## Search found 73 matches

Thu Jan 21, 2021 7:30 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Textbook 6.B.3
Replies: 3
Views: 13

### Re: Textbook 6.B.3

I agree with everyone! For another way to look at part b, the solution was diluted, so you can use M1 x V1 = M2 x V2. We're trying to find M2, the actual concentration of the solution prepared, and we can use this M2 to find the actual pH of the solution. M1 = 0.025 M H3O+, V1 = 0.2000 L, and V2 = 0...
Thu Jan 21, 2021 7:22 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Week 2 Sapling #5
Replies: 9
Views: 66

### Re: Week 2 Sapling #5

I agree, I did not disregard the X because the calculation is not too difficult even without disregarding the X. The quadratic formula is not needed in this calculation since we are solving for the initial concentration of the amine instead of solving for the equilibrium [OH-] like we usually do.
Thu Jan 21, 2021 7:14 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Textbook 6B.9
Replies: 4
Views: 20

### Re: Textbook 6B.9

It just says "omit due to errors." Here's the solution manual errors: https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf
But I think as long as we understand the concept of this problem, which I'm sure you do, we'll be okay!
Thu Jan 21, 2021 7:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: textbook 6.A.19
Replies: 4
Views: 15

### Re: textbook 6.A.19

There's a typo in this question, so it should say 3.1 x 10^-3 mol.L^-1, not 3.1 mol.L^-1.
https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf
Thu Jan 21, 2021 6:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5.I.33
Replies: 1
Views: 11

### Re: 5.I.33

This problem gives information that you can use to find the equilibrium concentration of CO2 (equilibrium mass and volume). Since ammonia carbamate is in the solid phase in this reaction, ammonia carbamate is not considered in the Kc value. The products NH3 and CO2 are both considered in Kc because ...
Fri Jan 15, 2021 11:46 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Week 1 Sapling #9
Replies: 5
Views: 23

### Re: Week 1 Sapling #9

For this question, you can first calculate Kc using the given equilibrium concentrations on the first line of the problem. You know that Kc will stay the same, since there is no temperature change mentioned in the problem. After the NO has been added, the system is no longer at equilibrium. So, you ...
Thu Jan 14, 2021 7:04 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Identifying Bases
Replies: 7
Views: 41

### Re: Identifying Bases

Is there a quick way to identify a strong base from a weaker base? Like if it has an OH in it (for example, KOH) does that indicate anything as compared to a molecule without an OH (like CaO)? Strong bases are group 1 and group 2 oxides and hydroxides. For example, LiO2, NaOH, CaO, and Mg(OH)2 are ...
Thu Jan 14, 2021 6:58 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Long term vs short term changes in conc.
Replies: 6
Views: 28

### Re: Long term vs short term changes in conc.

I think you are correct! Adding a reactant results in an increase in that reactant after a short period of time. But in the long term, the reaction proceeds towards the formation of the products, meaning that there is a decrease in that reactant.
Thu Jan 14, 2021 6:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pKa and pH
Replies: 10
Views: 45

### Re: pKa and pH

To add on to what everyone else has said, pKa is a fixed value for a given acid. pKa allows us to compare the strength of different acids, no matter what the concentration of each acid is, since a lower pKa value means that the acid is stronger. pH depends on the H3O+ concentration. This means that ...
Mon Jan 11, 2021 10:45 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Problem 5.39
Replies: 1
Views: 46

### Re: Textbook Problem 5.39

Table 5G.2 had an error with the given Kc value. It should be 6.1 x 10^-3 instead of 6.1 x 10^23.
Dr. Lavelle updated the solutions manual errors: https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf
Mon Jan 11, 2021 10:42 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Problem 5.39
Replies: 6
Views: 76

### Re: Textbook Problem 5.39

Edward Tang 1k wrote:Dr.Lavelle has updated the document solution manual errors. I've copied the part pertaining to this question below:

Table 5G.2 in the textbook has an error.
For the reaction N2O4 ⇌ 2NO2 at 298 K, the Kc value is 6.1 x 10-3

Thank you for the update! :)
Sat Jan 09, 2021 12:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Problem 5.39
Replies: 6
Views: 76

### Re: Textbook Problem 5.39

I think there might be a typo or error with this problem. When I checked the solutions manual, the Kc value (for $N_{2}O_{4}\rightleftharpoons 2NO_{2}$) used in the calculation was 6.1 x 10^-3, but Table 5G.2 says the Kc is 6.1 x 10^23, so I'm not sure which Kc value we should use.
Thu Jan 07, 2021 4:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Preset values of K
Replies: 5
Views: 38

### Re: Preset values of K

I agree with Hannah, I think the equilibrium constant is only dependent on temperature. Even with a pressure change, the system would respond to this change until the system reaches equilibrium again, and the equilibrium constant still remains the same.
Thu Jan 07, 2021 4:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium Part 3, #20
Replies: 4
Views: 28

### Re: Chemical Equilibrium Part 3, #20

I agree with Hannah, for my x-value I also got 4.94 x 10^-6 because the numerator was (2x)^2.
Wed Jan 06, 2021 12:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Converting bar to mol/L
Replies: 5
Views: 27

### Re: Converting bar to mol/L

Here's the unit conversion: \frac{nRT}{V}=P (\frac{mol}{L})(\frac{L\bullet atm}{K\bullet mol})(K)=atm (\frac{L\bullet atm}{K\bullet mol}) is the units for the constant R. In the lecture today, Dr. Lavelle said 1 bar is equal to approximately 1 atm, so we are usually g...
Wed Jan 06, 2021 12:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solvents absence in equilibrium constant eq
Replies: 3
Views: 22

### Re: Solvents absence in equilibrium constant eq

To add on, when writing the Kc expression, even if you included the concentration of solvent as a product in the numerator and the concentration of solvent as a reactant in the denominator, these concentrations would be so similar in value that they would end up canceling (dividing them would give a...
Wed Jan 06, 2021 12:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Part 3 Module Review Question 16
Replies: 2
Views: 36

### Re: Part 3 Module Review Question 16

Since the initial concentration of PCl5 and Kc are given, I set up an ICE (Initial concentration, Change in concentration, Equilibrium concentration) table to find the equilibrium concentrations. Initial concentrations: 1.50 mol / 0.500 L = 3.00 M PCl5 ; 0 M PCl3 ; 0 M Cl2 Change in concentration: -...
Tue Dec 08, 2020 1:56 pm
Forum: Bond Lengths & Energies
Topic: Compound stability
Replies: 5
Views: 36

### Re: Compound stability

I think we look at the intramolecular bonds when determining the most stable compound. IMFs can be taken into account when we think about the solid, liquid or gas phase of a compound at room temperature, or when we think about melting or boiling points.
Tue Dec 08, 2020 1:51 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Textbook question 6C.17
Replies: 3
Views: 64

### Re: Textbook question 6C.17

I found the pKb values in the textbook if you scroll up in this section.
The pKb of morphine is 5.79 (from Table 6C.2)
The pKa of HBrO is given as 8.69 (from Table 6C.1). To find the pKb of BrO-, I subtracted 14.00 - 8.69 = 5.31.
Mon Dec 07, 2020 9:00 pm
Forum: Hybridization
Topic: Textbook Problem 2F.17
Replies: 2
Views: 39

### Re: Textbook Problem 2F.17

O also has a hybridization of sp2 because the O atom has 3 regions of electron density: 1 (double) bond with the central C atom + 2 lone pairs. 3 regions of electron density gives the hybridization of sp2. I hope this helps!
Mon Dec 07, 2020 8:29 pm
Forum: Conjugate Acids & Bases
Topic: acidic and basic salts
Replies: 2
Views: 14

### Re: acidic and basic salts

A salt is basic when the cation is from group 1 or 2 on the periodic table, and the anion is the conjugate base of a weak acid. For example, in the salt NaF, the F- ion is the conjugate base of the weak acid HF (F- will remove a proton from water, generating OH-). Na+ does not affect the pH because ...
Mon Dec 07, 2020 2:55 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Determining Valence e-
Replies: 3
Views: 47

### Re: Determining Valence e-

I'm not quite entirely sure either, but here is what I think. For Mn for example, since its electron configuration is [Ar] 3d5 4s2, I would think Mn has 7 valence electrons (5 in the 3d subshell and 2 in the 4s subshell). When Mn becomes Mn 4+, it thus loses 4 valence electrons, 2 electrons from the...
Mon Nov 30, 2020 9:57 pm
Forum: Hybridization
Topic: pcl3
Replies: 8
Views: 50

### Re: pcl3

The lone pair on the central P atom and the three P-Cl bonds all count as regions of electron density, so there are 4 total regions of electron density. Since the number of regions of electron density = the number of hybrid orbitals, we know there must be 4 sp3 hybridized orbitals to represent the V...
Mon Nov 30, 2020 9:52 pm
Forum: Biological Examples
Topic: Hemoglobin Subunits
Replies: 3
Views: 50

### Re: Hemoglobin Subunits

I agree with Brittney, I think myoglobin refers to the entire molecule, including the Heme complex and histidine. For hemoglobin, I think we just have to know that hemoglobin has four myoglobin-like molecules, but the structure of each subunit of hemoglobin is not entirely the same as myoglobin.
Mon Nov 30, 2020 9:46 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AX2E3 Bond Angle
Replies: 7
Views: 70

### Re: AX2E3 Bond Angle

Thank you all!
Mon Nov 30, 2020 9:42 pm
Forum: Hybridization
Topic: identification
Replies: 5
Views: 66

### Re: identification

First, you can determine the number of regions of electron density in order to determine the number of hybrid orbitals in BrF3 (number of regions of electron density = number of hybrid orbitals). After drawing the Lewis structure, we see that there are 5 regions of electron density, meaning there mu...
Mon Nov 30, 2020 9:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Week 7 & 8 Sapling #18
Replies: 2
Views: 29

### Re: Week 7 & 8 Sapling #18

Here's a picture of H2CCCH2 that hopefully helps in visualizing the orbitals. The central C atom has 2 sp2 hybridized orbitals (in blue) and 2 unhybridized p-orbitals (in green). These 2 p-orbitals (involved in the 2 π bonds) must be perpendicular to one another (like how px, py, and pz are all perp...
Mon Nov 30, 2020 3:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AX2E3 Bond Angle
Replies: 7
Views: 70

### AX2E3 Bond Angle

Since the shape of AX2E3 is linear, would its bond angle be 180 degrees?
Tue Nov 24, 2020 5:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling #6
Replies: 5
Views: 57

### Re: Sapling #6

Here is a picture I found online of the shape of XeF2. The lone pairs are represented by the color yellow, and the F atoms are represented by white. I hope this helps!
Tue Nov 24, 2020 5:44 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14B
Replies: 9
Views: 91

### Re: Chem 14B

I think he means that we might take our exams during lecture time instead of during our discussion sections, so we should keep our lecture times open just in case.
Mon Nov 23, 2020 7:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Nonpolar molecules
Replies: 3
Views: 30

### Re: Nonpolar molecules

A molecule is nonpolar when the molecule has no net dipole moment, such as when the the dipole moments in a molecule cancel each other. For example, CF4 is a nonpolar molecule. The difference in electronegativity between C and F creates a dipole moment. These four dipole moments cancel each other ou...
Mon Nov 23, 2020 7:04 pm
Forum: Hybridization
Topic: hybridization of phosphorus (Sapling Q.11)
Replies: 21
Views: 96

### Re: hybridization of phosphorus (Sapling Q.11)

Looking at the Lewis structure, you see that the P atom has four regions of electron density. This means that there should be four hybrid orbitals. Even though there is a double bond, this still counts as one region of electron density. This might make a bit more sense if we think about the molecule...
Mon Nov 23, 2020 6:58 pm
Forum: Administrative Questions and Class Announcements
Topic: Wednesday Sections
Replies: 1
Views: 25

### Re: Wednesday Sections

Yes, there will be discussion section and lecture on Wednesday.
Thu Nov 19, 2020 4:49 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic v. Covalent Character
Replies: 6
Views: 58

### Re: Ionic v. Covalent Character

In an ionic bond, you would expect a complete transfer of an electron from one atom to another when the atoms are bonded together. However, we know that ionic bonds have some covalent character (covalent bonds entail sharing of electrons). This covalent character in ionic bonds is due to that shared...
Thu Nov 19, 2020 4:43 pm
Forum: Bond Lengths & Energies
Topic: Textbook Question 3F.15
Replies: 8
Views: 97

### Re: Textbook Question 3F.15

To add on to the previous responses, when you draw the Lewis structure of AsF3, you will notice that As, the central atom, has two lone pair electrons. This lone pair is the reason why AsF3 is a polar molecule. The lone pair creates a net dipole moment in the molecule, so we know that AsF3 has dipol...
Thu Nov 19, 2020 4:36 pm
Forum: Bond Lengths & Energies
Topic: Bond Strength and Polarizability
Replies: 4
Views: 31

### Re: Bond Strength and Polarizability

I think you might be confusing intramolecular and intermolecular forces as you said. Even if a molecule has strong bonds (which are intramolecular), it doesn't necessarily mean it will have strong intermolecular forces (such as London forces). I hope this helps!
Wed Nov 18, 2020 5:38 pm
Forum: Lewis Structures
Topic: Textbook Problem 2C.9
Replies: 1
Views: 16

### Re: Textbook Problem 2C.9

Before drawing the Lewis structure, you should count the total number of electrons in each molecule. For example, for XeF2, Xe has 8 electrons, and 7 electrons for F x 2 F atoms = 14 electrons. XeF2 has a total of 8 + 14 = 22 electrons. Next, you connect each F atom to the central atom Xe. With thes...
Wed Nov 18, 2020 4:57 pm
Forum: Octet Exceptions
Topic: Textbook 2C.5
Replies: 3
Views: 24

### Re: Textbook 2C.5

I agree with Sophia, it might have something to do with O having a higher electronegativity than Cl, meaning that O has a stronger pull on electrons than Cl does.
Fri Nov 13, 2020 6:40 pm
Forum: Lewis Acids & Bases
Topic: Determining Lewis Acids and Bases
Replies: 9
Views: 47

### Re: Determining Lewis Acids and Bases

To add on, molecules that have electron-deficient central atoms (for example, BeCl2) accept electrons and are thus Lewis acids.
Fri Nov 13, 2020 6:31 pm
Forum: Dipole Moments
Topic: Sapling W 5/6 #17
Replies: 10
Views: 108

### Re: Sapling W 5/6 #17

To add on, BCl3 also only has dispersion forces. For BCl3, Br2, and C2H6, the dipoles cancel out in each molecule, so there is no net dipole moment in each molecule, which tells us that there are no dipole-dipole interactions, only dispersion forces. CH3Cl has dipole-dipole interactions because the ...
Fri Nov 13, 2020 6:12 pm
Forum: Lewis Structures
Topic: Sapling Week 5-6 HW Question 6
Replies: 7
Views: 55

### Re: Sapling Week 5-6 HW Question 6

I am having some trouble with this question as well. In the explanation for why CO2 is a Lewis acid, Sapling says that molecules with polar double bonds accept electrons, but why are the double bonds in CO2 polar? Oxygen has a far greater electronegativity compared to Carbon, so the covalent bond i...
Tue Nov 10, 2020 5:16 pm
Forum: Dipole Moments
Topic: H-bond and Dipole-Dipole
Replies: 4
Views: 30

### Re: H-bond and Dipole-Dipole

I think a hydrogen bond is a special type of dipole-dipole interaction. It's kind of like how a square is always rectangle, but a rectangle isn't always a square. Hydrogen bonding is an intermolecular interaction that must involve two dipoles, but dipole-dipole interactions aren't always considered ...
Tue Nov 10, 2020 5:08 pm
Forum: Dipole Moments
Topic: Sapling Q14
Replies: 2
Views: 11

### Re: Sapling Q14

Claire_Latendresse_3J wrote:Hi Isabella,

Your reasoning is correct :) An N-H, O-H, or (sometimes) F-H bond can form hydrogen bonds, but a C-H bond has too small of an electronegativity difference to be viable for a hydrogen bond.

Thank you, that makes sense!!
Tue Nov 10, 2020 4:56 pm
Forum: Dipole Moments
Topic: Sapling Q14
Replies: 2
Views: 11

### Sapling Q14

Here is the question: Acetone can form hydrogen bonds with water. Four images are given which show an acetone molecule interacting with a water molecule. Hydrogen bonds are represented as dashed, green lines. I was wondering if my reasoning for this problem was correct. In this image, is the depicte...
Tue Nov 10, 2020 11:33 am
Forum: Lewis Structures
Topic: Sapling Week 5-6 HW Question 6
Replies: 7
Views: 55

### Re: Sapling Week 5-6 HW Question 6

I am having some trouble with this question as well. In the explanation for why CO2 is a Lewis acid, Sapling says that molecules with polar double bonds accept electrons, but why are the double bonds in CO2 polar?
Wed Nov 04, 2020 9:51 pm
Forum: Ionic & Covalent Bonds
Topic: Textbook Problem 2A.1
Replies: 4
Views: 25

### Re: Textbook Problem 2A.1

lauren_tran_3J wrote:I believe that even though d is a lower energy level it still has them as valence electrons because the shell is incomplete. I might be wrong! Hope this helps.

Wed Nov 04, 2020 9:48 pm
Forum: Octet Exceptions
Topic: Incomplete Octet example BF3
Replies: 1
Views: 35

### Re: Incomplete Octet example BF3

I would think that the top structure is the best Lewis structure when taking formal charge into consideration, since the formal charge of each atom is 0. The bottom structure with the double bond does not seem favorable to me because the formal charge of B is -1, and the formal charge of F is +1. Ma...
Wed Nov 04, 2020 9:39 pm
Forum: Octet Exceptions
Topic: "Octets" beyond 8
Replies: 6
Views: 42

### Re: "Octets" beyond 8

I don't think an expanded octet necessarily means the atom will be unstable. In the lecture, Dr. Lavelle said that certain atoms can accommodate more than 8 valence electrons because atoms in period 3 or higher have d-orbitals in their valence shell that can accommodate additional electrons.
Wed Nov 04, 2020 9:31 pm
Forum: Trends in The Periodic Table
Topic: Effective nuclear charge
Replies: 5
Views: 46

### Re: Effective nuclear charge

Effective nuclear charge is the net nuclear charge after taking into account the shielding caused by other electrons in the atom. Inner electrons shield outer electrons from the electrostatic attraction of the positive nucleus, so the effective nuclear charge is less than the actual nuclear charge. ...
Wed Nov 04, 2020 4:33 pm
Forum: Ionic & Covalent Bonds
Topic: Textbook Problem 2A.1
Replies: 4
Views: 25

### Textbook Problem 2A.1

Here is the question: Give the number of valence electrons (including d electrons) for each of the following elements: (a) Sb; (b) Si; (c) Mn; (d) B. I am confused as to which electrons count as valence electrons, specifically for Sb and Mn. Sb has 5 valence electrons, while Mn has 7 valence electro...
Thu Oct 29, 2020 9:12 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Bohr frequency question
Replies: 2
Views: 42

### Re: Bohr frequency question

Yes, when the electron drops to a lower energy level, the energy difference is given off as a photon. This release of energy explains the negative sign, like you said. Also, like Kayla said, according to the reference point, a bound electron has lower energy than a free electron.
Thu Oct 29, 2020 9:04 pm
Forum: Trends in The Periodic Table
Topic: Oxygen ionization energy
Replies: 3
Views: 54

### Re: Oxygen ionization energy

The ionization energy of oxygen is an exception to the general trend in the periodic table. For oxygen, there are four electrons in the 2p subshell. Two of these electrons are in the same orbital, so they experience electron-electron repulsion. This repulsion causes the ionization energy to be sligh...
Wed Oct 28, 2020 10:33 pm
Forum: Photoelectric Effect
Topic: UA Session Question
Replies: 2
Views: 46

### Re: UA Session Question

Since the wavelength of the electrons is given (1.7 x 10^5 m), you can first find the velocity of the ejected electrons by using De Broglie's wave equation: \lambda = \frac{h}{mv} . After finding velocity of the ejected electron, you can find the kinetic energy of the ejected electron ( \frac{1}{2}m...
Wed Oct 28, 2020 10:24 pm
Forum: Einstein Equation
Topic: Sapling HW #7
Replies: 7
Views: 84

### Re: Sapling HW #7

From the photoelectric effect experiment, we know that E_{photon}- \Phi (work function) = E_{k} . Since you are calculating the maximum or longest wavelength possible that will eject electrons, you can assume that the kinetic energy is 0, so E_{photon} = \frac{hc}{\lambda } = \Phi , and you ...
Wed Oct 28, 2020 6:54 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra wave-like or particle-like properties
Replies: 3
Views: 54

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

According to the Bohr frequency condition, when a high energy electron drops to a lower energy level, the difference in energy is given off as a photon, so light would be behaving like a particle in an experiment involving atomic spectra.
Tue Oct 20, 2020 11:50 am
Forum: Properties of Electrons
Topic: Wave Properties of Electrons and Diffraction Patterns
Replies: 2
Views: 22

### Re: Wave Properties of Electrons and Diffraction Patterns

Constructive interference (or waves in phase) means that the peak of one wave overlaps the peak of another wave, and the trough of one wave overlaps the trough of another wave. Destructive interference (waves out of phase) means that the peak of one wave overlaps with the trough of another. Waves in...
Mon Oct 19, 2020 10:01 pm
Forum: Student Social/Study Group
Topic: Workshops
Replies: 3
Views: 34

### Re: Workshops

Each workshop has problems separate from other workshops because each UA creates their own worksheets, so going to multiple workshops will give you more practice problems to do.
Mon Oct 19, 2020 9:38 pm
Forum: Balancing Chemical Reactions
Topic: Formula Unit vs. Molecules
Replies: 3
Views: 55

### Re: Formula Unit vs. Molecules

I believe that formula units are used when referring to ionic compounds, and molecules are used when referring to molecular compounds. I hope this helps!
Mon Oct 19, 2020 9:32 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Difference in Equations
Replies: 4
Views: 50

### Re: Difference in Equations

En = -hr/(n^2) is an empirical equation for an H atom that can be used when finding the energy difference between two energy levels. For example, if you were asked to find the energy emitted when an electron makes a transition from the fourth to the second principle quantum level, you could use this...
Mon Oct 19, 2020 9:21 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Problem 1B.25
Replies: 6
Views: 85

### Re: Problem 1B.25

For this problem, you would use Heisenberg's uncertainty equation: Δp x Δx ≥ h/(4π). We also know that Δp = m x Δv. Since the problem is asking for minimum uncertainty in the speed of an electron, we are trying to solve for Δv. The problem gives you Δx = 350. pm (but you should convert this to mete...
Mon Oct 19, 2020 9:15 pm
Forum: Photoelectric Effect
Topic: Concept question photoelectric effect
Replies: 1
Views: 33

### Re: Concept question photoelectric effect

The photoelectric effect tells us that light is made up of photons, and when trying to eject electrons from a metal surface, the energy of each photon must be sufficient to overcome the binding energy between the atom and the electron (or the threshold energy). Each photon interacts with one electro...
Thu Oct 15, 2020 1:14 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Textbook Problem 1A.11
Replies: 2
Views: 21

### Re: Textbook Problem 1A.11

Within a series, the final energy level is the same. For example, in the Balmer series, the lower or final energy level is n = 2, and in the Lyman series, the lower energy level is n = 1. Furthermore, the Balmer series is the visible light region, and the Lyman series is the ultraviolet region. I ho...
Thu Oct 15, 2020 1:05 pm
Forum: Einstein Equation
Topic: Converting from MHz to Hz
Replies: 5
Views: 45

### Re: Converting from MHz to Hz

1 MHz = 10^6 Hz, so I would check to make sure you converted MHz to Hz correctly. Also, I believe the answer for this problem should be 1 m. I hope this helps!
Tue Oct 13, 2020 4:26 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Question 19 Heisenberg Indeterminacy Equation
Replies: 2
Views: 32

### Re: Question 19 Heisenberg Indeterminacy Equation

We know that Δp = m x Δv, so Δv = Δp / m. You would use the value of Δp that you already found and the mass of the electron (in kg) as stated in the problem in order to calculate the uncertainty in velocity. Hope this helps!
Tue Oct 13, 2020 4:21 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Problem 1B.25
Replies: 6
Views: 85

### Re: Problem 1B.25

For this problem, you would use Heisenberg's uncertainty equation: Δp x Δx ≥ h/(4π). We also know that Δp = m x Δv. Since the problem is asking for minimum uncertainty in the speed of an electron, we are trying to solve for Δv. The problem gives you Δx = 350. pm (but you should convert this to meter...
Mon Oct 12, 2020 8:53 pm
Forum: Photoelectric Effect
Topic: Electromagnetic Spectrum
Replies: 2
Views: 27

### Re: Electromagnetic Spectrum

I think we should know the different types of radiation and their corresponding wavelengths, or at least, for example, the order of the radiation types based on their wavelengths from longest to shortest. If you take a look at some assigned 1A problems on the syllabus, like 1A.5 and 1A.9, you would ...
Mon Oct 05, 2020 2:50 pm
Forum: Molarity, Solutions, Dilutions
Topic: Fundamentals G23 [ENDORSED]
Replies: 3
Views: 51

### Re: Fundamentals G23[ENDORSED]

I only did one step differently: I added the moles of Cl- up to find the total moles of Cl- first, and then I divided the moles of Cl- by 0.1000 L to find the molarity. I also did not round during any intermediate steps and was able to get 0.13 M as my answer. I hope this helps!
Mon Oct 05, 2020 2:32 pm
Forum: Limiting Reactant Calculations
Topic: Fundamentals M5
Replies: 7
Views: 82

### Re: Fundamentals M5

I would divide the moles of each reactant by its stoichiometric coefficient in order to determine which reactant is in excess. For example, you are given 12 mol of ClO2, so divide 12 mol of ClO2 by 6 mol of ClO2 (as indicated by the stoichiometric coefficient of ClO2), and you get 2. You can do the ...
Mon Oct 05, 2020 1:59 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect Post-Assessment Questions 29-30
Replies: 2
Views: 39

### Re: Photoelectric Effect Post-Assessment Questions 29-30

For number 29, the work function is given in units of kJ/mol. However, since the question is asking for the energy required per sodium atom, you would need to use Avogadro's constant to convert from moles to atoms. After getting this answer, you should get a different answer for number 30 as well. I...
Mon Oct 05, 2020 12:52 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant Fundamentals Section M Exercise M.11
Replies: 4
Views: 42

### Re: Limiting Reactant Fundamentals Section M Exercise M.11

I think there is supposed to be a space after the colon! P4O6 is not part of the reactants for that chemical equation.
Mon Oct 05, 2020 12:44 pm
Forum: Limiting Reactant Calculations
Topic: Fundamentals M11
Replies: 3
Views: 56

### Re: Fundamentals M11

For part c, since you know the moles of O2 like you said, you can find the moles of P4O6 used in the reaction by using the molar ratio (1 mol P4O6 : 2 mol O2). Then you would subtract this used number of moles from the initial number of moles of P4O6. The initial moles of P4O6 can be calculated from...
Mon Oct 05, 2020 10:58 am
Forum: Balancing Chemical Reactions
Topic: Law of Conservation with Exothermic/Endothermic Reactions
Replies: 11
Views: 131

### Re: Law of Conservation with Exothermic/Endothermic Reactions

Since heat is not necessarily considered one of the reactants or products in a chemical reaction, heat is not factored into the total masses. However, you are right that heat is involved in the law of conservation of energy.
Sat Oct 03, 2020 2:21 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Fundamentals Problem E9
Replies: 3
Views: 122

### Re: Fundamentals Problem E9

For this problem, since the mass in grams of MgSO4 • 7 H2O was given (5.15 g), I first converted the mass to moles of MgSO4 • 7 H2O by using its molar mass. I used the molar ratio (11 moles of O in 1 mole of MgSO4 • 7 H2O) to find the moles of O and then converted moles of O to the number of O atoms...