## Search found 60 matches

Sat Jan 16, 2021 5:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: hw question #3
Replies: 10
Views: 41

### Re: hw question #3

multiply out the denominator( (a + b)^2 = a^2 + 2ab + b^2) then cross multiply with 53.3. Move everything to one side so you can find X using the quadratic formula.
Sat Jan 16, 2021 5:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: hw question #4
Replies: 5
Views: 38

### Re: hw question #4

The total pressure is the sum of all the partial pressures of a system. The problem gives you the Kp and the initial concentration of PCl5, so you can set up an ICE box to find an equation for x, and then plug in x to find each of the partial pressures of PCl5, PCl3, and Cl2. Add them all together ...
Sat Jan 16, 2021 5:30 pm
Forum: Student Social/Study Group
Topic: Comfort Movies
Replies: 108
Views: 238

### Re: Comfort Movies

Clueless and Heathers are my comfort movies and New Girl and Skins are my comfort shows. There are a bunch of other movies/shows that I like to rewatch over and over again but these are my most-watched.
Sat Jan 16, 2021 5:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: sapling homework #2
Replies: 5
Views: 36

### Re: sapling homework #2

I made an ICE table and found the initial concentration of SO3 by dividing .680 mol/3.5L. The initial concentrations for SO2 and O2 are 0. Then I put in the change, which is -2x for SO3, +2x for SO2 and +x for O2, and since we are given the amount of O2 in moles at equilibrium, we can find x by divi...
Sat Jan 16, 2021 5:22 pm
Forum: Student Social/Study Group
Topic: Study Habits
Replies: 91
Views: 245

### Re: Study Habits

I've been trying to spread my studying out instead of cramming right before and I think that has helped. Also, while doing the textbook problems, I focused on what I got wrong so I didn't make the same mistakes during the midterm or final.
Fri Jan 08, 2021 3:33 pm
Forum: Ideal Gases
Topic: Finding x for K using quadratic equation
Replies: 6
Views: 40

### Re: Finding x for K using quadratic equation

Concentrations can't be negative so pick the X value that makes it so the concentrations of the products and reactants aren't positive.
Fri Jan 08, 2021 3:29 pm
Forum: Administrative Questions and Class Announcements
Topic: Sapling Assignments
Replies: 26
Views: 124

### Re: Sapling Assignments

They are optional but they are good practice! They were helpful for me last quarter before the midterms/final.
Fri Jan 08, 2021 3:27 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temperature Effect on the Direction of the Reaction
Replies: 4
Views: 23

### Re: Temperature Effect on the Direction of the Reaction

Similar to what others said above, an easy way to remember this is by thinking of heat as either a "product" or "reactant" in the reaction. If the reaction is endothermic, heat is a "reactant," so increasing temperature shifts the reaction to the right and increases K....
Fri Jan 08, 2021 3:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: I.C.E.
Replies: 7
Views: 26

### Re: I.C.E.

Some reactants are being turned into products so the reactant concentration will decrease (-X) from it's initial concentration of 3 and the product concentrations will increase (+X) from their initial concentration of 0.
Fri Jan 08, 2021 3:16 pm
Forum: Ideal Gases
Topic: Change in pressure and inert gas
Replies: 6
Views: 34

### Re: Change in pressure and inert gas

Hi! An inert gas is just a gas that, when added to the equilibrium system, won't cause a chemical reaction. When an inert gas is added to the sealed reaction vessel, it does increase the pressure but because the volume of the reaction vessel itself doesn't change, the volume of the gases contained ...
Wed Dec 09, 2020 8:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook 2E #25
Replies: 3
Views: 33

### Re: Textbook 2E #25

I had the same question! The Lewis structure I drew makes it seem like it's polar and when I looked it up a bunch of websites said it is polar so I think it might be a mistake.
Wed Dec 09, 2020 8:48 pm
Forum: Bronsted Acids & Bases
Topic: Textbook 6A.5
Replies: 2
Views: 17

### Re: Textbook 6A.5

A Bronsted acid is a proton (H+) donor and a Bronsted base is a proton acceptor. In the textbook problem HNO3 donated a proton to HPO4 so HNO3 is the bronsted acid and HPO4 is the base.
Tue Dec 08, 2020 11:29 am
Forum: General Science Questions
Topic: coordination #s
Replies: 2
Views: 38

### Re: coordination #s

There's a helpful list in section 9C (table 9C.1) of the textbook with a list of common ligands that also tells you if the ligand is monodentate, bidentate, tridentate, or hexadentate. Using this, count up the number of sites ligands are attached to the metal and that's the coordination number.
Tue Dec 08, 2020 11:23 am
Forum: Naming
Topic: Complex Name for [Fe(CN)6]4-
Replies: 3
Views: 41

### Re: Complex Name for [Fe(CN)6]4-

Hi! Dr. Lavelle mentioned in lecture that both the -ido and -o are the same thing, except -ido is a newer notation and -o is the one we will mainly use in this course. So technically, both hexacyanoferrate(II) and hexacyanidoferrate(II) are correct. If the ligand ends with -ide, you change the endi...
Tue Dec 08, 2020 11:22 am
Forum: Determining Molecular Shape (VSEPR)
Topic: textbook #2E13
Replies: 4
Views: 44

### Re: textbook #2E13

I was confused about this too! There are five regions of electron density, and three of those are lone pairs. Since a trigonal bipyramidal shape has three equatorial positions and two axial positions, it makes sense for the two atoms to go on the axial positions (making their bond angle 180) and the...
Sat Dec 05, 2020 11:37 am
Forum: General Science Questions
Topic: study methods/recs
Replies: 37
Views: 278

### Re: study methods/recs

The UA worksheets are helpful. I also like to go through my notes and the textbook and rewrite the main concepts in an organized way.
Sat Dec 05, 2020 11:35 am
Forum: Naming
Topic: what does (en) mean?
Replies: 23
Views: 155

### Re: what does (en) mean?

Claire_Kim_2F wrote:https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/NamingCoordinationCompounds.pdf here is the link for anyone who needs it!

Thank you!
Sat Dec 05, 2020 11:33 am
Forum: Administrative Questions and Class Announcements
Topic: Chem 14A Final
Replies: 21
Views: 172

### Re: Chem 14A Final

Katie Lam 2G wrote:I read the final exam information on Dr. Lavelle's website, and he said it will be approximately weighted to the amount of time covered in the syllabus. He wrote that quantum was the biggest section, so we should expect more questions from that section. Hope this helps!

Sat Dec 05, 2020 11:32 am
Forum: Student Social/Study Group
Topic: How are you?
Replies: 111
Views: 753

### Re: How are you?

Tue Dec 01, 2020 10:22 am
Forum: Naming
Topic: Oxidation Number while Naming
Replies: 9
Views: 63

### Re: Oxidation Number while Naming

Sophia Hu 1C wrote:We know H2O and NH3 is neutral. All halogens have a typical oxidation state of -1. Since there are two Chlorines then there is two -1 charges. However, it is all neutral which means Co must have a +2 charge.

Fri Nov 27, 2020 11:10 am
Forum: Lewis Structures
Topic: Octet Rule
Replies: 17
Views: 133

### Re: Octet Rule

Elements in the p-block of period 3 or later have empty d-block orbitals that can hold electrons so they can have more than 8 electrons in their outer shell. S, P, and Cl are some common atoms that can have expanded octets. This confused me at first too!
Fri Nov 27, 2020 11:06 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling 16
Replies: 6
Views: 54

### Re: Sapling 16

Compounds with double or triple bonds (meaning there's at least one pi bond) and resonance structures have delocalized pi bonds because the bonds can have multiple positions in the compound.
Fri Nov 27, 2020 10:57 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling Question #6 (Week 8)
Replies: 5
Views: 52

### Re: Sapling Question #6 (Week 8)

The lone pairs have stronger repulsion and therefore want to stay as far away from each other as possible. Occupying the equatorial positions allows for this, as the axial positions would still require one pair to take up an equatorial position, creating a smaller angle between the lone pairs. At t...
Fri Nov 27, 2020 10:55 am
Forum: Student Social/Study Group
Topic: Final Exam Tips
Replies: 24
Views: 139

### Re: Final Exam Tips

I find the textbook problems super helpful, but before I start a section I like to look through the textbook and my notes and write down some of the key concepts for that topic. Once I'm done, I check my answers and figure out what topics I struggle with and need to focus on the most.
Mon Nov 23, 2020 3:15 pm
Forum: Student Social/Study Group
Topic: How have your study habits changed?
Replies: 45
Views: 299

### Re: How have your study habits changed?

My notes are a lot more organized now and I like to divide them up by topic instead of putting as much information as possible onto a page. I also am learning to study over a few days instead of cramming the night before.
Wed Nov 18, 2020 11:35 am
Forum: Octet Exceptions
Topic: Octet Rule Exceptions
Replies: 20
Views: 169

### Re: Octet Rule Exceptions

I am slightly confused about drawing lewis structures, and specifically the octet rule. Do elements with 1 or 2 valence electrons have to fill an octet? For example, when drawing out a compound that contains the element Na (which has one valence electron), is it ever possible for it to fill the oct...
Wed Nov 18, 2020 11:27 am
Forum: Student Social/Study Group
Topic: Midterm 2
Replies: 19
Views: 183

### Re: Midterm 2

The textbook problems on the outline help me the most because I can see what topic I need to focus on based on which problems I get wrong.
Wed Nov 18, 2020 11:25 am
Forum: Electronegativity
Topic: Periodic Table Trends
Replies: 9
Views: 82

### Re: Periodic Table Trends

Megan Singer 1F wrote:
I thought the atom with the lowest ionization energy/lowest electronegativity goes in the middle

Yes! The atom with the lowest ionization energy does go in the middle. For example, C is in the middle in CCl4 and C has a lower ionization energy than Cl.
Wed Nov 18, 2020 11:20 am
Forum: Administrative Questions and Class Announcements
Topic: Chem 14B enrollment [ENDORSED]
Replies: 7
Views: 130

### Re: Chem 14B enrollment[ENDORSED]

Angelica Soriano 1F wrote:Professor Lavelle just came out and said that winter enrollment in all his classes will increase! :D I linked it down below.

viewtopic.php?f=157&t=67870

Wed Nov 18, 2020 11:16 am
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Covalent Character and Polarizability
Replies: 4
Views: 61

### Re: Covalent Character and Polarizability

When the cation is small with a high charge (high polarizing power), it can distort a large anions (high polarizability) electrons really well so there is a shared region between the two ions. This shared region gives the ionic bond covalent character. In a covalent bond, atoms share electrons, so a...
Sat Nov 14, 2020 5:05 pm
Forum: Ionic & Covalent Bonds
Topic: Textbook 2A #9
Replies: 3
Views: 18

### Re: Textbook 2A #9

I solved this problem by adding the 2 electrons back into the configuration so I could tell what metal M was more easily. For a) the non-ionic e- configuration would be [Ar] 3d7 4s2, which is Co. For b) the e- configuration would be [Ar] 3d6 4s2 so the metal is Fe.
Sat Nov 14, 2020 5:02 pm
Forum: Octet Exceptions
Topic: Octet Rule Exceptions
Replies: 8
Views: 82

### Re: Octet Rule Exceptions

Elements in row 3 or higher (specifically p-block elements) can have expanded octets because they can utilize their d-orbitals when bonding. Group 13 elements (like B and Al) typically don't have complete octets because they would need to gain 5 e- which is a lot. However these compounds do have a ...
Wed Nov 11, 2020 6:34 pm
Forum: Student Social/Study Group
Topic: Studying From Home
Replies: 91
Views: 470

### Re: Studying From Home

Studying at home is hard for me too. I like to study or do work for a little while, like an hour, then take a break and do something else for 15 or 20 minutes. I think my breaks are most effective when they don't include more screen time, so usually I'll go outside or make a snack or talk to my room...
Wed Nov 11, 2020 6:31 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Sapling #9
Replies: 5
Views: 61

### Re: Sapling #9

The sum of oxidation numbers for each element must add up to the overall charge of the molecule (so in this case, it should equal -1). Oxygen has an oxidation of -2, and since there are four oxygen atoms, the sum of oxidation states for oxygen is -8. Now, you can pick an oxidation state for the chl...
Wed Nov 11, 2020 6:27 pm
Forum: Resonance Structures
Topic: Sapling HW Bond length
Replies: 3
Views: 43

### Re: Sapling HW Bond length

This confused me too. Since the experimental bond lengths were in between the values for single and double bonds for both carbon-oxygen and carbon-nitrogen bonding, I answered that there is ample C=N and ample C=O bond character.
Sat Nov 07, 2020 12:55 pm
Forum: Student Social/Study Group
Topic: Favorite TV shows
Replies: 176
Views: 850

### Re: Favorite TV shows

Hannah Montana is my go to show but I also recently watched The Haunting of Hill House and The Haunting of Bly Manor and I highly recommend.
Thu Nov 05, 2020 1:55 pm
Forum: Student Social/Study Group
Topic: Test Anxiety
Replies: 62
Views: 346

### Re: Test Anxiety

I try not to get too stuck on difficult problems so I'll make not of questions I'm unsure about and revisit them later. I'm also a lot less nervous when I feel confident going into the test, so I like to do a lot of practice problems until I'm at the point where I can correctly answer most of them a...
Thu Nov 05, 2020 1:52 pm
Forum: Electronegativity
Topic: Periodic Table Trend
Replies: 37
Views: 387

### Re: Periodic Table Trend

Electronegativity increases going right on the periodic table because the number of protons in the nucleus increases, the electronegativity or attraction will increase. The nucleus brings in the electrons closer together because of the increase in attraction. Electronegativity will then decrease go...
Thu Nov 05, 2020 1:51 pm
Forum: Student Social/Study Group
Topic: Studying Tips
Replies: 23
Views: 158

### Re: Studying Tips

For me, practice problems are super helpful and I pay close attention to where I make mistakes so I can watch out for that on tests. I also like to rewrite my notes because it helps me remember some of the key concepts from the lectures.
Mon Nov 02, 2020 5:12 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14B Enrollment
Replies: 27
Views: 308

### Re: Chem 14B Enrollment

I was wondering this too. I think I'll probably try enroll during my second pass and hopefully it works out!
Sat Oct 31, 2020 1:35 pm
Forum: Trends in The Periodic Table
Topic: Sapling Question #30
Replies: 6
Views: 72

### Re: Sapling Question #30

Anions usually have a bigger radius than cations/the parent element because there's more electron repulsion, and cations have smaller ionic radii because there's less repulsion and Rb+ would have no electrons in the n=5 energy level.
Sat Oct 31, 2020 1:29 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Replies: 6
Views: 26

### Re: Atomic and Ionic Radius

I struggle with remembering size patterns but it helps me to think of what happens when moving across a period vs down a group. Across a period, nuclear charge increases and e- are pulled in more so atomic radius increases. Down a group, the number of energy levels increases so atomic radius decreas...
Sat Oct 31, 2020 1:23 pm
Forum: Trends in The Periodic Table
Topic: Trends
Replies: 14
Views: 88

### Re: Trends

I struggle with this too! It helps me to think of why the radius would increase or decrease, like when going across a period, the nuclear charge increases so the electrons are more tightly bound and the radius is smaller. When going down a group, n increases so the additional energy shells means the...
Thu Oct 29, 2020 3:55 pm
Forum: Student Social/Study Group
Topic: How to relax
Replies: 113
Views: 593

### Re: How to relax

I like going on walks to take a break from staring at a screen all day!
Thu Oct 29, 2020 3:49 pm
Forum: Properties of Electrons
Topic: Sapling Week 4 #25
Replies: 4
Views: 51

### Re: Sapling Week 4 #25

I plugged in the mass of an electron for m, which is 9.11 x 10^-31 kg to get the electron's energy.
Fri Oct 23, 2020 11:32 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Outline question heisenberg indeterminancy
Replies: 3
Views: 28

### Re: Outline question heisenberg indeterminancy

This confused me too! There's a pdf on the Chem 14A website called solution manual errors and it says the correct answer for this problem is 6.7 x 10-37 m which is what I got when I used 10 m/s for Δv.
Fri Oct 23, 2020 11:29 am
Forum: Student Social/Study Group
Topic: How are you studying?
Replies: 203
Views: 1269

### Re: How are you studying?

I like to rewrite some of my notes/key concepts and do a bunch of practice problems from the textbook, sapling, audio-visual modules, etc. It helps me to pay close attention to what problems I get wrong or common mistakes I make so I don't make the same mistakes during the midterm.
Wed Oct 21, 2020 1:35 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Balmer and Lyman series
Replies: 2
Views: 32

### Re: Balmer and Lyman series

E = hc/wavelength so wavelength and energy are inversely proportional. A smaller wavelength means higher energy so that's why the Lyman series has n=1. The Balmer series wavelengths are longer than the Lyman series, so they start at n=2 instead of n=1.
Tue Oct 20, 2020 1:52 pm
Forum: Quantum Numbers and The H-Atom
Topic: 1D.23 on Homework
Replies: 3
Views: 44

### Re: 1D.23 on Homework

- For (a) n=2 and l=1 means we are looking at the 2p subshell. Since l=1, ml can be -1, 0, and 1, so the 2p subshell can have 3 orientations or 3 orbitals - For (b) n=4 and l=2, which is the 4d subshell, and we are given ml = -2, so there is only 1 possible orientation, so 1 possible orbital. - For ...
Tue Oct 20, 2020 1:31 pm
Forum: Quantum Numbers and The H-Atom
Topic: 1D.23
Replies: 2
Views: 43

### Re: 1D.23

Since we are only given n, the answer is all of the orbitals in the n=2 energy level. So the answer would be 4 since there is 1 2s orbital and 3 for 2p!
Fri Oct 16, 2020 11:52 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Textbook Problem 1b27
Replies: 6
Views: 60

### Re: Textbook Problem 1b27

So is delta v equal to the change in velocity, essentially the uncertainty they give us in the problem? Also, I was under the impression that when we were using uncertainties like ± 5.0 m/s we had to double it for it to be equal to delta v. I thought this because in this case the answer could be an...
Wed Oct 14, 2020 12:06 pm
Forum: DeBroglie Equation
Topic: Number 32 on the Module
Replies: 2
Views: 54

### Re: Number 32 on the Module

For me, it helps to convert the wavelength into a frequency. If the frequency is bigger than the speed of light, which it would be in this case, then it probably isn't possible to measure the de Broglie wavelength.
Tue Oct 13, 2020 6:04 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect Post-Module #28
Replies: 4
Views: 37

### Re: Photoelectric Effect Post-Module #29

The mass of an electron is 9.11 x 10^-31 kg, so use that and the given velocity to find the kinetic energy!
Tue Oct 13, 2020 6:01 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Textbook problem 1A.15
Replies: 5
Views: 37

### Re: Textbook problem 1A.15

I was confused about this too, but first I used the given wavelength to solve for frequency so I could use the equation frequency = -R [1/n1^2 - 1/n2^2]. The textbook tells us that for the Lyman series (the lines in the UV region), n1 = 1, so we only need to solve for n2 since n1 is given.
Tue Oct 13, 2020 5:44 pm
Forum: DeBroglie Equation
Topic: What causes a diffraction pattern?
Replies: 9
Views: 111

### Re: What causes a diffraction pattern?

Yes, both constructive and destructive interference create diffraction patterns. The diffraction patterns look different depending on which type of interference it is.
Fri Oct 09, 2020 4:41 pm
Forum: Limiting Reactant Calculations
Topic: Determining the Limiting Reactant
Replies: 4
Views: 43

### Re: Determining the Limiting Reactant

Hi! I think the balanced equation for this problem is actually C14H18N2O5 + 16O2 –> 14CO2 + 9H2O + N2. In that case, O2 would actually be the limiting reactant because 1 mol of C14H18N2O5 needs 16 moles O2 to react, and .0068 mol C14H18N2O5 * 16 is .1088 moles which is more than the amount of O2 (.0...
Fri Oct 09, 2020 4:27 pm
Forum: Molarity, Solutions, Dilutions
Topic: Fundamentals G, Question 5: Molarity Question, Significant Figures
Replies: 2
Views: 48

### Re: Fundamentals G, Question 5: Molarity Question, Significant Figures

I usually wait until the end of the problem to apply significant figure rules so my answer is as accurate as possible. When I rounded at each step I noticed that my answers were a little bit off from the given answers.
Wed Oct 07, 2020 11:04 am
Forum: Significant Figures
Topic: How man Sig Figs to use in the Textbook Problems
Replies: 7
Views: 80

### Re: How man Sig Figs to use in the Textbook Problems

It depends on the problem! When multiplying or dividing, use as many sig figs as the number with the least amount of sig figs. When adding and subtracting, round to the lowest number of decimal places.
Wed Oct 07, 2020 10:41 am
Forum: Empirical & Molecular Formulas
Topic: Sapling HW 9
Replies: 21
Views: 225

### Re: Sapling HW 9

Hey Guys, in regards to sapling HW. I was finally able to grab a hold on the access code. Are the HW problems in the syllabus, are the problems submitted on sapling? The textbook problems in the syllabus are highly recommended for review but the actual homework is on the Sapling website under the a...
Wed Oct 07, 2020 10:37 am
Forum: Administrative Questions and Class Announcements
Topic: Submitting Sapling Homework
Replies: 3
Views: 34

### Re: Submitting Sapling Homework

I think you are ok to leave it as is as long as you have completed every problem!