CHEMISTRY COMMUNITY

Margaret Xu 3C

Hello! We know molarity = moles of solute (mol) / volume of solution (L). When we rearrange the ideal gas law so that n/V, we realize that this is the same thing as mol/L, which is concentration.

Margaret Xu 3C

We don't include solids or liquids when solving ICE tables. When water is a gas, I believe we include it in the ICE table because the partial pressure of the gas will affect the overall equilibrium. Please correct me if I'm wrong!

Margaret Xu 3C

I think you'll know whether to use Kp or Kc depending on the values given in the problem. If the problem gives molarity (mol.L^-1) we use Kc and if they give values in atm/bar we use Kp.

Margaret Xu 3C

I think these refer to the examples that Dr. Lavelle will present in lectures. In Chem 14A he talked about hemoglobin in the context of coordination compounds so he tried to incorporate these ideas into a biological context. When he lists these things I think he is referring to his discussion of th...

Margaret Xu 3C

I'm pretty sure it's a typo and there's supposed to be a 2H₂ to balance the equation.

Margaret Xu 3C

Hi everyone! On the Chemical Equilbirum Outline, there was an objective that stated "Biological examples. For example: ATP hydrolysis; osmotic pressure". Could someone explain what this means?

Margaret Xu 3C

Based on the midterms and final we took in 14A, I think it's definitely a good idea to do the textbook problems listed on each outline. Rather than focusing on memorizing specific problems, I suggest doing multiple so that you know how to approach any type of problem that may be thrown at you on the...

Margaret Xu 3C

Hi Lilly! You are correct. The reaction quotient, Q, is used to represent the concentration/partial pressure of products divided by the concentration/partial pressure of reactants of the reaction at ANY time. The equilibrium constant, K, represents the reaction at equilibrium.

Margaret Xu 3C

Molarity, or molar concentration, is defined by the number of moles of solute per liter of solution, mol/L. In the ideal gas law, PV = nRT, n is the number of moles and V is volume, so n/V can be rewritten as concentration (mol/L). I hope this explanation wasn't too confusing!

Margaret Xu 3C

When using the ideal gas law, write the temperature in Kelvin.

Margaret Xu 3C

Hi Sera! When a reaction favors products, the reaction "shifts" to the right, and more products are being formed than reactants at equilibrium. When a reaction favors reactants, the reaction "shifts" to the left, meaning that more reactants are being formed than products at equil...

Margaret Xu 3C

thank u!! <3

Margaret Xu 3C

Metal oxides are typically basic, nonmetal oxides are usually acidic, and metalloid oxides are usually amphoteric.

Margaret Xu 3C

Thank you! You're the best

Margaret Xu 3C

In part b, ClO^- is actually a polyatomic ion called hypochlorite, so ClO^- can be considered as a single unit and the Cl is not removed. Hypochlorite is an anion that is considered a weak base in water. In part c, the Cl^- anion does not have an effect so it is treated as a spectator ion.

Margaret Xu 3C

I made the same mistake, but the problem states that H₂PO₄^- is acidic in this scenario so we have to remove the H⁺ and it forms a conjugate base.

Margaret Xu 3C

Although the two lone pairs are drawn next to each other in a H₂O Lewis structure, the electron repulsion pushes them away so that they aren't close together in a real molecule. Imagine each lone pair occupying a large region of electron density, resulting in them being further away.

Margaret Xu 3C

In order to consider if a molecule is polar or nonpolar, I always draw the Lewis structure first to see if the dipoles cancel out of it there are lone pairs.

Margaret Xu 3C

I think my TA mentioned that we wouldn't be allowed to use the ligand sheet for the final. It would probably be best if you tried to memorize them. The more problems you do the easier it becomes to memorize the ligands!

Margaret Xu 3C

My TA said that if by the end of the quarter you don't have 50 posts, they might look at the posts you've already made to see how thorough they are, taking quality over quantity into consideration. Also, it probably won't hurt to have 50 posts by the end of week 10 just in case your TA does decide t...

Margaret Xu 3C

I really recommend going to the UA workshops every week! I started attending them recently and I've found them to be super helpful. For the final, I think I'm going to review my notes and skim over past homework problems.

Margaret Xu 3C

Reiterating what people have said before, we can say angular or bent when referring to the shape. I don't think it matters which one we use but I think the textbook refers to it as angular.

Margaret Xu 3C

This happened to me as well, I logged out of Sapling and then signed in again and the issue was fixed. I'll also copy and paste the customer service email they sent: Install and use Google Chrome. If you already have Chrome installed continue to step 2, but if you just installed Chrome then skip to ...

Margaret Xu 3C

In high school, I would cram for tests the night before and basically teach myself all the content for the first time. I've tried to change my study habits by studying a little bit across several days before the exam so I don't get overwhelmed. I like to review homework/textbook problems I've done a...

Margaret Xu 3C

A molecule can have polar bonds between atoms, but if they cancel out then there is no net dipole moment so the overall molecule isn't polar.

Margaret Xu 3C

I like working out to Blogilates videos. Cassey has a monthly calendar that lists different workouts to do each day which makes exercising interesting!

Margaret Xu 3C

What you stated for bond multiplicity and atomic radius is correct. As for unpaired electrons, I think unpaired electrons will repel each other in order to achieve a lower energy state and become more stable, so the more unpaired electrons, the lower the bond dissociation energy.

Margaret Xu 3C

Good luck to everyone about to take the midterm this week! I took mine today, and to wind down I took a nap and watched Saiki-K!

Margaret Xu 3C

I'm comforted by the fact that other people are also worried about their grades. This quarter has been super difficult for a lot of people because of Zoom schooling and being stuck at home, but we're all going through similar experiences and we'll get through it together!

Margaret Xu 3C

This thread is so supportive! Don't feel discouraged about the midterm grades, this quarter has been really difficult for a lot of people because of online school and being stuck at home. You'll also have a lot of chances to make up points with Sapling homework and chem community!

Margaret Xu 3C

Hi Natalie! We look at intermolecular forces because the bonds between the molecules are being broken, not the bonds holding each molecule together. Compounds with stronger IMFs will have higher melting/boiling points.

Margaret Xu 3C

Hey everyone, I was wondering if we need to memorize polyatomic ions and their charges for Midterm 2.

Margaret Xu 3C

Since electronegativity is calculated experimentally, if we ever needed to solve for the electronegativity difference we would be given a chart with the values. Also, Professor Lavelle said that elements with an electronegativity difference between 1.5 and 2 would require experimentation to study th...

Margaret Xu 3C

Yep! You calculate the formal charges for each atom in the structure. The structure with the least formal charges (the most zeros) will require lower energy.

Margaret Xu 3C

Hey Eliana! The textbook states that delocalization means that a shared electron pair is distributed over several pairs of atoms and cannot be identified with just one pair of atoms. Electrons that are shown in different positions in a set of resonance structures are said to be delocalized. In my ow...

Margaret Xu 3C

In the answer key, N is the central atom double-bonded to O and single-bonded to F. You can check if your structure is correct by counting the formal charges. The molecule with the least amount of formal charges is most likely the correct structure. The formal charges for the structure you originall...

Margaret Xu 3C

Adding on to the previous responses, after drawing the Lewis structure for a molecule, it's a good idea to check the formal charges of each atom. The molecule with the least amount of formal charges is most likely to be the structure we're looking for. When drawing Lewis structures, there will be so...

Margaret Xu 3C

Selling Sunset is a reality show on Netflix about selling real estate in LA. It ended up being really fun to watch! I've also been rewatching Criminal Minds recently.

Margaret Xu 3C

I hope we'll be able to go over the midterm with our TAs. I'm wondering if I made silly calculation mistakes or if I just completely misunderstood concepts.

Margaret Xu 3C

My TA says we don't have our discussion session on Wednesday, but the powerpoints and practice problems will be posted on CCLE. I'm not sure about the lecture though.

Margaret Xu 3C

Hi, To show which orbital each electron is in for the p orbital, we wrote it as 2px^2 2py^2 etc... and for d it was xy yz and zx, but I am just wondering what it would be for the f orbital? I don't think that we would have to know it, but just curious. :) Thanks Hey, I don't think we'll need to kno...

Margaret Xu 3C

Hi Kaylee! I read that whenever you have the opportunity to complete a half d-shell or a full d-shell (going from 4 electrons to 5 or 9 electrons to 10), then you take 1 electron away from the s-shell and put it into the d-shell. I believe this is because a half or full d-shell is more stable and re...

Margaret Xu 3C

When a problem asks for shorthand electron configuration, I believe they are referring to noble gas configuration, which is why the shorthand of Si starts with the noble gas [Ne].

Margaret Xu 3C

I also really liked learning with the modules! I think it helped prime my brain for future lectures so it wouldn't be as overwhelming as learning each topic for the first time.

Margaret Xu 3C

For the Heisenberg uncertainty equation, I believe you always use meters in order to keep the units consistent (since velocity is also written in meters/sec). This way they'll cancel out when calculating.

Margaret Xu 3C

I believe the midterm covers all the material from Outline #1 and I did the textbook exercises for Outline #2 up to 1B. I think it's recommended that we read the textbook up to 1D Section 2.

Margaret Xu 3C

Hey! Just wanted to add that if you want a brief review of exponents and unit conversions, I recommend looking at Appendix 1B and 1D in the textbook. It was a nice refresher :)

Margaret Xu 3C

I like to cook or make myself a quick snack to relax and take a break from school work! I've also been watching new k-dramas on Netflix. :)

Margaret Xu 3C

How I like to think about it is if the uncertainty is 10Å, then it is just 10 x10^-10 m, while if it gives you +/-10Å, it will be 10x10^-10 m in the positive direction and 10x10^-10 m in the negative direction as the uncertainty. Hope this helps! This was a helpful way of thinking about it, thank y...

Margaret Xu 3C

When doing calculations, I believe the quantities are supposed to be written in meters! However, since the midterm is multiple choice, you'll be able to see if the final answer is going to be m or nm.

Margaret Xu 3C

The units for frequency are usually written in Hz (1s^-1), and the unit written for wavelength is meters. However, in a lot of problems I see the wavelength written in nm. A tip is to write 10^-9 behind the original number to convert from nm to m for easy calculations.

Margaret Xu 3C

To study for the midterm, I'm going to refer to the outlines posted on Professor Lavelle's website and review the notes and past homework we've done. I think I'm going to look over the Sapling questions and redo any textbook problems I've found difficult in the past!

Margaret Xu 3C

Hey Juwan! A molecule is composed of two or more elements that are covalently bonded. For example, H₂O or CO₂ are molecules because a nonmetal element bonding with another nonmetal element forms covalent bonds. A formula unit refers to the ratio of ions in an ionic compound, such as the salt NaCl.

Margaret Xu 3C

Yes! The work function, also known as the threshold energy, is the minimum amount of energy required to eject an electron from the surface.

Margaret Xu 3C

Yes! The work function, also known as the threshold energy, is the minimum amount of energy required to eject an electron from the surface.

Margaret Xu 3C

According to the equation E photon = h v , we see that the energy of a photon is directly proportional to the frequency of light. Therefore, if the frequency increases, the energy of the photon increases, allowing electrons to be ejected. However, increasing the intensity of light only increases the...

Margaret Xu 3C

I agree with the previous replies on this post. Protons and neutrons have approximately the same mass, 1.67 x 10^-24 grams (1 amu), while electrons are much smaller.

Margaret Xu 3C

Can electrons jump up multiple energy levels at once or do they have to reach a certain stage before they can reach the next energy level afterwards? For example, if an electron was at energy level n = 1, could it jump up to n = 4, or would it have to pass/stop(?) through energy levels n = 2 and n ...

Margaret Xu 3C

lauren_tran_3J wrote:I remember it as K.H.D.U.D.C.M : King Henry Doesn't Usually Drink Chocolate Milk. Or Kilo, Hecto, Deca, Unit (for example: gram), Deci, Centi, Mili. Hope this helps!

This is super helpful, thank you!

Margaret Xu 3C

Hey Daniela! Since doubling the volume decreases the concentration by half each time, and this process is repeated 90 times, the problem can be written as 1.0M x (0.5)⁹⁰.

Margaret Xu 3C

Hey Abby! mmol stands for millimole; 1 mmol = 1 x 10^-3 mole

Margaret Xu 3C

Hi Adam! Since a catalyst is a substance that increases the rate of chemical reaction without going under any chemical change itself, it does not affect the chemical equation. In the textbook, the catalyst name was written above the arrow in a chemical equation to indicate that a catalyst had been a...

Margaret Xu 3C

Hey Savannah! I think writing (aq) after 0.123 M HCl(aq) is just to indicate that the HCl has been diluted with water to form an aqueous solution. I don't think you have to include the phase of matter in your final answer or calculations unless the problem specifies.

Margaret Xu 3C

Do you calculate formula units the same way we calculate number of atoms in a molecule from molar mass and avogadros number? Hi Mary! Since 1 mole always means 6.0221 x 10 23 of 'things', you can use Avogadro's number as a conversion factor so that there are 6.0221 x 10 23 formula units in 1 mole o...

Margaret Xu 3C

When solving for a dilution problem (M initial V initial = M final V final ), it doesn't matter if you use mL or L as long as you keep the units consistent for V initial and V final . If you are solving for volume, and the problem specifies that you should use mL or L, then convert to those units. I...

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