a midterm or final! But I like that this class is structured with the same type of homework every week so I never feel like I'm forgetting something.

Alex Mele 2A

Dipoles come from atoms with different electronegativity values. When one atom in a molecule attracts electrons more than another, it creates slightly positive and negative regions.

Alex Mele 2A

In general, polar solvents dissolve polar solutes. Like others have said, the polarity of water is what separates a Na+ cation from a Cl- anion. Salts will dissolve in water because they are ionic and polar.

Alex Mele 2A

What I did on sapling was click on the atom I wanted in the center then click in the answer box to set it down. I clicked on whatever bond I wanted to use then clicked on the central atom to attach them. Then, I replaced any incorrect atoms with the ones of the element I wanted. I clicked on single ...

Alex Mele 2A

This notation shows the charge of the ion as a whole (not formal charge of each atom). You know to put + outside of the lewis structure of something with a net +1 charge, +2 for +2 charge, - for a -1 charge, and so on. You don't need to put a charge outside of brackets for a neutral atom.

Alex Mele 2A

It's also helpful for me to have a designated study spot without many distractions. I like to have tea or coffee with me in a quiet spot and my phone in another room. It also helped me when studying for this midterm to make a checklist of everything I wanted to review. I listed lecture notes, textbo...

Alex Mele 2A

These exceptions occur because half- and fully filled d sublevels are more stable than other partially filled d sublevels. Electrons will generally want to be in the lowest (most stable) energy state, so for Cu or Cr they will fill up a d sublevel halfway or fully instead of the s sublevel.

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