## Search found 52 matches

Fri Jan 15, 2021 12:51 am
Forum: Administrative Questions and Class Announcements
Topic: Question on counting of Chem Community Posts
Replies: 1
Views: 16

### Question on counting of Chem Community Posts

I had a quick question about when the chem community posts start getting counted again for the new week? For example, if I post a question this coming Sunday (of week 2), that post will be counted for Week 3 right? Because I do know that Saturday Midnight is the last day you can post something for i...
Thu Jan 14, 2021 11:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6A #23 [ENDORSED]
Replies: 2
Views: 20

### Re: 6A #23[ENDORSED]

I'm just going to walk through the steps I took to check your answer: First, convert 0.43 g Ba(OH)2 into moles by dividing by the molar mass of Ba(OH)2 (which is 171.344 g/mol). Then divide that value (0.0025mol) by 0.100 L to get 0.025 M as your Ba(OH)2 concentration. I'm not sure where you got 0....
Thu Jan 14, 2021 11:32 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6A #23 [ENDORSED]
Replies: 2
Views: 20

### 6A #23[ENDORSED]

So for this problem I was able to get the initial molar concentration for Ba(OH)2 and I got 5.577x10^-3. To get that I first divided 0.43 grams by the molarity of Ba(OH)2, which I got as 171.327 (0.43g/171.327g.mol), and got 2.509*10^-3. Then I took that result and divided by 0.450L to get the initi...
Sun Jan 10, 2021 5:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5.i #15
Replies: 2
Views: 17

### Re: 5.i #15

Actually, since NH3 and H2S are on the product side of the reaction, you would add 0.200 to x (0.200+x) for NH3 and H2S would correspond to +x. If NH3 and H2S were on the reactant side, then you would subtract x from 0.200 for NH3. Using the quadratic formula, you should get 0.0008 for x. Once you ...
Sun Jan 10, 2021 1:30 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5.i #15
Replies: 2
Views: 17

### 5.i #15

For this problem, I was wondering how NH3=0.2 and how H2S= 8.04x10^-4? doesn't NH3 start with 0.2 mol.L so we subtract 0.2 with our answer that we got from the quadratic formula, and that would equal 8.04x10^-4 for NH3, and since H2S isn't mentioned on how much it's initial molar concentration was, ...
Sun Jan 10, 2021 12:03 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5.i #13 (b)
Replies: 1
Views: 19

### 5.i #13 (b)

For part b, I already have an understanding of what I need to do, but I keep getting an error for the square root part in the quadratic formula. I was wondering if someone can explain or point out if the numbers I got are wrong (which Im pretty sure are wrong, but I've done the problem like 4 times ...
Thu Jan 07, 2021 10:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5.i #13
Replies: 1
Views: 27

### 5.i #13

"(a) In an experiment, 2.0 mmol Cl2(g) was sealed into a reaction vessel of volume 2.0 L and heated to 1000. K to study its dissociation into Cl atoms. Use the information in Table 5G.2 to calculate the equilibrium composition of the mixture." Can someone explain how to do this problem? I ...
Thu Jan 07, 2021 8:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5.i #11
Replies: 4
Views: 24

### 5.i #11

So for the answer for 5.i #11, the textbook states Q=6.9 I was wondering where that number came from because when I do the reaction quotient formula (P / R), the product is (SO3)^2 and the reactants are ([SO2]^2 * [O2]) and after plugging in their respected concentrations ([0.10]^2 / [1.20]^2 * [0.5...
Thu Jan 07, 2021 5:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE tables
Replies: 11
Views: 63

### Re: ICE tables

HannahRobinson3L wrote:You can also go watch the Audio Visual Focus Topics on Dr. Lavelle's website if you want to hear an explanation directly from the professor! I think it is the Chemical Equilibrium Part 2 where he goes over ICE charts.

I recommend doing what Hannah said. In the module, he goes over it super well!
Thu Jan 07, 2021 5:31 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Temperature and Kc
Replies: 4
Views: 27

### Re: Temperature and Kc

Dr. Lavelle mentioned in lecture that temperature affect equilibrium, but how does it factor into the equation for the equilibrium constant? In one of the module's, I remember him stating that later on in Chem 14B, we'll be using temperature that affects the Kc. I don't think it's something to worr...
Tue Jan 05, 2021 6:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Question 5H3)
Replies: 4
Views: 20

### Re: Textbook Question 5H3)

Hi! I believe you have to start by looking at the K values given in the table. These values are for the individual reactions that make up this broad reaction. What you have to do is combine the two reactions to create the overall reaction. When you combine the reaction though you must multiply the ...
Tue Jan 05, 2021 6:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Question 5H1)
Replies: 5
Views: 29

### Re: Textbook Question 5H1)

a) they switched the placements of the reactants/products so you would just take the inverse of K, so K in this problem would be 1/41 b) the given equation is the given equation in the problem but the coefficients are just divided by 2 so you would take the square root of 41 as your answer (~6.4). ...
Fri Dec 11, 2020 1:03 pm
Forum: Polyprotic Acids & Bases
Topic: Textbook 6C.19
Replies: 7
Views: 55

### Re: Textbook 6C.19

HCl is stronger because it has a longer bond than HF, due to trends in the periodic table. Lavelle also mentioned that the longer the A-H bond, the stronger the acid because a property of a strong acid is it gives off protons easily. So if a bond is long, the proton isn't easily held to the nucleus ...
Fri Dec 11, 2020 1:01 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Bookwork 6B #3
Replies: 6
Views: 33

### Re: Bookwork 6B #3

Also, how do you know V1=.200L ? and V2=.250L ?

Is it because we initially "think" we used .200 L at first?
Fri Dec 11, 2020 12:45 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Bookwork 6B #3
Replies: 6
Views: 33

### Re: Bookwork 6B #3

For the pH of the desired solution, you just use the concentration of HCl, which is desired to be 0.025M. 0.025 M of HCl is 0.025 M of H+ since HCl is a strong acid and completely dissociates into H+ and Cl-. pH= -log[H+], therefore, the pH of the desired solution is -log(0.025). For the second par...
Fri Dec 11, 2020 12:23 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6B1
Replies: 3
Views: 54

### Re: 6B1

Hi! Here's how I solved this problem: 1. the molarity of H+ ions is equal to the molarity of HCl because HCl is a strong acid so its ions will completely dissociate 2. pH of initial HCl solution = -log([HCl]) and pH of diluted HCl solution = -log(0.12 x [HCl]) 3. I divided the pH of the diluted HCl...
Fri Dec 11, 2020 12:19 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Textbook 6B.1
Replies: 8
Views: 69

### Re: Textbook 6B.1

Jordi M 2F wrote:Is that all the information the question gives?

Yes, it only gives that.
Thu Dec 10, 2020 12:03 am
Forum: Bronsted Acids & Bases
Topic: Determining if an ion is basic or acidic
Replies: 1
Views: 16

### Determining if an ion is basic or acidic

This may seem like a simple question but how do you determine an ion is acidic or basic?
Thank you!
Tue Dec 01, 2020 7:50 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Focus Exercise 2.27
Replies: 4
Views: 34

### Re: Focus Exercise 2.27

I had question about the radical part. So they are not radicals because they at least have paired electrons? So they're only radicals if the central atom has 1 unpaired electron?
Tue Dec 01, 2020 6:58 pm
Forum: Hybridization
Topic: Textbook Q 2F #7
Replies: 4
Views: 53

### Textbook Q 2F #7

The question states:

" Identify the hybrid orbitals used by the atom in boldface red type in each of the following species: b) AsF3"

the back of the book says the answer is sp^3. Can someone explain how they got the answer? Please! Thank you!
Sat Nov 28, 2020 11:55 pm
Forum: Hybridization
Topic: dsp^3 vs sp^3d
Replies: 2
Views: 16

### Re: dsp^3 vs sp^3d

I think Lavelle mentioned something about this in his lecture stating that some textbooks write it either way and that it's the same thing but that he prefers writing it the "sp^3d" way because it's the order of the energy states.
If I'm wrong someone correct me please.
Sat Nov 28, 2020 11:52 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling HW #18
Replies: 7
Views: 56

### Sapling HW #18

One of the questions on my sapling problem asked about the relative positions of the atoms in the lewis structure.
What do they mean by the positions of the atom in the lewis structure? and how do you figure it out?
the answer mentioned something about being in the same plane.
Wed Nov 25, 2020 11:43 pm
Forum: Hybridization
Topic: Sapling Week 7 & 8 HW Question 11
Replies: 14
Views: 108

### Re: Sapling Week 7 & 8 HW Question 11

Lavelle in his lecture from Monday (week 8) he gave a little key on how to find the hybridization of a molecule. He said that the # of regions of electron density around the central atom (or the least ionized element), equals the # of hybrid orbitals. So for example, if there are 2 regions of electr...
Wed Nov 25, 2020 11:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: What does delocalized π bond mean?
Replies: 18
Views: 125

### Re: What does delocalized π bond mean?

A lewis structure has delocalized Pi bonds when the lewis structure has resonance. Meaning there are delocalized electrons (aka shared electrons) throughout the whole molecule.
Tue Nov 24, 2020 10:53 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook 2E #17
Replies: 3
Views: 16

### Textbook 2E #17

the question states: 2E.17 Predict the bond angles at the central atom of the following molecules and ions: (a) ozone, O3 I drew the Lewis structure for "a" and I thought it would have an angular shape due to the loan pairs on the Oxygen atom in the middle. So with the 4 regions of electro...
Fri Nov 13, 2020 11:53 pm
Forum: Electronegativity
Topic: Textbook 2D problem #7
Replies: 3
Views: 24

### Textbook 2D problem #7

the problem states: Compounds having bonds with a high covalent character tend to be less soluble in water than similar compounds that have low covalent character. Use electronegativities to predict which of the following compounds is the more soluble in water: (b) MgO or BaO. In the back of the boo...
Thu Nov 12, 2020 10:54 pm
Forum: Octet Exceptions
Topic: Texbook Questions 2C1
Replies: 6
Views: 30

### Re: Texbook Questions 2C1

I don't know exactly why they put A as an answer as well. But I was reading some posts on chem community how O is a special exception to the radical rule because it always has two lone pairs. To back it up, i found this in the reading of the book: "One of the most important examples is the oxy...
Thu Nov 12, 2020 10:50 pm
Forum: Octet Exceptions
Topic: Texbook Questions 2C1
Replies: 6
Views: 30

### Re: Texbook Questions 2C1

I don't know exactly why they put A as an answer as well. But I was reading some posts on chem community how O is a special exception to the radical rule because it always has two lone pairs. To back it up, i found this in the reading of the book: "One of the most important examples is the oxyg...
Thu Nov 12, 2020 10:37 pm
Forum: Octet Exceptions
Topic: Elements that can have Expanded Octet
Replies: 5
Views: 27

### Re: Elements that can have Expanded Octet

Only elements from the 3rd period and down can have an expanded octet. Because they all have "n" states bigger than 2, which means their "l" states can be s, p, d, or f orbitals, depending on the particular element you're focusing on and what their "n" state is.
Wed Nov 11, 2020 9:36 pm
Forum: Lewis Structures
Topic: Textbook q 2B #15
Replies: 2
Views: 14

### Textbook q 2B #15

The question states: Draw the Lewis structures that contribute to the resonance hybrid of nitryl chloride, ClNO2 (N is the central atom). I know how to draw the lewis structure. But i've been confused on why N is in the middle. I know ionization energy decreases down a group and increases across a p...
Wed Nov 11, 2020 8:09 pm
Forum: Lewis Structures
Topic: homework 2B.3
Replies: 5
Views: 42

### Re: homework 2B.3

Sinc Br is in the 4th period of the periodic table, it has the ability to have an expanded octet. This means n=4, so l=3 (because l is solved by n-1). So since l=3, Br has the s,p, d, and f orbitals. Meaning it has extra orbitals to gain extra electrons, apart of only 8 from the octet rule. just as ...
Wed Nov 11, 2020 8:00 pm
Forum: Lewis Structures
Topic: Textbook HW #7
Replies: 3
Views: 21

### Textbook HW #7

The following Lewis structure was drawn for a Period 3 element. Identify the element.

textbook q.png (8.66 KiB) Viewed 21 times

the back of the book says Phosphorus. How does it get to that answer? can someone explain how they solved it? please! Thank you!
Thu Nov 05, 2020 7:53 pm
Forum: Ionic & Covalent Bonds
Topic: textbook problem from 2A #17
Replies: 2
Views: 23

### textbook problem from 2A #17

2A.17 Predict the number of valence electrons present for each of the following ions: a.) Mn^4+ I need help understanding why the answer is 3 valence electrons in the answer section. Because I saw a youtube video saying we count all the electrons of the highest "n" value in the electron co...
Wed Nov 04, 2020 5:36 pm
Forum: Lewis Structures
Topic: Expanded Octet
Replies: 6
Views: 37

### Re: Expanded Octet

He said in lecture today that the elements from the 3rd period and down have the expanded octet. But then again, he said we'll generally only be focusing on the first three periods of the periodic table for the class because they're more widely used. So I wouldn't really worry about further periods.
Wed Nov 04, 2020 5:30 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem community posts
Replies: 4
Views: 28

### Re: Chem community posts

I remember him sending an email or reading it somewhere that the points don't carry over for the next week. Each week your points reset, if that makes sense. So each week we have to get those 5 points.

Which, I'm trying to do right now x)
Wed Nov 04, 2020 5:24 pm
Forum: Administrative Questions and Class Announcements
Topic: Lavelle's Office Hours (5-6 p.m.)
Replies: 1
Views: 26

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

Anybody attending Lavelle's office hours right now, from 5-6 p.m., and still waiting to be accepted into the meeting? or is he taking students one by one?
Thu Oct 29, 2020 7:22 pm
Forum: DeBroglie Equation
Topic: Sapling HW #14
Replies: 7
Views: 50

### Re: Sapling HW #14

Anh Trinh 1B wrote:Make sure to convert grams to kilograms before solving!

Yes thank you! I totally forgot about converting to kg x)
Thu Oct 29, 2020 6:33 pm
Forum: DeBroglie Equation
Topic: Sapling HW #14
Replies: 7
Views: 50

### Sapling HW #14

The question states: What would the speed of each particle be if it had the same wavelength as a photon of orange light ( "lambda" =625.0 nm)? proton (mass=1.673×10−24 g) speed: (blank) m/s neutron (mass=1.675×10−24 g) speed: (blank) m/s electron (mass=9.109×10−28 g) speed: (blank) m/s I k...
Thu Oct 29, 2020 12:19 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Sapling HW #11
Replies: 2
Views: 29

### Sapling HW #11

the question states: A violet line is observed at 434.0 nm in the spectrum of atomic hydrogen. Determine the values of "n" for the beginning and ending energy levels of the electron during the emission of energy that leads to this spectral line. n2= ? n1=? I know n1 is 2 but I'm having tro...
Thu Oct 29, 2020 12:06 am
Forum: Photoelectric Effect
Topic: Sapling HW #11
Replies: 5
Views: 55

### Sapling HW #11

the question states: A violet line is observed at 434.0 nm in the spectrum of atomic hydrogen. Determine the values of "n" for the beginning and ending energy levels of the electron during the emission of energy that leads to this spectral line. n2= ? n1=? I know n1 is 2 but I'm having tro...
Wed Oct 28, 2020 10:53 pm
Forum: Photoelectric Effect
Topic: Rydberg Equation question
Replies: 3
Views: 30

### Rydberg Equation question

Is the Rydberg Equation given in the textbook (equation 2: v = R {1/n1 - 1/n2} ) the same as the equation given to us in lecture: ( En = -hR/n^2 )? I know they don't look the same lol, but it's because in one of the Sapling homework problems I had to use the the first equation, given in the book, wh...
Wed Oct 28, 2020 10:02 pm
Forum: Einstein Equation
Topic: Sapling HW #7
Replies: 7
Views: 84

### Sapling HW #7

the problem states: "As you may well know, placing metal objects inside a microwave oven can generate sparks. Two of your friends are arguing over the cause of the sparking, with one stating that the microwaves "herd" electrons into "pointy" areas of the metal object, from w...
Mon Oct 26, 2020 10:44 pm
Forum: Einstein Equation
Topic: Sapling HW #4
Replies: 2
Views: 56

### Sapling HW #4

I need help solving this problem:

A liquid is exposed to infrared radiation with a wavelength of 4.84×10−4 cm. Assume that all the radiation is absorbed and converted to heat. How many photons are required for the liquid to absorb 25.34 J of heat?
Thu Oct 22, 2020 12:06 am
Forum: Einstein Equation
Topic: Textbook Question 1B.7
Replies: 4
Views: 54

### Re: Textbook Question 1B.7

Assuming that you have already calculated the answer to part a), you would already know that the energy an excited sodium emits is around E= 3.37 x 10^-19 J Now, the next step is that we covert the 5mg of sodium atoms first to moles of sodium atoms and then from moles to total number of atoms by us...
Sat Oct 17, 2020 11:59 pm
Forum: Student Social/Study Group
Topic: How are you studying?
Replies: 203
Views: 1251

### Re: How are you studying?

I quickly skim my notes after every lecture. Then, every other day that we dont have lecture, I review my notes again and if I have time I just quickly skim the pre-recorded lecture to review the most important concepts. Then on weekends I just review all of my notes of that week. It helps retain th...
Fri Oct 16, 2020 1:56 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: E=h*V explanation in atomic spectra
Replies: 3
Views: 29

### E=h*V explanation in atomic spectra

Why does professor Lavelle compare E (energy of photon) to (delta)E ? I'm having a hard time understanding why. Can someone give their explanation why? Please !!
Mon Oct 12, 2020 2:20 pm
Forum: Properties of Light
Topic: Clarification on intensity and amplitude [ENDORSED]
Replies: 6
Views: 54

### Re: Clarification on c = (lambda) * V[ENDORSED]

Hi! So yes you are correct that the amplitude of the wave is the intensity of the wave, but increasing amplitude doesn't effect the frequency. As seen in the equation you were talking about C= wavelength*frequency, wavelength and frequency effect each other but not the amplitude. Also, if you graph...
Mon Oct 12, 2020 2:11 pm
Forum: Properties of Light
Topic: Clarification on intensity and amplitude [ENDORSED]
Replies: 6
Views: 54

### Clarification on intensity and amplitude[ENDORSED]

Is it safe to say amplitude can be characterized as intensity of the wave?

if so, would it also be safe to say increasing amplitude (aka intensity) increases frequency?

if I'm wrong in any of this or mixed up any definitions please feel free to correct me! I'm trying to understand this x).
Sun Oct 11, 2020 12:47 am
Forum: Molarity, Solutions, Dilutions
Topic: sapling hw #7
Replies: 17
Views: 165

### Re: sapling hw #7

After reading some of the replies, I'm afraid I have a silly question. People are saying to "multiply 0.325 with 590.1g" but my question is what they did to get 0.325 and why. Thank you! Don't be afraid! Because I too was wondering the same thing. Thank you for asking before I did! We're ...
Sat Oct 10, 2020 6:34 pm
Forum: Molarity, Solutions, Dilutions
Topic: Self Test G.3
Replies: 1
Views: 28

### Self Test G.3

I know this wasn't part of the assigned problems on the syllabus but I just wanted to know how this problem is figured out [Part of Fundamentals G]: What volume of 1.25 x 10^-3 M C6H1206 contains 1.44 um (micromol) of glucose molecules? the answer was given: [Answer: 1.15mL] I know we have to use th...
Wed Oct 07, 2020 11:02 pm
Forum: SI Units, Unit Conversions
Topic: SI Units
Replies: 13
Views: 122

### Re: SI Units

I'm pretty sure it's always going to have the units you need to use in the question.
Tue Oct 06, 2020 12:04 am
Forum: Balancing Chemical Reactions
Topic: Stoichemetric Coeffiecients
Replies: 12
Views: 141

### Re: Stoichemetric Coeffiecients

With stoichiometric coefficients you're always supposed to have the lowest whole number. So if you find that one of your coefficients is like 3.5 or 8.5, etc, you would multiply both sides of the reaction (reactants and products) by 2. That will give you the lowest whole number coefficients and kee...

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