Search found 93 matches

by Darlene Lien 3E
Tue Jan 26, 2021 5:53 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: KA2 Help
Replies: 3
Views: 12

Re: KA2 Help

You would ignore the second ionization when Ka1>>Ka2. I think there are a few questions in Topic 6E that you could refer to in the outline that cover this. Hope this helps!
by Darlene Lien 3E
Tue Jan 26, 2021 5:49 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Ka and Kb values
Replies: 4
Views: 16

Re: Ka and Kb values

I wouldn't worry about having to know or memorize Ka or Kb values. They should be given!
by Darlene Lien 3E
Tue Jan 26, 2021 12:10 am
Forum: General Science Questions
Topic: Study Tips for midterm
Replies: 16
Views: 37

Re: Study Tips for midterm

Hi, personally I recommend doing the textbook problems and redoing the ones that you had trouble with. Also, attend UA sessions if possible!
by Darlene Lien 3E
Tue Jan 26, 2021 12:06 am
Forum: General Science Questions
Topic: equilibrium concentrations versus just concentrations
Replies: 2
Views: 18

Re: equilibrium concentrations versus just concentrations

Hi, I believe regular molar concentrations would just refer to concentrations not at equilibrium, so basically at any time during the reaction. For instance, you would use these concentrations to solve for Q if needed. Equilibrium concentrations are explicitly the concentrations at equilibrium. Hope...
by Darlene Lien 3E
Tue Jan 26, 2021 12:02 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Approximating Method for ICE Table
Replies: 4
Views: 17

Re: Approximating Method for ICE Table

To add on, Dr. Lavelle mentions this approximation method a few times, such as in Lecture 6, so definitely take a look back if you want explanations on the 5% rule too. Hope this helps!
by Darlene Lien 3E
Sun Jan 24, 2021 12:47 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Kelvin or Celsius?
Replies: 70
Views: 1368

Re: Kelvin or Celsius?

You would use Kelvin. If you look at the constants and equations sheet, the units for the rate are in Kelvin. Hope this helps!
by Darlene Lien 3E
Sun Jan 24, 2021 12:44 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solids in Ice Tables
Replies: 11
Views: 23

Re: Solids in Ice Tables

I agree with the above comments. Solids and liquids are not included in the ice charts.
by Darlene Lien 3E
Sun Jan 24, 2021 12:39 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm Timing
Replies: 15
Views: 47

Re: Midterm Timing

In 14A, there was ample time to complete the midterms. I had enough time to double check and work through the questions at a good pace.
by Darlene Lien 3E
Wed Jan 20, 2021 1:00 am
Forum: Student Social/Study Group
Topic: Midterm Practice
Replies: 9
Views: 53

Re: Midterm Practice

If there are also any other topics that you are unsure about, I also recommend watching videos or searching up other examples to further your understanding.
by Darlene Lien 3E
Wed Jan 20, 2021 12:57 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: friday week 2 lecture question (approximation of weak acids)
Replies: 5
Views: 26

Re: friday week 2 lecture question (approximation of weak acids)

Hi, to add on, for that question if we were to calculate the ionization, we see that (1.3E-3/0.10) x 100% gives 1.3%, and since this is less than 5%, we know that this approximation is valid. Hope this helps!
by Darlene Lien 3E
Wed Jan 20, 2021 12:48 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Rounding E Values in ICE charts
Replies: 17
Views: 51

Re: Rounding E Values in ICE charts

Hi, I believe Dr. Lavelle mentioned in the lectures that if K<10^-4 then the change in x is very small where it essentially becomes negligible, but I believe it could sometimes work when K<10^-3. Like the comment above said, a good rule of thumb is to use the 5% rule to check if the estimation works!
by Darlene Lien 3E
Wed Jan 20, 2021 12:45 am
Forum: Ideal Gases
Topic: 5I.3
Replies: 4
Views: 28

Re: 5I.3

Hi, I agree with the above comment. You use Kc=160 from Table 5G.2 and set up your equilibrium ratio accordingly. :)
by Darlene Lien 3E
Wed Jan 20, 2021 12:43 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Textbook 6B.5
Replies: 1
Views: 10

Re: Textbook 6B.5

Hi, for 2.00 mL of 0.175M KOH(aq) after dilution to 0.500 L: you could use the dilution formula M1V1=M2V2 to solve for the concentration of OH- after dilution. The concentration would be 7.0x10^-4 M. Then you would use this value to find the pOH and then pH. For 13.6 mg of NaOH dissolved in 0.350 L ...
by Darlene Lien 3E
Thu Jan 14, 2021 12:47 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE
Replies: 7
Views: 23

Re: ICE

Hi, generally you would use ICE charts to help when you have an initial concentration and an equilibrium concentration. When you solve for the change in concentration, you are able to get the equilibrium concentrations and use Kc accordingly. Typically, when the question gives or states that the con...
by Darlene Lien 3E
Thu Jan 14, 2021 12:43 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pH and pOH vs. pKa and pKb
Replies: 9
Views: 50

Re: pH and pOH vs. pKa and pKb

Hi, to add on, I believe pka is more specific than pH. While pH measures the concentration of H+ ions, pKa typically is an indicator of the strength of an acid. Hope this helps!
by Darlene Lien 3E
Mon Jan 11, 2021 1:11 pm
Forum: Administrative Questions and Class Announcements
Topic: Lecture 4_Cubic Equations
Replies: 5
Views: 21

Re: Lecture 4_Cubic Equations

You're correct. For this class we won't have to worry about solving cubic equations, but as Dr. Lavelle mentioned in the lecture, we can use that same approximation even for quadratic equations when K is very small as well. Hope this helps!
by Darlene Lien 3E
Mon Jan 11, 2021 1:08 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temperature Affecting Acids and bases
Replies: 4
Views: 30

Re: Temperature Affecting Acids and bases

I agree with the above comment, and I believe it would follow Le Chatelier's Principle.
by Darlene Lien 3E
Mon Jan 11, 2021 1:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Cubic Equations
Replies: 6
Views: 37

Re: Cubic Equations

Yep, and I believe Dr. Lavelle mentioned that for this class you can omit the "-x" since the equilibrium constant will be very small, so we won't have to solve the cubic equations.
by Darlene Lien 3E
Sun Jan 10, 2021 7:57 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: reaction quotient
Replies: 6
Views: 31

Re: reaction quotient

Hi, the reaction quotient has the same form as K, but instead, it uses the activities evaluated at an arbitrary stage of the reaction (not at equilibrium). Hope this helps!
by Darlene Lien 3E
Wed Jan 06, 2021 1:50 pm
Forum: General Science Questions
Topic: step up sessions
Replies: 11
Views: 124

Re: step up sessions

Hi, there is a link on his website! https://lavelle.chem.ucla.edu/wp-conten ... PL_ALL.pdf
by Darlene Lien 3E
Wed Jan 06, 2021 9:48 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Exercise 5.39
Replies: 1
Views: 17

Re: Textbook Exercise 5.39

Hi, I had the same issue as you! I think there might be an error in the textbook. The K value I got from the chart was 6.1E23 too.
by Darlene Lien 3E
Wed Jan 06, 2021 9:45 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Calculating the reaction quotient Q in a 3.00L vessel
Replies: 3
Views: 25

Re: Calculating the reaction quotient Q in a 3.00L vessel

Yes, you would divide the moles of each by 3.00 to get the concentration. Then you would plug these values in to solve for Q. Hope this helps!
by Darlene Lien 3E
Wed Jan 06, 2021 9:44 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Table 5G.2
Replies: 4
Views: 10

Re: Textbook Table 5G.2

Hi, so when the homework tells you to look at Table 5G.2 for the K value, you look at the temperature they give you in the problem and then locate the K value that has that respective temperature. Hope this helps!
by Darlene Lien 3E
Wed Jan 06, 2021 9:41 am
Forum: Administrative Questions and Class Announcements
Topic: Chemistry Community Points
Replies: 13
Views: 57

Re: Chemistry Community Points

I don't believe the points carry over. I think you must complete another 50 posts this quarter.
by Darlene Lien 3E
Sat Dec 12, 2020 7:32 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Strong & Weak Acids and bases
Replies: 3
Views: 31

Re: Strong & Weak Acids and bases

In the textbook, they also list the strong acids and bases, so definitely check that out!
by Darlene Lien 3E
Thu Dec 10, 2020 5:08 pm
Forum: General Science Questions
Topic: Grading
Replies: 5
Views: 116

Re: Grading

I think sometimes it takes a while for the grade to update, so if you wait a bit it should update!
by Darlene Lien 3E
Thu Dec 10, 2020 11:14 am
Forum: Conjugate Acids & Bases
Topic: HW 6C.17
Replies: 3
Views: 23

Re: HW 6C.17

Hi, I think you're supposed to look at Table 6C.2 to get the kB values!
by Darlene Lien 3E
Mon Dec 07, 2020 11:39 pm
Forum: Bronsted Acids & Bases
Topic: electronegativity and acidity
Replies: 3
Views: 30

Re: electronegativity and acidity

Hi, I think that in this case HI is actually a stronger acid than HCl because you would compare the bond length first before looking at electronegativity. The HCl bond length is longer/weaker which allows it to lose H+ more easily; therefore, HI is a stronger acid than than HCl.
by Darlene Lien 3E
Mon Dec 07, 2020 11:32 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 10 Review Sessions
Replies: 7
Views: 83

Re: Week 10 Review Sessions

I think they should be an hour each since they're held during what would have been the TA's office hours, which is only an hour long.
by Darlene Lien 3E
Mon Dec 07, 2020 11:30 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: edta ligand
Replies: 2
Views: 30

Re: edta ligand

I believe it has a -4 charge.
by Darlene Lien 3E
Mon Dec 07, 2020 11:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Ebook/Textbook problems
Replies: 9
Views: 88

Re: Ebook/Textbook problems

I've had the same issue too! I think I let it it set there for a while, and it randomly came back.
by Darlene Lien 3E
Mon Dec 07, 2020 5:01 pm
Forum: Bronsted Acids & Bases
Topic: Sapling #6 week 10
Replies: 4
Views: 68

Re: Sapling #6 week 10

Also, most of the time, acids begin with a Hydrogen. So, HCN is a weak acid. Hope this helps!
by Darlene Lien 3E
Mon Dec 07, 2020 4:57 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: From pOH- to [H+]
Replies: 3
Views: 28

Re: From pOH- to [H+]

Hi, there are two ways you could do this.

The first way is:
1. Find the pH from the given pOH. pH=14-pOH.
2. Solve for [H+] from the formula pH=-log[H+]

The second way is:
1. Solve for [OH-] from the formula pOH=-log[OH-]
2. Solve for [H+] from the formula [H+]=(1x10^-14)/[OH-]

Hope this helps!
by Darlene Lien 3E
Mon Dec 07, 2020 10:08 am
Forum: Administrative Questions and Class Announcements
Topic: Lecture Videos Not Playing [ENDORSED]
Replies: 16
Views: 139

Re: Lecture Videos Not Playing [ENDORSED]

Hi, the same thing is happening to me too!
by Darlene Lien 3E
Sun Dec 06, 2020 2:15 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Does pH indicate strength of an acid?
Replies: 26
Views: 148

Re: Does pH indicate strength of an acid?

Yes, since pH measures the concentration of hydrogen ions in a solution, strong acids fully dissociate; thus, strong acids typically have a lower pH. Hope this helps!
by Darlene Lien 3E
Mon Nov 30, 2020 10:14 pm
Forum: Naming
Topic: Tips for Naming Coordination Compounds
Replies: 6
Views: 50

Re: Tips for Naming Coordination Compounds

Hi, I personally don't have any strategies, but I found it a little easier the more I did the practice problems. Also, there might be YouTube videos that you could search up that could give tips on naming the coordination compounds. Hope this helps!
by Darlene Lien 3E
Mon Nov 30, 2020 5:07 pm
Forum: Naming
Topic: Naming Conventions for Polyatomic Ion Ligands
Replies: 2
Views: 25

Re: Naming Conventions for Polyatomic Ion Ligands

Definitely check Toolbox 9C.1 since it goes more into depth for naming coordination compounds!
by Darlene Lien 3E
Mon Nov 30, 2020 4:52 pm
Forum: Naming
Topic: Ferrate v Iron
Replies: 7
Views: 79

Re: Ferrate v Iron

I believe ferrate will always be used because for some metals, Latin names are used, and iron is one of them. Hope this helps!
by Darlene Lien 3E
Mon Nov 30, 2020 4:41 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling #5 for Week 9
Replies: 4
Views: 59

Re: Sapling #5 for Week 9

Hi, also, I think Dr. Lavelle posted a worksheet on his website that would help with naming coordination compounds, so definitely check that out! Hope this helps!
by Darlene Lien 3E
Tue Nov 24, 2020 11:51 am
Forum: Administrative Questions and Class Announcements
Topic: Final Exam Date
Replies: 21
Views: 219

Re: Final Exam Date

Helena Hu 3E wrote:Will week 10 be review then?

I'm not entirely sure if Week 10 will be review, but I would assume that if anything we'll be wrapping up all the topics by then.
by Darlene Lien 3E
Tue Nov 24, 2020 11:50 am
Forum: Student Social/Study Group
Topic: Exercising Our Minds and Bodies
Replies: 103
Views: 516

Re: Exercising Our Minds and Bodies

I normally go out on afternoon jogs or evening walks! It really helps to clear out your mind :)
by Darlene Lien 3E
Tue Nov 24, 2020 11:47 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling Question #1
Replies: 7
Views: 52

Re: Sapling Question #1

Hi, so for sulfite ion, when you draw the Lewis structure, you would have a VSEPR formula of AX3E, which is trigonal pyramidal (sulfur as the central atom with one double bonded oxygen, 2 single bonded oxygens, and one lone pair on sulfur). A tetrahedral shape would have a formula of AX4 (no lone pa...
by Darlene Lien 3E
Tue Nov 24, 2020 11:42 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2 Results
Replies: 10
Views: 125

Re: Midterm 2 Results

Also, I believe he'll send out an email once the results are out!
by Darlene Lien 3E
Tue Nov 24, 2020 11:38 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook Section 2E Exercise glitch
Replies: 3
Views: 35

Re: Textbook Section 2E Exercise glitch

Hi, I also had that problem, and even if it doesn't show up after you refresh the page, I think if you wait a bit it'll appear normally. Hope this helps!
by Darlene Lien 3E
Fri Nov 20, 2020 5:52 pm
Forum: Octet Exceptions
Topic: textbook 2C.3 d)
Replies: 4
Views: 47

Re: textbook 2C.3 d)

Hi, I agree with the comment above. Since oxygen is more electronegative, it should have the more negative formal charge. Therefore, it would be better if arsenic's formal charge is 0, so there should only be one double bond in total. Hope this helps!
by Darlene Lien 3E
Fri Nov 20, 2020 5:47 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14BL
Replies: 5
Views: 56

Re: Chem 14BL

Hi, to add on, I think it's also pretty common for people to take Chem 14B and 14BL separately! I wouldn't worry about it if you can't take them together :)
by Darlene Lien 3E
Fri Nov 20, 2020 5:41 pm
Forum: Administrative Questions and Class Announcements
Topic: Question about Chem Community Posts
Replies: 5
Views: 65

Re: Question about Chem Community Posts

Hi, since you could get a max of 5 points from 5 posts each week, I think by the end of Week 7, you should have at least 35 posts. Hope this helps!
by Darlene Lien 3E
Fri Nov 20, 2020 5:39 pm
Forum: Lewis Structures
Topic: Midterm Q
Replies: 2
Views: 48

Re: Midterm Q

Hi, I believe that since we haven't covered nomenclature, we wouldn't have to know the names of them. However, for more common ones especially, it would be good to know. Hope this helps!
by Darlene Lien 3E
Fri Nov 20, 2020 5:36 pm
Forum: Bond Lengths & Energies
Topic: Boiling vs. Melting Point
Replies: 15
Views: 102

Re: Boiling vs. Melting Point

Hi, to add on, I think for this unit with IMF, the main idea that we should get from it is that boiling points and melting points follow the same trend, where a stronger IMF=higher boiling/melting point. Hope this helps!
by Darlene Lien 3E
Wed Nov 18, 2020 8:32 pm
Forum: Student Social/Study Group
Topic: CHEM 14B Time Conflict
Replies: 13
Views: 163

Re: CHEM 14B Time Conflict

Hi, also, I believe it was also mentioned that there is a possibility of having midterm exams during the lecture times and not discussions as well. To be safe, it is best to avoid class conflicts. Hope this helps!
by Darlene Lien 3E
Wed Nov 18, 2020 8:06 pm
Forum: Ionic & Covalent Bonds
Topic: Covalent character and solubility
Replies: 5
Views: 57

Re: Covalent character and solubility

Hi, if I believe the greater the ionic character (less covalent character), the more soluble the compound is. In other words, more polarizable = more covalent = less soluble, less polarizable = more ionic = more soluble. Also, since larger anions are more polarizable, this would mean that smaller an...
by Darlene Lien 3E
Wed Nov 11, 2020 5:33 pm
Forum: Administrative Questions and Class Announcements
Topic: Audio-Visual Modules for MD 2 Material?
Replies: 5
Views: 48

Re: Audio-Visual Modules for MD 2 Material?

Hi, from what I've heard, I don't think there will be anymore Audio-Visual modules since I think Dr. Lavelle mentioned that they take a lot of time and work to make.
by Darlene Lien 3E
Wed Nov 11, 2020 1:59 pm
Forum: Administrative Questions and Class Announcements
Topic: Step-Up Sessions
Replies: 3
Views: 32

Re: Step-Up Sessions

I believe they are still being held!
by Darlene Lien 3E
Wed Nov 11, 2020 1:57 pm
Forum: Dipole Moments
Topic: Energy Released from LDFs
Replies: 2
Views: 20

Re: Energy Released from LDFs

I'm not exactly sure if it is at STP, but I think -2 kJ/mol for LDF is just the typical energy released.
by Darlene Lien 3E
Wed Nov 11, 2020 1:51 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: F-block?
Replies: 7
Views: 61

Re: F-block?

I don't think we have to know how to write the electron configuration for an element in the f block, but let's say the element is in the 6p block, for example, then we would have to include 4f in the electron configuration, if that makes sense.
by Darlene Lien 3E
Wed Nov 11, 2020 1:48 pm
Forum: Octet Exceptions
Topic: Texbook Questions 2C1
Replies: 6
Views: 30

Re: Texbook Questions 2C1

By definition, a radical has an unpaired electron, so typically when you see odd numbers of valence electrons this could kind of tell you that it is a radical. For NO2-, there are a total of 18 valence electrons and the Lewis structure is drawn with N as the central atom with a double-bonded O and s...
by Darlene Lien 3E
Wed Nov 11, 2020 1:38 pm
Forum: Dipole Moments
Topic: Negative Energy
Replies: 4
Views: 55

Re: Negative Energy

To add on, this has to do with the law of conservation of energy. So, when energy is used to break a bond, energy is also released when the bonds are broken. Hope this helps!
by Darlene Lien 3E
Wed Nov 11, 2020 1:33 pm
Forum: Dipole Moments
Topic: Dipole Dipole vs Induce Dipole Induced Dipole
Replies: 2
Views: 15

Re: Dipole Dipole vs Induce Dipole Induced Dipole

I believe this has to do with the idea of polarity. Hydrocarbons typically are nonpolar, and therefore, would have induced dipole-induced dipole forces. However, in HF, the structure is polar and has partial charges: a partial positive on H and a partial negative on F; as a result, HF has dipole dip...
by Darlene Lien 3E
Wed Nov 11, 2020 1:30 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
Replies: 5
Views: 54

Re: Hydrogen Bonding

I believe that in order for hydrogen bonding to occur, two things have to happen:

1. In the first molecule, Hydrogen is attached to N, O, or F.
2. In the second molecule, there has to be a lone pair on either N, O, or F.

Hope this helps!
by Darlene Lien 3E
Wed Nov 04, 2020 11:25 am
Forum: Lewis Structures
Topic: Line in place of paired dots
Replies: 8
Views: 43

Re: Line in place of paired dots

Hi, based on the examples in the lecture, I think it would be best to use dots to represent the lone pair electrons and lines to represent the bonds.
by Darlene Lien 3E
Wed Nov 04, 2020 11:19 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and Stability
Replies: 7
Views: 20

Re: Formal Charge and Stability

Hi, I agree with the comment above about how resonance structures are essentially just changing positions of the bonds. A formal charge of 0 would be most stable. Hope this helps!
by Darlene Lien 3E
Wed Nov 04, 2020 11:18 am
Forum: Lewis Structures
Topic: Lewis Acid-Base
Replies: 6
Views: 41

Re: Lewis Acid-Base

Hi, to add on, I don't think a double bond would work as well because then the formal charge for the double bonded Fluorine would be +1 as opposed to 0. Hope this helps!
by Darlene Lien 3E
Wed Nov 04, 2020 11:14 am
Forum: Properties of Light
Topic: Study Advice
Replies: 50
Views: 295

Re: Study Advice

I would recommend going to the UA sessions if you are unsure about certain topics. The UA sessions really help especially if you're having trouble on a topic. Hope this helps!
by Darlene Lien 3E
Mon Nov 02, 2020 8:04 pm
Forum: Student Social/Study Group
Topic: Post Midterm Blues
Replies: 71
Views: 614

Re: Post Midterm Blues

I love this thread! Don't worry, we all got this!!
by Darlene Lien 3E
Mon Nov 02, 2020 8:01 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm 1
Replies: 9
Views: 119

Re: Midterm 1

Hi, Dr. Lavelle mentioned during today's discussion section that it should be up on Thursday!
by Darlene Lien 3E
Thu Oct 29, 2020 12:21 pm
Forum: DeBroglie Equation
Topic: Problem 1B.5
Replies: 3
Views: 43

Re: Problem 1B.5

Hi, for this problem E=(1/2)mv^2 and de Broglie's equation won't work because this problem concerns photons. E=(1/2)mv^2 involves the kinetic energy of an electron while de Broglie's equation is used for electrons/things with mass (not photons). Therefore, you should use E=hv and c=(lambda)v or lamb...
by Darlene Lien 3E
Wed Oct 28, 2020 8:38 pm
Forum: General Science Questions
Topic: practice problem E15 help
Replies: 2
Views: 30

Re: practice problem E15 help

Hi, I was confused with this problem as well! I think it is essentially asking you to first solve for the mystery metal, M. Then you would find the molar mass of the metal sulfide, so Mystery metal + Sulfur. First, you would solve for the molar mass of (OH)2, which would be 34.02 g/mol. Then you wou...
by Darlene Lien 3E
Wed Oct 28, 2020 8:12 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect post module
Replies: 4
Views: 64

Re: Photoelectric Effect post module

Hi, for this question the work function is given and since kinetic energy equals to 0, the energy per photon is equal to the work function. Therefore, you could solve for the wavelength by using the formula lambda=hc/E, where E=3.607E-19 J. Hope this helps!
by Darlene Lien 3E
Tue Oct 27, 2020 8:08 pm
Forum: Properties of Electrons
Topic: Sapling hw #13
Replies: 3
Views: 86

Re: Sapling hw #13

Hi, for this problem to find the energy of the electron, you would first use de Broglie's wave equation to solve for the velocity of the electron, but make sure to convert the micrometers to meters first! Then you would use the velocity you get, and plug it into the kinetic energy formula, E=(1/2)mv...
by Darlene Lien 3E
Tue Oct 27, 2020 8:02 pm
Forum: SI Units, Unit Conversions
Topic: Temperature Conversions
Replies: 6
Views: 71

Re: Temperature Conversions

Hi, although we probably don't need to use temperature conversions now, I think either way it would be good to know the conversions since there are only a few.
by Darlene Lien 3E
Tue Oct 27, 2020 7:47 pm
Forum: Administrative Questions and Class Announcements
Topic: UA Worksheet Answers
Replies: 7
Views: 80

Re: UA Worksheet Answers

Hi, I think some of the UA worksheets might have answer keys available, but for the most part, in order to get the answers you have to attend the UA session. Hope this helps!
by Darlene Lien 3E
Tue Oct 20, 2020 11:33 pm
Forum: Photoelectric Effect
Topic: Textbook 1B.7, joules per atom
Replies: 3
Views: 69

Re: Textbook 1B.7, joules per atom

Hi, 3.37 x 10^-19 J was the energy you get from part a. Hope this helps.
by Darlene Lien 3E
Tue Oct 20, 2020 11:31 pm
Forum: Administrative Questions and Class Announcements
Topic: Formula Sheet
Replies: 2
Views: 18

Re: Formula Sheet

Hi, I believe he will also send out an updated one on Wednesday!
by Darlene Lien 3E
Mon Oct 19, 2020 4:35 pm
Forum: Limiting Reactant Calculations
Topic: Study for these types of problems
Replies: 6
Views: 42

Re: Study for these types of problems

Another good way to get practice problems might be to google them. There are a lot of good practice problems on the web, so I'm sure just searching them up would be a good way to get practice problems. Hope this helps!
by Darlene Lien 3E
Mon Oct 19, 2020 3:17 pm
Forum: General Science Questions
Topic: Webcams
Replies: 17
Views: 128

Re: Webcams

Hi, the webcams are highly recommended. There are a lot of good webcams on Amazon, and I think anything with 4+ stars should be sufficient. Hope this helps!
by Darlene Lien 3E
Mon Oct 19, 2020 3:14 pm
Forum: Properties of Light
Topic: Sapling HW Week 2, 3, 4 Question #7
Replies: 10
Views: 118

Re: Sapling HW Week 2, 3, 4 Question #7

Hi, the equation used to find the energy per photon is E=hc/lambda which is a combination of E=hv and c=v(lambda). Hope this helps!
by Darlene Lien 3E
Mon Oct 19, 2020 2:59 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Sapling week 2/3 question 8
Replies: 3
Views: 37

Re: Sapling week 2/3 question 8

Hi, to add on, when using the Rydberg equation v=R[(1/n1^2)-1/n2^2)], the n2 value should be the value you're solving for, and n1=2. I wanted to just clarify since putting in the wrong values for n would result in different answers. Hope this helps, too!
by Darlene Lien 3E
Mon Oct 19, 2020 12:48 pm
Forum: Photoelectric Effect
Topic: What is equation is this ?
Replies: 11
Views: 76

Re: What is equation is this ?

c= 3.00x10^8 m/s is the speed of light. In the lecture today, it was used to derive the de Broglie equation.
by Darlene Lien 3E
Mon Oct 19, 2020 12:46 pm
Forum: Photoelectric Effect
Topic: Units of the Work Function
Replies: 7
Views: 50

Re: Units of the Work Function

As with what the others said, the units of the work function should be Joules (or Joules per electron), but if you are asked in terms of moles then you would most likely have to use Avogradro's number accordingly. Hope this helps!
by Darlene Lien 3E
Mon Oct 12, 2020 6:35 pm
Forum: Properties of Electrons
Topic: protons and electrons
Replies: 33
Views: 191

Re: protons and electrons

They have different masses!
The mass of an electron is 9.109 x 10^-31 kg. The mass of a proton is 1.672 x 10^-27 kg. The mass of a neutron is 1.674 x 10^-27 kg.
by Darlene Lien 3E
Mon Oct 12, 2020 1:48 pm
Forum: Properties of Light
Topic: E(photon) >/= E(energy remove e-) Clarification
Replies: 2
Views: 37

Re: E(photon) >/= E(energy remove e-) Clarification

No, E(photon)>E(remove e-) is correct as is. I think the phrasing might be the part that is a little confusing to comprehend because of "unless," but it could help if you read the statement as "e- is not emitted even for high intensity light unless E(photon)>E(remove e-)." Hope t...
by Darlene Lien 3E
Mon Oct 12, 2020 1:40 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 5
Views: 61

Re: Photoelectric Effect

In simple terms, the energy of a photon + the energy required to remove an electron = the energy of the removed electron (the excess/what remains). Hope this helps!
by Darlene Lien 3E
Mon Oct 12, 2020 1:33 pm
Forum: Quantum Numbers and The H-Atom
Topic: high intensity light
Replies: 3
Views: 59

Re: high intensity light

The key idea to note from this is that each photon must have enough energy to remove an electron. In addition, we must consider the idea that one photon interacts with one electron. Increasing the intensity/amplitude of the light only increases the number of photons, not the energy of each individua...
by Darlene Lien 3E
Mon Oct 12, 2020 1:23 pm
Forum: Photoelectric Effect
Topic: Solving photoelectric effect questions
Replies: 4
Views: 31

Re: Solving photoelectric effect questions

So does the fact that the work function is in kJ instead of J.mol^1 not apply to this question? For part b when it asks for the energy required to remove an electron from one sodium atom, then the unit conversion would matter. You would have to convert the work function from kJ to J. In part a, the...
by Darlene Lien 3E
Mon Oct 12, 2020 1:13 pm
Forum: Photoelectric Effect
Topic: Solving photoelectric effect questions
Replies: 4
Views: 31

Re: Solving photoelectric effect questions

Hi, there is no need for a unit change for that part of the question. To solve for the kinetic energy of the ejected electron you would use the formula: E=(1/2)mv^2. m=mass of an electron which is known to be 9.109x10^-31 kg v=6.61x10^5 m/s You would then plug these values into the formula according...
by Darlene Lien 3E
Mon Oct 12, 2020 1:00 pm
Forum: Properties of Light
Topic: Properties of light
Replies: 3
Views: 47

Re: Properties of light

The correct answer I believe is "wave, particle." Hope this helps!
by Darlene Lien 3E
Mon Oct 12, 2020 12:59 pm
Forum: Administrative Questions and Class Announcements
Topic: chem community posts
Replies: 3
Views: 59

Re: chem community posts

Yes, I personally use what the above comment says to check how many/what my posts were. "Quick links" --> "Your posts"
It should show all of the posts that you made on Chemistry Community. Hope this helps!
by Darlene Lien 3E
Tue Oct 06, 2020 11:41 am
Forum: SI Units, Unit Conversions
Topic: Rounding in Between Steps [ENDORSED]
Replies: 22
Views: 204

Re: Rounding in Between Steps [ENDORSED]

Hi, I believe that you wouldn't round in between steps until your final answer. This would make your answer as accurate as possible. Hope this helps!
by Darlene Lien 3E
Tue Oct 06, 2020 11:31 am
Forum: Molarity, Solutions, Dilutions
Topic: HW G.17
Replies: 3
Views: 79

Re: HW G.17

Hi, personally, what helped was to first look at the given information and try to apply it to what you know about the topic. Given: volume of CuSO4 (250 mL), molarity of CuSO4 (0.20 M), molar mass of CuSO4 (calculate to get 159.62 g/mol) Want: mass of CuSO4 (g) By looking at this, we know that we ne...
by Darlene Lien 3E
Tue Oct 06, 2020 11:12 am
Forum: Significant Figures
Topic: Tips for counting sig figs?
Replies: 9
Views: 86

Re: Tips for counting sig figs?

Hi, in case you wanted to refer back to tips for sig figs, you could visit Dr. Lavelle's website! There's a pdf titled "Everything you want to know about sig fig" explaining sig figs in depth. Hope this helps!
by Darlene Lien 3E
Tue Oct 06, 2020 11:10 am
Forum: Significant Figures
Topic: Sig Figs for Molar Mass
Replies: 14
Views: 115

Re: Sig Figs for Molar Mass

Personally, I've been using two decimal places as well for the molar masses, and my answer hasn't been off by too much. I think either should work. Hope this helps!
by Darlene Lien 3E
Tue Oct 06, 2020 11:05 am
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant and Limiting Reagent
Replies: 7
Views: 96

Re: Limiting Reactant and Limiting Reagent

Hi, just in case you wanted to refer back, I believe in the third Audio-Visual Focus topic (Limiting Reactant Calculations) Dr. Lavelle mentioned that limiting reactants and limiting reagents could be used interchangeably. Hope this helps!
by Darlene Lien 3E
Mon Oct 05, 2020 4:35 pm
Forum: Limiting Reactant Calculations
Topic: L35
Replies: 2
Views: 66

Re: L35

Yes! If you check Dr. Lavelle's website, there is a link to textbook errors titled "Solution Manual Errors 7th Edition."

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