## Search found 70 matches

Sat Jan 16, 2021 9:31 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change in pressure due to inert gas
Replies: 6
Views: 22

### Re: Change in pressure due to inert gas

While it will change the total pressure, it does not affect the individual concentrations of the reactants leading to no effect on Q.
Wed Jan 13, 2021 10:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kb and Ka
Replies: 2
Views: 16

### Re: Kb and Ka

We will not have to memorize Ka or Kb values. If they are needed to solve a problem we will be given them. Otherwise, we should be able to solve for them with the information given.
Wed Jan 13, 2021 3:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Approximations when K is small
Replies: 2
Views: 9

### Re: Approximations when K is small

I believe 10^-3 is the cut off, but during lecture Lavelle did say it was safer to use 10^-4, but I doubt he would give us any questions where there was question about whether or not you could ignore it.
Wed Jan 13, 2021 10:58 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change in K (P&T)
Replies: 9
Views: 30

### Re: Change in K (P&T)

Temperature will change the K value, but pressure will not. Pressure can change the concentrations which could shift the reaction to the left or right, but it will not change the K.
Wed Jan 13, 2021 10:53 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temperature
Replies: 16
Views: 46

### Re: Temperature

We would need to know if the reaction is endothermic or exothermic and then we could determine which is favors based on the temperature change.
Tue Jan 12, 2021 8:44 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6B Question #9
Replies: 3
Views: 14

### Re: 6B Question #9

I had the same question. I kept getting -.176 as well and I don't see this one listed as an error on the solution manual error list.
Mon Jan 11, 2021 4:17 pm
Forum: Student Social/Study Group
Topic: Midterms?
Replies: 8
Views: 68

### Re: Midterms?

Here is the link https://lavelle.chem.ucla.edu/wp-conten ... hedule.pdf
Our first midterm is Jan 29 and our second midterm is Feb 19. Our final is March 14.
Mon Jan 11, 2021 11:57 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K in relation to shifting right/left
Replies: 8
Views: 33

### Re: K in relation to shifting right/left

You are correct. Small equilibrium constants will lie to the left because the reactants will be greater than the products and reactions with large equilibrium constants will lie to the right because the products will be greater than the reactants.
Tue Jan 05, 2021 5:36 pm
Forum: Administrative Questions and Class Announcements
Topic: Textbook Logistics and Sapling
Replies: 5
Views: 28

### Re: Textbook Logistics and Sapling

Once you are on sapling, go to the home page. Under the resources tab there is a PDF named Atkins 7e SSM. This is the solutions manual that you can use!
Tue Jan 05, 2021 5:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling HW #9
Replies: 7
Views: 43

### Re: Sapling HW #9

Hi there! I just realized that my sapling has a different value for the initial values of N2 and O2. So while mine would be k=36, it seems yours is K=4. Sorry for the confusion!
Tue Jan 05, 2021 10:29 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling HW #9
Replies: 7
Views: 43

### Re: Sapling HW #9

Hi there,

For this problem you would set the initial value of NO as .900M. We can determine the value of K from the given concentrations, which turns out to be K=36. From there, you can use an equilibrium table to find the final NO, and use K=36, since that value does not change. Hope this helps.
Mon Jan 04, 2021 6:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling hw #5
Replies: 2
Views: 33

### Re: Sapling hw #5

Hi there, You're on the right track but to get started you will want to use the 1st and 3rd equations. First I multiplied H2(g) + I2 (g) ⇌ 2HI by 3 to get 3[H2(g) + I2 (g) ⇌ 2HI]. By multiplying the entire equation by 3, the K value is put to the power of 3, so 160^3. The second equation I used was ...
Mon Jan 04, 2021 6:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling 5
Replies: 2
Views: 28

### Re: Sapling 5

Hello, I used the same equations as you. First I multiplied H2(g) + I2 (g) ⇌ 2HI by 3 to get 3[H2(g) + I2 (g) ⇌ 2HI]. By multiplying the entire equation by 3, the K value is put to the power of 3, so 160^3. The second equation I used was also N2(g) + 3H2(g) ⇌ 2NH3(g). For this equation I just invert...
Mon Jan 04, 2021 12:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: If K is large...
Replies: 11
Views: 49

### Re: If K is large...

When he says a reaction is at equilibrium, it means that both products and reactants are being formed at the same rate. This does not mean that they have the same concentrations. Instead, both the forward and backward reactions are happening at the same rate causing the reaction to stay at one equil...
Tue Dec 08, 2020 8:07 pm
Forum: Conjugate Acids & Bases
Topic: Amphoteric
Replies: 11
Views: 89

### Re: Amphoteric

As stated before, Amphoteric substances can act as either acids or bases. The generally follow the same diagonal pattern as the metalloid band but do not line up exactly.
Tue Dec 08, 2020 8:03 pm
Forum: Bronsted Acids & Bases
Topic: Acid strength through bonds
Replies: 6
Views: 41

### Re: Acid strength through bonds

That is correct. The longer the bond, the weaker and more easily the bond is broken. That makes the weaker bond the stronger acid.
Tue Dec 08, 2020 5:59 pm
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 and melting points
Replies: 3
Views: 28

### Re: hydrogen bonding and melting points

Hydrogen bonds are the strongest intermolecular force. This means that the molecules are more tightly held together and require more energy to break the bond between them. This results in a higher boiling point.
Mon Dec 07, 2020 8:28 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Sapling Homework W10 Problem#8
Replies: 2
Views: 18

### Re: Sapling Homework W10 Problem#8

Hello, First, I would classify the pH values, remembering that pH<7 is acidic, pH=7 is neutral, and pH>7 is basic. Next, to classify the [H+] values, remember that acidic solutions have a high [H+], specifically greater than 1*10^-7M, basic solutions have a low [H+], less than 1*10^-7M, and neutral ...
Mon Dec 07, 2020 8:22 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Sapling Homework W10 Problem#5
Replies: 4
Views: 41

### Re: Sapling Homework W10 Problem#5

Hi,

If we are given the pH of the solution, we can use [H+]=10^-pH. From there, we can also use pOH=14-pH to find the pOH. And then we can use [OH-]=10^-pOH.

Hope this helps
Wed Dec 02, 2020 9:28 am
Forum: Naming
Topic: Topic 9C Question 1 Part C
Replies: 4
Views: 47

### Re: Topic 9C Question 1 Part C

I see what you're saying. However, I think it is meant to be Co (cobalt) and it may just be a typo. Otherwise, there would be no metal to bond to.
Tue Dec 01, 2020 3:20 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling Number 3
Replies: 8
Views: 60

### Re: Sapling Number 3

Trigonal bipyramidal is associated with the coordination number 5. It has 5 bonds not 4.
Tue Dec 01, 2020 3:12 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling Number 3
Replies: 8
Views: 60

### Re: Sapling Number 3

The coordination number is the number of bonds. Both square planar and tetrahedral have four bonds. This is why is it is both of these. Hope this helps.
Tue Dec 01, 2020 3:05 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Energy level of orbitals
Replies: 5
Views: 57

### Re: Energy level of orbitals

Yes you got it. The energy levels go s<p<d<f
Mon Nov 30, 2020 2:48 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Number and Geometry
Replies: 3
Views: 54

### Re: Coordination Number and Geometry

The coordination number is the number of bonds on the central atom. So the number of ligands attached to the transition metal. Based on the number of ligands attached, we can use our knowledge of molecular geometry to determine the geometry of a complex.
Mon Nov 30, 2020 10:29 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling Homework Week 9-Problem#6
Replies: 4
Views: 48

### Re: Sapling Homework Week 9-Problem#6

Hi, The sum of the charges in the complex must be equal to the overall charge on the compound. The one chloride ion outside the brackets has a charge of -1, so the overall charge of the coordination sphere must be +1. The ammine ligands are neutral, and there is one negative charge on the Cl. So the...
Fri Nov 27, 2020 3:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling Week 7-8 #3
Replies: 2
Views: 26

### Re: Sapling Week 7-8 #3

For a molecule with 5 regions of electron density, with 3 lone pairs and 2 bond pairs, the structure would be linear. This makes the smallest bond angle 180.
Fri Nov 27, 2020 3:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: I3-
Replies: 2
Views: 18

### Re: I3-

With an overall charge of -1, the central I atom has 3 lone pairs and two bond pairs. This makes the geometry trigonal bipyramidal, but the shape would be linear.
Fri Nov 27, 2020 6:29 am
Forum: Molarity, Solutions, Dilutions
Topic: Molarity other than solutions
Replies: 6
Views: 54

### Re: Molarity other than solutions

The units for molarity are mols/liters. This is only ever used to determine the concentration of a solution and is not used for solids or gases.
Wed Nov 25, 2020 10:40 am
Forum: General Science Questions
Topic: Finals
Replies: 39
Views: 360

### Re: Finals

Also, how can you calculate what grade you need on the final to get an A? You can figure out how many points you have already lost by looking on My UCLA. There are a total of 500 points so you can miss 35 points for an A, and 50 points for an A-. So you can count up your total and see the maximum n...
Wed Nov 25, 2020 7:09 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook 2E #17
Replies: 3
Views: 16

### Re: Textbook 2E #17

As stated above, Ozone's central oxygen has three regions of electron density, both the other oxygens as well as a long pair. This makes the molecular geometry trigonal planar, but because there is one lone pair the shape is bent. This makes the angle <120 degrees.
Tue Nov 24, 2020 1:03 pm
Forum: Student Social/Study Group
Topic: Final Exam Tips
Replies: 24
Views: 139

### Re: Final Exam Tips

I feel the same way. Personally, I like going back through the old sapling homework because they give detailed solutions and how to solve them. I also think the textbook problems are a great way to practice and make sure you understand the concepts.
Wed Nov 18, 2020 6:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 11/18/20 Lecture VSEPR Notation
Replies: 4
Views: 24

### Re: 11/18/20 Lecture VSEPR Notation

Hi,
That is correct. X is for bonded atom and E is for lone pairs around the central atom.
Mon Nov 16, 2020 10:28 pm
Forum: Electronegativity
Topic: Textbook Problem 2D.3
Replies: 5
Views: 36

### Re: Textbook Problem 2D.3

Hi,
You are correct in that you are supposed to find the largest difference in electronegativity. For this question, that largest electronegativity difference would be BaBr2, making it the most ionic.
Mon Nov 16, 2020 10:19 pm
Forum: Lewis Structures
Topic: Lewis Acids and Bases
Replies: 5
Views: 38

### Re: Lewis Acids and Bases

Hi,

Lewis acids accept electrons whereas Lewis bases donate electrons. Metal cations accept electrons in acid-base reactions. Molecules with an excess of electrons, such as anions or molecules with a lone pair electrons, can donate electrons. Such as H2O
Mon Nov 16, 2020 10:07 pm
Forum: Dipole Moments
Topic: 3F5
Replies: 3
Views: 19

### Re: 3F5

Hello,
While both butanol and diethyl ether have the correct elements for hydrogen bonding, you have to look at the structure. Butanol has a H bonded with the O while diethyl ether has the H bonded to the C, not the O. It definitely helps to draw out the structures and visualize them. Hope this helps!
Mon Nov 16, 2020 10:04 pm
Forum: Quantum Numbers and The H-Atom
Topic: Textbook Problem 1D.23
Replies: 3
Views: 46

### Re: Textbook Problem 1D.23

You are correct that the 4d state has 5 orbitals, but this problem specifies the ml number as -2, which corresponds to only one orbital.
Fri Nov 13, 2020 8:55 am
Forum: Resonance Structures
Topic: Resonance Hybrid Structures
Replies: 6
Views: 31

### Re: Resonance Hybrid Structures

Hello,
We may not have to draw them because the test will most likely be multiple choice. However, you should be able to identify them and which ones contribute to the overall structure. This includes finding the formal charge to determine the resonance structure.
Tue Nov 10, 2020 11:50 pm
Forum: Ionic & Covalent Bonds
Topic: 2A.15
Replies: 2
Views: 15

### Re: 2A.15

Gallium is in group 13 which has 3 valence electrons. The ion most likely formed would want to give away 3 electrons to make a full valence shell. So the charge of Ga will be +3.
Tue Nov 10, 2020 1:34 pm
Forum: Resonance Structures
Topic: Sapling HW Q9
Replies: 2
Views: 12

### Re: Sapling HW Q9

The formal charges for each molecule are given. To find the most plausible resonance structures you want to find the ones with the least formal charges. In this case it would be C and D, both of which only have one negative charge whereas others have multiple.
Tue Nov 10, 2020 1:31 pm
Forum: Lewis Structures
Topic: Sapling HW Q4
Replies: 3
Views: 48

### Re: Sapling HW Q4

The answer is C because it has two negative charges and one positive charge. Both A and B only have one negative charge which lowers the total energy.
Tue Nov 10, 2020 1:29 pm
Forum: Lewis Structures
Topic: Sapling HW Q4
Replies: 1
Views: 21

### Re: Sapling HW Q4

Hello, for one resonance structure you will simply switch the double bond from the one Oxygen to the other, making sure you also include the formal charge. For the other there is a double bond between the Nitrogen and Carbon, and single bonds between the Carbon and Oxygen, also make sure to include ...
Sat Nov 07, 2020 2:13 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge of the Same Element
Replies: 15
Views: 60

### Re: Formal Charge of the Same Element

Each atom has its own formal charge, and the summation of them give you to total formal charge
Fri Nov 06, 2020 8:35 am
Forum: Ionic & Covalent Bonds
Topic: Drawing Lewis structures (sapling)
Replies: 3
Views: 45

### Re: Drawing Lewis structures (sapling)

Yes you need to calculate the formal charge for each atom. The overall charge of the molecule is made up of the individual charges of the atoms so you need to find those.
Thu Nov 05, 2020 6:59 pm
Forum: Trends in The Periodic Table
Topic: Midterm 2 Study Group
Replies: 7
Views: 63

### Re: Midterm 2 Study Group

That would be super helpful. I would love to be a part.
Wed Nov 04, 2020 2:15 pm
Forum: Student Social/Study Group
Topic: Constants and Equations Page
Replies: 8
Views: 71

### Re: Constants and Equations Page

Yes we will have to memorize it. Anything not on the formula sheet needs to be memorized.
Wed Nov 04, 2020 2:14 pm
Forum: Administrative Questions and Class Announcements
Topic: missing discussion
Replies: 8
Views: 72

### Re: missing discussion

Discussions are not mandatory so it will not affect your grade. You may want to contact your TA or other classmates to ensure you didn't miss anything important.
Mon Nov 02, 2020 3:51 pm
Forum: SI Units, Unit Conversions
Topic: Using a Calculator
Replies: 10
Views: 86

### Re: Using a Calculator

You can also store constants in your calculator which I find very helpful. That way you do not have to type out long numbers like planks constant or avogadro's number. Just type the number, push sto-> and any letter. Then use that letter the same way you would the number going forward.
Sat Oct 31, 2020 11:58 am
Forum: Ionic & Covalent Bonds
Topic: Sampling 28
Replies: 10
Views: 54

### Re: Sampling 28

The value of l can be 0,1,2,3,...,(n-1). With 0 corresponding to the s-orbital, 1 with the p-orbital, 2 with the d-orbital, and so on.
Wed Oct 28, 2020 7:03 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Problem Help
Replies: 2
Views: 30

### Re: Problem Help

The first step here is recognizing that 102.557nm is part of the Lyman series, meaning that the first energy level will be n=1. I use the following equation: v=-R((\frac{1}{n^2})-(\frac{1}{n^2})) You then need to convert the wavelength 102.557nm to frequency, giving you 2.93x...
Tue Oct 27, 2020 5:49 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 13
Views: 119

### Re: Photoelectric Effect

Im pretty sure Prof Lavelle said that if the energy of the photon is less than the work function that it just passes through and is not absorbed.
Mon Oct 26, 2020 9:49 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: H-Atom Equations for Midterm 1
Replies: 1
Views: 29

### Re: H-Atom Equations for Midterm 1

While Professor Lavelle prefers the En one, I think we can use either. The test is also multiple choice so he wouldn't be able to tell which one you used.
Mon Oct 26, 2020 4:31 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Module Question
Replies: 2
Views: 35

### Re: Module Question

If you know the radius of a Hydrogen atom, you can just find 1% of that to find your uncertainty. In this case it would be .05nm * .01= 5*10^-13, which would be your uncertainty position.
Wed Oct 21, 2020 4:43 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Homework up to Q19 and Midterm 1 [ENDORSED]
Replies: 7
Views: 137

### Re: Homework up to Q19 and Midterm 1[ENDORSED]

I am confused about this as well. I hope it is not on the midterm because he hasn't gone over anything other than the very basic descriptions of the levels, but I am not sure.
Wed Oct 21, 2020 8:49 am
Forum: Photoelectric Effect
Topic: Absorption of a photon
Replies: 4
Views: 35

### Re: Absorption of a photon

If the energy of the photon is less than the threshold energy, the photons will just pass through the metal.
Tue Oct 20, 2020 6:52 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Post Module Question #14
Replies: 2
Views: 27

### Re: Post Module Question #14

The correct answer is D. The uncertainties in position, speed, and momentum of a moving object are not noticeable or measurable. Heisenberg’s uncertainty principle deals with moving objects. The formula is λ = h/p where p is mv. There has to be some velocity or else the denominator would be zero, so...
Tue Oct 20, 2020 10:11 am
Forum: Administrative Questions and Class Announcements
Topic: The Midterm
Replies: 9
Views: 77

### Re: The Midterm

We will have a constants/equation sheet that we will have to print out before hand. You can find it on his website. https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf
Mon Oct 19, 2020 9:05 pm
Forum: Photoelectric Effect
Topic: textbook solutions
Replies: 2
Views: 37

### Re: textbook solutions

There is a solutions manual on sapling under resources.
Mon Oct 19, 2020 2:50 pm
Forum: Administrative Questions and Class Announcements
Topic: Multiple choice test?
Replies: 7
Views: 70

### Re: Multiple choice test?

Yes, I believe you are correct. The midterm will be multiple choice.
Thu Oct 15, 2020 1:14 pm
Forum: Einstein Equation
Topic: Converting from MHz to Hz
Replies: 5
Views: 45

### Re: Converting from MHz to Hz

Check to make sure you have all your units correct. 1 MHz is equal to 10^6 Hz, and the answer for this questions is supposed to be 1m.
Wed Oct 14, 2020 8:11 pm
Forum: Properties of Light
Topic: Sapling HW Q 4
Replies: 3
Views: 44

### Re: Sapling HW Q 4

The second half of question 4 is asking for the maximum number of electrons that could be ejected from the metal by a burst of photons with a total energy of 3.84*10^-7. We know that the work function of this metal is 5.28*10^-19 from part one of this question. To find the maximum number of electron...
Wed Oct 14, 2020 9:54 am
Forum: Empirical & Molecular Formulas
Topic: Rounding up Molar Ratios
Replies: 6
Views: 75

### Re: Rounding up Molar Ratios

I have the same problem as well. Sometimes im not sure if I'm meant to round up or find another value to multiply it by. In general, if the values are .95 or above I will round up. Otherwise I will try to find another number to multiply by. Most of our textbook/homework questions will have answers t...
Wed Oct 14, 2020 9:47 am
Forum: Administrative Questions and Class Announcements
Topic: Chemistry Community Posts [ENDORSED]
Replies: 3
Views: 42

### Re: Chemistry Community Posts[ENDORSED]

You can either click on your name or you can click on quick links in the top left and then your posts.
Wed Oct 14, 2020 8:32 am
Forum: Properties of Light
Topic: Textbook Homework 1A.9
Replies: 4
Views: 33

### Re: Textbook Homework 1A.9

MHz stands for Megahertz, which is 10^6 hertz.
Sun Oct 11, 2020 9:03 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Calculating number of moles of an element
Replies: 10
Views: 85

### Re: Calculating number of moles of an element

We use 100g simply because it is easier to visualize the mass percentage composition. You could use other values but it would make it more difficult. It just depends on the method that works best for you.
Sun Oct 11, 2020 9:01 am
Forum: Administrative Questions and Class Announcements
Topic: Homework
Replies: 6
Views: 51

### Re: Homework

Hello,
The post-assessments are just for your benefit. They are not graded and do not count as homework, but it is good practice and Dr Lavelle recommends everyone completes them. Sapling is the only homework that we have.
Thu Oct 08, 2020 8:20 pm
Forum: SI Units, Unit Conversions
Topic: Rounding
Replies: 20
Views: 160

### Re: Rounding

Like what was said above, you should wait to round until the final answer. If you round before then, especially if the question has many steps, you can cause your answer to be skewed.
Thu Oct 08, 2020 1:42 pm
Forum: Significant Figures
Topic: Sapling HW #4
Replies: 31
Views: 309

### Re: Sapling HW #4

950000 only has 2 sig figs because the last four zeros are trailing zeros. The only sig figs here are the 9 and 5. 80060 has 4 sig figs because the two zeros between the 8 and the 6 are significant. The last zero is not because it is a trailing zero.
Wed Oct 07, 2020 9:52 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Review of Chemical and Physical Principles Fundamentals E.15
Replies: 7
Views: 44

### Re: Review of Chemical and Physical Principles Fundamentals E.15

In this question the M from M(OH)2 is a placeholder for a metal, it is not an actual element. The question asks to find the molar mass of the metal, which would just be 74.1g/mol-34.02g/mol = 40.08g/mol. This is the molar mass of Calcium.
Mon Oct 05, 2020 10:51 am
Forum: Molarity, Solutions, Dilutions
Replies: 14
Views: 145

Hello,

He uses 100g to better represent the mass percentage composition. He used the values of each element of Vitamin C and expressed it as a percentage of the whole compound.
Mon Oct 05, 2020 10:47 am
Forum: Molarity, Solutions, Dilutions
Topic: Mol VS Mole
Replies: 17
Views: 213

### Re: Mol VS Mole

Hello,

Yes Mole and mol are the same thing. Mol can be shorthand for Mole.

Hope this helped!