## Search found 62 matches

Thu Jan 14, 2021 1:41 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q and K
Replies: 21
Views: 63

### Re: Q and K

Yes you're correct. Q is measured at any instant of the reaction but K is only measured after the reaction reaches equilibrium.
Thu Jan 14, 2021 1:36 am
Forum: Ideal Gases
Topic: n/V = concentration
Replies: 13
Views: 55

### Re: n/V = concentration

Accoding to the ideal gas law, PV=nRT. If we divide both sides with V, we could have the equation for pressure: P=(nRT)/V Because n (in moles) divided by volume V(in liters) would result in concentration (in moles per liter), we could substitute n/V in the equation with concentration. Therefore, P =...
Thu Jan 14, 2021 1:32 am
Forum: Ideal Gases
Topic: Inert Gases
Replies: 11
Views: 30

### Re: Inert Gases

Hi. Dr. Lavelle brought this up to demonstrate that the change caused by adding/deducting pressure isn't strictly associated by moles of gases. It's associated with concentration of gases. Adding an inert gas to a container with fixed volume only changes pressure. It does not participate in the reac...
Thu Jan 14, 2021 1:27 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Increase in Pressure
Replies: 13
Views: 29

### Re: Increase in Pressure

This only applies to gases. Liquid pressure has very little association with volume.
Thu Jan 14, 2021 1:23 am
Forum: Ideal Gases
Topic: reversing reactions
Replies: 56
Views: 331

### Re: reversing reactions

K would also be inversed. It will become 1/K because the equilibrium constant for the inversed reaction is adopting a reversed product-reactant relationship.
Thu Jan 14, 2021 1:21 am
Forum: Ideal Gases
Topic: T variable in pv=nrt [ENDORSED]
Replies: 36
Views: 250

### Re: T variable in pv=nrt[ENDORSED]

T must always be in Kelvin. But if you are given in Celcius, you can convert it into Kelvin with the equation Kelvin = Celsius + 273.15.
Thu Jan 07, 2021 4:04 am
Forum: General Science Questions
Topic: mole vs. M
Replies: 16
Views: 88

### Re: mole vs. M

You're right M means is molarity and represents moles per Liter.
Thu Jan 07, 2021 4:00 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constant
Replies: 8
Views: 42

### Re: Equilibrium Constant

Yes, if the denominator is the greater concentration, equilibrium constant K would be less than 1. The equilibrium lies more to the left, favoring reactants.
Sat Dec 12, 2020 11:34 pm
Forum: Conjugate Acids & Bases
Topic: textbook 6.21 Thymine (& EDTA) [ENDORSED]
Replies: 1
Views: 61

### textbook 6.21 Thymine (& EDTA)[ENDORSED]

Hi. The solution for 6.21 says that protons can only bind to the lone pairs on nitrogen. And Dr. Lavelle's reply in another post explains that: "Oxygen, as the more electronegative element, holds more tightly to its lone pair than the nitrogen. The nitrogen lone pair, therefore, is more availab...
Sat Dec 12, 2020 9:41 pm
Forum: Lewis Acids & Bases
Topic: textbook 6A.15
Replies: 1
Views: 19

### textbook 6A.15

For question b), I drew SO2 with 2 double bonds, 2 lone pairs on each of the two O atoms, and a S with expanded octet. Everything else is like what the solution has shown.
Is my answer also correct? Does the structure of SO2 have to have 1 single and 1 double bond in this case?
Sat Dec 12, 2020 9:49 am
Forum: Coordinate Covalent Bonds
Topic: textbook 9C.5 b)
Replies: 1
Views: 17

### textbook 9C.5 b)

Can someone explain why carbonato (CO3^2-) can be either monodentate or bidentate?
The solution says it can bind a metal ion through either one or two of the oxygen ions.
How does this happen? And why is the third oxygen ion left out?
Fri Dec 11, 2020 8:07 am
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: Hard/soft water clarification
Replies: 3
Views: 46

### Hard/soft water clarification

Dr. Lavelle mentions soft water is alkaline and hard water is acidic in lecture.
But all my google results tell me that "hard water is more alkaline and has a higher mineral content than soft".
Which one should I believe in? Or does it depend on specific situations?
Fri Dec 11, 2020 12:14 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Sapling Week 10 #13
Replies: 7
Views: 63

### Re: Sapling Week 10 #13

Adding on, if pH > pKa, it means that the environmnet (solution) is more alkaline. The acid would give out a proton to form an anion to neutralize it (acid is deprotonated).
if pH < pKa, the environment is more acidic than the acid. The acid does not change anything (acid is protonated).
Wed Dec 09, 2020 10:03 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: week 10 Sapling Q12
Replies: 2
Views: 27

### week 10 Sapling Q12

Could someone please explain why would the strength of the bond to hydrogen decrease as the number of oxygen atoms increases?
Thank you!
Wed Dec 09, 2020 9:23 am
Forum: Identifying Acidic & Basic Salts
Topic: week 10 Sapling Q7
Replies: 5
Views: 63

### week 10 Sapling Q7

I am stuck with this problem. Could someone tell me what I did wrong?
The feedback says I have not identified all the basic salts.
Much appreciated
Wed Dec 09, 2020 7:55 am
Forum: Bronsted Acids & Bases
Topic: Sapling #6 week 10
Replies: 4
Views: 55

### Re: Sapling #6 week 10

Hi. I had the same question before and found this response by varlam17 on https://www.reddit.com/r/chemistry/comments/c5z6be/how_is_hydrogen_cyanide_hcn_defined_as_a_lewis/. "If a compound has a lone pair that does not guarantee that it's a base. Base and acid are relative, not absolute. A mole...
Wed Dec 09, 2020 7:21 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Sapling Q #1
Replies: 7
Views: 55

### Re: Sapling Q #1

Here's a tip for memorizing strong acids that I learnt from Michael's UA session.
All the capitalized letters will remind you of a strong acid:

SO I BRought NO CLean ClOthes
SO: H2SO4
I: HI
BR: HBr
NO: HNO3
CL: HCl
CLO: HClO4 & HClO3

I don't know if there's one for strong bases though.
Wed Dec 02, 2020 9:19 am
Forum: Naming
Topic: Oxidation State for Sapling q. 6
Replies: 2
Views: 31

### Re: Oxidation State for Sapling q. 6

You can approach this problem like this.
Since the coordination compound is neutral, it has a net charge of 0.
Co+5(NH3)+5Cl+2Cl=0
Co+5(NH3)+5Cl= - 2Cl
Co+5(NH3)+5Cl= +2
Hope this helps!
Wed Dec 02, 2020 9:11 am
Forum: Biological Examples
Topic: en and edta
Replies: 6
Views: 168

### Re: en and edta

Adding on, there is also a coordination compound called diethylenetriamine (dien) that is on the naming coordination compound sheet: https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/NamingCoordinationCompounds.pdf I memorize this together with en by looking at the number of N in the...
Wed Dec 02, 2020 8:45 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: how to tell coordination number
Replies: 3
Views: 44

### how to tell coordination number

I usually find coordination # directly from the molecular formula by counting the number of ligands in the bracket. Is this always correct? Are there any special cases where we need to draw the lewis structure to find out?
Tue Dec 01, 2020 7:27 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: 4 ligands shape
Replies: 5
Views: 62

### 4 ligands shape

Dr. Lavelle mentioned in class that if coordination number is 4, the shape would be either square planar or tetrahedral.
Why isn't the seesaw shape included?
Fri Nov 27, 2020 2:02 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape Names
Replies: 50
Views: 272

### Re: Shape Names

You are correct. It can be called angular or bent.
Fri Nov 27, 2020 1:58 am
Forum: Bond Lengths & Energies
Topic: Textbook Question 3F.15
Replies: 8
Views: 91

### Re: Textbook Question 3F.15

AsF3 has a higher boiling point because it has both dipole-dipole and LDF, while AsF5 only has LDF.
AsF3 is a trigonal pyramidal shape while AsF5 is tribgonal bipyramidal (symmetrical).
Therefore, dipole moments of AsF3 do not cancel, making it a polar molecule.
Fri Nov 27, 2020 1:49 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Textbook 3f. 3
Replies: 3
Views: 49

### Re: Textbook 3f. 3

Adding on, if all the atoms except for the central atom are the same, and if the shape is a base geometry (meaning that there are no lone pairs), then the molecule would be always non-polar and dipole moments always cancel out!
Fri Nov 27, 2020 1:35 am
Forum: Hybridization
Topic: Sp3d or dsp3
Replies: 22
Views: 849

### Re: Sp3d or dsp3

Both are correct and I prefer to use sp3d because it is easier to memorize!
Fri Nov 20, 2020 8:22 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: hydrogen bonding
Replies: 7
Views: 81

### hydrogen bonding

I am confused with how we can determine if a molecule satisfies the requirements for hydrogen bonding just by looking at the molecular formula. I know we need to draw lewis structures, but I don't know under what circumstances an atom does NOT bond to the central atom. For example, H2SeO4 in textboo...
Fri Nov 20, 2020 12:19 am
Forum: Octet Exceptions
Topic: textbook 2C.3 d)
Replies: 4
Views: 45

### textbook 2C.3 d)

Why is this structure wrong for arsenic ion (first pic)? The text book solutions included only 1 double bond.
Fri Nov 20, 2020 12:16 am
Forum: Octet Exceptions
Topic: textbook 2C.3 c)
Replies: 2
Views: 42

### textbook 2C.3 c)

Hi. For chloric acid, how do we know if H is bonded to O instead of being bonded to the central atom Cl?
Mon Nov 16, 2020 7:17 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Textbook 2A.15 d)
Replies: 2
Views: 27

### Re: Textbook 2A.15 d)

Benjamin_Hugh_1G wrote:The electron configuration is actually [Ar] 3d10 4s2 4p1. I believe the reason why Ga3+ is preferred over Ga+ is that removing 3 electrons will give Gallium a full shell, making it more stable.

Gotcha. thank you! I meant Ga+: [Ar]3d10 4s2 in my question. Sorry about the typo.
Mon Nov 16, 2020 4:48 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Textbook 2A.15 d)
Replies: 2
Views: 27

### Textbook 2A.15 d)

Write the most likely charge for the ions formed by each of the following elements: d) Ga

Why is the answer Ga3+ instead of Ga+? Isn't it better to remove 1 electrons and form Ga: [Ar]3d10 4s2?
Thu Nov 12, 2020 5:35 am
Forum: Lewis Structures
Topic: Sapling hw 3
Replies: 11
Views: 83

### Sapling hw 3

Hi. Can someone please tell me why is this lewis structure wrong for nitrate ion?
Wed Nov 11, 2020 8:43 am
Forum: Dipole Moments
Topic: Definition of Dipole
Replies: 7
Views: 75

### Re: Definition of Dipole

Dipole means that electrons are not shared equally! So they only exist in covalent bonds where atoms share electrons to form bonds.
Wed Nov 11, 2020 8:22 am
Forum: Electronegativity
Topic: periodic table
Replies: 16
Views: 127

### Re: periodic table

Basically electronegativity, electron affinity, and ionization energy all follow the same trend: increasing across a period and increasing up a group. I like to memorize the increasing trends with an arrow pointing to the upper right corner of the periodic table if that makes sense. Atomic radius is...
Wed Nov 11, 2020 8:17 am
Forum: Lewis Structures
Topic: C Valence Electrons
Replies: 5
Views: 38

### Re: C Valence Electrons

Hi! To determine the valence electrons I usually count from the first element in the period. In this case, C is the 4th element in the period (Li, Be, B, C). Therefore, 4 valence electrons.
Wed Nov 11, 2020 8:04 am
Forum: Electronegativity
Topic: London Dispersion Forces
Replies: 9
Views: 87

### Re: London Dispersion Forces

I usually just rule out the ones that have other intermolecular forces. Look out for polar molecules and ions. If there is a polar molecule, then we can identify either ion-dipole, dipole-dipole, dipole-induced dipole and hydrogen bonding. If there are two ions, we can identify ion-ion. So we are lo...
Wed Nov 11, 2020 7:54 am
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: increasing polarizability
Replies: 5
Views: 46

### Re: increasing polarizability

I agree with everyone else that bigger anions have larger polarizability. I just want to add that this is because bigger anions' electron clouds are more easily distorted because they are farther from the neucleus and less tightly held.
Fri Nov 06, 2020 1:21 am
Forum: Coordinate Covalent Bonds
Topic: Coordinate covalent bond lecture example
Replies: 4
Views: 22

### Re: Coordinate covalent bond lecture example

Dr. Lavelle used BF3 to discuss an exception of the octet rule: in this case B only has 6 electrons.
and he used BF4– as an example of when B completes its octet with both 2 electrons provided by F–
Fri Nov 06, 2020 1:12 am
Forum: Resonance Structures
Topic: Delocalized e-
Replies: 5
Views: 50

### Re: Delocalized e-

Delocalized electrons are electrons that is not fixed occur in a specific bond, and have equal probability of being located in any of the bonds involved in the resonance structure.
Fri Nov 06, 2020 1:03 am
Forum: Octet Exceptions
Topic: Group 13 Elements
Replies: 13
Views: 115

### Re: Group 13 Elements

It is okay for all group 13 elements to not have an octet because they all have 3 valence electrons that requires an unrealistic amount of electrons to form octet.
Fri Nov 06, 2020 12:51 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge Equation
Replies: 16
Views: 72

### Re: Formal Charge Equation

L represents the number of lone pairs and you can count the number of dots around each atom from the lewis structure.
Fri Nov 06, 2020 12:37 am
Forum: Ionic & Covalent Bonds
Topic: Size of Bonds
Replies: 28
Views: 99

### Re: Size of Bonds

Double bonds (4 e) have more electrons than single bonds (2 e), and have a stronger negative charge, atrracting the nuclei of the bonding atoms that are charged positively. The attraction is stronger, thus the half distance between centers of the bonding atoms is shorter.
Mon Oct 26, 2020 1:41 am
Forum: Properties of Light
Topic: Incident Light
Replies: 5
Views: 50

### Re: Incident Light

Incident light is the incoming light.
For example, in the photoelectric effect experiment, energy of the incident light = work function + kinetic energy of electrons ejected.
Mon Oct 26, 2020 1:37 am
Forum: Einstein Equation
Topic: m vs nm
Replies: 66
Views: 400

### Re: m vs nm

I agree with everyone that as long as conversion is correct, you're fine.
But if the unit for the anwser is already implied in the question, do what the question asks.
Mon Oct 26, 2020 1:34 am
Forum: Properties of Electrons
Topic: Balmer and Lyman Series
Replies: 3
Views: 28

### Re: Balmer and Lyman Series

The Lyman series is the UV region. Excited electrons return to the n=1 shell.
The Balmer series is the visual light region. Excited electrons return to the n=2 shell. If you see the light has colors in the question, this means that they fall into the Balmer series (e.g. blue light, red light etc).
Mon Oct 26, 2020 1:24 am
Forum: Properties of Electrons
Topic: Absorption and emission spectrum
Replies: 4
Views: 41

### Absorption and emission spectrum

Hi.
I was wondering why is the emission spectrum dark with colored lines, and why does the absorption specturm have black lines?
What caused this difference?
Mon Oct 26, 2020 1:17 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Textbook 1B.25
Replies: 1
Views: 26

### Textbook 1B.25

"What is the minimum uncertainty in the speed of an electron confined within a lead atom of diameter 350. pm? Model the atom as a one-dimensional box with a length equal to the diameter of the actual atom." The solution manual assumed that "the uncertainty in the position of the elect...
Mon Oct 19, 2020 9:24 am
Forum: Properties of Electrons
Topic: Lyman vs. Balmer series
Replies: 20
Views: 164

### Re: Lyman vs. Balmer series

The lyman series is the UV light region, with electrons transitions to ground state (shell n=1). They have the high energy because of the large gap between n=2 and n=1.
The Balmer seires is the visual light region, with electrons transitions to shell n=2.
Mon Oct 19, 2020 9:19 am
Forum: Properties of Electrons
Topic: calculating the frequency of light
Replies: 4
Views: 41

### Re: calculating the frequency of light

We are using the empirical equation for H-atom. En= - hR/n^2
Professor Lavelle was using an example with transitions from n=4 to n=2.
So it would be (-1/16)*hR and (-1/4)*hR.
Mon Oct 19, 2020 9:13 am
Forum: Properties of Electrons
Topic: Energy per Photon
Replies: 7
Views: 39

### Re: Energy per Photon

The energy of a photon is equal to the required energy to remove an electron only if there is no excess energy (i.e. kinetic energy of the electron = 0).
If there is excess kinetic energy, than the energy of a photon is greater than the required energy to remove an electron.
Hope that makes sense.
Mon Oct 19, 2020 9:08 am
Forum: Properties of Electrons
Topic: Electrons Excited or Ejected
Replies: 19
Views: 142

### Re: Electrons Excited or Ejected

So an electron has to be excited first for it to be ejected out of the shell? Or are they completely unrelated?
Mon Oct 19, 2020 9:02 am
Forum: Properties of Electrons
Topic: Sapling 2 HW #6
Replies: 10
Views: 134

### Re: Sapling 2 HW #6

Hi! From what I saw on Sapling, the question said "the electron in a hydrogen atom is excited to the n=6 shell", so I assume there was a typo in your question. If it is currently excited to the n=6 shell, it could return to either n=5, n=4, n=3, n=2, n=1. So there are 5 possible outcomes o...
Tue Oct 13, 2020 1:55 am
Forum: Properties of Light
Topic: Photoelectron Effect: POST/PRE Module Assessment #28-30
Replies: 6
Views: 63

### Re: Photoelectron Effect: POST/PRE Module Assessment #28-30

For Part C, I followed through those steps, but I still got the wrong answer. Can someone point out where I went wrong? Ephoton= 1.506 x 10^5 + 1.99x10^-19 (answer from part a) Ephoton= 150600 You haven't converted from Joule per mole to Joule per atom 1.506*10^5 is still in Joules per mole. Just d...
Tue Oct 13, 2020 1:50 am
Forum: Properties of Light
Topic: What exactly is Φ?
Replies: 16
Views: 153

### Re: What exactly is Φ?

It is the work function/threshold energy: the energy to remove electrons. It is usually given in the question so you don't have to worry! If not, then you would have to find it using the equation hv=Ek + Φ. I am sure the other conditions will be given for you to apply this equation.
Tue Oct 13, 2020 1:34 am
Forum: Properties of Light
Topic: Light Intensity and Frequency
Replies: 7
Views: 82

### Re: Light Intensity and Frequency

Hi. Intensity of light is related to amplitude of a wave, that is the distance from the crest (peak) of a wave to the rest position of that particle. It has nothing to do with frequency of a wave. Energy of light is related to the equation E= planck's constant * frequency. So energy of light is prop...
Tue Oct 13, 2020 1:25 am
Forum: Properties of Electrons
Topic: Kinetic energy of electrons
Replies: 3
Views: 46

### Re: Kinetic energy of electrons

^^I agree with the previous response.
Also, you could see a list of these constants on Sapling under "resources" >>--- "Chempendix".
Tue Oct 13, 2020 1:17 am
Forum: Properties of Light
Topic: video modules
Replies: 10
Views: 95

### Re: video modules

I personally found these modules helpful!! The post-assessments also helped me after today's lecture. Although they might be easier than what we have on the textbooks, they are definietly helpful if you are new to these concepts.
Wed Oct 07, 2020 12:55 am
Forum: Molarity, Solutions, Dilutions
Topic: mmol/mL vs. mol/L
Replies: 6
Views: 70

### Re: mmol/mL vs. mol/L

By definition molarity (M) is moles of solute/ liters of solution.
Technically number of mmol/mL of a given solution would be the same as in mol/L, so it wouldn't affect your ultimate answer.

But I think it's better to convert to mol/L for accuracy and clarity.
Wed Oct 07, 2020 12:45 am
Forum: Significant Figures
Topic: Integers in calculations
Replies: 6
Views: 46

### Integers in calculations

Hi!
Does integers affect the sig fig in calculations?
Like for example 325 has 3 sig figs, 0.10101 has 5 sig figs, right?
Would the answer to 325 * 0.10101 have 3 sigfigs?

How many sig figs would the answer to 32+2 have? and 32 * 2 ?
Wed Oct 07, 2020 12:31 am
Forum: Empirical & Molecular Formulas
Topic: Audio Visual Topic Video Question
Replies: 6
Views: 43

### Re: Audio Visual Topic Video Question

Hi! we only care about molar ration when dealing with empirical formulas. The mass percent composition can be seen as the mass ratio of different elements in a sample. The ratio won't be affected by sample mass. And I want to add that when we want to find the molecular formula when given an empirica...
Wed Oct 07, 2020 12:03 am
Forum: SI Units, Unit Conversions
Topic: Including the units when solving
Replies: 8
Views: 66

### Re: Including the units when solving

I don't think we will get penalized for not putting the units, but it would be great help if you do (to keep track of your thinking process). And it would help to articulate your work better, in case you're using another innovative method.
Tue Oct 06, 2020 11:51 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Replies: 31
Views: 361