## Search found 65 matches

Fri Jan 22, 2021 2:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka and Kb vs [H+] and [OH-] confusion
Replies: 2
Views: 8

### Re: Ka and Kb vs [H+] and [OH-] confusion

Hi! So both [H3O+][OH-] = 1.0 * 10^-14 and (Ka)(Kb) = 1.0 * 10^-14 because 1.0 * 10^-14 is the autoprotolysis constant of water. This constant, or Kw, comes from the autoprotolysis of water reaction where two water molecules react to produce OH- and H30+. In this reaction, if you multiply the concen...
Fri Jan 22, 2021 11:14 am
Forum: Phase Changes & Related Calculations
Topic: Non-State Properties
Replies: 4
Views: 14

### Re: Non-State Properties

Hi! Work is not a state property because it is proportional to the distance an object moved, which means that work is dependent on the path taken. Similarly, heat is not a state property either because it depends on how the system changes from initial to final state.
Fri Jan 22, 2021 9:26 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: lecture 6 question
Replies: 2
Views: 11

### Re: lecture 6 question

Hi! So the question asks what the pH is for acetic acid. In order to find the pH, we must first find the concentration of H30 + because the definition of pH is -log [H30+]. When you find the concentration of [H30+] at equilibrium, you are then able to find the pH of the acetic acid.
Fri Jan 15, 2021 2:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka and Kb equation
Replies: 3
Views: 20

### Re: Ka and Kb equation

Hi! Yes, what you described definitely makes sense! It also helps to think that Kw is a constant so Ka and Kb have to balance each other out, meaning if Ka is high than Kb must be low.
Fri Jan 15, 2021 1:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: KA KB predicting trends (outline)
Replies: 6
Views: 30

### Re: KA KB predicting trends (outline)

Hi ! So if Ka is large, then it is a stronger acid and if the Kb is large, then it is a stronger base. If Ka is small, then it is a weaker acid and if Kb is small, then it is a weaker base.
Fri Jan 15, 2021 1:56 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: acid base problems
Replies: 3
Views: 20

### Re: acid base problems

And to clarify, should we use 10^-3 or 10^-4 as the threshold to when we can ignore the +/- x to avoid a quadratic equation? Lavelle has mentioned both. Hi! I think it is safer to use 10^-4. If you want to use 10^-3, you can double check that it is fine to use by making sure x is less than 5% of th...
Thu Jan 14, 2021 10:25 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Which Acids and Bases to remember
Replies: 3
Views: 30

### Re: Which Acids and Bases to remember

Hi! I just wanted to add that organic acids are generally weak. For example, acids containing a carboxyl group (like COOH) are weak acids.
Wed Jan 13, 2021 12:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Amphoteric vs Amphiprotic
Replies: 5
Views: 21

### Re: Amphoteric vs Amphiprotic

Hi! So I believe that all amphiprotic compounds are amphoteric as well but the opposite is not always true. Amphiprotic compounds can act as a proton donor and proton acceptor. Amphoteric compounds have both acidic and basic character but that does not necessarily mean that they are amphiprotic as w...
Sat Jan 09, 2021 10:52 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatlier's Principle concerning change in temperature
Replies: 2
Views: 16

### Le Chatlier's Principle concerning change in temperature

Hi! I was wondering if Le Chatlier's Principle is applied when there is a change in temperature since K changes?
Sat Jan 09, 2021 7:51 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Changes in Q vs K
Replies: 6
Views: 46

### Re: Changes in Q vs K

Hi! K does not change because the reaction returns to the same P/R ratio eventually by shifting either right or left. For example, if the pressure doubles (the volume halves), then Q will change and be different than K but the reaction will shift to the right in order to return back to equilibrium. ...
Sat Jan 09, 2021 7:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating concentration using the quadratic formula
Replies: 6
Views: 29

### Re: Calculating concentration using the quadratic formula

Hi! I think that usually you will get a positive and negative value from the quadratic formula, so you do not have to worry about getting 2 positive values.
Fri Jan 08, 2021 11:39 pm
Forum: Ideal Gases
Topic: Ideal Gas
Replies: 3
Views: 15

### Ideal Gas

Hi! What exactly does an ideal gas mean?
Wed Jan 06, 2021 3:26 pm
Forum: Ideal Gases
Topic: Temperature in Ideal Gas Law
Replies: 14
Views: 60

### Re: Temperature in Ideal Gas Law

Hi! I'm pretty sure we have to use Kelvin for temperature
Sat Dec 12, 2020 12:21 pm
Forum: Student Social/Study Group
Topic: SATURDAY Q+A W/ MEL
Replies: 5
Views: 114

### Re: SATURDAY Q+A W/ MEL

Hi! Can you go over how to tell which molecules show least covalent character? For example NaCl vs KCl and HF vs. HBr? Also what is the difference between polarizability and polarizing power? Also how can you tell what is a weak acid and weak base? Last question lol, what is the difference between h...
Fri Dec 11, 2020 3:50 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelating Ligands vs Polydentate ligands
Replies: 5
Views: 30

### Re: Chelating Ligands vs Polydentate ligands

Hi! Yes chelating ligands and polydentate ligands are the same thing :)
Fri Dec 11, 2020 3:12 pm
Forum: Calculating the pH of Salt Solutions
Topic: Hard Water vs. Soft Water
Replies: 9
Views: 63

### Hard Water vs. Soft Water

Hi! I am a little confused on the difference between hard and soft water? So is hard water alkaline and soft water acidic? Or is it the other way around ? Also is soft water the one with the soapy feel?
Wed Dec 09, 2020 8:19 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Alkaline solution
Replies: 3
Views: 27

### Alkaline solution

Hi! Are alkaline solutions the same thing as a basic solution?
Tue Dec 08, 2020 9:45 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: T-shaped
Replies: 2
Views: 32

### Re: T-shaped

Hi! T-shaped molecular geometry is different than trigonal planar because it has 3 bonds and 2 lone pairs while trigonal planar molecular geometry only has 3 bonds and 0 lone pairs.
Tue Dec 08, 2020 9:42 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH vs. pKa
Replies: 1
Views: 14

### pH vs. pKa

Hi! What's the difference between pH values and pKa values?
Fri Dec 04, 2020 11:16 pm
Forum: Hybridization
Topic: Unhybridized orbitals
Replies: 3
Views: 43

### Unhybridized orbitals

Hi! How do you know when you have an unhybridized orbital and how do you know how many unhybridized orbitals to have? For example, how do you know that CO2 has 2 unhybridized 2p orbitals?
Fri Dec 04, 2020 11:06 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Heme complex
Replies: 2
Views: 36

### Heme complex

Hi! What exactly is the porphyrin ligand in a heme complex?
Fri Dec 04, 2020 7:35 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Naming Coordination Compounds
Replies: 7
Views: 65

### Re: Naming Coordination Compounds

Hi! You can tell the ionic charge of an element by looking at the periodic table but this is only possible for the s-block and p-block. For example, the charge of group 1 elements is +1, group 2 is +2, group 13 is +3, group 14 is +4/-4, group 15 is -3, group 16 is -2, and group 17 is -1.
Fri Dec 04, 2020 7:14 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Relative Acidity
Replies: 2
Views: 19

### Re: Relative Acidity

Hi! So with the example of hypochlorous acid, hypobromous acid, and hypoiodus acid from today's lecture, we cannot predict their acid strength based on bond length because they all form the same bond of O-H. When these acids dissolve in water, the bond of O-H breaks and the O is left with a negative...
Thu Dec 03, 2020 11:53 pm
Forum: Student Social/Study Group
Topic: Viewing Chemistry Community in High School?
Replies: 1
Views: 45

### Re: Viewing Chemistry Community in High School?

Hi! I was just thinking about this the other day! I definitely do remember seeing answers on Chemistry Community pop up when I searched a chem question in high school! Now I know what Chemistry Community actually is lol :)
Thu Nov 26, 2020 12:39 pm
Forum: Hybridization
Topic: Lecture 23 Question
Replies: 2
Views: 24

### Lecture 23 Question

Hi! During lecture 23 when Dr. Lavelle was talking about sp2 hybridization for ethene, he wrote that it forms sp3 hybrid orbitals. I was confused because I thought ethene formed sp2 hybrid orbitals? Could anyone clarify this? Thank you.
Thu Nov 26, 2020 12:31 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Ligand Bond Formation
Replies: 1
Views: 25

### Re: Ligand Bond Formation

Hi! Ligands are electron rich species, such as Lewis bases, that interact with a transition metal. Because they are Lewis bases and are electron pair donors, they can form a coordinate covalent bond with transition metals which are usually cations. Sometimes these ligands have multiple electron lone...
Thu Nov 26, 2020 12:11 pm
Forum: Administrative Questions and Class Announcements
Topic: how to access saved drafts
Replies: 2
Views: 28

### Re: how to access saved drafts

Hi! You can find your saved drafts by clicking on your name in the upper right hand corner and then click user control panel. Then click overview and on the left hand side click manage drafts. Hope that helps!
Thu Nov 26, 2020 12:03 pm
Forum: Biological Examples
Topic: Chemotherapy drug
Replies: 2
Views: 42

### Re: Chemotherapy drug

Hi! I believe that the platinum atom of the cisplatin molecule covalently binds to the N7 position of a guanine.
Thu Nov 26, 2020 11:57 am
Forum: Administrative Questions and Class Announcements
Topic: Chem Community Posts during Thanksgiving break
Replies: 10
Views: 109

### Re: Chem Community Posts during Thanksgiving break

Hi! Yes, we should have 40 posts by this Sunday.
Wed Nov 18, 2020 11:30 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Electron density in VSEPR models
Replies: 4
Views: 36

### Re: Electron density in VSEPR models

Hi! Lone pairs push down on the bonded electrons because the repulsion strength of a lone pair-bonding pair is greater than the repulsion between a bonding pair-bonding pair. The lone pairs thus push down on the bonding pairs and slightly distort the bonding angles. This is what was in the lecture a...
Wed Nov 18, 2020 11:25 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizing Power vs Polarizability
Replies: 4
Views: 58

### Re: Polarizing Power vs Polarizability

Hi! Polarizing power refers to small, highly charged cations (I like to remember it like they're tiny but mighty). Polarizability refers to bigger atoms with lots of electrons that are easily distorted.
Wed Nov 18, 2020 11:17 pm
Forum: Resonance Structures
Topic: Resonance Structures Conceptual Question
Replies: 1
Views: 23

### Re: Resonance Structures Conceptual Question

Hi! So the real structure of molecules with resonance is called a resonance hybrid. This resonance hybrid spreads multiple bond character over a molecule and lowers its energy, causing it to be more stable. This is why the best representation of molecules with resonance is a resonance hybrid because...
Wed Nov 18, 2020 11:05 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: atomic orbitals and probability
Replies: 2
Views: 40

### Re: atomic orbitals and probability

Hi! So this refers to Schrodinger's equation. The energy that we get out of Schrodinger's equation matches the energy of a specific orbital and can be compared to spectroscopic data. The higher the energy, the larger the orbital (meaning s,p,d,f). Also, Schrodinger's equation squared represents the ...
Wed Nov 18, 2020 10:56 pm
Forum: Electronegativity
Topic: Electronegativity Trends
Replies: 8
Views: 89

### Re: Electronegativity Trends

Hi! The trend for electronegativity is the same as ionization energy. So, electronegativity increases from left to right across a period and decreases down a group. However, this trend does not apply to the noble gases because they do not want another electron. In the case of N and S, nitrogen would...
Fri Nov 13, 2020 3:39 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Valence electrons in d orbital ?
Replies: 3
Views: 19

### Valence electrons in d orbital ?

Hi! Are there ever any valence electrons in the d orbital since it is never the outermost shell?
Fri Nov 13, 2020 3:26 pm
Forum: Bond Lengths & Energies
Topic: Lecture 17 Question
Replies: 3
Views: 41

### Lecture 17 Question

Hi! In Lecture #17, Dr. Lavelle says that -250 kJ/mol is the magnitude of attractive interactions between Na+ and Cl-. What exactly is the mole of? Is it per mole of Na+ and Cl- together or per mole of bonds?
Tue Nov 10, 2020 5:10 pm
Forum: Ionic & Covalent Bonds
Topic: Lewis Structure
Replies: 3
Views: 44

### Re: Lewis Structure

He subtracted 1 electron because the ammonium had a positive charge. This means the ammonium had to lose 1 electron to be positively charged.
Tue Nov 10, 2020 4:48 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic v. Covalent Bonding
Replies: 16
Views: 130

### Re: Ionic v. Covalent Bonding

Hi! Dr. Lavelle mentioned in one of his lectures before that if two elements are close together on the periodic table, then they will form a covalent bond. If two elements are on opposite sides of the periodic table and bind, then they will most likely form an ionic bond.
Mon Nov 09, 2020 9:05 pm
Forum: Ionic & Covalent Bonds
Topic: "Interactions that Give Rise to Attractive forces" Question
Replies: 2
Views: 29

### Re: "Interactions that Give Rise to Attractive forces" Question

Hi! This number is the magnitude of attractive interactions between the two ions. The number is negative because energy is being released, which is favorable.
Wed Nov 04, 2020 5:39 pm
Forum: Administrative Questions and Class Announcements
Topic: Lavelle's Office Hours (5-6 p.m.)
Replies: 1
Views: 26

### Re: Lavelle's Office Hours (5-6 p.m.)

I am in it right now. Make sure you are signed in with SSO first using this: https://ucla.zoom.us
And the zoom link is on CCLE
Wed Nov 04, 2020 5:36 pm
Forum: Octet Exceptions
Topic: Expanded Valence Shells
Replies: 2
Views: 15

### Re: Expanded Valence Shells

Hi! Yes you are right. An expanded valence shell means that an atom has more than 8 valence electrons.
Wed Nov 04, 2020 5:22 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2A.21 Textbook Question
Replies: 5
Views: 27

### Re: 2A.21 Textbook Question

Dr. Lavelle just said in his office hours that we do not need to know how to do part d for that question and he will update the outline to omit part d.
Wed Nov 04, 2020 2:58 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Lecture O Formal Charge Ex
Replies: 4
Views: 18

### Re: Lecture O Formal Charge Ex

Hi! So formal charge is calculated by calculating the number of valence electrons minus the sum of the number of lone pair electrons plus the number of shared electrons divided by 2, or FC= V- (L + S/2) So oxygen has 6 valence electrons since it is in the 6th group excluding the d-block. In SO4, oxy...
Wed Nov 04, 2020 2:51 pm
Forum: Trends in The Periodic Table
Topic: Nuclear Charge
Replies: 6
Views: 30

### Nuclear Charge

Hi! Why does nuclear charge increase across a period? I know increasing nuclear charge causes the atomic radii to decrease across a period but I cannot figure out why. Thanks!
Fri Oct 30, 2020 12:04 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Worked example, lecture #7
Replies: 4
Views: 53

### Re: Worked example, lecture #7

Hi! Yes you can use the second equation (the Rydberg equation) but the first equation just helps you to better understand what is going on. The first equation helps you to clearly recognize if the Energy is being emitted ( a negative value for E) or absorbed (a positive value for E).
Thu Oct 29, 2020 11:57 pm
Forum: Einstein Equation
Topic: Sapling hw # of photons
Replies: 3
Views: 57

### Re: Sapling hw # of photons

Hi! You have to do 333.6 J/g x 423 g first. Then you use E=hc/λ and plug in 819x10^-9 m for λ and find E. Once you have this energy in J/ photon, you can find the number of photons. You just take what you got from your first calculation ( 141,113 J) and divide it by what you got in your second calcu...
Mon Oct 26, 2020 6:18 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra wave-like or particle-like properties
Replies: 3
Views: 54

### Atomic Spectra wave-like or particle-like properties

Hi! Does light in the atomic spectra experiment behave like a wave or a particle?
Mon Oct 26, 2020 4:54 pm
Forum: Balancing Chemical Reactions
Topic: Balancing Equations Textbook Problem
Replies: 1
Views: 31

### Re: Balancing Equations Textbook Problem

Hi! I would start off by balancing nitrogen first and getting 2C10H15N + O2 -> CO2 + H2O + CH4N2O Then, balance the carbon to get 2C10H15N + O2 -> 19CO2 + H2O + CH4N2O Now we can balance hydrogen to get 2C10H15N + O2 -> 19CO2 + 13H2O + CH4N2O Lastly we balance oxygen to get the final equation of 2C1...
Mon Oct 26, 2020 4:18 pm
Forum: Einstein Equation
Topic: E=pc vs E=hv
Replies: 15
Views: 153

### E=pc vs E=hv

Hi! When do we use the Einstein equation E=hv versus the equation E=pc?
Wed Oct 21, 2020 9:52 pm
Forum: Photoelectric Effect
Topic: Application
Replies: 5
Views: 44

### Re: Application

Hi! Yes, it only applies to metals because the original experiment was done by shining light on a metal surface to measure the energy needed to eject electrons from the surface.
Wed Oct 21, 2020 9:08 pm
Forum: Properties of Electrons
Topic: Calculating Wavelength of Spectral Line
Replies: 3
Views: 31

### Re: Calculating Wavelength of Spectral Line

It should be given to you. A detector is the only thing that can find the wavelength. Wavelength can be calculated if you are given frequency by doing λ=c/v
Wed Oct 21, 2020 4:06 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: S Orbitals and nodal planes
Replies: 5
Views: 60

### Re: S Orbitals and nodal planes

Hi! Yes, I believe no nodal plane means that there is no electron density distribution of 0 in the s plane.
Wed Oct 21, 2020 2:52 pm
Forum: *Shrodinger Equation
Topic: Electron Density
Replies: 5
Views: 35

### Electron Density

What exactly is electron density?
Wed Oct 21, 2020 12:07 am
Forum: Properties of Light
Topic: Longer wavelength means larger wavelength?
Replies: 5
Views: 52

### Re: Longer wavelength means larger wavelength?

Hi! Yes, I believe a longer wavelength is the same as a larger wavelength.
Fri Oct 16, 2020 2:29 pm
Forum: Properties of Electrons
Topic: Electron Transition
Replies: 7
Views: 36

### Electron Transition

What does electron transition mean?
Wed Oct 14, 2020 10:37 pm
Forum: Properties of Light
Topic: Excited state of an electron
Replies: 4
Views: 32

### Re: Excited state of an electron

Since the energy levels of an electron are quantized, it is not possible to have a middle energy level between n=1 and n=2 for example. There is no such thing as n=1.5 because light does not act like a continuous wave when it interacts with these electrons.
Wed Oct 14, 2020 10:27 pm
Forum: Properties of Light
Topic: Balmer vs Lyman
Replies: 12
Views: 108

### Re: Balmer vs Lyman

The Balmer series occurs in the visible region and involves the n=2 state. Th Lyman series occurs in the UV region and involves the n=1 state. Which state the electron is in is random. However, all the electrons do eventually come back to the ground state, which is n=1.
Wed Oct 14, 2020 5:52 pm
Forum: Properties of Electrons
Topic: Combining Equations
Replies: 10
Views: 98

### Re: Combining Equations

Hi! So since c= λv, we can rearrange that equation to solve for v which is v=c/λ. Now we can substitute c/λ for v in the equation E=hv and we get E=hc/λ. I think you got mixed up and thought E=hc/v which is wrong. Hope that helps!
Tue Oct 13, 2020 12:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Webcam
Replies: 5
Views: 118

### Re: Webcam

Hi! I got an email from my TA that we have to have an external webcam that we can plug into a computer and move around independently of a laptop screen/desktop. So a built-in camera on a laptop will not work.
Fri Oct 09, 2020 12:37 am
Forum: Significant Figures
Topic: Sig fig guide
Replies: 5
Views: 73

### Re: Sig fig guide

I also found this different sheet hyperlinked under Math Assistance on Dr. Lavelle's website if that helps!

https://lavelle.chem.ucla.edu/wp-conten ... ussion.pdf
Wed Oct 07, 2020 2:35 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant Calculations Post-Module Assessment #19
Replies: 2
Views: 42

### Re: Limiting Reactant Calculations Post-Module Assessment #19

Oh I see! I used the molar mass of 2H20 instead of just H20 to calculate the number of moles in H20. That's what messed up my answer in case anyone was wondering what my mistake was. Thanks again!
Wed Oct 07, 2020 2:04 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant Calculations Post-Module Assessment #19
Replies: 2
Views: 42

### Limiting Reactant Calculations Post-Module Assessment #19

Hi! For question 19 in the limiting reactant calculation post-module assessment, I keep getting H2O as the limiting reactant but that is not the answer. Could anyone help me get the right answer? Thanks. 19.) For the following reaction if 1.00 x 102 g H2O reacts with 1.00 x 102 g CaC2 identify the l...
Mon Oct 05, 2020 10:57 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant and Limiting Reagent
Replies: 7
Views: 96

### Re: Limiting Reactant and Limiting Reagent

In section H of the fundamentals in the ebook, it defines reagents as all chemicals available in a lab. The book also says that a reagent is only called a reactant when it is being used in a particular reaction. So there is a difference in the terms.
Mon Oct 05, 2020 6:07 pm
Forum: Administrative Questions and Class Announcements
Replies: 1
Views: 34