CHEMISTRY COMMUNITY

Sabine Salvucci 2E

Hello! I am pretty sure that intermediates will be produced as a product then consumed as a reactant while catalysts go from reactant to product.

Sabine Salvucci 2E

Hello! I am pretty sure the ions go closest to the salt bridge (||) and the electrodes are written on the far ends of the diagram. This is what sapling said: "In the shorthand notation, the anode is written on the far left and the cathode on the far right. The different phases in the cell are s...

Sabine Salvucci 2E

Like everyone has already said, oxidation (loss of electrons) occurs at the anode and reduction (gain of electrons) occurs at the cathode. A way I like to remember this though is the acronym OIL RIG (oxidation is loss; reduction is gain). I also associate oxidation and anode because they both start ...

Sabine Salvucci 2E

Hello! I agree with the other posts that we probably won't ever to have to determine the slow step by just looking at the reactions. We should be given enough info to determine it or use it if necessary.

Sabine Salvucci 2E

Hey! Catalysts aren't consumed like normal reactants. I agree with the earlier posts that says that by consumed, Prof Lavelle probably means that the catalyst will show up on both sides of a reaction (so it's like they are being consumed then reproduced).

Sabine Salvucci 2E

Another good analogy I saw was a relay/team race. If everyone in the race is very fast, but there is one person who is very slow, the groups performance would mostly be determined by the slowest person. In other words, the majority of the time it takes to finish the race and the time that contribute...

Sabine Salvucci 2E

These reactions are generally in aqueous conditions so there is an excess of water and hydronium/hydroxide ions. Since we have so many extra water molecules and ions in the solution, we can use these to balance our equations.

Sabine Salvucci 2E

I'm pretty sure most TAs are fine with you just posting 50 by the end of the quarter. If you want to be 100% sure though you could always ask your TA.

Sabine Salvucci 2E

The purpose of the salt bridge is to keep the charges balanced on either side of the cell. As electrons move from one side to the other, ions move the opposite direction through the salt bridge to balance the charge.

Sabine Salvucci 2E

Hello! I was also really confused about this, but this is something Chem_mod said in a previous post: "Since both pressure (1 atm approximately equal to 1 bar) and concentration are referenced (standard reduction potentials) with respect to standard conditions (gases 1 bar, solutions 1M), one c...

Sabine Salvucci 2E

To find out how many electrons to put on each side of the equation, you first have to calculate the charges on each side of the equation after you have otherwise balanced it. Then just add electrons so the charges on both sides match. For example, if the charge of the reactants is +2 and the charge ...

Sabine Salvucci 2E

My fav songs right now are Kamikaze by Omar Apollo and First Love/Late Spring by Mitski!

Sabine Salvucci 2E

When Breath Becomes Air by Paul Kalanithi! It is a memoir and I don't usually read nonfiction, but this book is super good. It is sad though if you are looking for something more fun.

Sabine Salvucci 2E

I think I followed the process you guys described. I had calculated Ecell = 0.34 - (-0.44) = 0.78. However, Sapling said my answer is wrong. Can someone help me figure out what I'm doing wrong? Thank you! Hello! I can't think of anything conceptually you are doing wrong so since Sapling kind of ran...

Sabine Salvucci 2E

Hi! I'm struggling on the same problem. I'm pretty sure I am inputting it exactly as you said, but I am still not getting the right answer? To be honest, I'm on my 22nd try on this question lol. HELP! Hello! Your charges for the reduction reaction aren't balanced. It looks like you only put 1 elect...

Sabine Salvucci 2E

Hello! Entropy is a measure of the disorder of a system. If the change in entropy (delta S) is positive, entropy is increasing and the process is spontaneous. If delta S is negative, entropy is decreasing and the process is non-spontaneous.

Sabine Salvucci 2E

Textbook questions and UA/TA sessions/worksheets definitely help a lot! The test questions often look pretty similar to what you see in the textbook and on previous exams. I took 14A with Prof Lavelle and the final was a bit harder than the midterms, but if you do all the practice problems and make ...

Sabine Salvucci 2E

how's the workload if we take 14c and 14bl? Hello! I can't speak to 14c, but I'm in 14bl right now and the workload is definitely manageable. We have weekly lab reports that take 1-2 hours in addition to the lab sections. We also have a writing assignment at the end of the quarter. I'm taking it wi...

Sabine Salvucci 2E

Hello! I was just wondering how much/what we have to know about translational, vibrational, and rotational energy for the midterm. It's in the textbook and I vaguely remember Professor Lavelle mentioning it during lecture, but it isn't on the outline so I just wanted to make sure. Thank you!

Sabine Salvucci 2E

When delta H and delta S are both positive the reaction will be spontaneous at certain temperatures. When the temperature is high the reaction is more likely to be spontaneous. because of the relationship between delta S, delta H, and delta G (delta g= delta h - t(delta s)).

Sabine Salvucci 2E

I agree with everyone else that is recommending UA sessions and workshops. Something else that I find helpful when I do the Sapling homework and the textbook questions is to make sure I'm really understanding how to do the problems. In the past, since the solutions are available, I've noticed that I...

Sabine Salvucci 2E

Hello! I am taking Chem 14BL online right now and I'm glad I decided to take it online. It's definitely way less time-consuming (and probably easier) online since our labs are videos or online simulations. I think deciding whether to take it in-person or online though really depends on what you want...

Sabine Salvucci 2E

I don't know why the signs would be different in other study books but I'd just stick with the way we learned it in this class. So, if work is done on the system it's positive and if work is done by the system it's negative.

Sabine Salvucci 2E

I agree with all of the other posts about phase changes. The way I like to think about it is that all the heat/energy is going toward the phase change so the temperature doesn't change. If you look at the phase change graph, you'll notice the flat portions of the graph that correspond to phase chang...

Sabine Salvucci 2E

I'm not 100% sure, but I also heard that only outlines 3 and 4 will be on the midterm. Lavelle will probably send out an email later with specifics about the midterm.

Sabine Salvucci 2E

Something I recently learned was the difference between heat-safe and regular glass. Heat-safe glass (like the kind you can use oven, eg. Pyrex) is made of borosilicate glass, which has a low coefficient of thermal expansion and therefore is less likely to break at high temperatures. I think this is...

Sabine Salvucci 2E

Hello! Molar heat capacity is how much heat is necessary to raise the temperature of one mole of a pure substance by one degree. Specific heat capacity is a how much heat is necessary to raise the temperature of one gram of a pure substance by one degree. To know which one to use, just look at the u...

Sabine Salvucci 2E

I think it’s up to your TA so definitely ask them if you need 5 per week or just 50 by the end of the quarter. Personally, my TA just wants us to get 50 by the end of quarter, but that probably that might not be the case for everyone.

Sabine Salvucci 2E

Heat capacities can't be negative so if you have a negative q, deltaT is also going to be negative but c will still be positive. When a system is exothermic and q is negative, the final temperature will be lower than the initial temperature so deltaT is negative. This way, heat capacity can remain p...

Sabine Salvucci 2E

I've definitely been having the same problem where I just have no motivation to do anything even though I know I have so much that I need to do and this has definitely been hurting my performance at school. Something I recently started doing that has kind of helped is just starting off with small ta...

Sabine Salvucci 2E

Hi! I agree with all of the above answers but just wanted to add a way that helps me remember the difference. In tensive properties are In dependent of the amount of substance present (basically, intensive and independent both start with "in"). I'm not sure how helpful this but I personall...

Sabine Salvucci 2E

I think Sapling problems are useful for testing your understanding of general concepts, but the textbook questions usually reflect the difficulty of the test more. It would definitely be helpful to do both. Something nice about Sapling is the detailed explanations of the solutions which really helps...

Sabine Salvucci 2E

Hey! I have a part time job where I work 20ish hours a week and I find that making sure I have time where I can focus just on school helps me get everything done. I also like to plan ahead when I am going to complete each assignment so I am not scrambling at the last minute. Honestly, it can get pre...

Sabine Salvucci 2E

There isn't an option to review them by yourself as Professor Lavelle doesn't release the answers with the grades, but if you want to review questions, you can ask your TA to go over it with you.

Sabine Salvucci 2E

Hello! I'm currently taking Chem 14BL right now, and I just want to advise that this class, while not the most difficult material, is a lot of work. So if you think you are already going to have a busy schedule next quarter, you might want to consider whether you can handle this extra workload (wee...

Sabine Salvucci 2E

I think we just have to know what's on the outline/what he covered in lecture. You should probably know the relationship between volume/pressure, concentration, and temperature changes and equilibrium.

Sabine Salvucci 2E

I think you are correct. If you increase the concentration of the products, the reverse reaction would occur so the reaction reaches equilibrium again.

Sabine Salvucci 2E

Hello! To determine whether a salt is acidic, basic, or neutral, you have to look at the ions the salt is composed of. If the salt is composed of an anion of strong acid and a cation of a weak base, for example, the salt would be acidic. If the salt is composed of an anion of weak acid and a cation ...

Sabine Salvucci 2E

Since solids don’t affect the equilibrium constant, you wouldn’t have to include them in the ICE tables.

Sabine Salvucci 2E

How do we compare these terms to graphs / visually? Hello! For reactions that are endothermic/endergonic, there will be more energy on the products side of the reaction and for reactions that are exothermic/exergonic, there will be more energy on the reactants side. Here’s a graph of the two: https...

Sabine Salvucci 2E

Hello! Doing textbook problems was really helpful because I found those most similarly resembled the kind of questions we would get on assessments. It is also important to understand the material conceptually; something that helped me with this is making my own study guides for the lectures and text...

Sabine Salvucci 2E

Hello! I think if you post this coming Sunday (of week 2) it would count for week 2. That being said, for many of the TAs there isn't a strict deadline for when you need to make the posts as long as you have 50 by the end of the quarter. Both these questions are probably good ones to ask your TA sin...

Sabine Salvucci 2E

Can someone who had Lavelle for 14B explain what Respondus is and how we use it for the midterms? Hello! Respondus is basically a lockdown browser that Lavelle wants us to use during the exams so we can't look up info during the test. To use it you have to download Respondus and when you take the m...

Sabine Salvucci 2E

will there be a zoom link given to us for lect? couldn't find it on CCLE Hello! All of our lectures are prerecorded so there won't be any zoom links for lectures. If you are looking for the lectures, they are under Media Resources on CCLE. There are, however, a lot of study sessions, discussions, o...

Sabine Salvucci 2E

Hello! There probably won't be anymore Audio Visual Focus Topics. In 14A, there were also only modules for the first section. It seems like they are mostly to help us get back into the school mindset and to give us a preview of the material before class starts.

Sabine Salvucci 2E

Are there solutions posted anywhere for the extra practice textbook problems (not the Sapling questions)? Yes! When you open the Sapling home page for Chem 14B, the answer key for all of the odd textbook problems should be in the resource section. It is the PDF called Atkins 7e SSM. I don't think t...

Sabine Salvucci 2E

Hello! Q and K are calculated using the same formula, but they represent different things. K (equilibrium constant) is calculated only when the reaction is at equilibrium, but Q (reaction quotient) is calculated at any time during the reaction. When Q does not equal K, the reaction will approach equ...

Sabine Salvucci 2E

Hello! The answer to this question would be C because at equilibrium, although it looks like there is no reaction because the concentration of products and reactants aren't changing, the reaction is still taking place.

Sabine Salvucci 2E

Hello! The ideal gas law uses atmospheres as the unit for pressure so you would usually want to convert the pressure to atm. Since 1 atm is equal to about 1.01 bar, however, it isn't really necessary to do any conversion calculations; you can just plug the pressure in bar into the ideal gas law. Hop...

Sabine Salvucci 2E

Hello! I think K and Kc are basically the same thing, both representing the equilibrium constant, but Kc is more specific. K can refer to concentration, pressure, etc., while Kc specifically refers to concentration. Hope this helps!

Sabine Salvucci 2E

I'm pretty sure it was the double slit experiment.

Sabine Salvucci 2E

Hello! This is how I like to determine it. I compare the strengths of the acids and bases that the anions and cations come from. If both are strong, the strengths cancels out and the salt is neutral. In the case of KBr, since both KOH and HBr are strong, the strengths cancel out and the salt is neut...

Sabine Salvucci 2E

Hello! This is how my TA solved this problem. To start, it is important to recognize that [HCl]=[H] since there is only 1 H atom in HCl, so you can use [HCl] in place of [H+] when you are solving for pH. To find the difference in pH values of the 2 solutions, you subtract the pH of the original from...

Sabine Salvucci 2E

Hello! The lone pairs are placed where there is the least repulsion between electron pairs. For example, if you have the electron geometry trigonal bipyramidal with one lone pair, the lone pair would be placed in the equatorial plane rather than the axial plane because that minimizes electron repuls...

Sabine Salvucci 2E

I don't think the final is going to be focused specifically on stuff we recently learned. It will probably be weighted similarly to how the stuff we learned was (ie. if we spent more time on a topic it will be more focused on on the final).

Sabine Salvucci 2E

Water can act as either an acid of a base depending on what the situation requires. It can donate or accept a proton, making OH- or H3O respectively. Hope this helps!

Sabine Salvucci 2E

Hello! My TA also only went up until the steric number 6 (including all the lone pair configurations) so it should probably be fine to just memorize all of those models.

Sabine Salvucci 2E

Hello! I don't think the chart of all the molecular shapes/bond angles based on steric number and lone pairs will be provided on the final so you should probably try to memorize that.

Sabine Salvucci 2E

Hello! The ones my TA mentioned are silver-argentate, gold-aurate, and lead-plumbate. I think tin also is named with its latin name. Hope this helps!

Sabine Salvucci 2E

Hello! You can probably write the name either as 1 long word or with hyphens depending on what you are more comfortable with. If the coordination complex is attached to another ion (like in [Co(NH3)4Cl2]Cl), the part inside the brackets (Co(NH3)4Cl2) and the part outside the brackets (Cl) would be w...

Sabine Salvucci 2E

Hello! If you are given a 2D representation, you can use it to find the 3D shape of the molecule based on the number of lone pairs and terminal atoms. From the 3D shape, you can find the bond angles. Hope this helps!

Sabine Salvucci 2E

Hello! To determine the polarity of a bond, compare the electronegativities of the two atoms. If there is a difference in electronegativity, the bond is polar (and vice versa). To determine the polarity of the overall molecule, look at all of the dipoles in the molecule (that was found when determin...

Sabine Salvucci 2E

What if the electronegativity difference is equal? Hello! If there is no difference in electronegativity between 2 atoms, the bond would be non polar (like O2). If 2 different dipoles that face opposite directions on the same molecule have equal differences in electronegativity, the dipoles would c...

Sabine Salvucci 2E

Hello! This question is specifically asking about P in P4O6 so you want to find the hybridization of any of the Ps in the molecule. To do this, pick any P and determine how many areas of electron density there are, 4 in this case. The hybridization of an atom with 4 regions of electron density is sp...

Sabine Salvucci 2E

Hello! I am pretty sure the 3 bonded atoms in the T-shaped geometry are all in the same plane. This is because of how where the lone pairs are on the molecule. The bond angles would be 90° and 180°. Hope this helps!

Sabine Salvucci 2E

Hello! For a molecule with dipole moments to be non polar, the dipoles have to point in opposite directions. In cis-dichloroethene the dipoles point in different directions, but since the Cl atoms are on the same side of the molecule, they aren't completely opposite and wouldn't cancel each other ou...

Sabine Salvucci 2E

Hello! Since CO2 does not have a lone pair on the central atom, its shape is linear. However, since SO2 does have a lone pair on the central atom, its shape is bent. This happens because the lone pair basically repels electrons from the other bonds. Since CO2 is linear and symmetrical it is non pola...

Sabine Salvucci 2E

Hello! Elaborating on what Lisa said, it seems like the 'one structure' version is used for covalently bonded molecules, like methanol, whereas the [] version is used for ionic compounds, like NaCl. Hope this helps!

Sabine Salvucci 2E

Hello! I believe that 14CL is required for med school because you need 1 year of organic chemistry, including lab. UCLA has a pdf available that tells you most of the pre-health requirements: https://www.aap.ucla.edu/wp-content/upl ... ements.pdf
Hope this helps!

Sabine Salvucci 2E

Yep! All molecules have LDFs since LDFs are just caused by the movement of electrons in atoms/molecules and electrons move around in all molecules/atoms.

Sabine Salvucci 2E

Yep! The VSEPR model helps show the 3D shape of the molecule and therefore whether a molecule is symmetrical or asymmetrical. The symmetry of a molecule is directly related to its polarity, with symmetrical molecules being non polar and asymmetrical molecules being polar. Hope this helps!

Sabine Salvucci 2E

Hello! H2O ... H-CH3 doesn't have an H-bond because the hydrogen in H-CH3 is attached to a carbon. For a H-bond to form, one side of the bond has to be N, O, or F and the other side has to be hydrogen bonded to N, O, or F. Basically, H has to be surrounded on both sides by N, O, or F. In this exampl...

Sabine Salvucci 2E

Hello! Ionization energy increases as you across a period because as you go across a period, the atomic number (and therefore the number of protons in the atom) increases. When you have more protons in an atom, the positive charge is greater and the nucleus has a stronger pull on the negatively char...

Sabine Salvucci 2E

Screen Shot 2020-11-12 at 1.26.17 PM.png Hello! This was my structure for phosphite (note: its kind of hard to see but there is a lone pair attached to phosphorus). Phosphite doesn't require an expanded octet. To create this structure, you would just follow the general rules for lewis structures, w...

Sabine Salvucci 2E

I don't think we went over this in lecture but I'm pretty sure oxidation number is basically a theoretical charge assigned to each of the atoms in a molecule, taking electronegativity into account. In most cases, we can assume the oxidation number of O to be -2 (because of its high electronegativity...

Sabine Salvucci 2E

Hi! The electron configuration for Cu+ is [Ar]3d10. Although normally when you fill shells, you would fill the S orbital first, a half full S orbital and a full d orbital is more stable in this case. When you remove an electron to go from Cu to Cu+, the electron is removed from the S orbital and not...

Sabine Salvucci 2E

The S-block elements, like Na, Ca, Mg, and K, have a lower ionization energy than those in the P-block, which makes it much easier to remove electrons. The ionization energy is so much lower because elements in the S-block only have 1 or 2 valence electrons and are therefore much more likely to want...

Sabine Salvucci 2E

The negative or positive sign outside the brackets represents the charge of the molecule. For example, if you are drawing the lewis structure of NO3-, you would put a - outside the bracket. If you are drawing SO42-, you would put 2- outside of the brackets. Hope this helps!

Sabine Salvucci 2E

Like Alexa said, the most effective way to figure out the best structure is with formal charges. When the formal charges are closer to 0, the molecule will be more stable. I think Lavelle showed an example of this in the Monday's lecture if you want a more in depth explanation. Hope this helps!

Sabine Salvucci 2E

Lavelle mentioned in an email he sent that the average for the class was 86% (including a 5% boost from just downloading respondus). He also said that some of the harder questions were from the homework so if you find them, you could probably use the textbook to review those. I'm not sure about any ...

Sabine Salvucci 2E

My question on Sapling had the value 0.0225nm, not 0.0315, but the concept should be the same when solving the problem. Since this problem is asking you to solve for kinetic energy, you would use the formula KE=½mv^2. To use this equation, however, you need to find the velocity associated with the e...

Sabine Salvucci 2E

I think everyone will finish by tonight, so hopefully soon. I read that someone mentioned something about partial credit. How would that work? Yah. I was wondering the same thing. Does anyone know? I think for some of the questions they might make the answer choices worth different amounts of point...

Sabine Salvucci 2E

I think usually, if an atom is in a lower period (eg. K is in a lower period than Cl), the atom in the lower period (K) would be larger. This happens because as you go down a group, another shell is added (the principle quantum number, n, goes up by 1).

Sabine Salvucci 2E

I think that it is probably doable to take Chem 14B and BL simultaneously, it would just be a lot more work. I've heard that it isn't vital to know all of the content in B before you take BL, but it definitely wouldn't hurt. It mostly depends on how ready you feel to add another class and what your ...

Sabine Salvucci 2E

arisawaters3D wrote:How do you know if an electron is spin up or spin down?

I am pretty sure that at first, you can choose whether spin is up and down. I usually start with spin up for consistency. Just make sure you follow Hund's Rule and that all the orbitals are singly-occupied before you double up on one.

Sabine Salvucci 2E

Since violet is part of the visible region, we know that it is part of the Balmer Series so n1=2. First you want to find the frequency of the light at 434nm. Then, you can plug this frequency and n1=2 into the Rydberg Equation to solve for n2. Hope this helps!

Sabine Salvucci 2E

The constants are the same, but R=1.09x10^7 one is in terms of 1/m, whereas R=3.29x10^15 is in terms of Hz. You can convert between the two using c=vλ. If you use the equation we were given in class, En = -(hR)/(n^2), or v=R(1/n^2-...) use the R=3.29x10^15. If you wanted to use the equation 1/λ=R(1/...

Sabine Salvucci 2E

The mass of a single fluorine molecule is what is listed on the periodic table of elements. Since it is diatomic, you should double the amu. To get the correct wavelength, you have to convert the g/molecule into kg/molecule. Then using, wavelenth=h/(mv), the kg in the m will cancel with the kg in p...

Sabine Salvucci 2E

I think my TA told us that they wouldn't have questions where you have to choose between two answers with different sig figs. It probably wouldn't hurt to look at the sig figs document Lavelle posted though if you are still worried!

Sabine Salvucci 2E

I am also kind of confused about this, but looking at the textbook sections on orbitals and wavefunctions helped me a lot. From my understanding, the Schrodinger Equation (Hψ = Eψ) is used to calculate the wavefunction, ψ, for a particle and can also be used to calculate the energy of the electron. ...

Sabine Salvucci 2E

The energy gaps are smaller because as you move farther from the nucleus it takes less energy to remove the electron. The positive charge of the nucleus has a stronger pull on the negatively charged electron when the electron is closer, making it harder to be removed.

Sabine Salvucci 2E

In your answer, use the same number of sig figs as the value with the lowest number of sig figs in the problem (unless stated otherwise). I think my TA mentioned that we would be slightly penalized for sig fig errors.

Sabine Salvucci 2E

The mass of an electron is a known value. It can be found on the constants and equations sheet posted on the Chem14A website. Hope this helps!

Sabine Salvucci 2E

Yes, a photon is a particle-like packet of electromagnetic radiation. "Quantum of light" refers to the idea that photons are discrete and quantifiable.

Sabine Salvucci 2E

For this problem, you don't need to use the molar mass of sodium. You would instead plug the mass of the electron, 9.11x10^-31kg, into the kinetic energy equation (KE=½mv^2) since it asks for the energy of the ejected electron, not the energy of the sodium surface. You then would plug in the given v...

Sabine Salvucci 2E

First you would convert the 55.1g of KCl to moles using the molar mass (74.55g/mol):
55.1g/(74.55g/mol)=0.739mol
Then you would calculate the molarity using the volume (125mL=.125L) and the equation, M=n/v:
0.739mol/.125L=5.91mol/L
You can basically disregard the 75mL in this problem.

Sabine Salvucci 2E

The link for Discussion 1C is posted on the TA's website (the link to the website is on the site info page of CCLE). I'm not sure about other discussion links though.

Sabine Salvucci 2E

Since the problem is using oxygen gas (O2), we would use the molar mass for O2, 32.00g/mol.

Sabine Salvucci 2E

The problem might specify that there is more than 1 mole. If you want to be totally sure though, you could always write the formulas of the given diagrams and try to balance the equation from there.

Sabine Salvucci 2E

As long as the initial and final units are the same it doesn't matter whether you use mL or L. When you use mL, it's implied that you're basically multiplying both sides of the equation by 1000 to go from L to mL.

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