CHEMISTRY COMMUNITY

Sandra Kim 2B

6.45: Volta discovered that when he used different metals in his “pile,” some combinations had a stronger effect than others. From that information, he constructed an electrochemical series. How would Volta have ordered the following metals, if he put the most strongly reducing metal first: Fe, Ag, ...

Sandra Kim 2B

i saw the calculations for this part since i was very lost and saw that ln(1/[Cl-]^10) just suddenly became ln([Cl-]^10) and then suddenly ln[Cl-]?? is there some sort of rule about natural logs that i don't recall or what calculations occurred that led to it cause i am pretty confused as to how it ...

Sandra Kim 2B

can't help you with the first part but i know that you omit water since it's just a solvent and not really being active in the rxn so you wouldn't add it

Sandra Kim 2B

yup and mostly relates to gibbs free energy/deltaG i believe

Sandra Kim 2B

you could try going into the "Unanswered topics" quick link and there's a lot of chem_mod/chemadmin posts that arent commented on and then you could click the number of posts under their name (or that general area) to get to all the posts they've interacted with/made and maybe bookmark the...

Sandra Kim 2B

oh man i want to move into dorms in the fall! but does anyone know if it'll be only single dorms or if there's a chance to have doubles? (i'm pretty sure a single dorm would be a hefty cost for me but i think i might still try? not too sure lol)

Sandra Kim 2B

i don't really understand what it means when the textbook says to use an inert conductor (like platinum) when both the oxidized and reduced are in the "same solution." like what does it mean by "same solution"? also is that the only reason to use an inert conductor or are there m...

Sandra Kim 2B

hi! when i work on these types of problems i lay out a lil template for each and fill in the stoichiometric coefficients as i go! (X=reactant, Y=product) acidic: reduction: X + H+ + e- -> Y + H20 oxidation: X + H20 -> Y + H+ + e- basic: reduction: X + H20 + e- -> Y + OH- oxidation: X + OH- + H20 -> ...

Sandra Kim 2B

I have the same problem! If you do receive the Cal grant though, I think you can request to have it be applied to your summer classes through a petition. I found most of my information on this website: https://www.financialaid.ucla.edu/Undergraduate/Summer-Information#495121507-maintaining-summer-a...

Sandra Kim 2B

hi! can someone explain to me how the summer session costs work for someone who receives financial aid? i saw something about UCLA students only paying the unit fees but how does our financial aid come into play? do we just use our financial aid refunds from previous quarters to pay for the summer s...

Sandra Kim 2B

i know a lot of people said organic chemistry tutor on youtube already but another pretty good youtuber that helped me thru chem14a was melissa maribel! she explains things to you like you're an elementary student so if you're kinda braindead (like me) at the moment, give her channel a shot for any ...

Sandra Kim 2B

I think for that redox reaction the solid platinum is just acting as an inert conductor so you would just take into account that it's in contact with the anode but you would mainly focus on the other molecules when writing the equation out. and i'm pretty sure cell notation has the anode/oxidation o...

Sandra Kim 2B

in the balanced equation, why are we allowed to keep the coefficient as 3 in the H2O on the product's side? does the fat dot in the middle of that imply that it's multiplied to the 2Fe2O3 so the coefficient 2 would extend to the 3H2O or is it something totally different? am confused :(

Sandra Kim 2B

dana hu 1B wrote:Thank you for your response

I then got this which is also wrong:
2MnO4-(aq0 + 4H2O(l) + 3S+2(aq) -> 2MnO2(s) +3S(s) +8OH-(g)

What did I do wrong here? Are my states wrong?

i think your OH should be aqueous (not a gas) since the info says it's a basic aqueous solution. hope this helps!

Sandra Kim 2B

Do we need to remember the rules for oxidation states for the final or would it be an irrelevant topic to focus on for the exam? like the general rules and for oxygen/hydrogen in the chempendix thingy from sapling

Sandra Kim 2B

i was finishing up lectures for this week and i just want to know what exactly is a coulomb? i think i lost the definition or idea of it during the explanations of work and stuff but how did y'all note what it was?

Sandra Kim 2B

to find the number of electrons that go on like the opposite sides of the half-reactions, do we just see how many electrons it would take to reduce the oxidation number in the reduction reaction? or is there a better way to think about this?

Sandra Kim 2B

According to current theories of biological evolution, complex amino and nucleic acids were produced from randomly occurring reactions of compounds thought to be present in the Earth’s early atmosphere. These simple molecules then assembled into increasingly complex molecules, such as DNA and RNA. I...

Sandra Kim 2B

Hi! The solutions manual for this problem says that we calculate enthalpy of the reaction using "tabulated enthalpies of formation," so I tried to look at Appendix 2A to find them but most of the values weren't there. Is there another table we should be using? Thanks! I believe Appendix 2...

Sandra Kim 2B

You could start by writing out the balanced chemical equation representing the reaction. The question then asks for the final temperature which hints that you need to find the heat transferred during the reaction (q). In constant pressure, q=delta H and you can find delta H of reaction using the ch...

Sandra Kim 2B

Hydrochloric acid oxidizes zinc metal in a reaction that produces hydrogen gas and chloride ions. A piece of zinc metal of mass 8.5 g is dropped into an apparatus containing 800.0 mL of 0.500 M HCl (aq). If the initial temperature of the hydrochloric acid solution is 25°C, what is the final temperat...

Sandra Kim 2B

I believe there's also standard molar entropy (Sm⁰) as well!

Sandra Kim 2B

Hi Mrudula! So the way I solved this problem was basically by looking at the units of each answer and working backwards. The first thing you have to do to determine enthalpy is find out how many kilojoules of energy are being supplied to the system. Using 550 W (which is equal to 550 J/s) you can c...

Sandra Kim 2B

one red molecule could move upwards to form an L shape to create 4 more possible positions and then an upside-down L for 4 more positions if these were the possible positions you didn't notice

Sandra Kim 2B

this applies to ΔH, ΔH⁰, ΔS, and ΔS⁰ as well but I forgot the difference between ΔG and ΔG⁰ and I feel like it was too small of a detail that made me unable to find in my notes what the difference was (and it's been hanging in my head for a while lol). does anyone know? thanks!

Sandra Kim 2B

can someone explain why NO is likely to have a residual entropy in their crystalline forms at T = 0K for #1 in the sapling week 5/6 hw? i don't really understand the solution explanation and at first, i didn't think the orientation of N and O really differed enough in NO to reach that conclusion ._.

Sandra Kim 2B

so first you gotta find the heat of the ice and the heat of the water to find the heat(ice): mol(ice) x deltaH(fusion) + q(ice) to find heat(water): q(water) then set both of them equal to each other and solve for T(final) it helps to know what values to use when u look at the units and see what can...

Sandra Kim 2B

on week3/4 sapling #19, it said to assume the constant-pressure molar specific heat for N2 is 7R/2. on the constants and equations sheet, it has different fractions for the specific heat (Cv and Cp) of ideal gases (because of nonlinear/linear molecules, i'm guessing?) but how would we know what frac...

Sandra Kim 2B

does anyone know what other value i'm supposed to use to answer part (b) apart from the 1.45x10^5 J from part (a) and ofc 100% to find the percentage of the heat used to raise the temperature of the water :(

Sandra Kim 2B

if we're given grams of the molecule/whatever solution/atom, can we just manipulate the equation q=nCΔT to use grams instead of moles (n) and use a value of C in units of J/(C.grams) rather than changing the grams of the solution to moles? (ofc just all depending on what's given in the problem) also...

Sandra Kim 2B

how do you tell q is negative or positive in a problem? i encountered this issue in textbook problem 4B7 and i assumed the q was positive since it just didn't have a sign in front of it, but from "The cooling system that surrounds the chamber absorbs 947 kJ as heat," what are, like, the tr...

Sandra Kim 2B

Zoe FC 1C wrote:where can we find the outlines? are they on the website or on ccle?

they're on the chem14b website! just scroll down a bit and you should find them :)

Sandra Kim 2B

i think it depends on whether there are more products or reactants. if K is less than 1, then there's more R so reactants are more stable (since it's P/R so R is larger than P to make it a value less than 1). if K is more than 1, then there's more P so products are more stable ( this is just somethi...

Sandra Kim 2B

i'm also trying to take bl (and 14c if i can) next quarter to finish the chem series soon

Sandra Kim 2B

just to grasp the concept, imagine you're driving from point A to point B and it's a 5 mile distance. somewhere else, your friend is driving from point C to point D and it's also a 5 mile distance. the points are at different places but the distance driven is still the same. the temperatures are at ...

Sandra Kim 2B

Does anybody have the answers collected for some of the past weeks' UA sessions? I, unfortunately, haven't been able to make it to many and I am trying to review old worksheets to study for the midterm so I would really appreciate being able to check my work :) try going under "Unanswered Topi...

Sandra Kim 2B

just to start, make sure you use Kb by doing Kw/Ka so you can get [OH-] through the usual ice table! Kw is 1.0x10^-14 btw. and then get your pOH and then your pH after all your calculations :)

Sandra Kim 2B

definitely try to going to the UA sessions if you can and review the textbook problems! the problems in the textbook tend to be similar to the ones that appear on exams i think

Sandra Kim 2B

for a, how would i calculate it so that the end result is in joules like how would the - 1.00 atm x 1.20L be converted into joules so i could compare it to what i got for b?

Sandra Kim 2B

Can someone explain to me why sometimes the [H30+] or [OH-] are assumed to have the same initial molarity as the given reactant and how can I tell this will occur when I'm given the reactant and its molarity? (I happened to do 6E1 wrong at first because I carelessly went right ahead solving it witho...

Sandra Kim 2B

when finding Ka of benzoic acid in a .110M solution with 2.4% percentage deprotonation, what goes in the denominator for the Ka equation? i already know that the numerator is (.00264)^2 but could someone explain what numbers would go in the denominator and why?

Sandra Kim 2B

For the parts in 6D5, how would we find Kb in order to get the value of x ([OH-])? I'm not sure where to go after I made the Kb equation since I only have the molarity of the reactants :/

Sandra Kim 2B

I personally like Hannah Chew! She's really helpful when it comes to questions you may have and going thru the processes imo

Sandra Kim 2B

i'm pretty sure finding the pH of a conjugate wouldn't be asked on like an exam since pH is more based on the solution as a whole. I would assume that the strength of it would be considered more rather than pH.

Sandra Kim 2B

When calculating the equilibrium constant for problem 5.35, how do you know that each value was a hundredth on the graph? Why isn't it just Pb=5, Pc=10, and Pa=18?

Sandra Kim 2B

For letter d of textbook problem 5J5, it said that there was no change to 2HD(g) + H2(g) ⇌ D2(g) when the total pressure increases because there was the same number of moles on each side of the equation. When I look at it, it doesn't look like they have the same number of moles? So I'm pretty confus...

Sandra Kim 2B

based on what was said in the module 4 video, exothermic reactions (releases heat) shift to the right/products and K increases while endothermic reactions (uses up heat) shift to the left/reactants and K decreases. so, you would have to determine the type of reaction it is first if you wanted to see...

Sandra Kim 2B

^i agree with the person who posted above for forwards reactions but would it be different for chemical reactions that are reverse reactions? or do problems generally not consider reverse reactions?

Sandra Kim 2B

if you're worried that different units will be on the test for constant R, don't worry! on the constants and equations sheet that we are allowed to use during tests, Dr. Lavelle put the value of R for many different units! you can find the sheet on the 14b website :)

Sandra Kim 2B

Just to make sure, are products more stable than reactants when Q<K (forward reaction) and reactants more stable when Q>K (reverse reaction)? Also, is this notion about stability applicable when K is large or small respectively?

Sandra Kim 2B

I didn't have Dr. Lavelle for 14A and was wondering how tests were formated as well as any other tips to better prepare for the tests? from what i learned from chem 14a with lavelle, what really helps to prepare for the tests is to do the textbook problems in the syllabus and to review them. also, ...

Sandra Kim 2B

A researcher fills a 1.00 L reaction vessel with 1.84 x 10^-4 mol of BrCl gas and heats it to 500 K. At equilibrium, only 18.3 % of the BrCl gas remains. Calculate the equilibrium constant, assuming the following reaction is taking place. 2BrCl(g) ⇌ Br2 (g) + Cl2(g) I came across a pretty old chemis...

Sandra Kim 2B

I originally came in as a Labor Studies major because that's what I put on my application, but I tried to change to Marine Biology at New Student Orientation. Unfortunately the change doesn't seem to have gone through :/ Oh nooo do you know why it didn't go through? I'm a bit worried that my (poten...

Sandra Kim 2B

I feel like a problem where we actually have to calculate something using it won't appear on the final but it would be something to keep in mind for 14b. but maybe knowing the concept of its relation to acidity could come in handy.

Sandra Kim 2B

I think he meant to say that each individual C atom in the C2H2 are sp hybridized (2 bonding regions on each C atom) and as a whole, the molecule has sp2 hybridization. since NH3 only has one N atom, it is solely labeled as sp3 hybridized with N's three bonds and one LP. you could also note that eac...

Sandra Kim 2B

One way to distinguish the strength of the acidity between two acids is to look at the bond lengths of H-bonds based on atomic radii (bigger radii-> longer+weaker bond-> more acidic since it loses the H-atom more easily). Another thing to look at is the electronegativity of the compound based on the...

Sandra Kim 2B

I know I'm going to be binging a bunch of games with my friends for hours straight once winter break comes :) Even though it's just two weeks, I want to indulge in it as much as I can.

Sandra Kim 2B

Just a bit confused but what does it mean when an acid/base is completely/partially ionized in water and how does this relate to how strong/weak an acid/base is?

Sandra Kim 2B

6B asks for the difference in the pH values of the two solutions when the molar concentration of HCl in hydrochloric acid is reduced to 12% of its initial value by dilution. I'm not even sure how to start this problem; how do you approach a problem where the solution is being diluted and being reduc...

Sandra Kim 2B

What's the importance of saying that the solution is at 25 degrees celsius? I've seen it in a lot of problems on calculating pH and I was not sure why it specified that.

Sandra Kim 2B

(a) Potassium hexacyanidochromate (III) is written as K 3 [Cr(CN) 6 ]. We know that Cr has a charge of +3 because of the Roman numeral (III) we see in its name. We also know that (CN) always has a charge of -1. Since there are six (CN) - and one Cr +3 , the overall charge is [Cr(CN) 6 ] -3 . And si...

Sandra Kim 2B

not sure if this was asked already but are we going to be expected to remember the names of ligands for the final/in general (like en, edta, oxalato, etc.)?

Sandra Kim 2B

for textbook problems 9C3 (a) and (c), it gives potassium hexacyanidochromate(III) and tetraamminediaquacobalt(III) bromide respectively, and told us to write the formula for them. the potassium in (a) was K3 and the bromide in (c) was Br3. How would you figure out that there were three of those ato...

Sandra Kim 2B

like some people have said, i feel like i'm a little behind on classes and prep for finals but also a bit fatigued when i barely have any friends (if at all) in my classes this quarter, so i haven't really had anyone close to reach out to. but in the end, i know the last two weeks will fly by super ...

Sandra Kim 2B

Hi there! It's only been a quarter, but there's honestly no problem with switching your major at anytime (as long as you have enough time to finish your lower divisions and upper divisions). Just make sure to pursue something that aligns with your interests and that you are healthy and taking care ...

Sandra Kim 2B

the quarter's about to end and i was wondering if anyone is going to/thinking about switching majors! honestly, it's only been one quarter yet i'm realizing more and more that maybe choosing a stem major to please my parents wasn't that great of an idea... and i know switching majors is pretty commo...

Sandra Kim 2B

i think this might be how ion-dipole interactions are stronger than dipole-dipole interactions. (but i am also not too sure; there could be more to it)

Sandra Kim 2B

the s character is the s orbital's contribution in hybridization. This is basically the bond angle from what I can find. So an increase in the s character I believe would = an increase in bond angle because they are proportional. to correct myself, s character isn't the same as bond angle so my sec...

Sandra Kim 2B

for textbook problem 2F17, it asks how an increase in s-character in a hybrid would affect its bond angle. Does anyone know what they meant by "s-character" (i just don't recall ever hearing this term) and how its increase would increase the bond angle rather than decrease?

Sandra Kim 2B

In the recent lecture, Dr. Lavelle said that octet expansion involves d-orbitals but I feel like I have seen instances where elements like Si, P, and S have had expanded octets in their Lewis structures. Where do the d-orbitals come into play with these elements in the 3p orbital or is my brain mess...

Sandra Kim 2B

Hello Dr. Lavelle! I just wanted to let you know that the "water on Mars" joke at the end of one of your lectures made me genuinely smile during a long depressive episode. I think it was the first time I really smiled for a while when that happened and I truly always appreciate the positiv...

Sandra Kim 2B

Revisiting past textbook and sapling problems along with the notes are probably going to be the biggest form of studying for me since it's hard to go to the UA sessions (just personally can't; though I do hear great things about them!) I wish everyone good luck studying when the time comes around :)

Sandra Kim 2B

For part b of 3F5, it said that butanol (C4H9OH) had H-bonding when diethyl ether (C2H5OC2H5) didn't, which made butanol have a higher melting point. I was wondering if anybody knows how you would know one would have H-bonding and one wouldn't when it seems like both would or how you would tell in g...

Sandra Kim 2B

based on the lectures: atomic/ionic radii: increases down (more shells=e- farther from nucleus), decreases across (more nuclear charge pulls e- closer) ionic radii: cations smaller than parent/anion larger than parent ionization energy: decreases down (bigger size=farther e-=less energy req.), incre...

Sandra Kim 2B

^ yup and also in general, you shouldn't give your halogens a double bond since it would lead to it having a +1 charge instead of its usual -1 charge which would make it more reactive which is bad

Sandra Kim 2B

generally, you shouldn't make your halogens, like Cl, have a double bond because that would make it have a +1 charge which would make it more unstable (most halogens have a -1 charge to make it stable like a noble gas yk?) so that's why you can only make the resonance structures differ between the O...

Sandra Kim 2B

I was having a hard time with the Lewis acids and bases too, can someone please explain the difference. it helps to have a visual structure of the molecules/atoms so you can see whether there are any lone pair electrons that can be shared (Lewis base) or if it's deficient in electrons (Lewis Acid)....

Sandra Kim 2B

i think when a molecule has polar double bonds, it has a higher polarizing power (the atom's ability to pull electrons to it) which makes it a Lewis acid (since it would take the electron pair). hope this helped a little :)

Sandra Kim 2B

i'm also definitely worried about the grade in general but i wouldn't stay too stressed considering you only need 50% to pass the class. i know it's not ideal to set standards that low haha but knowing that we have that kind of safety net (?) to at least pass is pretty reassuring and decreases the w...

Sandra Kim 2B

I'm in the same boat! I took regular hs chem in 10th grade and definitely haven't seen a lot of the stuff that's been taught this quarter before while just vaguely remembering the stuff in the fundamentals :(

Sandra Kim 2B

Massimo_Capozza_1H wrote:If it doesn't fit in our schedule can we still take 14B spring semester or do we have to wait?

I'm pretty sure the class itself would be available spring quarter but I would take into consideration that it might not be Dr. Lavelle teaching it

Sandra Kim 2B

pretty hard to keep up when it's all online and surrounded by distractions haha :) and not doing so well but it is what it is :/ i'll have to change my habits or something for next quarter somehow

Sandra Kim 2B

here's the discord!
https://discord.gg/PBKZEzcF

Sandra Kim 2B

I didn't do so hot either LOL although it was hard to not beat myself up over it, it's definitely motivation to prepare myself better for the next one. It's also nice to consider this as a good warning about how future midterms could be like and how fast the quarter system is since I'm just a freshm...

Sandra Kim 2B

The reason why there's only one orbital is because of the third quantum number. The third quantum number will specify which orbital you're in. We don't know what orbital +1 is referring to (since there's no set standard for ml numbers...for example +1 could be 3dxy or 3dxz), but we know it's referr...

Sandra Kim 2B

For letter d of 1D23 in the textbook, the solutions manual says that there's only 1 orbital for an atom with quantum numbers n=3, l=2, ml=+1. At first, I thought it would have been 4 orbitals since l=2 has -2, -1, 0, +1, +2, so up to +1 would have been 4 orbitals. Can someone tell me what's incorrec...

Sandra Kim 2B

it might take a bit longer than expected since they found an error in a problem recently so they have to go through all the exams again Did you have a problem in your exam too? In one of my questions there wasnt a correct answer in the multiple choice... I thought I was just making a mistake until ...

Sandra Kim 2B

yeah, i'm pretty sure we can just think they want the full electron configurations on sapling as a default

Sandra Kim 2B

it might take a bit longer than expected since they found an error in a problem recently so they have to go through all the exams again

Sandra Kim 2B

I'm also wondering if the midterms are curved :( would love it if it was

Sandra Kim 2B

Eve Gross-Sable 2B wrote:I do not think there will be very many since it's only a 50 minute period, but on a related note, does anyone know the format?

they will be one-part (as in no part a, part b, etc.) multiple-choice questions (thank [censored])

Sandra Kim 2B

We're going to be allowed to have multiple empty sheets of paper for scratch work, right? I feel like just one wouldn't suffice for me :(

Sandra Kim 2B

By just using the Heisenberg Uncertainty Principle, it gives you the minimum uncertainty since the principle tells us that the atoms must be bigger than whatever you get for the answer after using the equation (since there is a physical limit to the minimum size that atoms can exist based on physica...

Sandra Kim 2B

I saw in the student solution manual for exercise 1B9 that they used the function: E=hcλ^-1 to find how many photons are generated. I just want to know how they got this equation to solve the problem.

Sandra Kim 2B

This fundamentals exercise gives names of the compounds being reacted/produced (like (a) Calcium metal reacts with water to produce hydrogen gas and aqueous calcium hydroxide.). I was just wondering if we are going to be expected to know how to write it into an actual chemical equation given just th...

Sandra Kim 2B

Doing all the textbook problems has been a good way to memorize the concepts and steps to solving problems :)

Sandra Kim 2B

So we aren't expected to memorize them, right?

Sandra Kim 2B

Is there a reason why it was specifically converted to km in the answer key? I don't see the question asking for the answer to be in km

Sandra Kim 2B

lol sorry for replying again but I just saw that we will probably be given the same periodic table for the exams so that everyone would use the same numbers for things like molar mass!

Sandra Kim 2B

I'm pretty sure we aren't expected to memorize the constants and will be allowed to have sheets of both the periodic table and constants with us. But I'm sure it would be nice to memorize some of the constants that are often used.

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