CHEMISTRY COMMUNITY

Jenny Chau 1I

Usually before a midterm, do UAs who hold sessions typically do review for material on the midterm or do they focus on the material that we learn that week?

Jenny Chau 1I

Hello! I also got the same answer for that first row, but I think we were supposed to skip it because the solution manual errors on Dr. Lavelle's site mentions that 6B.9 has errors. Thanks for answering I honestly thought I was going crazy when I couldn't figure it out. Does the manual error possib...

Jenny Chau 1I

I feel like this is dumb but I'm getting a weird answer for the first row of problem 9. It's given that [H3O+] has a molar concentration of 1.50 mol.L^-1. So I assume to find [OH-] you would divide 1x10^-14 by 1.50 M. However, I keep getting a value 6.67x10^-15 and when you plug that into -log([OH-]...

Jenny Chau 1I

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)? From what I remember about 14A, the content on the midterm was usually around up to week 3, a week before the midterm. And I'm gue...

Jenny Chau 1I

I heard the midterm will be taken during lecture instead of discussion section this time but will we be taking them at our respective lecture time or one general lecture time?

Jenny Chau 1I

I ended up assuming that the D was supposed to represent deuterium which is just an isotope of hydrogen. So in order to make the equation balanced, I put a 3 in front of the d2. And because the moles are equal on both sides, this would mean there's no change in the equilibrium distribution. Can anyo...

Jenny Chau 1I

On problem d, the chemical equilibrium looks as it does on the textbook:

Is d2 supposed to be shorthand for something?

Jenny Chau 1I

Sorry if I was a bit unclear but I was referring to how my x values are different from the ones presented in the textbook. I kept getting x= 8.712 and .074 but the textbook has x = 9.2 and .071 instead of what I got. So I was just wondering if maybe the textbook has it wrong or if I made a mistake o...

Jenny Chau 1I

On tests will we be expected to remember weak/strong acid and bases or will it be told on the test? I was just wondering because I know a few people who didn't take 14A and therefore don't know what to classify as strong or weak acid or base.

Jenny Chau 1I

Is the answer in the answer key for this problem wrong? I've checked through my calculations multiple times, changed the way I calculated on the calculator several times and checked that all the numbers are correct but I'm getting 8.712 and .074 instead of what's on the answer key. Did anyone get th...

Jenny Chau 1I

Does anyone else's pdf of the answer key have some text that overlap? At the bottom, the "this material is copyrighted" is usually overlapping some of the solution text and I can't understand the solution entirely. Does anyone know how to fix this?

Jenny Chau 1I

I hope this isn't a dumb question but how do we know when to use ICE as opposed to just plugging in values into: Kc = [products]/[reactants]? I've been doing problems the latter way when the problem is solved through ICE in the answer key.

Jenny Chau 1I

Hi! I was under the impression that we say the change is negligible when the K is smaller than 10^-3. 10^-4 is also a small enough K value, but Lavelle did say in his most recent lecture that the cutoff is 10^-3. Just thought that clarification might help. On your other concern, I recall that we ar...

Jenny Chau 1I

I hope I don't sound dumb asking this but on the lecture posted Monday, Professor Lavelle basically said cubic equations are hard to solve but if the Kc is very little, you can use approximation instead of actually solving for x. But this was if the Kc was very small (at least up to 10^-4). Is there...

Jenny Chau 1I

Yes I believe so! It would make sense that both of those flasks would have the same amount of X and X2 since flask 3 represents the point equilibrium was reached. Once equilibrium is reached, the concentrations of the product and reactant don't change over time, so flask 4 should be the same as fla...

Jenny Chau 1I

Is flask 3 and flask 4 supposed to contain the same amount of X2 and X?

Jenny Chau 1I

Is the equation for this problem not balanced correctly? The equation is >> 4 NH3(g) + 6 NO(g) --> 7 N2(g) + 6 H2O(g). There's only 10 N's on the left side and 14 on the right. Is this a mistake because I feel like N2 should be a 5 instead? Or did I overlook something and made a mistake somewhere?

Jenny Chau 1I

Jessie Hsu 2A wrote:I just checked both the online and bookshelf version of the textbook and they both work fine for me. Maybe try logging out and logging in again on your desktop app?

I logged back in and it worked. Thank you!

Jenny Chau 1I

I use the bookshelf app to read the textbook offline and because sometimes the browser version through sapling has some text issues but I noticed section 5G does not load at all. I've waited a while and it still hasn't loaded while sections before and after 5G will load. It works fine on Sapling but...

Jenny Chau 1I

In Professor's Lavelle lecture this Friday, he has on his notes "if pressure of reaction vessel is increased by adding an inert gas, the moles of R, P and volume are constant." If increase/decrease of pressure leads to decrease/increase of volume, respectively, then why does volume not cha...

Jenny Chau 1I

How would we determine what the gas constant R is? Is it something that would have to be given or is it something that we might be expected to find?

Jenny Chau 1I

I paid for the 24 month access one (I think) so when I clicked on Sapling through CCLE, it directed me to the page where you can enter the prepaid access card but there is another option that's says "credit." The option about credit is the one that worked for me.

Jenny Chau 1I

From what I know, I think session from Tuesday at 3PM was recorded. Some students requested the TA to record it since they'll be missing it. He said during the review that he would email those students a video of it but I think he said he would post the lecture for everyone to see (but doesn't know ...

Jenny Chau 1I

Why is NH2NH3+ an acid? I drew out the lewis structure (I think I drew it correctly...hopefully) and I got a lone pair on the NH2 part. Wouldn't that make it a base instead since it can accept a H+? Does it have to do with its charge (like it wants to remove an H+ because it's charge is +)?

Jenny Chau 1I

Yeah I'm pretty sure it should be tetrahedral.

Jenny Chau 1I

I'm not entirely sure either but on his email he said it will be Bruincast and in another email, he said his review will be in class, so I'm assuming it's going to be a recorded video like his lectures.

Jenny Chau 1I

I'm not sure if I'm interpreting your question correctly but I can explain how the structure works. When drawing out SOCl2, there are 4 regions of electron density surrounding O, the center atom. So the arrangement would be tetrahedral and the determined bond angles of a tetrahedral arrangement are ...

Jenny Chau 1I

I noticed that in pdf that provides the answers to the textbook problems, the answer for the net ionic equation is OH- + H+ --> 2H2O. Why is there a 2 in front of the H2O?

Jenny Chau 1I

Does anyone know if all the review sessions held by TAs are an hour each or will they vary depending on the TA? I went to the one today and it was an hour (though I think it may be because the TA had a TA meeting to go to right after).

Jenny Chau 1I

I feel like I'm thinking about this too hard but how would you be able to identify a Bronsted acid and base if there isn't a reaction? For example, problem J1 asks to identify whether NH3, HBr, etc are acids or bases.

Jenny Chau 1I

Why is the problem written as sodium bisoxalato(diaqua)ferrate(III)? Shouldn't diaqua come before bisoxalato because a goes before o?

Jenny Chau 1I

Oh got it. I think Prof. Lavelle mentioned that in his lectures and I completely forgot. Thank you!

Jenny Chau 1I

I'm aware that cyanide's ligand name is cyano (as according to the chempendix) so why it named cyanido in problem 9C.3 part a? I can see that -ido was probably added because cyanide ends in -ide and the rule is to drop that and add -ido, but why is the naming different when it's the same ligand?

Jenny Chau 1I

Because it wouldn't work geometrically. The lone pairs of CO would have to be oriented in a way that the metal ion can bind to both lone pairs, but the bonding pairs of the metal atom in the center will be at least 90deg apart for a square planar and octahedral shaped compound, or 109.5deg for a te...

Jenny Chau 1I

I looked at the chempendix of sapling to look at ligands and their names and it states that CO is monodentate. Why wouldn't CO be bidentate if there's two lone pairs?

Jenny Chau 1I

How do you know what ligand is named what? For example, in lecture 25, NH3 in [Co(NH3)5 Cl] Cl.2H20 is named ammine. Is there a pattern we're supposed to know like adding -ine or something?

Jenny Chau 1I

How do you determine how many bonds a transition metal can make?

Jenny Chau 1I

I was reviewing hybridization and I think I started confusing myself but how do we know if there is an unhybridized p orbital when doing hybridization?

Jenny Chau 1I

I sometimes have this problem too with the math not "Typesetting", so I downloaded the Bookshelf app from the Microsoft Store. It's available offline and it loads like 10 times faster, it's really helpful! I forgot to thank you for your solution so thank you :) Also I can confirm that the...

Jenny Chau 1I

I've noticed this problem before and it managed to fix itself but I can't get it to work on the VSEPR chapter. Basically, some of the names of the molecules aren't loading. Like for example, problem 2E.4 says "Draw the structures and name the shapes of the following molecules: (a) (b) " wh...

Jenny Chau 1I

Here's a picture of H2CCCH2 that hopefully helps in visualizing the orbitals. The central C atom has 2 sp2 hybridized orbitals (in blue) and 2 unhybridized p-orbitals (in green). These 2 p-orbitals (involved in the 2 π bonds) must be perpendicular to one another (like how px, py, and pz are all per...

Jenny Chau 1I

I managed to solve #18 but I'm confused on the stuff about whether the hydrogens on the end of the molecule are coplanar or not. The solution says that the C=C π bonds on H2CCCH2 are perpendicular whereas in the other two the bonds are parallel but how would you come about in determining that? And h...

Jenny Chau 1I

I don't know if I missed this during lecture or something but what's the difference between polar/non-polar bonds and molecules?

Jenny Chau 1I

I don't think he mentions anything on this, but he does say 50% or higher is required to pass with a C- or higher. I saw that too and was so confused... He is saying if you earn a 50% in the class you automatically pass? No,, if you earn a 50% or more on homework you will be able to pass with the h...

Jenny Chau 1I

On lecture 23 (I think), Professor Lavelle started out the lecture with an example of NH3 and wrote out the electron configuration of N. According to my notes, he then mentioned that when you draw out the electron configuration you'll notice that it won't give you the correct shape because the overl...

Jenny Chau 1I

Jonathan3L wrote:Yes they have changed, I start studying for an exam about 2 weeks before to avoid cramming. I am still not getting the grades I want though.

I feel this. It's a bit disappointing because I feel like I'm spending a sufficient amount of time studying but it doesn't seem like it paid off in the end.

Jenny Chau 1I

Hi, I also noticed during the lecture that he wrote sp3 next to the bonds of the lewis structure for ethene. He initially wrote sp2 next to one of the bonds but then started writing 2sp3. I don't think anyone explained why he did that though. Was it because there's an electron in 2p and that's why h...

Jenny Chau 1I

Does anyone know if there will be discussion on Thursday or Friday or if students who have discussions on those days have to join another one?

Jenny Chau 1I

I was also wondering about this as well. I thought maybe it has to do with the intermolecular/interionic attractions like dipole-dipole (like for example, an attraction is formed between two H-F molecules or maybe hydrogen bonding because a lone pair is involved). But I don't know if this is correct.

Jenny Chau 1I

Hi, I'm not too sure on solubility trends myself but I think using the electronegativity trend could work. Question 2D.7 asks you to determine which compound would be more soluble using electronegativities. The higher the difference of the electronegativity between two atoms would mean it has lower ...

Jenny Chau 1I

For me, I used the electronegativities chart the textbook provided in section 2D but how would you be able to determine differences without the chart. Would you kind of just guess based on the electronegative trend of the periodic table?

Jenny Chau 1I

If a molecule has a permanent dipole moment, would the molecule be considered polar?

Jenny Chau 1I

Can someone explain exactly why group 13 elements don't normally follow the octet rule? I know that they are exceptions but I'm unsure as to why they are.

Jenny Chau 1I

My TA said that the midterm will cover 1D, 1E, 1F, 2A, 2B, 2C, 2D, 3F.4, and 3F.5. However, I'm not too sure about whether Friday's lecture will be on the midterm. The topics I just listed don't include VSEPR so I don't know about that one.

Jenny Chau 1I

Hi, if I remember correctly, the exception for Chromium is that it's electron configuration is [Ar]4s^1 3d^5 instead of [Ar]4s^2 3d^4 because a half full d subshell is more stable than one that is partially filled. As for copper, its electron configuration is [Ar]4s^1 3d^10 instead of [Ar]4s^2 3d^9 ...

Jenny Chau 1I

I don't know if this is the right topic to post this in since this is kind of random, but I mentioned in my notes about the boiling points of methane and tetrachloromethane but I didn't write why there's a change. Is the reason why tetrachloromethane has a higher boiling point is because the Cl is b...

Jenny Chau 1I

He sent out an email on November 8th that said he "will have class this Wednesday but all discussion sections and office hours on Wednesday Nov 11 are cancelled." When he says class, does that mean he will post a lecture video then?

Jenny Chau 1I

I only took honors chem but it was enough that I have some understanding of the content in this class. But I suppose my chem class only scratched the surface because there were some fundamentals I don't remember even learning in my high school chem class. So I'd say it's a balance. There's some stuf...

Jenny Chau 1I

Hi! You could change bond between the carbon and the other oxygen into a double bond. That counts as resonance.

Jenny Chau 1I

What does bond character exactly mean? And does the expected bond length have something to do with it?

Jenny Chau 1I

I was also confused about this as well. Looking up delocalized, I'm assuming it refers to electrons that aren't strictly associated to an atom so that would mean it can move around more freely compared to the ones that are localized. But I don't know if delocalized electrons cause resonance or vice ...

Jenny Chau 1I

I think formal charge just means the charge of a particular atom when it's forming a bond. So it would indicate whether the atom has gained or lost an electron in the process. Formal charge can also help with determining the Lewis structure of an atom.

Jenny Chau 1I

If we did need to know F orbitals, would it be the Ianthanoids and actinoids??

Jenny Chau 1I

I was also curious about that when I saw it in the lecture. Should we just loosely use the guidelines then since it seems there are some exceptions?

Jenny Chau 1I

To follow up on her question,I still get confused when it asks about n2 and n1. Going by the logic of the comments above, this means that n2 is the final state and n1 is the initial state, correct? Or would it be the other way around? This is something I'm also a little confused about because on th...

Jenny Chau 1I

Why does oxygen not follow the ionization energy trend in the periodic table, especially when compared to nitrogen and fluorine?

Jenny Chau 1I

Since we don't really have to do any calculations for Schrodingers equation on the midterm, what should conceptually be known about it?

Jenny Chau 1I

1D.1 and 1D.2 seem to be about energy levels and wave functions. Looking at the 1D problems assigned, there don't seem to be any problems that correspond to these topics. This is probably because 1D.1 and 1D.2 are more conceptual, so as long as you know the concepts regarding the Lyman/Balmer serie...

Jenny Chau 1I

Does anyone know which problems on the syllabus correspond to 1D.1 and 1D.2 since those two sections will be tested on the midterm?

Jenny Chau 1I

Sunny Wu 2C wrote:Hi! To quote directly from the IUPAC website, "a number in parentheses indicates the uncertainty in the last digit of the atomic weight."

Thank you for answering! I'm going to assume we just ignore it then :)

Jenny Chau 1I

In the IUPAC periodic table that was linked in an email for us to use in tests, there's a number in parentheses next to the atomic mass. For example, hydrogen's is 1.00794(7). What does the number in the parentheses mean?

Jenny Chau 1I

You can try using the formula that is derived from the one you stated: frequency = -R(1/n1^2 -1/n2^2). Plugging in the energy levels, you could get frequency = -R(1/9 - 1). From there, you can use the formula c = λν to get wavelength in meters which can easily be converted to nanometers. I'm curiou...

Jenny Chau 1I

I would do what Lillian suggested which is to use v = R{1/n1^2 - 1/n2^2}. Once you find the frequency, you can use lambda = c/v. If there are still errors, maybe it has to do with unit conversions.

Jenny Chau 1I

In the PDF that shows how to do problems listed on the syllabus, I saw that the mass of the electron was converted from g to kg in part a of 1B.15. What is the reason on why it has to be converted from g to kg?

Jenny Chau 1I

Thank you for explaining. I definitely got it now.

Jenny Chau 1I

I was wondering if anyone has seen this equation pop up in the text portion of the textbook: Δp = mΔv. I only saw it in example 1B.5 in the "plan" part of the example. I couldn't find a breakdown of the equation so if anyone understands this equation, could you explain why uncertainty in m...

Jenny Chau 1I

Both definitely have their benefits and cons. I currently use an iPad for my notes and using the standard notes app that comes with iPhones and iPads. I think in a real lecture that's not pre-recorded, I'd have a lot more trouble using the iPad. It takes time using the tools such as erasing or movin...

Jenny Chau 1I

Why does Balmer start at n1=2 and Lyman n1=1? Does Balmer's number indicate that an electron is already at a higher energy state whereas Lyman is at ground state? And when would you know when to apply which series?

Jenny Chau 1I

When an electron is hit with light and becomes energized, it's said to move to a higher energy state. Does this mean that it moves farther from the nucleus and closer to the next level, stage or however it's called? And do the hydrogen spectral lines correspond to this? I'm also a bit confused on wh...

Jenny Chau 1I

I would say that there is a limiting reactant in all chemical equations because there's probably always excess of one reactant (which would make the others limiting) or not having enough (which would then be limiting). I guess the only time there isn't really a limiting reactant is if the stoichiome...

Jenny Chau 1I

I would say it's reasonable because hydrogen is a very small atom, consisting of only a proton and deuterium is just an isotope of hydrogen so I don't think the difference in their volume would be too drastically different.

Jenny Chau 1I

For me, I attempted the problem this way: I got the mass of 2-butanone by multiplying the .25 mL given by the g.mol that is also given. That gives us the mass of 2-butanone which I then divided by the molar mass of 2-butanone which I think you can derive from the visual but I just googled it. That g...

Jenny Chau 1I

I think integer as a result of measurements are counted for sig figs, and the rules have been answered by previous students. Exact numbers derived from counting or integers that are defined numbers, however, aren't counted for sig fig because they do not affect the accuracy of calculation nor preci...

Jenny Chau 1I

I emailed someone about why it says processing and they told me they ran out of codes and they're waiting for more codes to arrive.

Jenny Chau 1I

I think that 110g +/- 10 is saying 100g give or take 10 g so the molar mass would be in between 100-120g.

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