Search found 17467 matches

by Chem_Mod
Mon Oct 07, 2019 3:21 pm
Forum: Balancing Chemical Reactions
Topic: Homework Question H21
Replies: 5
Views: 51

Re: Homework Question H21

For this problem, start by balancing the N because it appears the least, then H, then C, then lastly balance the O. Hope this helped.
by Chem_Mod
Mon Oct 07, 2019 3:20 pm
Forum: Properties of Electrons
Topic: Balmer and Lyman series
Replies: 2
Views: 41

Re: Balmer and Lyman series

When an electron makes a transition from a higher energy state (higher n) to a lower energy state (lower n), it releases energy in the form of a light photon. Any transitions from higher energy levels to level n=2 correspond to the balmer series which generally releases the light with energy equival...
by Chem_Mod
Mon Oct 07, 2019 3:14 pm
Forum: Empirical & Molecular Formulas
Topic: Combustion Analysis
Replies: 1
Views: 80

Re: Combustion Analysis

This is not an assigned textbook problem as it is beyond the scope of the class. You won't have to worry about this type of question, but if you are interested, here is a brief walkthrough: Assume you have 100 g total of the precipitated substance (of this 100g, an unknown percentage is C14H20O2N an...
by Chem_Mod
Mon Oct 07, 2019 3:11 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Total Coulombic potential energy
Replies: 1
Views: 24

Re: Total Coulombic potential energy

F=k(Q^2)/(r^2). Q is the charge of the particle. There are two charges and therefore two Q values which are either positive negative or zero. k is a constant. Both of these two parameters are directly proportional to the Force of the bond between them. r denotes the distance between both particles a...
by Chem_Mod
Mon Oct 07, 2019 3:04 pm
Forum: Molarity, Solutions, Dilutions
Topic: E.13
Replies: 2
Views: 40

Re: E.13

Whenever you post a homework problem, please include the entire question, along with the edition of the textbook, and not just the question number.
by Chem_Mod
Mon Oct 07, 2019 3:02 pm
Forum: Balancing Chemical Reactions
Topic: Homework Question H21
Replies: 5
Views: 51

Re: Homework Question H21

If you are ever posting a homework problem on Chemistry Community, please post the entire question and not just the question number.
by Chem_Mod
Mon Oct 07, 2019 3:01 pm
Forum: Limiting Reactant Calculations
Topic: M11: Grams vs. Moles in Intermediate Calculations
Replies: 1
Views: 27

Re: M11: Grams vs. Moles in Intermediate Calculations

I would go back and check that the molar masses you used are correct because those values are off by a significant amount; this is not typical of a result of using moles vs. grams.
by Chem_Mod
Mon Oct 07, 2019 3:00 pm
Forum: Photoelectric Effect
Topic: Kinetic Energy
Replies: 1
Views: 27

Re: Kinetic Energy

The kinetic energy can be used in calculations in the photoelectric effect, such as with Photon Energy, Work Function, and KE.
by Chem_Mod
Mon Oct 07, 2019 2:59 pm
Forum: Photoelectric Effect
Topic: light as wave or photon
Replies: 1
Views: 32

Re: light as wave or photon

Light has both wave and particle properties. In photoelectric effect questions and for atomic spectra, we think of light as photons, though it will always have wavelike properties. In this case, it would help to think of light as a photon. Photons interact with electrons in a one-on-one interaction,...
by Chem_Mod
Mon Oct 07, 2019 12:20 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student [ENDORSED]
Replies: 133
Views: 83092

Re: Advice from a Medical Student [ENDORSED]

Jaklin Astvatsatryan 3G wrote:Thank you for the advice!! Update us on how Med school is going.


Check out my other post "Advice from a Medical Student - Part II". I just posted it and it is a two year update regarding clinical rotations and how it's different than lectures the first two years of medical school.
by Chem_Mod
Mon Oct 07, 2019 12:19 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student [ENDORSED]
Replies: 133
Views: 83092

Re: Advice from a Medical Student [ENDORSED]

Do you have any advice for professors who are not as accommodating as Lavelle? Did you ever struggle in a specific class because of a lack of resources/support? With other courses, you need to find a way to get your questions answered. It's harder because there isn't a 24/7 forum like Chemistry Com...
by Chem_Mod
Mon Oct 07, 2019 12:17 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

Thank you so much for sharing. I am also thinking about Medical school -- as someone who has already gone through it, do you recommend doing anything specific as an undergraduate to make a Medical School application especially stand out? I know it is extremely competitive. Thank you again for your ...
by Chem_Mod
Mon Oct 07, 2019 12:14 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

wow that's so cool. Do you have advice for first years who want to potentially go to grad school and become physicians? I'd probably say focus on your academics; medical schools want to make sure that if accepted you will be able to pass and so they will pick applicants who they think have a strong...
by Chem_Mod
Mon Oct 07, 2019 12:11 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

It was super inspiring and motivating to hear your experience as a medical student! As a first year premed, I'm wondering how you were able to balance your social and academic life? Honestly, first year (at least first quarter) was tough. I wanted to start off strong and figure out how this quarter...
by Chem_Mod
Mon Oct 07, 2019 12:08 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

Rich Zodda 4B wrote:Thank you so much. This was probably the most helpful post I've read so far


Thank you so much for that feedback. If you have any questions, feel free to ask. I'm happy to guide you :)
by Chem_Mod
Mon Oct 07, 2019 9:16 am
Forum: Administrative Questions and Class Announcements
Topic: Grades
Replies: 4
Views: 52

Re: Grades

You mean HW score.
Collect it in discussion section this week, or on MyUCLA.
by Chem_Mod
Mon Oct 07, 2019 12:34 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra
Replies: 3
Views: 30

Re: Atomic Spectra

Dr. Lavelle will address atomic spectra later this week.
by Chem_Mod
Mon Oct 07, 2019 12:21 am
Forum: Balancing Chemical Reactions
Topic: H 1
Replies: 5
Views: 54

Re: H 1

In the future, please try typing your chemical equation like this: Cu + SO2 --> CuO + S, separating the reactants and products as well as keeping compound subscripts attached to the element symbols. Otherwise it makes it extremely hard to read. You can't just add an O to the products side because th...
by Chem_Mod
Mon Oct 07, 2019 12:14 am
Forum: Limiting Reactant Calculations
Topic: L 35 Textbook Typo [ENDORSED]
Replies: 4
Views: 59

Re: L 35 Textbook Typo [ENDORSED]

For more solution manual errors see the "Solution Manual Errors 7th Edition" tab on the class website: https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf
by Chem_Mod
Sun Oct 06, 2019 10:34 pm
Forum: SI Units, Unit Conversions
Topic: Calculate using kg or g?
Replies: 5
Views: 31

Re: Calculate using kg or g?

The kg is the SI unit of mass and you will have to convert most masses to kg for calculations. However, this will depend on the question asked and what you are solving for.
by Chem_Mod
Sun Oct 06, 2019 10:28 pm
Forum: SI Units, Unit Conversions
Topic: Calculators Permitted on the Test
Replies: 2
Views: 22

Re: Calculators Permitted on the Test

Calculators that are non-programmable and non-graphing are permitted on exams.
by Chem_Mod
Sun Oct 06, 2019 10:25 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Formula Unit
Replies: 3
Views: 37

Re: Formula Unit

A formula unit refers to the lowest whole number ratio of ions in an ionic compound. For example, NaCl is the formula unit for the ionic compound sodium chloride. 1 mole contains 6.022 X 10^23 of any units (formula units included).
by Chem_Mod
Sun Oct 06, 2019 10:19 pm
Forum: Administrative Questions and Class Announcements
Topic: KAREN SUN 5-7PM WORKSHOP - DOWNLAOD WORKSHEETS HERE
Replies: 25
Views: 405

Re: KAREN SUN 5-7PM WORKSHOP - DOWNLAOD WORKSHEETS HERE

Do we have to sign up for your workshops or are students welcome to just show up? No sign ups needed! Just show up. Are these questions representative of how Test 1 will be? I wrote these questions based on my experience with Dr. Lavelle over the years and some questions were adapted from old exams...
by Chem_Mod
Sun Oct 06, 2019 10:14 pm
Forum: SI Units, Unit Conversions
Topic: Avogadro's Number
Replies: 4
Views: 38

Re: Avogadro's Number

Avogadro's number refers to the number of units in one mole of a substance, equal to 6.022 X 10^23. The units may be formula units, atoms, ions, or molecules depending on the nature of the substance.
by Chem_Mod
Sun Oct 06, 2019 8:59 pm
Forum: Balancing Chemical Reactions
Topic: Include Catalysts in Balanced Chemical Equations?
Replies: 2
Views: 25

Re: Include Catalysts in Balanced Chemical Equations?

Catalysts are not included in the balanced chemical equation as they are not consumed nor produced in the reaction. Catalysts lower the activation energy of a reaction, increasing the reaction rate. This is outside the scope of 14A though; you'll learn more about catalysts and reaction rates in 14B.
by Chem_Mod
Sun Oct 06, 2019 8:55 pm
Forum: Balancing Chemical Reactions
Topic: Steps of question L35
Replies: 1
Views: 22

Re: Steps of question L35

The goal here is to convert our initial unit, tons of NaBr, to our final unit, g/kg of Fe. In order to do this, you need to use the stoichiometric coefficients of the balanced reactions to find the mole ratios of the compounds. Keep in mind here that this is a 3-step reaction, so the product of one ...
by Chem_Mod
Sun Oct 06, 2019 8:46 pm
Forum: Limiting Reactant Calculations
Topic: Homework M. 15
Replies: 3
Views: 34

Re: Homework M. 15

Cl2 is actually the limiting reactant as it produces a theoretical yield of 671g, not 6710g as mentioned in the answer above. The work/steps are correct but there must have been some calculation mistake at the end. Hope this clears things up.
by Chem_Mod
Sun Oct 06, 2019 6:03 pm
Forum: Photoelectric Effect
Topic: Explaining Photoelectric Effect
Replies: 1
Views: 14

Re: Explaining Photoelectric Effect

Scientists shone a light, which has energy on a metal. That light energy is stored in discrete packets called photons. If the photon has enough energy, then one photon can eject one electron from the metal. If you have a light with weak photons and turn up the Intensity, you are not making the photo...
by Chem_Mod
Sun Oct 06, 2019 5:58 pm
Forum: Significant Figures
Topic: Inaccurate Answer
Replies: 1
Views: 29

Re: Inaccurate Answer

Continue using the values given in your periodic table, but the solutions manual may be using a less accurate periodic table. Such as your Oxygen is 15.994 while the Solutions Manual may use Oxygen as 16. Given that you are off in the .01 digit, there is no need to worry because that is just a diffe...
by Chem_Mod
Sun Oct 06, 2019 5:55 pm
Forum: *Black Body Radiation
Topic: Black Body Radiation
Replies: 10
Views: 38

Re: Black Body Radiation

Black body radiation is more of physics experiment and is unnecessary to know for this course. Of course, you may investigate what it is for your own enjoyment.
by Chem_Mod
Sun Oct 06, 2019 5:51 pm
Forum: Properties of Light
Topic: Wave-particle duality
Replies: 1
Views: 22

Re: Wave-particle duality

As you will see in an upcoming lecture, Dr. Lavelle will go more in depth in de Broglie's equation, which considers the wave-particle duality you are talking about. As objects become large, like a baseball vs something atomic, they lose wave behaviors.
by Chem_Mod
Sun Oct 06, 2019 5:50 pm
Forum: SI Units, Unit Conversions
Topic: Peer Learning [ENDORSED]
Replies: 2
Views: 27

Re: Peer Learning [ENDORSED]

1. They are great! :-)

2. There is no enrollment. Go to any that suit your schedule. I made it this way to make it flexible and helpful.
by Chem_Mod
Sun Oct 06, 2019 5:49 pm
Forum: Einstein Equation
Topic: Kinetic Energy
Replies: 3
Views: 41

Re: Kinetic Energy

KE= .5mv^2

We are given the velocity and the mass of an electron is provided in the constants & equations sheet. This equation is also given in that sheet, no need to memorize anything here.
by Chem_Mod
Sun Oct 06, 2019 5:45 pm
Forum: Properties of Light
Topic: Unit of Wavelength Amplitude
Replies: 2
Views: 22

Re: Unit of Wavelength Amplitude

To clarify, we are not very interested in the amplitude/height of waves, although this would probably be measured in meters. We are more concerned with the frequency (cycles per second) and wavelength (the distance between peaks, in meters) aka lambda.
by Chem_Mod
Sun Oct 06, 2019 5:44 pm
Forum: Balancing Chemical Reactions
Topic: HW problem H11
Replies: 4
Views: 30

Re: Balancing Equation

Balance the Fe and C first, because they are the "simplest" ones because they only appear once on each side. Now you should have 5 O on left and 2 O on right. Because the right side Oxygen's can only increase in multiples of 2 (from CO2), you must find the least common multiple of 2. the l...
by Chem_Mod
Sun Oct 06, 2019 5:41 pm
Forum: Properties of Light
Topic: HW help
Replies: 2
Views: 40

Re: HW help

For 1A.7, if you recall, for any wave model the product of the frequency and wavelength equals a constant. For the wave model of light, the relationship is frequency (in Hz) x wavelength (in m) = speed of light (~3.00x10^8 m/s). You will have a better understanding of how to answer 1b.3 after Monday...
by Chem_Mod
Sun Oct 06, 2019 5:32 pm
Forum: Balancing Chemical Reactions
Topic: Alternative to Guess and Check?
Replies: 5
Views: 24

Re: Alternative to Guess and Check?

Yes there is an effective way. Balance the simplest species first and then move on to the harder ones. By simplest, I mean which appears the least amount of times on each side of an equation. Take this typical combustion reaction-which you should know the reactants and products of. CH4 + O2 ==> CO2 ...
by Chem_Mod
Sun Oct 06, 2019 5:30 pm
Forum: Limiting Reactant Calculations
Topic: Homework M.11
Replies: 3
Views: 46

Re: Homework M.11

The easiest way to solve this problem is the use the Law of Conservation of Mass (in chemical reactions). Since oxygen is the limiting reactant, it is completely consumed in the reaction, leaving your product (P4O10) and the excess reactant (P4O6). You should have already solved for the mass of P4O1...
by Chem_Mod
Sun Oct 06, 2019 5:26 pm
Forum: Limiting Reactant Calculations
Topic: Net Ionic Equation
Replies: 6
Views: 51

Re: M9

A net ionic reaction is an equation listing only the species involved in the reaction. In this case, the question wants us to examine the product of Cu(II)OH, wo we should only examine these species in our net ionic equation. Thus we can leave out the nitrate and sodium because it is not seen in Cu(...
by Chem_Mod
Sun Oct 06, 2019 5:17 pm
Forum: Limiting Reactant Calculations
Topic: Step two in limiting reactants
Replies: 3
Views: 21

Re: Step two in limiting reactants

The question asks you to find the percent yield of carbon dioxide. Therefore, you need to calculate the theoretical yield of carbon dioxide by converting the moles of octane to grams of carbon dioxide using the mole ratio of octane to carbon dioxide in the balanced chemical equation. Had the questio...
by Chem_Mod
Sun Oct 06, 2019 5:16 pm
Forum: SI Units, Unit Conversions
Topic: Formula Units
Replies: 3
Views: 20

Re: Formula Units

It is one entity of a substance, a unit for a formula, like 1 H2O molecule. The way we use them in our course, they are synonymous with molecules or atoms in the sense that they are associated with Avogadro's number.
by Chem_Mod
Sun Oct 06, 2019 3:53 pm
Forum: Administrative Questions and Class Announcements
Topic: KAREN SUN 5-7PM WORKSHOP - DOWNLAOD WORKSHEETS HERE
Replies: 25
Views: 405

Re: KAREN SUN 5-7PM WORKSHOP - DOWNLAOD WORKSHEETS HERE

Oduwole 1H wrote:Where will these workshops be held please?


Covel 210 Sunday 5-7pm!
by Chem_Mod
Sun Oct 06, 2019 1:30 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

Thank you so much for taking the time to share your experience with us and answer our questions! Your advice is extremely helpful and motivating. Is there anything you didn't expect to experience as a medical student that you wish you knew before starting medical school? It wasn't really an experie...
by Chem_Mod
Sun Oct 06, 2019 12:08 pm
Forum: Limiting Reactant Calculations
Topic: Showing Work for Limiting Reactant Calculations on Tests [ENDORSED]
Replies: 56
Views: 532

Re: Showing Work for Limiting Reactant Calculations on Tests [ENDORSED]

Yes

In class I usually go through worked examples step by step using and discussing concepts that assist in understanding and therefore developing a strong foundation.
by Chem_Mod
Sun Oct 06, 2019 12:05 pm
Forum: Limiting Reactant Calculations
Topic: Chem Community logistics [ENDORSED]
Replies: 4
Views: 35

Re: Chem Community logistics [ENDORSED]

Just click on your user name.
by Chem_Mod
Sun Oct 06, 2019 10:35 am
Forum: Administrative Questions and Class Announcements
Topic: Test
Replies: 2
Views: 30

Re: Test

All tests and exams are free response.
by Chem_Mod
Sun Oct 06, 2019 10:30 am
Forum: SI Units, Unit Conversions
Topic: When is Test #1?
Replies: 9
Views: 67

Re: When is Test #1?

You can find the test and exam schedule under "Test and Exam Schedule" on the class website: https://lavelle.chem.ucla.edu/wp-conten ... hedule.pdf
by Chem_Mod
Sun Oct 06, 2019 10:29 am
Forum: SI Units, Unit Conversions
Topic: When is Test #1?
Replies: 9
Views: 67

Re: When is Test #1?

You can find the test and exam schedule under "Test and Exam Schedule" on the class website: https://lavelle.chem.ucla.edu/wp-conten ... hedule.pdf
by Chem_Mod
Sun Oct 06, 2019 10:05 am
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

Loved reading about your experience! Thank you for sharing this with us but I was wondering what kept you motivated to keep going? I know a lot of people just give up because it is too difficult from or switch career paths because they think they're not able to continue with medicine. You need to m...
by Chem_Mod
Sun Oct 06, 2019 3:27 am
Forum: Limiting Reactant Calculations
Topic: M.11 Question
Replies: 1
Views: 30

Re: M.11 Question

Take this problem step-by-step. First work with the first chemical equation only. How much oxygen remains after all the phosphorus is used up? Then use this information and the second chemical reaction to find out whether P4O6 or O2 is the limiting reactant in this second reaction.
by Chem_Mod
Sun Oct 06, 2019 3:22 am
Forum: Empirical & Molecular Formulas
Topic: Limiting Reactants
Replies: 4
Views: 20

Re: Limiting Reactants

Yes, this type of question is fair game and you could expect to see it on an exam
by Chem_Mod
Sun Oct 06, 2019 3:21 am
Forum: Empirical & Molecular Formulas
Topic: Hydrates
Replies: 2
Views: 13

Re: Hydrates

We will go over hydrated compounds later in the course. For test 1 it will not be necessary to know
by Chem_Mod
Sat Oct 05, 2019 9:53 pm
Forum: Empirical & Molecular Formulas
Topic: Fundamental m.19
Replies: 3
Views: 27

Re: Fundamental m.19

Please provide the context of the problem such as what is provided and what part you need help with, not just putting what problem it is. Thank you.
by Chem_Mod
Sat Oct 05, 2019 2:55 pm
Forum: Empirical & Molecular Formulas
Topic: Is there an easier way to figure out which integer to multiply the number of atoms with to get a whole number?
Replies: 4
Views: 19

Re: Is there an easier way to figure out which integer to multiply the number of atoms with to get a whole number?

The identity of the decimal numbers can help you determine what number you need to multiply by. For example, 0.5 tells you to multiply by 2, 0.33 tells you to multiply by 3 and .167 tells you to multiply by 6. You can begin to recognize these patterns by doing more practice problems, but in general,...
by Chem_Mod
Sat Oct 05, 2019 2:51 pm
Forum: Empirical & Molecular Formulas
Topic: Combustion Analysis
Replies: 6
Views: 42

Re: Combustion Analysis

A typical combustion reaction contains O2 and the combusting substance on the reactants side of the equation and CO2 and H2O on the products side. You can then solve this like other molecular/empirical formulas discussed in class.
by Chem_Mod
Sat Oct 05, 2019 2:29 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg equation [ENDORSED]
Replies: 42
Views: 391

Re: Rydberg equation [ENDORSED]

In class I will cover this topic in detail using more fundamental concepts to solve problems (and not directly using the Rydberg equation).
by Chem_Mod
Sat Oct 05, 2019 2:21 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 2 Homework Problems [ENDORSED]
Replies: 63
Views: 634

Re: Week 2 Homework Problems [ENDORSED]

I sent email to the class: "As stated in the Syllabus, students submit homework on recently covered material. Since students want to focus on the high school review topics for test 1 they can hand in homework #2 covering review topics and/or quantum. HW #3 (Week 3) will be only quantum topics.&...
by Chem_Mod
Sat Oct 05, 2019 2:18 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty in Speed [ENDORSED]
Replies: 9
Views: 281

Re: Uncertainty in Speed [ENDORSED]

I will be covering this topic in class during Week 2.

Calculate 1% of the hydrogen radius (0.05 nm) in meters and use it as the uncertainty in position, delta x, of the electron in the Heisenberg Indeterminacy (Uncertainty) Equation.
by Chem_Mod
Sat Oct 05, 2019 12:49 pm
Forum: Properties of Light
Topic: E=hv quantization
Replies: 1
Views: 14

Re: E=hv

The textbook is stating that given a particle oscillating at frequency v (nu), the particle can only exchange energy in discrete E values (that correspond to E=hv). Thus, for a given v value, the particle can exchange energy with values of hv, 2hv, 3hv and so on.
by Chem_Mod
Sat Oct 05, 2019 12:38 pm
Forum: Properties of Light
Topic: Oscillation
Replies: 1
Views: 19

Re: Oscillation

Something that is oscillating varies periodically with time. The frequency of oscillation is the number of cycles per second (where a cycle is measured from one state and away and back to the same state). An electromagnetic wave is"time-varying" as the strength of the fields oscillate and ...
by Chem_Mod
Sat Oct 05, 2019 12:34 am
Forum: Significant Figures
Topic: Sig Figs in % Yield
Replies: 10
Views: 64

Re: Sig Figs in % Yield

You would use normal rounding rules and round up to 64%.
by Chem_Mod
Fri Oct 04, 2019 8:25 pm
Forum: *Black Body Radiation
Topic: Wavelength and Temperature
Replies: 2
Views: 25

Re: Wavelength and Temperature

Temperature is inversely proportional to the maximum wavelength. This problem is solvable using Wien's law and the constant 2.9mm*K.
by Chem_Mod
Fri Oct 04, 2019 7:47 pm
Forum: Molarity, Solutions, Dilutions
Topic: Dilution post assessment problem 25
Replies: 1
Views: 18

Re: Dilution post assessment problem 25

By volume ratios, I assume you mean the M 1 V 1 =M 2 V 2 formula? If so that is probably your quickest option. Otherwise, you could look at it like a dimensional analysis such as: 5g\(\frac{mol}{158.034})(\frac{1}{0.150L})(\frac{0.020L}{1})(\frac{1}{0.250L})= 1.69*10^...
by Chem_Mod
Fri Oct 04, 2019 7:22 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: atomic weight, molecular weight, and formula weight
Replies: 2
Views: 14

Re: atomic weight, molecular weight, and formula weight

The atomic weight is the mass when only considering atoms themselves. Molecular weight is the sum of the component atom's masses using the compound's molecular formula. The formula weight is typically used for the empirical formula mass. In other words, molecular weight is a sum of the atomic weights.
by Chem_Mod
Fri Oct 04, 2019 4:56 pm
Forum: Einstein Equation
Topic: 1B.7 (sixth edition)
Replies: 1
Views: 28

Re: 1B.7 (sixth edition)

First, you would have to find the frequency using the speed of light (since you are given the wavelength). Then, you would plug in the frequency and multiply it by Planck's constant to find the energy in a mole of photons. And then you would multiply that number by Avogadro's number to find how much...
by Chem_Mod
Fri Oct 04, 2019 4:49 pm
Forum: Balancing Chemical Reactions
Topic: Fundamental F.3
Replies: 1
Views: 22

Re: Fundamental F.3

Do you have the specific question from the text?
by Chem_Mod
Fri Oct 04, 2019 4:47 pm
Forum: Balancing Chemical Reactions
Topic: Fundamentals G.5
Replies: 1
Views: 14

Re: Fundamentals G.5

Usually the fastest way is to balance elements like carbon and nitrogen first, while saving oygen and hydrogen till the end. Another way is to make a systems of equations. Example: HF + SiO2 --> SiF4 + H20 aHF + bSiO2 --> cSiF4 + dH20 For each element: H: 1a= 2d F: 1a= 4c Si: 1b= 1c O: 2b=1d Then, i...
by Chem_Mod
Fri Oct 04, 2019 4:40 pm
Forum: Limiting Reactant Calculations
Topic: Chem Community logistics [ENDORSED]
Replies: 4
Views: 35

Re: Chem Community logistics [ENDORSED]

If you click on the drop down of "quick links" the first option should be "your posts" and you should be able to track your posts through that :)
by Chem_Mod
Fri Oct 04, 2019 4:37 pm
Forum: Empirical & Molecular Formulas
Topic: L. 39
Replies: 2
Views: 27

Re: L. 39

For part a, you would find the percentages of each reactant, assume 100g, and then solve for the empirical formula from there. For part b, you would have to write out the chemical reaction to determine the product.
by Chem_Mod
Fri Oct 04, 2019 4:25 pm
Forum: Administrative Questions and Class Announcements
Topic: KAREN SUN 5-7PM WORKSHOP - DOWNLAOD WORKSHEETS HERE
Replies: 25
Views: 405

KAREN SUN 5-7PM WORKSHOP - DOWNLAOD WORKSHEETS HERE

Greetings Chem 14A students! My name is Karen Leung, one of your UAs this quarter. I will be hosting workshops every Sunday 5-7pm this quarter, and I use worksheets I have made to facilitate my workshops. They will be posted on this SAME post here every week (I'll try to have them posted by Friday n...
by Chem_Mod
Fri Oct 04, 2019 2:43 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

This is some really valuable advice, so thank you. I've always been curious about medical school, and this post helped a ton. I think this is important because it allows students to understand better what they're getting themselves into with STEM. Also, what advice do you have for those that want t...
by Chem_Mod
Fri Oct 04, 2019 2:37 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

Thank you so much for sharing your experiences and story. I love hearing people's experiences in medical school because it motivates me to actually keep pursuing. When I see other people go through medical school I feel like I can get through it. Do you havee any advice with studying for medical sc...
by Chem_Mod
Fri Oct 04, 2019 12:27 pm
Forum: Limiting Reactant Calculations
Topic: M11
Replies: 1
Views: 24

Re: M11

This is similar to the example Dr. Lavelle showed in class.
For part c, you need to first determine how much of the excess reactant was used by the reaction (which is dependent on how much of the limiting reagent you have) and then work from there to determine how much mass is left in excess.
by Chem_Mod
Fri Oct 04, 2019 12:23 pm
Forum: Limiting Reactant Calculations
Topic: M9
Replies: 2
Views: 24

Re: M9

For part a you should find the balanced chemical reaction and for part b you need to find the limiting reactant to be able to determine how the maximum mass of copper(II) hydroxide (theoretical yield).
by Chem_Mod
Fri Oct 04, 2019 12:21 pm
Forum: Limiting Reactant Calculations
Topic: Temperature Effect on Reactions
Replies: 2
Views: 18

Re: Temperature Effect on Reactions

This is not something that you have to worry about right now. For now, the limiting reactant will determine how much product is produced by the reaction.
by Chem_Mod
Fri Oct 04, 2019 12:20 pm
Forum: Limiting Reactant Calculations
Topic: General Limiting Reactant Question
Replies: 4
Views: 15

Re: General Limiting Reactant Question

For M.3 you didn't need to find the limiting reactant because there was only one reactant. You will usually be given the number of moles/grams for each reactant and you will have to determine the limiting reactant from that in order to solve the problem.
by Chem_Mod
Fri Oct 04, 2019 12:18 pm
Forum: Administrative Questions and Class Announcements
Topic: Time Spent Studying
Replies: 1
Views: 32

Re: Time Spent Studying

It really depends on how comfortable you are with the material we are learning and your experience with chem previously. I would recommend at least 7/8 hours even per week though :)
by Chem_Mod
Fri Oct 04, 2019 12:15 pm
Forum: Limiting Reactant Calculations
Topic: M5
Replies: 2
Views: 21

Re: M5

You need to determine the limiting reagent and then you would multiply it by the mole ratios. In this case the limiting reagent is ClO2 and the balanced chemical equation would give you the mole ratio for the products and reactants. Example: 12 mol ClO2 x 1 mol Br2/ 6 mol ClO2 = 2 mol Br2 Hope this ...
by Chem_Mod
Fri Oct 04, 2019 11:58 am
Forum: Molarity, Solutions, Dilutions
Topic: Homework Question H11
Replies: 3
Views: 36

Re: Homework Question H11

Fe3O4 + CO ---> Fe + CO2
Balance Iron first, then balance the carbon and oxygen.
This one is a bit hard but you should end up with Fe3O4 + 4 CO ---> 3 Fe + 4 CO2
by Chem_Mod
Fri Oct 04, 2019 11:44 am
Forum: Balancing Chemical Reactions
Topic: homework question M15
Replies: 4
Views: 27

Re: homework question M15

We balance chemical equations to show the conservation of mass in our reaction. You should only use molar mass to convert to grams if the question requires a second part but you shouldn't be using grams to balance the reaction.
by Chem_Mod
Fri Oct 04, 2019 11:42 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Theoretical vs. Actual Yield
Replies: 38
Views: 204

Re: Theoretical vs. Actual Yield

You should be familiar with this concept :)
by Chem_Mod
Fri Oct 04, 2019 11:34 am
Forum: General Science Questions
Topic: Kelvin
Replies: 3
Views: 27

Re: Kelvin

Absolute zero is the lowest limit of the thermodynamic temperature scale and its equal to 0 K or -273.15°C.
by Chem_Mod
Fri Oct 04, 2019 11:30 am
Forum: Balancing Chemical Reactions
Topic: balancing charges
Replies: 4
Views: 35

Re: balancing charges

You will practice that more when we start studying redox reactions, Dr. Lavelle hasn't gone over it yet so I wouldn't worry about it too much :)
by Chem_Mod
Fri Oct 04, 2019 11:24 am
Forum: Molarity, Solutions, Dilutions
Topic: Dilution Calculation
Replies: 5
Views: 20

Re: Dilution Calculation

Because the units will cancel out when you divide the Molarity over, you can leave it in mL and you should still get the right answer and then you wouldn't have to convert your final answer.
by Chem_Mod
Fri Oct 04, 2019 11:22 am
Forum: Empirical & Molecular Formulas
Topic: Determining Molecular Formulas
Replies: 1
Views: 22

Re: Determining Molecular Formulas

That should work. It might also be easier to just assume 100g and work your way up from empirical to molecular, like Dr. Lavelle showed in class.
by Chem_Mod
Fri Oct 04, 2019 11:21 am
Forum: Molarity, Solutions, Dilutions
Topic: Homework Question E9 Part A
Replies: 1
Views: 18

Re: Homework Question E9 Part A

Your work looks good, I plugged it in and got the right answer. I would just try plugging it into your calculator again :)
by Chem_Mod
Fri Oct 04, 2019 11:15 am
Forum: Empirical & Molecular Formulas
Topic: Order of elements in formulas
Replies: 5
Views: 27

Re: Order of elements in formulas

Usually you would put Carbon first,Hydrogen second, and then any other elements would go in alphabetical order.
by Chem_Mod
Fri Oct 04, 2019 11:12 am
Forum: Limiting Reactant Calculations
Topic: Mass of AgCl produced?
Replies: 2
Views: 18

Re: Mass of AgCl produced?

After you've found the limiting reactant and you've determined the number of moles of AgCl that would be produced by the reaction, you would multiply the # of moles of AgCl you calculated by the molar mass of AgCl and that should give you the mass of AgCl produced.
by Chem_Mod
Fri Oct 04, 2019 9:47 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Wavelength Plausibility
Replies: 17
Views: 284

Re: Wavelength Plausibility

The context here is when does a particle cease to have detectable wave-like properties. In other words only particle-like behavior will be observed. Typically a particle with a de Broglie wavelength less than 10 -15 m does not have detectable wave-like properties. Obviously the higher the mass, the ...
by Chem_Mod
Thu Oct 03, 2019 10:10 pm
Forum: SI Units, Unit Conversions
Topic: 1.Homework 1 Problem: G5
Replies: 1
Views: 41

Re: 1.Homework 1 Problem: G5

Once you find the molarity of Na2CO3, you can find the volume needed to produce x amount of Na+, CO3 2-, etc. For part a, you are asked to find the volume to produce 2.15 mmol Na+. There are two mol of Na+ per mol of Na2CO3, as given by the subscript 2. Therefore, you would need to divide by 2, not ...
by Chem_Mod
Thu Oct 03, 2019 9:58 pm
Forum: Balancing Chemical Reactions
Topic: Combustion
Replies: 12
Views: 49

Re: Combustion

That is correct.
by Chem_Mod
Thu Oct 03, 2019 9:58 pm
Forum: Molarity, Solutions, Dilutions
Topic: G. 25
Replies: 3
Views: 31

Re: G. 25

Logarithms are used to solve for unknowns that are the exponent of something (in this case 1/2 to the nth power). Logarithms allow us to easily solve for n. Refreshing on your logarithm rules would be helpful!
by Chem_Mod
Thu Oct 03, 2019 9:54 pm
Forum: Administrative Questions and Class Announcements
Topic: Audio-Visual Modules Update Date
Replies: 2
Views: 10

Re: Audio-Visual Modules Update Date

The modules are not posted weekly. All the modules are posted already and are all relevant to Week 0 and 1 material to provide extra review of high school concepts.
by Chem_Mod
Thu Oct 03, 2019 9:10 pm
Forum: Limiting Reactant Calculations
Topic: M.11
Replies: 3
Views: 69

Re: M.11

I worked the problem step-by-step, hope this is helpful. Please come to office hours with any questions/concerns! :) https://imgur.com/a/9wXOgg0
by Chem_Mod
Thu Oct 03, 2019 8:31 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

Thank you so much for sharing your experience! I know getting letters of recommendation is a part of the application process, and I was wondering if you had any advice on how to get close and comfortable enough with professors to ask for a letter? I am also not 100% sure I want to follow this path ...
by Chem_Mod
Thu Oct 03, 2019 8:26 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 111
Views: 1152

Re: Advice from a Medical Student - Part II [ENDORSED]

Thank you for sharing your personal experience. Do you have any advice for those of us unsure about our majors as first-years? If you don't know what major you want to be in, take classes from all different majors. The classes that you take that don't end up in the major you decide can help fulfill...
by Chem_Mod
Thu Oct 03, 2019 8:23 pm
Forum: Properties of Light
Topic: homework problem
Replies: 1
Views: 30

Re: homework problem

You are given the frequency 99.3 MHz and 1420. MHz. Convert those to Hz and solve using the relevant equation, c = wavelength x frequency. If you are still having trouble, please attend a Step-Up session!
by Chem_Mod
Thu Oct 03, 2019 8:20 pm
Forum: Properties of Light
Topic: HW 1A 19
Replies: 1
Views: 86

Re: HW 1A 19

The key word is ultraviolet, which is involved in the Lyman series (associated with n=1). The question also says emission, so the electron must drop from a higher to lower energy level (here n=1). You can solve for your initial n value since only one unknown is left.

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