## Search found 53 matches

Thu Jan 21, 2021 1:23 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Including (aq) Solvents
Replies: 4
Views: 12

### Re: Including (aq) Solvents

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.
Thu Jan 21, 2021 1:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling HW #5
Replies: 3
Views: 38

### Re: Sapling HW #5

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...
Thu Jan 21, 2021 1:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solids In Reaction
Replies: 4
Views: 25

### Re: Solids In Reaction

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...
Thu Jan 21, 2021 1:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K vs. Kc?
Replies: 5
Views: 24

### Re: K vs. Kc?

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?).
Thu Jan 21, 2021 1:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: sapling (week 3) #5
Replies: 2
Views: 38

### Re: sapling (week 3) #5

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+...
Thu Jan 07, 2021 2:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Including H2O
Replies: 7
Views: 29

### Including H2O

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?
Thu Jan 07, 2021 2:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Preset values of K
Replies: 5
Views: 38

### Preset values of K

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 ...
Thu Jan 07, 2021 2:40 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Positive and negative delta H
Replies: 5
Views: 25

### Positive and negative delta H

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...
Thu Jan 07, 2021 2:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium Part 3, #20
Replies: 4
Views: 28

### Re: Chemical Equilibrium Part 3, #20

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...
Thu Jan 07, 2021 2:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Intermediate Values of K
Replies: 6
Views: 17

### Re: Intermediate Values of K

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 ...
Thu Dec 17, 2020 9:36 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Psi in the Equation
Replies: 4
Views: 53

### Re: Psi in the Equation

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.
Thu Dec 17, 2020 9:35 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Minimum Uncertainty
Replies: 3
Views: 59

### Re: Minimum Uncertainty

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!
Thu Dec 17, 2020 9:33 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: H20
Replies: 6
Views: 49

### Re: H20

Why are the lone pairs so close then, instead of being on opposite sides?
Thu Dec 17, 2020 9:32 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Cis Trans Isomers
Replies: 7
Views: 53

### Re: Cis Trans Isomers

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...
Thu Dec 17, 2020 9:30 am
Forum: Naming
Topic: How to determine the charge of ligands?
Replies: 4
Views: 54

### Re: How to determine the charge of ligands?

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).
Thu Dec 17, 2020 9:28 am
Forum: Determining Molecular Shape (VSEPR)
Topic: A question from the final
Replies: 5
Views: 84

### Re: A question from the final

I looked it up after the test and I agree with tetrahedral!
Thu Dec 17, 2020 9:26 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone pairs in H2O
Replies: 1
Views: 46

### Lone pairs in H2O

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?
Sun Dec 06, 2020 7:07 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling Question #5
Replies: 4
Views: 45

### Re: Sapling Question #5

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...
Sun Dec 06, 2020 7:05 pm
Forum: Naming
Topic: Potassium
Replies: 8
Views: 89

### Re: Potassium

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.
Sun Dec 06, 2020 7:03 pm
Forum: Naming
Topic: Cl & Br3
Replies: 7
Views: 52

### Re: Cl & Br3

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.
Sun Dec 06, 2020 7:01 pm
Forum: Naming
Topic: Sapling Week 9 #1
Replies: 6
Views: 50

### Re: Sapling Week 9 #1

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.
Sun Dec 06, 2020 6:59 pm
Forum: Naming
Topic: Oxidation number
Replies: 5
Views: 61

### Oxidation number

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...
Sun Nov 29, 2020 11:59 pm
Forum: Hybridization
Topic: Hybridization of Carbon
Replies: 10
Views: 83

### Re: Hybridization of Carbon

Carbon needs full 8-e valence shell, which will always be 4 bonds and/or lone pairs
Sun Nov 29, 2020 11:59 pm
Forum: Hybridization
Topic: hydrogen atoms in same plane
Replies: 4
Views: 54

### Re: hydrogen atoms in same plane

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 ...
Sun Nov 29, 2020 11:57 pm
Forum: Hybridization
Topic: Sapling Hybridization Problems
Replies: 4
Views: 38

### Re: Sapling Hybridization Problems

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.
Sun Nov 29, 2020 11:55 pm
Forum: Hybridization
Topic: Double Bond Type
Replies: 4
Views: 43

### Re: Double Bond Type

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 ...
Sun Nov 29, 2020 11:53 pm
Forum: Hybridization
Topic: Determining the number of sigma and pi bonds
Replies: 8
Views: 55

### Re: Determining the number of sigma and pi bonds

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.
Sun Nov 22, 2020 10:16 pm
Forum: Ionic & Covalent Bonds
Topic: variable valence
Replies: 5
Views: 23

### Re: variable valence

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.
Sun Nov 22, 2020 10:15 pm
Forum: Coordinate Covalent Bonds
Topic: Lewis Diagram
Replies: 5
Views: 60

### Re: Lewis Diagram

I think I've also seen Lavelle notate coordinate covalent bonds with a dotted line to show the interaction/change occurring!
Sun Nov 22, 2020 10:13 pm
Forum: Coordinate Covalent Bonds
Topic: Non-charged molecules becoming Lewis acids/bases
Replies: 3
Views: 39

### Non-charged molecules becoming Lewis acids/bases

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...
Sun Nov 22, 2020 10:08 pm
Forum: Lewis Structures
Topic: Expanded Valence
Replies: 11
Views: 60

### Re: Expanded Valence

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.
Sun Nov 22, 2020 10:03 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2 Scores
Replies: 28
Views: 210

### Re: Midterm 2 Scores

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?
Sun Nov 22, 2020 10:02 pm
Forum: Administrative Questions and Class Announcements
Topic: 14B Enrollment [ENDORSED]
Replies: 26
Views: 1350

### Re: 14B Enrollment[ENDORSED]

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!
Sun Nov 15, 2020 11:56 pm
Forum: Ionic & Covalent Bonds
Topic: Hydrogen Bonds
Replies: 2
Views: 12

### Re: Hydrogen Bonds

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...
Sun Nov 15, 2020 11:51 pm
Forum: Ionic & Covalent Bonds
Topic: Sapling Week 5/6 HW #4
Replies: 2
Views: 17

### Re: Sapling Week 5/6 HW #4

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 ...
Sun Nov 15, 2020 11:48 pm
Forum: Ionic & Covalent Bonds
Topic: Between 1.5 and 2
Replies: 3
Views: 36

### Re: Between 1.5 and 2

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...
Sun Nov 15, 2020 11:47 pm
Forum: Ionic & Covalent Bonds
Topic: Workshop Hydrogen Bonding Question
Replies: 4
Views: 34

### Re: Workshop Hydrogen Bonding Question

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...
Sun Nov 15, 2020 11:44 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic vs Covalent Bonds
Replies: 9
Views: 30

### Re: Ionic vs Covalent Bonds

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...
Sun Nov 01, 2020 7:14 pm
Forum: *Shrodinger Equation
Topic: N L ML Atoms, Orbitals, number of electrons
Replies: 3
Views: 48

### Re: N L ML Atoms, Orbitals, number of electrons

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...
Sun Nov 01, 2020 7:09 pm
Forum: *Shrodinger Equation
Topic: Midterm Scores
Replies: 30
Views: 336

### Re: Midterm Scores

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...
Sun Nov 01, 2020 7:06 pm
Forum: *Shrodinger Equation
Topic: Guitar Analogy
Replies: 2
Views: 47

### Re: Guitar Analogy

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...
Tue Oct 27, 2020 12:48 pm
Forum: DeBroglie Equation
Topic: DeBroglie to Frequency
Replies: 2
Views: 61

### Re: DeBroglie to Frequency

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...
Tue Oct 27, 2020 12:41 pm
Forum: DeBroglie Equation
Topic: Finding the mass of a molecule
Replies: 6
Views: 85

### Finding the mass of a molecule

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...
Sun Oct 18, 2020 7:16 pm
Forum: Administrative Questions and Class Announcements
Topic: Tests
Replies: 6
Views: 67

### Re: Tests

I know that past quarters' classes have, in fact, had cumulative finals, not sure about the midterms. Hopefully that helps!
Sun Oct 18, 2020 7:14 pm
Forum: Administrative Questions and Class Announcements
Topic: UCLA Store Updates on Ebook/Sapling access card
Replies: 16
Views: 147

### Re: UCLA Store Updates on Ebook/Sapling access card

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...
Sun Oct 18, 2020 7:10 pm
Forum: Properties of Electrons
Topic: Work Function
Replies: 2
Views: 37

### Re: Work Function

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!
Sun Oct 18, 2020 7:07 pm
Forum: Properties of Electrons
Topic: "hR" graph label
Replies: 1
Views: 27

### "hR" graph label

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?
Fri Oct 16, 2020 11:16 am
Forum: Einstein Equation
Topic: Equation Sheet
Replies: 15
Views: 132

### Re: Equation Sheet

The individual problem will give you all the information you need to know
Fri Oct 09, 2020 12:31 pm
Forum: Limiting Reactant Calculations
Topic: Significant figures when using scientific notion
Replies: 5
Views: 57

### Re: Significant figures when using scientific notion

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...
Fri Oct 09, 2020 12:27 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Exercise E.9
Replies: 6
Views: 142

### Re: Exercise E.9

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...
Fri Oct 09, 2020 12:22 pm
Forum: Molarity, Solutions, Dilutions
Topic: What does mmol stand for?
Replies: 33
Views: 333

### Re: What does mmol stand for?

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.
Fri Oct 09, 2020 12:21 pm
Forum: SI Units, Unit Conversions
Topic: Kg to g
Replies: 13
Views: 138

### Re: Kg to g

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...
Fri Oct 09, 2020 12:14 pm
Forum: Significant Figures
Topic: Scientific notation and significant figures
Replies: 3
Views: 49

### Scientific notation and significant figures

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 ...