CHEMISTRY COMMUNITY

allyssa bradley 1H

You can include your solvent if you want but the concentration is so big on the products and reactants side (if it's a true solvent and not actually just a small amount of water reacted or produced) that you could just cancel them out.

allyssa bradley 1H

Hey Uyenvy, I wanted to direct you to this post I just replied on for more of a general solution, although I think the person who posted has different numbers: https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=49&t=72369&sid=04cbd78c8d18cb91ef41129b45c1c13f I just ran over your numbers mys...

allyssa bradley 1H

Hey Abril, this question took me a minute to wrap my head around as well but I found this link helpful for me: https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_A_Molecular_Approach_(Tro)/15%3A_Chemical_Equilibrium/15.05%3A_Heterogenous_Equilibria_-_Reactions_Involving_Solids_and_Liqu...

allyssa bradley 1H

This confused me too and I found it super annoying! As Jagveer said, K in the textbook is Kp, which is sort of counter-intuitive for the scope of this class since we usually assume K to be Kc, dealing with concentration and moles (like, most of Lavelle's ICE box examples, are molarity, right?).

allyssa bradley 1H

Your logic seems sound in the way that you walked us through your thought process and the [OH-]=4.8*10^-5 that Tracey calculated is totally correct. I agree with Tracey that you might have mixed up putting it in your calculator. Here is one point of clarification I have to offer: Remember [OH-]=[HB+...

allyssa bradley 1H

A couple hypothetical situations -- If an aqueous reaction needs a certain amount of water to balance the reaction, do we include it in K?
And in any formula, is liquid water still included in K when it just appears on one side of a balanced homogenous reaction?

allyssa bradley 1H

Hey guys, do we know if K values are set for particular temperature and pressure parameters, or does it depend on past manipulation? The 5G.2 table in the textbook does indicate certain temperatures correspond to certain K values in certain reactions, but I also feel like a compressed-volume system ...

allyssa bradley 1H

Hey, I feel like this is sort of a high school question, but it's been really confusing me with a couple of module problems! I was thinking that endothermic reactions would have a negative delta H because they absorb heat... meaning that the heat of the system goes down. By reading people's response...

allyssa bradley 1H

Anyone else having issues with this problem? I'm getting in the order of 10^-6, but my x-value is coming out to 2.47e-6 so that my [SO3] is 4.94e-6. Thinking it might be a rounding error, I selected the closest answer which rounds up a bit, but I'm still not getting it right. Would appreciate some g...

allyssa bradley 1H

We talked about this in my workshop today! It helps me to consider "a reaction's lean" as a completely different concept to "favoring reactants or products" (although, obviously, they both look very closely at boundaries of K). Relating K to 0.001 or 1000 is useful with reaction ...

allyssa bradley 1H

I'm pretty sure Heisenberg relates to the particle property and psi relates to the wave property, so I don't think they would overlap.

allyssa bradley 1H

This was another thing that confused me about the test, since it seemed to me like you could hypothetically get a BETTER answer than your estimate! But this makes a lot of sense, so thank you!

allyssa bradley 1H

Why are the lone pairs so close then, instead of being on opposite sides?

allyssa bradley 1H

How would we determine if a molecule is a cis/trans isomer based on its name? The name always includes the prefix "cis" or "trans," as we learned in lecture when it came to naming! I wonder if it's not named, if it's sort of like resonance structure where multiple versions appea...

allyssa bradley 1H

For molecules, you could try using formal charge, or the charge of each atom known from the periodic table (for example, NH3 is stable because N is 5- and H is 1+, which all cancels).

allyssa bradley 1H

I looked it up after the test and I agree with tetrahedral!

allyssa bradley 1H

Hi guys, maybe this was a topic already covered in lecture, but a previous topic on this board discussed how lone pairs are always put farthest apart to account for repulsion. Why doesn't this apply to the H2O molecule, where 2 are next to each other to make the bent shape?

allyssa bradley 1H

Exactly -- the coordination number just means how many things are attached to the central metal atom. When things like (CO) are grouped together, count it as just one "thing" attached to the metal atom. Also, note that the metal atom is always singular and at the front of the chemical form...

allyssa bradley 1H

The way I would go about this -- based on the given oxidation number, "balance" the molecule so you know how much charge the potassium part is expected to carry -- if it needs to have a +3 charge, for example, it would probably be 3 potassiums.

allyssa bradley 1H

I'm pretty sure that by itself, the chloride molecule is Cl2 and the bromide molecule is Br3 just by nature of the valence electrons, but when it's in the molecule you add the "ide" suffix when appropriate. For example, a bromide anion is Br- -- not just the triatomic molecule.

allyssa bradley 1H

Page 723 of the textbook helped me a lot on this one -- for the whole part in the [] brackets, name the ligands by the Greek numeral prefix, plus the correct version of the ligand name, and end with the name of the metal atom plus oxidation number.

allyssa bradley 1H

Does anyone have tips for calculating oxidation number? I get that it's the "charge" relative to all the other atoms in the coordination compound, considering the charge of the total compound, but I'm still having trouble, so I was hoping to hear some other people's thought processes. Also...

allyssa bradley 1H

Carbon needs full 8-e valence shell, which will always be 4 bonds and/or lone pairs

allyssa bradley 1H

Wait for question 5 on the sappling there are also 3 atoms that seem to be on the same plane but they are called equatorial, why is that? In that question, the 3 equatorial atoms would all be on the same plane, but it's sort of a different situation since the molecule is simpler; equatorial was in ...

allyssa bradley 1H

The chart was super helpful for me -- to get a full traditional valence shell, you have a total of 4 (lone pair or bond) units, which comes out to s + p*3 = sp^3. Subtract p orbitals from there if there are fewer bonds or valence.

allyssa bradley 1H

ok but like how does dipole work itself into this concept because on the sapling it was giving me feedback about dipole moments and I have zero clue on how they would apply in this situation. I was also confused about dipole moment since I didn't factor it into my answer, but I think dipole moment ...

allyssa bradley 1H

The molecule on sapling was sort of unusual because of the extra H, but count every bond as a sigma first, and any additional bond "line"/shared pair above single is a pi bond.

allyssa bradley 1H

I think it's important to know about the 3d/4s inconsistency around chromium, as I saw that on the second midterm, but that may be a little different from what you're asking.

allyssa bradley 1H

I think I've also seen Lavelle notate coordinate covalent bonds with a dotted line to show the interaction/change occurring!

allyssa bradley 1H

Hi guys, I'm a little confused on how a non-charged molecule could become a Lewis acid or base. I thought no net charge would mean that the molecule is perfectly stable, and there might just be some "polar covalent"-ness/ionic tendency to the bond that would make induced dipole or other ty...

allyssa bradley 1H

For the expanded valence shell, does this then mean that the maximum expanded valence shell is 10 or 12 (or more, if the atom has a negative charge)? I'm a little confused since the normal valence is 2 in s and 6 in p, but 12+ seems like a lot in the outer shell.

allyssa bradley 1H

I also noticed that there might have been some typos on this test-- does anyone know if questions ever get dropped in this class, or is it assumed that we should have been able to read through the typos?

allyssa bradley 1H

For our current class and 14B, the lecture times are listed as "online - recorded." I was wondering also if other classes with this caption are required to have the same asynchronous setup as this class and 14B, or if it depends on the professor!

allyssa bradley 1H

I agree with this response! Think about the individual charges. Hydrogen bonds are most well-known on water molecules, and obviously a water molecule is a polar but stable molecule in terms of its average charge. However, with there being 2 hydrogen and 1 oxygen, the oxygen has a slight -2 charge an...

allyssa bradley 1H

I agree that this was a pretty confusing question! In lecture, I feel like the prof articulated pretty well how the known theoretical size of atomic bonds is not exact for every single bond in a molecule, and when there is a combo of single/double/triple bonds in a molecule, the average length will ...

allyssa bradley 1H

Very good point, Kylie! A Lewis dot structure draws a line to form a bond of shared electrons between 2 atoms. In an ionic bond, this totally isn't the case -- the two atoms are not sharing electrons at all, they're kind of just two ions next to each other, right? So basically all of the molecules i...

allyssa bradley 1H

In one of the homework questions, it was mentioned that a hydrogen bond ideally works with a hydrogen atom in between 2 oxygen atoms. Basically, if the hydrogen atom is totally stable and "happy" in a molecule with carbon, it's not going to have any positive attraction! Since oxygen is sup...

allyssa bradley 1H

I agree with this! Also, I think it is worth mentioning that polar covalent bonds exist where the electrons are unequally shared, so the difference between ionic and covalent is kind of a case-by-case situation or a spectrum rather than having a specific rule. Vanessa's mention of the electronegativ...

allyssa bradley 1H

I was also initially confused about this on the homework, and the above explanations are super thorough and helpful, so thanks guys! If you want some review, Lavelle goes over ml in lecture 3.3 right after the electron spin experiment. He posts this formula that was really helpful to me: ml = l, l-1...

allyssa bradley 1H

On the topic of partial credit ^^, I also noticed some answer choices would fully have the right number and scientific notation and all, but then the units would be in nm instead of meters. In that case, you totally did all your math right, it seems like you were just stressed at the last second whe...

allyssa bradley 1H

I agree with you, Marcus! In lecture last week, Lavelle showed a diagram where he compared waves that were non-sinusoidal or out out of sync with a correct wave. The two ends of the wave correct have to end at the same point in the wavelength, otherwise they would be mismatched when you connect them...

allyssa bradley 1H

Even though, yes, the equation relating to the speed of light was originally derived for photons, Dr. Lavelle showed us a proof in lecture 3.1 where DeBroglie equated electromagnetic radiation equations to derive an equation that could be used with particles. The above reply definitely should have a...

allyssa bradley 1H

Hi guys, I came up with a question after working on problem 17 of the Sapling homework this week. I was a little confused about finding the mass of a diatomic hydrogen molecule -- presumably, this is about 2.014 amu, or 2 protons and 2 electrons, but our equation sheet doesn't offer a conversion qua...

allyssa bradley 1H

I know that past quarters' classes have, in fact, had cumulative finals, not sure about the midterms. Hopefully that helps!

allyssa bradley 1H

I was also automatically sent the code to my textbook, probably around the time the free trial was sent out -- to anyone looking for it in their mailbox, mine was sent at 10:31 am on October 8. I actually missed it the first time because I was really confused by this random number just sent to me, b...

allyssa bradley 1H

I agree with Sabrina, that this value is determined by a particular threshold, or a value that can be sort of approached from both sides. Good question!

allyssa bradley 1H

In the lecture, I noticed Dr. Lavelle used a graph to demonstrate electron energy transitions using a y-axis label including "-hR" multiplied by varying fractions. What do these variables represent, and how are the fractions determined?

allyssa bradley 1H

The individual problem will give you all the information you need to know

allyssa bradley 1H

Yes! Basically, you want to use the same amount of sigfigs as the value given in the problem with the least amount. If the given values were .0062, 5.098, and .76345, your answer should only contain 2 sigfigs. Hope this helped Can someone go through those 3 example numbers and explain how the small...

allyssa bradley 1H

My friend made this same mistake on that problem, and a tip that I have is to double-check your Google search. So if you type in the molecular name INCLUDING heptahydrate, the Google pop-up (like the most common answer) doesn't include it. If you look at the bottom of the answer box, it does not say...

allyssa bradley 1H

People who are familiar with the world of chemistry, this question is for you: is it common to see other notations like this other than for micro- and milli-? Like kilomole, or something like that.

allyssa bradley 1H

Thanks for the learning tool Sahaj! In high school chemistry, as a week one-type project, I remember making a little "conversion ladder" to reference when I had to make conversions, and I just kept it in one of the pockets of my dividers or in the back of my binder. Basically, there were s...

allyssa bradley 1H

Hi guys! Still figuring out chemistry community, hope it's appropriate that I created a new topic for this and it's not too obvious of a question, haha. In high school and previous classes at UCLA, I'm used to think of "significant figures" as simply the number of digits after the decimal ...

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