CHEMISTRY COMMUNITY

Aliya 1H

Phases are solid, liquid, gas. A phase change is any time that a substance changes from one phase to another: solid to liquid, liquid to gas, gas to liquid, liquid to solid, solid to gas, gas to solid. Melting, freezing, boiling, etc. are examples of phase changes.

Aliya 1H

If all of the energy (heat) applied to the system is used for, say, a phase change and none is directed to a change in temperature then the temperature will not change at all. This is why you see that the temperature remains constant during a phase change because all of the heat applied is used to b...

Aliya 1H

^^ what that person said, it'll say due midnight sunday week __ and I assume that means that it's due on the sunday at the end of that week

Aliya 1H

it's positive if it's on the reactant side and negative if on the product side and yes the value in front is determined by the stoich values given

Aliya 1H

the percent of a compound that has dissociated (ionized). this is 100% for strong acids/bases, but for weak acids/bases you calculate it [H+]/[HA] * 100%

Aliya 1H

mol * L^-1 = mol/L = M = [] = concentration = molarity (used interchangeably in many of the problems we're working with)

Aliya 1H

^^ as she said, multiply them. If you're on sapling also watch out for sig figs because I had to take a few attempts just from little calculator/sig fig errors

Aliya 1H

Yes, the left will be reactants and the right will be products. Remember that reactions we're looking at are going to be reversible, so things can dissociate back into its "reactants".

Aliya 1H

hi aliya! ok I'm back with good news lol. so it took me 4 attempts to solve this problem but i realized it was a small calculation error so i hope it's just a minor mis-step for you as well. a good starting place to begin this question/hear what other students had to say is through this post. this ...

Aliya 1H

I'm struggling to get the right answer for this question. I know you have to use Hess's Law, but I think I'm uncertain on how to manipulate the separate K values for the different equations when you have to, say, flip the reaction or multiply it by 3. Can someone please explain. What is Hess's Law?...

Aliya 1H

I've been trying to work this out with an ICE chart for a bit now but I can't get it. Please help.

Aliya 1H

You can think about it like this: the stronger the acid, the weaker its conjugate base & the stronger the base, the weaker its conjugate acid. This is because the [H3O+][OH-] concentrations make up the equilibrium constant K, so you can think about it like if [H3O+] increases, [OH-] must decreas...

Aliya 1H

For my part d I got 4x^{2}-21.28x+4.7793 and then used the quadratic formula to get the x I used (x=0.2349...). Then, I found \left [ N_{2}O_{4} \right ] by doing 0.319+x and \left [ NO_{2} \right ] by doing 2.89-2x. This gave me the correct answers, however it did take some toggling to get there be...

Aliya 1H

I'm struggling to get the right answer for this question. I know you have to use Hess's Law, but I think I'm uncertain on how to manipulate the separate K values for the different equations when you have to, say, flip the reaction or multiply it by 3. Can someone please explain.

Aliya 1H

Yes, it should work either way. I think it generally depends on what units you want your answers in and I did the same thing in HS but I seem to remember it being fine either way.

Aliya 1H

Hey! Molarity (M) is moles/liter. n/V is moles/volume and volume would be in liters, thus giving us molarity.

Aliya 1H

I'm not completely sure why the coefficient becomes the exponent but I believe it might be like this: when you have, say, 2 N_{2} , then when you put it in the equilibrium constant it's going to be [ N_{2} ] multiplied by a second [ N_{2} ] (since products and reactants are multiplied together in th...

Aliya 1H

Thank you Dr. Lavelle! You were my favorite professor this quarter and I'm so excited for 14B (and I was never this excited about chemistry before this class). I hope you have a great break!

Aliya 1H

I used this page https://lavelle.chem.ucla.edu/wp-conten ... pounds.pdf from Dr. Lavelle's website to make physical flashcards for myself to learn the ligand names :)

Aliya 1H

When something is ionized in an aqueous solution it means that it separates in water. Strong acids completely ionize in H₂O and weak acids don't. For example, HCl is a strong acid and therefore it breaks up into H+ and Cl- ions in water.

Aliya 1H

If you complete all textbook questions and sapling I think you will be in a good place. Generally, they will probably take similar questions with different values/compounds.

Aliya 1H

I got a tshirt for Hanukkah today with a chem joke on it and thought I'd share:

What do you call an acid with an attitude?
A-mean-oh-acid!

Aliya 1H

Ka calculations use concentrations aka molarity, which is indicated by the square brackets [ ] whenever you see like the Ka written like $\frac{[products]}{[reactants]}$ . Also, I believe it's only aqueous compounds from your chemical reaction that are included in Ka.

Aliya 1H

Since K₃ is outside of the brackets, that means it isn't directly bonded to Cr, so it must not be a ligand.

Aliya 1H

You can find pOH by using pOH = -log[OH]. Then, find the pH by using pH + pOH = 14.

Aliya 1H

Hey! What I've been doing that is generally working is I read through the book sections on my own and take pretty detailed notes. Then, I zoom with a friend every night for like 3-5 nights leading up to the day of the exam and we do the book problems together, then talk about the outline and any oth...

Aliya 1H

Hey everyone! With finals coming up, I know we're all probably on edge. I for one am trying to figure out how to balance my studying for each class. I just wanted to remind everyone to take time for yourselves and get some sleep . Listen to some music, eat comfort food, just do something to take a b...

Aliya 1H

Yes, the difference is that it is called ammine when it's a ligand as opposed to a regular compound.

Aliya 1H

Honestly, choose whatever major you want! You're going to UCLA you're already AMAZING AND SMART and nobody can contest that. Pick whatever you want to do, not what others want you to do, and find your path to achieve that!

Aliya 1H

Everyone, You must hear this: "Oh, her/his/their eyes, her/his/their eyes Make the stars look like they're not shinin' Her/his/their hair, her/his/their hair Falls perfectly without her/him/them trying She's/He's/They're so beautiful and I tell her/him/them everyday Yeah, I know, I know When I ...

Aliya 1H

Hey! I've found it super helpful to zoom with one or two friends that I study well with to do book questions, go over the outline, and discuss any questions we might have. It's a fun way of studying and I recommend doing it for 3-4 nights leading up to your exam. This has been really working for me,...

Aliya 1H

Hey! I think the difference is because they are not ligands/are outside of the brackets and that's why they have different names. We name the things outside of the brackets as they would normally be named. I hope that makes sense.

Aliya 1H

If we stacked up with 40 from before, do we need to do more to have them be from this week?

Aliya 1H

I think I saw another post saying they'll try to get them to us a week later but I'm not sure.

Aliya 1H

You should count all of the valence electrons. So, count the electrons the central atom began with and all shared electrons, you should get a number above 8.

Aliya 1H

hey! I don't think we are required to memorize names this quarter so I just looked them up to find the formula and went from there.

Aliya 1H

Hi! Start with what they give you for the M +2 , [Ar]3d 7 . Add back the 2 electrons you took away to get to the original element. So, you add the 2 electrons back into the s orbital to get [Ar]3d 7 4s 2 (cobalt). The same thing for the M 3+ : take the [Ar]3d 6 given and add the 3 electrons back (2 ...

Aliya 1H

All ion-ion interactions (and any other interactions) will experience london dispersion forces. The larger the molecule/ion, the larger the london dispersion forces.

Aliya 1H

Hydrogen is one of the exceptions and will not have 8 valence electrons! B and Be can have fewer sometimes I believe, third row in the periodic table and below can have an expanded octet.

Aliya 1H

Can someone please answer this with an explanation:
Which M³⁺ ions (where M is a metal) are predicted to have the following ground-state electron configurations: (a) [Ar]3d⁶; (b) [Ar]3d⁵

Aliya 1H

Hey! Here's the question: Place the following ions in order of increasing ionic radius: S 2- , P 3- , Cl - . I thought the ion that is most negative would have the larger ionic radius, however the textbook answer is: P 3- , S 2- , Cl - (This is showing an increase in ionic radius with less negative ...

Aliya 1H

Aliya Roserie 3I wrote:Hey! How are you? Nice to know there is someone out there with the same spelling too!

yoooo what's up Aliya we got the same name

[/quote]

Yea exactly! Follow me on ig lol nice to meet uuu

Aliya 1H

hey! N has a +, both O's have a - and the C doesn't have any charge on it.

Aliya 1H

Thank you for sharing this, it's very helpful!

Aliya 1H

For line structures of organic compounds, each point/end of the line represents a carbon in the carbon chain and then other elements will be written like in normal lewis structures, except for hydrogens attached to the carbons.

Aliya 1H

^ yea dr.lavelle didn't specifically mention diagonal relationships so I think we just have to focus on what he said in lecture but if something helps you it doesn't hurt to know it.

Aliya 1H

Yeah, the lone pair in NF3 makes it so that the fluorines are pushed away and thus changes the molecular shape as well so that it is polar/no longer symmetrical. The BF3 has no lone pairs and has a symmetrical shape/is non-polar.

Aliya 1H

Hey! For midterm 1, I read through the entire book section assigned for the topics covered on the midterm and took notes. Then, I went on zoom with a couple friends every night before I took the exam on Friday. We did the book problems and discussed them, read through the outline posted on Dr. Lavel...

Aliya 1H

Na- will have the largest radius because the - indicates that the Na has gained another electron. Na+ will have the smallest radius because it loses an electron.

Aliya 1H

Hey! Key things to remember are just to make sure that everything has an octet (if it's not an exception) and calculate the formal charges to get your lewis stricture in the most stable form (formal charges=0 if possible).

Aliya 1H

Aliya Roserie 3I wrote:Hey Guys! Honestly, I just want to appreciate everyone and the kind and supportive words. This midterm was definitely tough and I know with each other we can do our best on the next one.

yoooo what's up Aliya we got the same name

Aliya 1H

Brendan, "Don't look at me Everyday is so wonderful Then suddenly It's hard to breathe Now and then I get insecure From all the pain I'm so ashamed I am beautiful No matter what they say Words can't bring me down I am beautiful In every single way Yes words can't bring me down Oh no So don't y...

Aliya 1H

Hey! BF3 was an example of an exception of the octet rule (B only has 6 valence e-). Then, he gave the example of BF4- for an example of a coordinate covalent bond (both electrons provided by F for one of the bonds). These two are separate examples illustrating two different things.

Aliya 1H

Hi! From the lecture today, $BF_{3}$ has B as the central element and 3 F with single bonds to the B. In this case, B is an exception of the octet rule because it only has 6 valence electrons.

Aliya 1H

Hey! He said 2px2py2pz is better because it provides more detail but I don't think we'd get marked down for just 2p^3 on a test because it is still technically correct.

Aliya 1H

Brendan, "Don't look at me Everyday is so wonderful Then suddenly It's hard to breathe Now and then I get insecure From all the pain I'm so ashamed I am beautiful No matter what they say Words can't bring me down I am beautiful In every single way Yes words can't bring me down Oh no So don't yo...

Aliya 1H

Hi! There is no 2d subshell because there are only electrons in s and p at the second energy level. For the rest of them: We know that there is a 4d subshell.There are no known elements that have a g shell occupied, but I think that doesn't mean that there CANT hypothetically be something with g occ...

Aliya 1H

Hi! I'm pretty sure the photon just passes through because it isn't of high enough energy (frequency) to be absorbed

Aliya 1H

Hi! For the midterm it says on outline 2 that we have to be familiar with this topic: With respect to electron transitions that give rise to a UV or visible spectrum: understand the difference between electronic transitions in atomic orbitals (atomic spectroscopy) and electronic transitions in molec...

Aliya 1H

The question is this: Use the above uncertainty in velocity (correct model) to calculate the electron's uncertainty in kinetic energy. Then calculate the uncertainty in kinetic energy per mole of electrons (that is, per mole of hydrogen atoms). Comment on your value. For the previous question, I got...

Aliya 1H

May the [mass times acceleration] be with you.

Aliya 1H

Hi! I'm having trouble wrapping my head around this question. Can someone please explain how to solve: The hydrogen atom has a radius of approximately 0.05 nm. Assume that we know the position of an electron to an accuracy of 1 % of the hydrogen radius, calculate the uncertainty in the speed of the ...

Aliya 1H

^^ what sami said. It's important to note that this equation is comprised of the two other previously developed equations to get us a way to accurately calculate wavelength.

Aliya 1H

Hey! So the uncertainty (+-1) means that delta v is going to be equal to a range of 2. In our equation, we use this delta v to represent the uncertainty in speed to find the uncertainty in the position.

Aliya 1H

Hi! Light DOES act as both a wave and a particle (photon). In the photoelectric effect, however, light is acting as a particle. If light only acted as a wave, then increasing the intensity of light in the photoelectric effect would cause electrons to be emitted if they weren't already being emitted....

Aliya 1H

Hi! I had my discussion today and we went over this type of problem. She said to look at what the wavelength is (434 nm) and then look at what series that would be in. In this case, it would be in the Balmer series and the ending energy level is always going to be n=2 for this series. I am not sure ...

Aliya 1H

hey! so with c=\lambda v , you would rearrange it to get v=c/\lambda . Then, you can look back to the original E=hv equation and replace the v with the \frac{c}{\lambda } , getting E=\frac{hc}{\lambda } so you don't have to include a frequency in the equation and you have it in relation to wavelengt...

Aliya 1H

Hi! The photoelectric effect is when light is directed at a surface of metal. If the energy of the light photons matches or exceeds the work function (threshold energy), then electrons are emitted from the surface of the metal. The ratio of this is 1:1 (1 photon excites 1 electron and causes it to b...

Aliya 1H

In this problem the bromine and magnesium were probably omitted because bromine wasn't the limiting reagent and we didn't need it for the question it asked so I think they just left it off/left the reaction incomplete.

Aliya 1H

I think that's the case because then it says assignment is at 100%, but I haven't seen any concrete information about that.

Aliya 1H

Hey! You want to always use the value given in the problem with the least amount of sig figs as the basis for your answer (so, don't use molar mass as the basis). If you're having difficulty counting the sig figs in a value, something I heard is "Atlantic Absent decimal point, Pacific Present d...

Aliya 1H

Hi! I appreciate that you put this post up because I as well was heartbroken at the lack of jams in lecture. Cant wait to see what Dr. Lavelle will tune in with next time.

Aliya 1H

Hi! This problem took me a bit to figure out as well because I am not familiar enough with names of compounds yet, but if you look at the diagrams given/look up the chemical formulas you will find the following: 2-butanone is C_{4}H_{8}O , 1-bromopropane is C_{3}H_{7}Br , and 3-methyl-3-hexanol is C...

Aliya 1H

Hey! So if you look at "magnesium sulfate heptahydrate", you correctly recognized that magnesium sulfate is MgSO4. Then, you have to include the heptahydrate part now. Hydrate is, as you would think, H2O. Taking into account the prefix "hepta", which means 7, the heptahydrate par...

Aliya 1H

HI! I was confused for a second by "amu" as well, however I realized that this question wants the molar mass and that a conversion to amu is unnecessary. So, find the molar mass as you normally would and enter it (it comes out to 176.12). That answer is in amu already because the atomic ma...

Aliya 1H

Hi! I went back to the email and it says this:
"Four additional modules that must be completed and will assist with material in week 2"
So, I think we should have them complete by the end of week two.

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