CHEMISTRY COMMUNITY

Henri_de_Guzman_3L

Morphine will accept a proton on the N atom. This is a very weak base. The conjugate acid of BrO- is BrOH which is a weak acid. This suggests that BrO- is a relatively strong base, stronger than morphine

Henri_de_Guzman_3L

You mean BrO-

Henri_de_Guzman_3L

Lewis Acids and Bases are electron pair acceptors and donors respectively.
Bronsted Acids and Bases are proton donors and acceptors respectively.

Henri_de_Guzman_3L

Thank you everyone! Good luck on the final

Henri_de_Guzman_3L

Did Dr. Lavelle mention this in class?

Henri_de_Guzman_3L

They're different

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=60&t=38753&p=131013&sid=70e1f2e5be7591a4f070b01919368ec8&sid=70e1f2e5be7591a4f070b01919368ec8#p131013

Henri_de_Guzman_3L

Does anyone know if Dr. Lavelle gave instructions on doing sig figs in pH calculations? Apparently there is a special rule in chemistry. Each decimal place AFTER the decimal pointcounts as one sig fig. Everything to the LEFT of the decimal point does not count as a sig fig. For example: 7.3 has one ...

Henri_de_Guzman_3L

For example 6B.5c in the 7th edition textbook asks us to calculate the pH for 0.0092 M Ba(OH)2. This is 2 sig figs but the answer in the back gives 12.96. Should the answer instead be 13?

Henri_de_Guzman_3L

This is how I did it and I got the correct answers. The phrasing of the question is terrible. You have to assume that the solution of 250 ml is DILUTED with water

Henri_de_Guzman_3L

I'm stuck on this too. I can get the right answer for part A but part B doesn't make any sense. Wouldn't the pH of either volume be the same??

Henri_de_Guzman_3L

Aha, I might be getting Amphoteric and Amphiprotic mixed up. As2O3 is NOT Amphiprotic, as it can not donate an H+ ion. It IS Amphoteric because it can react with an acid (such as HCL) or with a base (such as NaOH) Am I correct in this logic? All amphiprotic substances are amphoteric but not all amph...

Henri_de_Guzman_3L

On one of the homework questions (I believe it was 6A.17 from the 7th edition) we had to classify As2O3 as basic, acidic, or amphoteric. I know the definition of amphoteric is that it reacts with both acids and bases. My question is how? here is the structure of As2O3 imgsrv.png I can see how it wou...

Henri_de_Guzman_3L

We don't need to know how they're derived although reading through the textbook I feel it is helpful in understanding how they work.

Henri_de_Guzman_3L

To what extent are we expected to know how to do ph calculations for the final?

Henri_de_Guzman_3L

Thank you VERY much! This is perfect!

Henri_de_Guzman_3L

I missed Wednesday's class 12/5 and I was just wondering if anyone could help out and let me know what Dr. Lavelle went over. He was scheduled to go over "only 3 pages" and was going to finish the syllabus. I'd appreciate any help!

Henri_de_Guzman_3L

I missed Wednesday's class 12/5 and I was just wondering if anyone could help out and let me know what Dr. Lavelle went over. He was scheduled to go over "only 3 pages" and was going to finish the syllabus. I'd appreciate any help!

Henri_de_Guzman_3L

That makes perfect sense thank you!

Henri_de_Guzman_3L

That makes perfect sense thank you!

Henri_de_Guzman_3L

Got it! AX2E3 is linear with three equatorial lone pairs.

Henri_de_Guzman_3L

So why does the bond angle increase as the s character of a hybrid orbital increase?

Henri_de_Guzman_3L

2E.1 part b gives you a bond angle of 180 degrees (linear shape) and asks whether around the central atom there: must be, may be, or cannot be one or more lone pairs. I'm pretty sure the answer is cannot be one or more lone pairs. Isn't the only way you can have a 180 degree bond angle (linear shape...

Henri_de_Guzman_3L

SF6 has a perfectly symmetrical octahedral shape right? The charges therefore "cancel out."

SF4 is AX4E which is a seesaw shape. This is not symmetrical. The F atoms pull in one direction. See the table on page 113 in the 7th edition textbook for a clear diagram on shapes and polarity.

Henri_de_Guzman_3L

To me trigonal planar for AX3E2 would make more sense, putting the lone pairs on axial positions. This way they are 180 degrees apart from each other. Since lone pairs have the strongest repulsion wouldn't this be optimal? Why is it T-shaped instead?

Henri_de_Guzman_3L

The book says either. My previous chem class we pointed to the partial negative charge. Does anyone know what Dr. Lavelle said regarding this?

Henri_de_Guzman_3L

I don't remember!

Henri_de_Guzman_3L

Up to which topics will be on test 3, anyone know?

Henri_de_Guzman_3L

I know it's period 3 elements and on but why? It's something to do with an available d orbital?

Henri_de_Guzman_3L

Remember:
# of hybridized orbitals = # of regions of electron density

Henri_de_Guzman_3L

They are the same, I've only heard of "bent" in my previous chem classes, I have never used angular. According to the book, they are the same

Henri_de_Guzman_3L

Just remember that it only occurs between hydrogen, nitrogen, oxygen or fluorine atoms (H N O F). What is it? Take water molecules for example. 2 hydrogen atoms are bonded with one oxygen atom. The oxygen atoms, because of higher electronegativity, pull the electrons closer to it than the hydrogen a...

Henri_de_Guzman_3L

It seems like all we need to know is formal charge? Is it worth it to go back and learn oxidation numbers?

Henri_de_Guzman_3L

If we don't "memorize" atom's electronegativity, is there a way to intuitively know what makes a polar vs nonpolar molecule?

Henri_de_Guzman_3L

I haven't had any feedback yet on my chem community discussion posts in terms of a grade. How do I know my 3 weekly posts are being counted?

Henri_de_Guzman_3L

It's a way to indicate the pull of electrons. It all depends on electronegativity. For example, O will pull electrons towards it in a C-O bond so this creates a dipole moment.

Henri_de_Guzman_3L

lone pair-lone pair > lone pair-atom > atom-atom

Henri_de_Guzman_3L

He hasn't officially announced either way but if we are ahead we will not have class. Basically to be determined.

Henri_de_Guzman_3L

Here's my tip: DON'T memorize anything! Start by getting very familiar with Lewis Structures. Once you can do them in your sleep, get familiar with finding the VSEPR models (AXE formula) for these Lewis structures. This should be fairly easy if you're comfortable with doing Lewis structures. Once yo...

Henri_de_Guzman_3L

To me the model is very intuitive but the definition can be overwhelming. Basically VSEPR models follow the basic formula of AXE with a number subscript on the X and E. We regard A as the central atom. X is the number of bonds of with other atoms (VSEPR doesn't care if they're single, double, or tri...

Henri_de_Guzman_3L

Hi Katelin, I believe you can use the VSEPR model in 2 instances here: One regarding the Be atom as the central atom (which would give you AX2, linear structure) and one for either of the carbon atoms as the central atom (this case giving you AX4, tetrahedral structure). The overall structure is lin...

Henri_de_Guzman_3L

For the midterm we have a to bring a photo ID, will my bruin card work?

Henri_de_Guzman_3L

For the midterm we have to bring a photo ID. Will my bruin card work?

Henri_de_Guzman_3L

I think the calculations are done automatically by the system so I think if you miss one week it automatically gives you a 0. If you had a valid excuse or reason talk to Dr. Lavelle or your TA

Henri_de_Guzman_3L

I spoke to Dr. Lavelle after class today as I had drawn resonance structures to answer this question. I drew O-S=O <-> O=S-O with a lone pair of electrons on S.

O=S=O is BETTER because this gives every atom a 0 formal charge and S can use it's d orbitals to hold extra electrons in bonding.

Henri_de_Guzman_3L

You would have to find the energy of the incoming photons. You would convert the wavelength of the elected electron into kinetic energy then add that to the work function. This gives you the energy of an incoming photon. Then you simply convert energy into frequency using E=hv

Henri_de_Guzman_3L

A radical typically has an unpaired valence electron. A good example is the chlorine atom which has 7 valence electrons. You would draw this as Cl with 7 dots around it

Henri_de_Guzman_3L

We will not be going over polarity or electronegativity

Henri_de_Guzman_3L

I THINK it'll be similar in format to the first 2 tests. 8 questions, just bring a pencil and non programmable calculator

Henri_de_Guzman_3L

Does anyone know?

Henri_de_Guzman_3L

Is there even a specific guideline or it doesn't really matter?

I am referring to [ ] these brackets. For example which is more correct?
[Na] Cl or Na [Cl] or [Na] [Cl] ? (Add charges and dots for electrons)

Henri_de_Guzman_3L

You're welcome! I just learned in discussion today that it is the same case for Ag+ ion which sits right below it on the periodic table. Happy studying!

Henri_de_Guzman_3L

Copper has a "half-filled" 4s subshell. It is a special case. Only 1 electron sits in it's 4s subshell while 10 electrons sit in it's 3d subshell. This is a special case. Therefore, Cu+ is [Ar] 3d^10

Henri_de_Guzman_3L

Dr. Lavelle has a great resource for sig figs on the class website. Here it is: https://lavelle.chem.ucla.edu/wp-conten ... OUT_SF.pdf

Henri_de_Guzman_3L

I think for any Chemistry test, practice practice practice and then practice some more. Practice until the material becomes so easy that you can do it in your sleep. Try as many different problems as you can. Do all the problems in your textbook, try Khan Academy, there are practice problems here ht...

Henri_de_Guzman_3L

Khan Academy is great. I also find this website to be somewhat helpful and there are a few practice problems on here: https://chem.libretexts.org/

Henri_de_Guzman_3L

Our grades for exam 1 and homework were posted to my ucla. My homework grade is 0/70. I have turned in completed homework for all 3 weeks so far so I'm wondering if this is in error. Does anyone else have this as well? I'm very OCD so I'm wondering what's going on here haha.

Henri_de_Guzman_3L

Basically think of what a wavelength is. It is the distance from one "peak" to another "peak." Think of a wavelength in a "box." It is bounded on 2 sides right? Therefore only a certain wavelength can "fit" into this box. A bigger or smaller wavelength will be...

Henri_de_Guzman_3L

Is there a way to access these so we can know if we're getting the right answers or not?

Henri_de_Guzman_3L

I was right all along then! Haha thank you so much

Henri_de_Guzman_3L

https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Mechanics/02._Fundamental_Concepts_of_Quantum_Mechanics/Heisenberg's_Uncertainty_Principle

Henri_de_Guzman_3L

This is for anyone looking for extra practice. There are good 5 problems on this site that I think cover this topic thoroughly and make you think about its practical use. https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_The...

Henri_de_Guzman_3L

This question gives the velocity of the bowling ball to be 5.00 +/- (plus or minus) 5.0 m/s. I plugged 5.0 m/s into the uncertainty formula and got the right answer. My question is why? The total uncertainty would be 10.0 m/s correct? This doesn't give me the correct answer though.

Henri_de_Guzman_3L

Yes this will be on the exam! To add on what has been replied to, this relates to hydrogen ONLY.

Henri_de_Guzman_3L

I think it's just one way to distinguish between different locations in a given shell. It's like filling _ _ _ with electrons except we use X, Y, and Z

Henri_de_Guzman_3L

Think about it, we don't know the mass of a photon right? Also, use landa x v =c

Henri_de_Guzman_3L

For calculation purposes, use light as a wave (do not use De Broglie formula). Use E=hv when doing light calculations. However it DOES has light-wave duality. Hope that helps!

Henri_de_Guzman_3L

The question asks: Does the photoelectric experiment need to be done under a vacuum? I'm reading the text and I can't seem to find it here and I don't think Dr. Lavelle explicitly mentioned it in class. My instinct is to say yes.

Henri_de_Guzman_3L

I don't know if correctness is a word but my question is will the homeworks be graded if the answers are correct or do we just full credit if we did 7 problems, right or wrong?

Henri_de_Guzman_3L

Has anyone received any grades yet for homeworks or the test? I have not.

Henri_de_Guzman_3L

Isn't it dumb how we need E=hv to solve this problem, yet that isn't given until 1B? Am I tripping?

Henri_de_Guzman_3L

For this problem, if I know the frequency and the wavelength, how do I find the energy of the photon? Is there a specific formula?

Henri_de_Guzman_3L

Yes I realized that! Problem solved, thank you!

Henri_de_Guzman_3L

They're due every week during your discussion

Henri_de_Guzman_3L

I'm curious if anyone has gotten grades for the week 1 homework or discussion yet. Does anyone know when these will be up if not?

Henri_de_Guzman_3L

For part b, I got 0.15 nm and the back of the book says 150. I'm confused??

Henri_de_Guzman_3L

So which is it?? lol

Henri_de_Guzman_3L

I am turning in my homework tomorrow (Friday) and I saw a couple posts related to doing problems from Review of Chemistry for week 2 homework. Can anyone confirm this?

Henri_de_Guzman_3L

While Dr. Lavelle didn't explicitly state to do so, I think it would generally be a good idea in chem to know these anyway. They're not hard! I pasted them below, they're pretty intuitive:

1: mono-
2: di-
3: tri-
4: tetra-
5: penta-
6: hexa-
7: hepta-
8: octa-
9: nona-
10: deca-

Henri_de_Guzman_3L

Thank you, I figured it's a total typo because otherwise it's impossible. I recommend to those with the same problem to just use Fe3Br8 as Ashish said.

Henri_de_Guzman_3L

A magnesium ion is Mg2+
Sulfate is SO4 2-
Together that makes MgSO4

The heptahydrate basically just adds H2O at the end. Hepta- is a prefix for 7.

So the official formula is MgSO4 . 7H2O
In chemistry, it's standard to add a little dot between the compound and the hydrate

Henri_de_Guzman_3L

So I'm assuming you converted grams of Na2CO3 to 39.84 mmoles of Na+. So now you have mmoles of Na+ in a volume of 250.0 ml and you want 2.15 mmol Na+. The mmoles of Na+ that you converted from the grams of Na2CO3 and the 250.0 ml are your "initial" mols and volume, respectively. Think of ...

Henri_de_Guzman_3L

By "never saw it," I mean it didn't pop up in the homework problems or examples but they did display it on the section reading covering SI units.

Henri_de_Guzman_3L

Hi Stephen, I think it would be safe to assume that the units Dr. Lavelle gave us were the only ones we'd be using for the class. Since he did not give us hecto-, I would assume that we would not need to use it for this class. However this does not mean that this is not an SI unit. As you mentioned ...

Henri_de_Guzman_3L

Hi Andrew, if you are referring to question L.5.a, it is totally ok to give the answer in either grams or kilograms. Prof. Lavelle even mentioned in class that both would be correct. The reason the textbook gives the answer in grams is think about it, 507.1 g Al versus 0.5071 kg Al. I think and the ...

Henri_de_Guzman_3L

Hi, so I was very stuck on the balancing part of this equation. I googled the answer and found links from Prof. Lavelle's chemistry community and I think there might be typo in my book. So my book asks the following question for L.35 "Sodium bromide, NaBr, which is used to produce AgBr for use ...

Henri_de_Guzman_3L

For the unbalanced equation we have: C10H15N + O2 --> CO2 + H2O + CH4N20 I started with balancing N first: 2C10H15N + O2 --> CO2 + H2O + CH4N20 Then H: 2C10H15N + O2 --> CO2 + 13H2O + CH4N20 Then C: 2C10H15N + O2 --> 19CO2 + 13H2O + CH4N20 Finally O: 2C10H15N + 26O2 --> 19CO2 + 13H2O + CH4N20

Henri_de_Guzman_3L

Like the subject asks. This is for Chem 14A Dr. Lavelle

Henri_de_Guzman_3L

Is there a minimum number of posts/replies to get full points?

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