## Search found 62 matches

Wed Jan 20, 2021 2:51 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 1
Replies: 9
Views: 52

### Midterm 1

Will we have to print out materials for the midterm as we did for 14A? I'm assuming we will be allowed to use the periodic table again, but is there a new equation sheet we should use or is the same one as 14A? I'm just trying to plan ahead what I will need to print because I don't have a printer in...
Mon Jan 18, 2021 1:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D.3 Concept; Standard Rxn Enthalpies
Replies: 3
Views: 12

### 4D.3 Concept; Standard Rxn Enthalpies

I'm confused by the following statement made in section 4D.3 of the textbook: The heat absorbed or released by a reaction can be treated as a reactant or product in a stoichiometric equation. What does this mean conceptually? I don't entirely understand how the known value would be used in this situ...
Sun Jan 17, 2021 6:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Week 1 Problem 2
Replies: 3
Views: 34

### Re: Sapling Week 1 Problem 2

It might help to attach a picture of your work if you have one, so people can help look for what went wrong? I got confused by this problem as well because I kept messing up the conversions from mole to molarity in the ICE table. What worked for me was setting up my ICE table using the values given ...
Fri Jan 15, 2021 4:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Week 1 #9
Replies: 3
Views: 18

### Sapling Week 1 #9

Can someone explain how they created an ICE table for this problem? I'm struggling with what values to use for the initial concentrations and how to set it up to represent the change in concentrations if we're already starting at equilibrium.
Fri Jan 15, 2021 3:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling #3
Replies: 5
Views: 37

### Sapling #3

I'm having trouble with question 3 on the first Sapling assignment. I attached a picture of my work. I think I set up the ICE table correctly, but I'm not sure because the equation it gives me seems different from what it usually looks like for these types of problems. If it is correct, how do I go ...
Fri Jan 15, 2021 3:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Week 1 #2
Replies: 3
Views: 31

### Re: Sapling Week 1 #2

Courtney Situ 2B wrote:Hello!

For Kc, you used the mols O2 instead of the concentration of O2. I believe that's the only problem!

Hope this helped!

Thank you! That was the mistake, I was able to get the correct answer after fixing it!
Fri Jan 15, 2021 3:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Week 1 #2
Replies: 3
Views: 31

### Sapling Week 1 #2

I'm having trouble with question #2 from the first Sapling HW assignment. The questions states: At a certain temperature, 0.960 mol SO3 is placed in a 2.50 L container. 2SO3(g)↽−−⇀2SO2(g)+O2(g) At equilibrium, 0.160 mol O2 is present. Calculate Kc. I attached a picture of my work, could someone help...
Sun Jan 10, 2021 11:40 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem Community Posts
Replies: 2
Views: 11

### Chem Community Posts

Are students currently enrolled in 14B able to get participation points by replying to posts made by students currently taking 14A, or can we only interact with students also in 14B?
Sun Jan 10, 2021 11:35 pm
Forum: Student Social/Study Group
Topic: GroupMe for lecture 1
Replies: 1
Views: 14

### Re: GroupMe for lecture 1

I don't know if there's a specific GroupMe for lecture 1 but I know there is one for all of Professor Lavelle's 14B classes this quarter. It's the same chat as the 14A one form the fall, the name is just different.
Sun Jan 10, 2021 1:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Example from lecture
Replies: 3
Views: 16

### Example from lecture

I got kind of lost during this example from Friday's lecture, can anyone explain where the number 5.40 is coming from and how we got to that?
Mon Jan 04, 2021 8:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Molar Concentration for Calculating K
Replies: 3
Views: 22

### Molar Concentration for Calculating K

In the example from today's lecture, the molar concentrations of the reactants and products were given when asked to calculate K for the reaction. For the sake of this class, will we always be given the molar concentration for these problems or will we at times need to find it ourselves? I know that...
Mon Jan 04, 2021 8:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Liquid (pure substance) vs Aqueous
Replies: 2
Views: 20

### Liquid (pure substance) vs Aqueous

I know that solids and liquids are not included in the K expression. In the example from lecture, a solid reactant was excluded but the aqueous products were used to calculate K. My understanding of this is that aqueous substances are liquid, but they don't count as pure substances because they are ...
Wed Dec 16, 2020 8:49 pm
Forum: Student Social/Study Group
Replies: 6
Views: 45

Varsha Ravi 2C wrote:I heard that Organic Chem Tutor on youtube has good videos for the topics discussed!

Thank you, I'll check that one out! Do you know if it cover topics through the entire 14 series?
Wed Dec 16, 2020 8:48 pm
Forum: Administrative Questions and Class Announcements
Topic: Chemistry Community posts after this quarter [ENDORSED]
Replies: 7
Views: 54

### Chemistry Community posts after this quarter[ENDORSED]

Hi, just wondering what happens to our Chemistry Community posts for 14A once this quarter ends? Will they stay up or are they removed at the end of the quarter? I'm curious as to whether we will be able to look back on our old posts in the future.
Wed Dec 16, 2020 8:45 pm
Forum: Student Social/Study Group
Replies: 6
Views: 45

Hi, just wondering if anyone found any outside resources particularly helpful throughout the quarter? I'm looking for additional ways to study for 14B in the winter.

Wed Dec 16, 2020 8:42 pm
Forum: Student Social/Study Group
Topic: Preparing for 14B
Replies: 6
Views: 48

### Preparing for 14B

For people taking 14B in the winter, are you planning to do any review of particular topics to prepare? I'm just wondering if anyone knows what we will be starting with/what would be most important to review, or if anyone has good resources for reviewing.
Wed Dec 16, 2020 8:37 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8506
Views: 1470597

### Re: Post All Chemistry Jokes Here

Throwback to the election
Sun Dec 13, 2020 9:50 am
Forum: Bronsted Acids & Bases
Topic: Amphoteric substances
Replies: 3
Views: 36

### Amphoteric substances

Why is HBrO2 not an amphoteric substance? It could act as a Bronsted acid and donate a proton to a base because it has a hydrogen ion, so what is preventing it from accepting a proton to act as a Bronsted base as well?
Sat Dec 12, 2020 5:08 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Electron affinity and acid strength
Replies: 3
Views: 22

### Electron affinity and acid strength

I'm struggling with the following concept: The greater the electron affinity (and therefore the electronegativity) of A, the stronger is the acid. (Where A is referring to the second element in a binary acid) Previously, we learned that a shorter, weaker bond corresponds to a stronger acid. By this ...
Fri Dec 11, 2020 12:15 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Bond strength
Replies: 1
Views: 27

### Bond strength

Are pi-bonds always weaker than sigma-bonds, or is this dependent on molecular shape?

If this is true, is it also true that the sum of 2 single bonds of any homonuclear diatomic molecule will be stronger than one double bond of the same molecule? Or is this only true for certain elements like carbon?
Wed Dec 09, 2020 10:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Predicting the shape of AsF5
Replies: 2
Views: 37

### Predicting the shape of AsF5

I'm doing a practice problem from the textbook, why would the shape of AsF5 be trigonal bipyramidal instead of square pyramidal? In general as well, how do you differentiate between the 2 after drawing the Lewis structure and establishing the number of regions of electron density?
Tue Dec 08, 2020 2:17 pm
Forum: Lewis Structures
Topic: Oxygen Lewis Structure
Replies: 1
Views: 13

### Oxygen Lewis Structure

Why does the Lewis structure for Oxygen have 2 unpaired electrons, making it a biradical? Does it have to do with lower energy levels? And does this apply to any other elements in the same period?
Sun Nov 29, 2020 10:03 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling #3
Replies: 3
Views: 36

### Sapling #3

For #3 on this week's Sapling assignment, the Lewis Structure I was shown was a trigonal bipyramid, meaning the smallest angles would be the axial bond angles of 90 degrees. However, the central atom had a lone pair of electrons. In lecture it was said that lone pairs force bonding electrons closer ...
Sun Nov 29, 2020 9:52 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AsO43-
Replies: 9
Views: 65

### Re: AsO43-

I think this is because even though there is a negative charge, there is no net dipole, so the molecule isn't polar. Dipole moment is a measure of polarity of a molecule, so that's what I look at when determining whether a molecule is polar, rather than looking at the overall charge for that molecule.
Sun Nov 29, 2020 9:48 pm
Forum: Hybridization
Topic: PBr5
Replies: 6
Views: 43

### Re: PBr5

The sp3d hybrid orbital corresponds to 5 bonded pairs and lone atoms. Since there are 5 Br atoms bound to P in this molecule, it corresponds to the sp3d orbital.
Sun Nov 29, 2020 9:46 pm
Forum: Hybridization
Topic: End vs side
Replies: 3
Views: 22

### Re: End vs side

I think it would depend on what other information you are given. Sigma bonds interact end to end while pi bonds interact side by side, so if you know what kind of bond it is you know how it will interact. If you don't know the bond type, you can also figure it out if you are given information on whe...
Wed Nov 18, 2020 11:25 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration of O-
Replies: 2
Views: 18

### Re: Electron Configuration of O-

The oxygen anion has a charge of 2-, not 1-, so you would add two electrons and get 2p^6. Maybe the 1- charge was a typo, because when oxygen forms an anion it carries a 2- charge. Thanks for your response, but I'm still confused now. The problem just said O-. Are we just supposed to know/assume th...
Wed Nov 18, 2020 11:19 pm
Forum: Administrative Questions and Class Announcements
Topic: Discussion participation
Replies: 2
Views: 35

### Re: Discussion participation

No, discussion attendance isn't graded. The only online discussion that counts towards final grade is posts on Chemistry Community.
Wed Nov 18, 2020 11:18 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration of O-
Replies: 2
Views: 18

### Electron Configuration of O-

I'm reviewing my TA's worksheet from week 6 and it says that the electron configuration for the anion O- is 1s^2 2s^2 2p^6. When I was trying the problem, I thought the configuration would be 1s^2 2s^2 2p^5, because the normal configuration for O is 1s^2 2s^2 2p^4, so I added one electron to account...
Wed Nov 18, 2020 9:09 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: outline 2 bullet point
Replies: 1
Views: 18

### Re: outline 2 bullet point

I think it relates to both quantum number n and the effect of shielding. In my notes on this objective, I said: Larger principal quantum number = farther from the nucleus = higher energy Shielding effect: The decrease in attraction between an electron and the nucleus of an atom with more than one el...
Wed Nov 18, 2020 9:06 pm
Forum: Dipole Moments
Topic: Dipole vs Polar molecule
Replies: 2
Views: 15

### Dipole vs Polar molecule

Are the terms dipole and polar molecule interchangeable? Or is there some distinction between the two?
Sun Nov 15, 2020 10:35 pm
Forum: Ionic & Covalent Bonds
Topic: London (Dispersion) Force
Replies: 3
Views: 22

### London (Dispersion) Force

This isn't about ionic or covalent bonds but I wasn't sure where else to post it. I know that larger, heavier atoms/molecules have stronger London forces, but I was wondering if there are any other additional factors that affect the strength of the force? This is the only one I know of but I think t...
Sun Nov 15, 2020 10:30 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Sapling #16
Replies: 2
Views: 30

### Sapling #16

I wasn't entirely sure where to post this question, but it has to do with hydrogen bonding and question #16 from sapling. This question asks you to identify the hydrogen bond crosslink between the 2 polymer chains, but I wasn't sure how to differentiate between 2 of the answer choices. I thought tha...
Sun Nov 15, 2020 10:18 pm
Forum: Bond Lengths & Energies
Topic: calculating bond lengths
Replies: 7
Views: 55

### Re: calculating bond lengths

I'm not 100% certain, but it isn't listed in the learning objectives we need to know for this midterm so I would assume not. I think we just need to know the different factors that effect bond length and how they change it, but not how to calculate an exact value.
Sun Nov 15, 2020 9:49 pm
Forum: Formal Charge and Oxidation Numbers
Topic: The most plausible structure
Replies: 4
Views: 34

### Re: The most plausible structure

Generally, I think the idea is that the ideal structure would minimize the amount of formal charges. So having less atoms with a formal charge would make the structure more plausible.
Sun Nov 15, 2020 9:40 pm
Forum: Electronegativity
Topic: Tips on remembering trend
Replies: 5
Views: 39

### Re: Tips on remembering trend

In general, electronegativity increases from left to right and decreases from top to bottom. I don't really have a specific way to remember this, but it might help to just think of a diagonal arrow going from the bottom left corner of the table to the top right, and knowing electronegativity increas...
Sun Nov 15, 2020 8:22 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2
Replies: 23
Views: 133

### Re: Midterm 2

I think it's the same amount of time, at least that's what the syllabus says.
Sun Nov 08, 2020 8:11 pm
Forum: Bond Lengths & Energies
Topic: Bond length
Replies: 11
Views: 41

### Re: Bond length

Double bonds are actually shorter than single bonds, and triple binds are even shorter than double bonds. It's because triple bonds have more electrons, so they have a stronger force which pulls the atoms closer together, so the bond length itself is shorter.
Sun Nov 08, 2020 8:09 pm
Forum: Octet Exceptions
Topic: Aluminum Chloride Structure
Replies: 4
Views: 19

### Aluminum Chloride Structure

I'm struggling with this concept from the textbook: Compounds of boron and aluminum may have unusual Lewis structures in which boron and aluminum have incomplete octets or halogen atoms that act as bridges. I was confused by the book's explanation of this statement. Is this just something we have to...
Sun Nov 08, 2020 7:17 pm
Forum: Quantum Numbers and The H-Atom
Topic: Pauli Exclusion Principle and Hund's Rule
Replies: 4
Views: 15

### Re: Pauli Exclusion Principle and Hund's Rule

The Pauli exclusion principle is just saying that no more than 2 electrons can occupy each orbital.

Hund's rule states that due to the natural electron repulsion, electrons in the same sub shell occupy different orbitals with parallel spin because this is the lowest energy state.
Sun Nov 08, 2020 7:13 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2 Question Count
Replies: 17
Views: 106

### Re: Midterm 2 Question Count

I'm not entirely certain, but I would assume it will be the same number of questions as midterm I because it's the same amount of time given and both are out of 110 points on the syllabus.
Wed Oct 28, 2020 5:16 pm
Forum: SI Units, Unit Conversions
Topic: SI Unit for Mass
Replies: 10
Views: 103

### SI Unit for Mass

Out of all the equations we've used so far in units 1 and 2, should mass always be in kg? I've been using g for mass for most of my work, but I noticed while reviewing the De Broglie equation that mass needs to be converted into kg for this example. Do some equations require mass in kg while some us...
Tue Oct 27, 2020 11:55 am
Forum: Balancing Chemical Reactions
Topic: Writing Reactions
Replies: 3
Views: 49

### Writing Reactions

One of the questions from the balancing equations post-assessment says: During a summer camping weekend 4 moles of butane (C4H10) gas were used for cooking. Chose the right balanced equation for the combustion of 4 moles of butane gas. What is the net number of moles of gas produced? I'm confused ab...
Tue Oct 27, 2020 10:36 am
Forum: Properties of Electrons
Topic: Wave Properties of Electrons Post-Assessment #34
Replies: 2
Views: 33

### Wave Properties of Electrons Post-Assessment #34

This question asked: If an electron (mass 9.11 x 10-31 kg) has an associated wavelength of 7.28 x 10-9 m, what is its speed? Is your answer reasonable, why? I calculated the speed to be 1.00x10^5 m/s, and I said this was not reasonable because the calculated speed is much slower than the speed of li...
Tue Oct 27, 2020 10:04 am
Forum: Properties of Electrons
Topic: Measurable Wavelike Properties
Replies: 1
Views: 17

### Measurable Wavelike Properties

What is the cut off of wavelength for a particle/object to have measurable wavelike properties? I know things like electrons and neutrons do while things like cars or baseballs don't, but I don't know if there's a numeric cutoff in terms of wavelength that determines this? I just have been assuming ...
Tue Oct 27, 2020 9:51 am
Forum: Properties of Electrons
Topic: Wave Properties and Electrons Post-Assessment #18
Replies: 3
Views: 19

### Wave Properties and Electrons Post-Assessment #18

The question states: When incident light (electromagnetic wave) hits a barrier with two or more holes does it give rise to an observed diffraction pattern? For this question, what is the significance if the barrier having two or more holes? Why would it not give rise to an observed diffraction patte...
Tue Oct 27, 2020 9:47 am
Forum: Properties of Electrons
Topic: Constructive vs Destructive
Replies: 6
Views: 77

### Constructive vs Destructive

I'm having trouble understanding this question conceptually from the Wave Properties of Electrons post-assessment: When the trough of one wave interacts with the trough of another wave is their interaction constructive or destructive? I know if the trough of one wave were to interact with the peak o...
Sun Oct 25, 2020 11:10 pm
Forum: Administrative Questions and Class Announcements
Topic: what kind of calculator
Replies: 4
Views: 17

### Re: what kind of calculator

Double check with your TA, but here's what mine said. Dr. Lavelle had originally said that we would need a non-graphing scientific calculator, but the last I heard we will now be allowed to use a graphing calculator. So any calculator you have should be allowed, since there's no restrictions on grap...
Sun Oct 25, 2020 11:06 pm
Forum: SI Units, Unit Conversions
Topic: nanometer conversion
Replies: 6
Views: 69

### Re: nanometer conversion

One meter is equal to 1x10^-9 nanometers, so to convert from meters to nanometers you would multiply the value by 10^9.

In the example you gave, 4.2X10^-7 m becomes 420 nm by multiplying the value in meters by 10^9.
Sun Oct 25, 2020 11:00 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Module #20
Replies: 1
Views: 21

### Re: Module #20

I could be wrong because I took this assessment last week, but I'm pretty sure all you need to do is multiply your answer from the first part by Avogadro's constant to get the answer for the second part. Because the first part gives you the electron's uncertainty in kinetic energy, so multiplying th...
Sun Oct 25, 2020 10:54 pm
Forum: DeBroglie Equation
Topic: De Broglie's Derived Eq
Replies: 3
Views: 33

### Re: De Broglie's Derived Eq

I asked my friend that took this class just to confirm, but yes basically what the other person said, you won't need to know how to derive it for any midterm/exam. Knowing it to some extent might help to better your understanding, though.
Sun Oct 25, 2020 10:51 pm
Forum: *Shrodinger Equation
Replies: 2
Views: 24

Will there be additional audio-visual focus-topics/assessments posted on the 14A website for Schrodinger Equation and the rest of the topics remaining in the quantum world unit? Or were those only available for the Review section and the first part of this section?
Sun Oct 25, 2020 10:37 pm
Forum: Administrative Questions and Class Announcements
Topic: Trouble Accessing Textbook
Replies: 1
Views: 15

### Trouble Accessing Textbook

Is anyone else suddenly unable to access the textbook through Macmillan? I've been using it through the same link this whole time and signed up with my access code in the beginning, but now it's saying I don't have access to the book. Did this happen to anyone else/were you able to fix it?
Sun Oct 18, 2020 9:09 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect Module Question #24
Replies: 3
Views: 31

### Photoelectric Effect Module Question #24

This question from the Photoelectric Effect Module post-assessment asks: "In photoelectric experiments, typically what part of the electromagnetic spectrum is the incoming light?" Would the answer to this be visible light? I'm really not sure at all, I just feel like we've discussed visibl...
Sun Oct 18, 2020 8:47 pm
Forum: Administrative Questions and Class Announcements
Topic: Built-in webcams/Equipment request [ENDORSED]
Replies: 22
Views: 735

### Re: Built-in webcams/Equipment request[ENDORSED]

Regarding the questions about phones, has anyone actually been able to open respondus through their phone and connect to zoom through it? I tired during discussion section last week but it didn't work, so I'm wondering if other people were able to.
Wed Oct 14, 2020 7:03 pm
Forum: Properties of Light
Topic: Exercise 1A.15
Replies: 2
Views: 49

### Exercise 1A.15

I'm very confused by this question in the textbook, even after looking at the answer. The problem states: "In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of ene...
Wed Oct 14, 2020 6:58 pm
Forum: Photoelectric Effect
Topic: Exercise 1B.3
Replies: 2
Views: 45

### Exercise 1B.3

In section 1B of the textbook, there is a question that asks: From the following list of observations, select the one that best supports the idea that electromagnetic radiation has the properties of particles. Explain your reasoning. (a) Black-body radiation. (b) Electron diffraction. (c) Atomic spe...
Sun Oct 11, 2020 7:10 pm
Forum: Limiting Reactant Calculations
Topic: Last Question on the Sapling Hw (Week 1)?
Replies: 12
Views: 156

### Re: Last Question on the Sapling Hw (Week 1)?

Hi I also have a question about the 1:1 ratio, how would we solve to get that, and were we suppose to find the chemical equation just from the question? You can tell that there is a 1:1 ratio of 2-butanone to 3-methyl-3-hexanol by looking at the reaction given. Since the equation shown is already b...
Thu Oct 08, 2020 4:30 pm
Forum: Administrative Questions and Class Announcements
Replies: 12
Views: 126

Adding on to this question, are the 5 posts due by Friday or Sunday of each week to get points? I may have missed the answer to this somewhere, but I couldn't find it in the syllabus.
Thu Oct 08, 2020 4:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Audio-Visual Focus-Topics Set 2
Replies: 3
Views: 45

### Audio-Visual Focus-Topics Set 2

The instructions for the audio-visual focus topics say that we should finish the second set of modules, photoelectric effect through Heisenberg uncertainty equation, by the end of week 2. I'm just wondering if there are any recommended readings and exercises from the textbook associated with theses ...
Wed Oct 07, 2020 8:03 pm
Forum: Empirical & Molecular Formulas
Topic: Formula Unit?
Replies: 2
Views: 50

### Re: Formula Unit?

I believe the reason it asks for formula units is because magnesium sulfate heptahydrate is an ionic compound, so that's the why formula units is used instead of molecules, as would be used for covalent bonds, or atoms, as would be used for single elements.
Wed Oct 07, 2020 7:11 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Exercise E.9
Replies: 6
Views: 135

### Exercise E.9

Question E.9 states: "Epsom salts consist of magnesium sulfate heptahydrate. Write its formula". I wrote MgSO4 as the formula for magnesium sulfate heptahydrate, but the answer key has MgSO4*7H20. Where did they get this? Why is water included in the formula and how do I know it should be ...