## Search found 65 matches

Sun Mar 10, 2019 6:34 pm
Forum: Balancing Redox Reactions
Topic: Question from textbook
Replies: 3
Views: 103

### Re: Question from textbook

The first step would be to balance all the phosphorus on both sides of the equation. Next, you would add an H2O to the reactant side in order to balance the oxygen. Once the oxygen and phosphorus are balanced, you add an H+ to whatever side is needed an balance the hydrogens. Since the reaction occu...
Sun Mar 10, 2019 6:23 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Microscopic reversibility
Replies: 3
Views: 146

### Re: Microscopic reversibility

Microscopic reversibility is always happening at equilibrium, because at equilibrium the forward and reverse rates are equal to each other. Microscopic reversibility states that at a small, molecular level, there is activity taking place between molecules but this activity cancels each other out (fo...
Sun Mar 10, 2019 6:19 pm
Forum: General Rate Laws
Topic: Reaction Order
Replies: 5
Views: 200

### Re: Reaction Order

A reaction would be first-order if the exponents on the elements in the rate law add up to 1. Likewise, the reaction would be second-order if the exponents on the elements in the rate law add up to 2.
Sun Mar 03, 2019 1:53 pm
Forum: General Rate Laws
Topic: Units of K
Replies: 4
Views: 174

### Re: Units of K

In a zero order, K has the units of concentration/time, in a first order the units are 1/time, and in a second order the units are 1/concentration*time.
Sun Mar 03, 2019 1:51 pm
Forum: General Rate Laws
Topic: Initial reaction rates
Replies: 2
Views: 107

### Re: Initial reaction rates

Initial reaction rates are a function of only reactant concentration, this allows us to find the order of the reactants only without getting product concentrations involved. The later rate would be that of the equilibrium and would not tell us how fast the reaction occurs.
Sun Mar 03, 2019 1:48 pm
Forum: First Order Reactions
Topic: Dividing Experiments to Find Order
Replies: 4
Views: 172

### Re: Dividing Experiments to Find Order

When solving for the reaction order, you want to try and divide the experiments as to end up with a whole number. However, ending up with fractions wouldn't necessarily make the problem wrong.
Sun Feb 24, 2019 3:01 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: gibbs free energy
Replies: 5
Views: 174

### Re: gibbs free energy

Gibbs free energy is a state function that tells us a reactions relationship between enthalpy (positive if exothermic, negative if endothermic) and the entropy along with temperature. Gibbs free energy is defined in terms of thermodynamic properties that are state functions as well. If the change in...
Sun Feb 24, 2019 2:55 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: salt bridge
Replies: 3
Views: 134

### Re: salt bridge

If the salt bridge was not present in a galvanic cell, there would be no ion transfer, meaning the solutions would not stay neutral. After a certain amount of electron transfer, the exchange would stop due to there being no salt bridge present to transfer ions. With no salt bridge, the galvanic cell...
Sun Feb 24, 2019 2:51 pm
Forum: Balancing Redox Reactions
Topic: Which Equation to Flip?
Replies: 9
Views: 486

### Re: Which Equation to Flip?

When calculating the Ecell, you know that you must always flip the value with a smaller voltage, as the Ecell must be positive since cells / batteries do work. The Cu has a smaller E value so when calculating the Ecell, the E value of Cu is "flipped".
Mon Feb 18, 2019 10:16 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: K vs. Delta G
Replies: 2
Views: 110

### Re: K vs. Delta G

Delta G refers to the change in Gibbs Free Energy, while K is the equilibrium constant which refers to the direction in which product and reactant formation is favored. When K=1 , the concentration of products is equal to the concentration of reactants, meaning there is no side of the reaction that ...
Mon Feb 18, 2019 10:04 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Negative Temperature
Replies: 5
Views: 182

### Re: Negative Temperature

When you are thinking of negative temperatures, you are most likely referring to a negative Celsius. However, when we look at temperature we must convert to Kelvin, and there can never truly be a negative temperature when referring to the temperature in Kelvin as 0 degrees K is the lowest possible t...
Mon Feb 18, 2019 10:01 am
Forum: Calculating Work of Expansion
Topic: Units for R
Replies: 10
Views: 600

### Re: Units for R

Depending on which value you use, R can have the constants: J*K-1*mol-1, L*atm*K-1*mol-1, L*bar*K-1*mol-1, or L*Torr*K-1*mol-1. You use the various values of R based on the other variables used, make sure all the units cancel out and you are left with the units you are trying to find.
Tue Feb 05, 2019 12:17 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: PdeltaV with Solids and Liquids
Replies: 3
Views: 119

### Re: PdeltaV with Solids and Liquids

Solids and liquids have a set volume, so there can be no change in volume. Hence, the change in V or delta V is 0.
Tue Feb 05, 2019 12:10 am
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Gas taking up more states
Replies: 2
Views: 128

### Re: Gas taking up more states

Solids are the most compact state, molecules are tightly packed together and this in turn creates rigid structures that do not change shape or volume. Liquids have weaker bonds, allowing for a change in shape but with a set volume. Gases have the weakest bonds out of the three, gases occupy the shap...
Tue Feb 05, 2019 12:07 am
Forum: Calculating Work of Expansion
Topic: ideal gas
Replies: 2
Views: 139

### Re: ideal gas

Unless stated otherwise, we assume that the gas we are working with is an ideal gas.
Wed Jan 30, 2019 9:08 pm
Forum: Calculating Work of Expansion
Topic: negative vs. positive internal energy
Replies: 2
Views: 146

### Re: negative vs. positive internal energy

When the change in internal energy of a system is negative, it means work is being done on the environment. When the change in internal energy of a system is positive, it means work is being done on the system from the environment.
Wed Jan 30, 2019 9:06 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Specific Heat Capacity
Replies: 2
Views: 89

### Re: Specific Heat Capacity

The heat required to raise the temperature of an object by 1 degree Celsius is considered the heat capacity . The heat required depends on the amount of substance, so heat capacity is considered an extensive property . When you divide the heat capacity by the amount of substance present (grams), you...
Wed Jan 30, 2019 9:03 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Engine and Body Open system
Replies: 3
Views: 153

### Re: Engine and Body Open system

A motor engine has pipes leading out of the engine, making it an open system as it takes in and releases air. A human body has a nose and mouth which take in and release air as well. These are both open systems as there is an exchange between the internal system (the engine and the human body) and t...
Mon Jan 21, 2019 11:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: partial pressures vs. concentrations
Replies: 3
Views: 141

### Re: partial pressures vs. concentrations

Kp can actually be converted into Kc using the equation Kp=Kc(RT)^delta n, showing that Kp and Kc are not always interchangeable. You solve for the equilibrium constant using what the question gives you (whether it is Kp or Kc), unless noted otherwise.
Mon Jan 21, 2019 11:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Stability
Replies: 3
Views: 94

### Re: Stability

K refers to which way a compound goes in a reaction. The larger the K for a reactant, the more the compound heads towards the products, leading to dissociation and making a compound with a large K more unstable. The smaller the K value for a reactant, the more the reactants are favored, making the c...
Mon Jan 21, 2019 11:15 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Finding Concentrations of H3O+ and OH-
Replies: 2
Views: 614

### Re: Finding Concentrations of H3O+ and OH-

[H3O+] is not 1x [BaOH2] because the equation we set up for the dissociation of Ba(OH)2 only includes Ba and OH. We can only use mole ratios to determine the concentration of [OH] because it is part of the dissociation equation of Ba(OH)2 whereas [H30] is not part of the equation so we cannot use mo...
Tue Jan 15, 2019 8:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table
Replies: 4
Views: 187

### Re: ICE table

105085381 wrote:Is the ICE table used purely to find missing concentrations?

The ICE table allows you to organize and solve for the change in concentration from the initial to equilibrium concentration, hence the name ICE (Initial, Change, Equilibrium).
Tue Jan 15, 2019 8:06 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Quotient
Replies: 10
Views: 336

### Re: Reaction Quotient

Q is a reaction quotient taken at any point of time for the reaction, whereas K is the reaction quotient taken specifically at equilibrium.
Tue Jan 15, 2019 7:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: homework
Replies: 1
Views: 100

### Re: homework

If it's a strong acid, we know that this compound dissociates completely. It is helpful to use an ICE table just out of habit, because not all compounds would dissociate completely.
Wed Jan 09, 2019 11:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Concentrations
Replies: 4
Views: 131

### Re: Equilibrium Concentrations

K is a constant referring to the equilibrium constant whereas Q refers to the equilibrium at a certain point in time.
Wed Jan 09, 2019 10:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Units for Kc and Kp
Replies: 1
Views: 309

### Re: Units for Kc and Kp

Kc and Kp themselves do not have units. However, when calculating for them, it does not hurt to use units, for example when calculating for Kp, the pressure of gases are often measured in a unit called bar.
Wed Jan 09, 2019 10:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework 11.39 Edition 6
Replies: 4
Views: 203

### Re: Homework 11.39 Edition 6

You typed out the question for 11.40 instead of 11.39, is it possible you are looking at the wrong problem?
Wed Jan 09, 2019 10:21 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: "Shifting"
Replies: 15
Views: 1066

### Re: "Shifting"

"Sitting" to the left simply means the reaction is favored towards the reaction side, or the left side of the equation.
Sat Dec 08, 2018 1:05 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Periodic trend of acid strength
Replies: 2
Views: 221

### Re: Periodic trend of acid strength

In the case of HBrO2 and HClO2, it is the O--H bond that is getting broken, and because Cl has a higher electronegativity it is the more stable atom after the hydrogen atom leaves, making HClO2 the stronger acid.
Sat Dec 08, 2018 12:59 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH vs. pOH
Replies: 2
Views: 144

### Re: pH vs. pOH

Yes. The pH + pOH of the same solution equals 14.
Sat Dec 08, 2018 12:58 pm
Forum: Naming
Topic: Latin Names
Replies: 2
Views: 114

### Re: Latin Names

Anything on this list is fair game, https://lavelle.chem.ucla.edu/wp-conten ... pounds.pdf. A UA said we most likely won't be tested on naming Iron but might as well know it just to be safe.
Sat Dec 08, 2018 12:57 pm
Forum: Ionic & Covalent Bonds
Topic: SiO2
Replies: 1
Views: 137

### Re: SiO2

Si-O bonds are polar, but SiO2 itself is non-polar because the dipoles cancel out.
Sat Dec 08, 2018 12:54 pm
Forum: Industrial Examples
Topic: Coordination compounds as Chemotherapy drugs
Replies: 5
Views: 751

### Re: Coordination compounds as Chemotherapy drugs

A coordination compound that is used as a chemotherapy drug is cisplatin. It binds to the replication site in DNA and prevents cancer cells from replicating.
Sat Dec 08, 2018 12:52 pm
Forum: Lewis Structures
Replies: 1
Views: 150

### Re: Drawing radicals

The radical usually ends up being the central atom in the lewis structure.
Sat Dec 08, 2018 12:51 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: Dispersion and Mass?
Replies: 1
Views: 266

### Re: Dispersion and Mass?

Yes, the larger the atom is, the more likely it is to have stronger dispersion forces.
Sat Dec 08, 2018 12:49 pm
Forum: Octet Exceptions
Topic: expanded octet bonding
Replies: 1
Views: 277

### Re: expanded octet bonding

Expanded octets rely on the d-orbital for bonding, so theoretically no more than 10 extra electrons can be bonded. However, usually the max amount of bonds won't pass 6 (SF6).
Sat Dec 08, 2018 12:45 pm
Forum: Naming
Topic: naming compounds
Replies: 6
Views: 312

### Re: naming compounds

You use di, tri, tetra, etc. when naming for compounds such as Fluorine if there is two or more in the compound. Bis, tris, and tetrakis would be used with compounds already containing di, tri, tetra, etc. already inside of a parenthesis. For example, if there are two ethylenediamine compounds, it w...
Sat Dec 08, 2018 12:41 pm
Forum: Naming
Topic: Naming
Replies: 3
Views: 152

### Re: Naming

We should be familiar with and be able to identify the compounds from name to formula and vice-versa.
Here's the link: https://lavelle.chem.ucla.edu/wp-conten ... pounds.pdf
Sat Dec 01, 2018 12:49 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: repulsion strength
Replies: 3
Views: 372

### Re: repulsion strength

The lone pair electron is more spread out and occupies a larger volume, which causes a higher repulsion between two lone pairs. Bonding pairs are pulled in more tightly and occupy less space, which is why lone- bonding pairs have a lower repulsion strength.
Sat Dec 01, 2018 12:44 pm
Forum: Resonance Structures
Topic: Resonance
Replies: 4
Views: 312

### Re: Resonance

The most stable structure would be the lewis structure with the least amount of charges on it, and has as many formal charges of 0 as possible.
Sat Dec 01, 2018 12:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Types of intramolecular forces
Replies: 4
Views: 211

### Re: Types of intramolecular forces

You can determine the type of forces present in a molecule by looking at the structure of the molecule and the elements bonded to each other. For example, if a Hydrogen is bonded to either a Fluorine, Oxygen, or Nitrogen, hydrogen bonding is present. A dipole-dipole interaction is a type of Van Der ...
Sun Nov 25, 2018 7:54 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: Dipole
Replies: 3
Views: 164

### Re: Dipole

Polar molecules must have polar bonds because of the difference in electronegativity between atoms. If the molecule is polar, it means the dipoles do not cancel.
Sun Nov 25, 2018 7:41 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: Dipole-Dipole forces
Replies: 3
Views: 165

### Re: Dipole-Dipole forces

If a molecule is polar, it has dipole-dipole forces.
Sun Nov 25, 2018 7:37 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Exam
Replies: 22
Views: 724

### Re: Final Exam

The final exam will most likely be cumulative, covering every topic we have gone over in Chemistry 14A.
Mon Nov 19, 2018 11:57 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles in 7E 2E.13.b
Replies: 4
Views: 155

### Re: Bond Angles in 7E 2E.13.b

Double bonds are almost negligible when finding bond angles, because we look at electron density in VSEPR, so double bonds and single bonds have the same value when calculating bond angles.
Mon Nov 19, 2018 11:52 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle
Replies: 8
Views: 317

### Re: Bond Angle

With bond angles being repulsed by lone pairs, you won't know the specific amount unless you look up previous experimental values. As for being asked questions on the bond angles, you simply need to know that a lone pair would make the bond slightly less due to repulsion.
Mon Nov 19, 2018 11:49 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Rotation from Sigma and Pi bonds
Replies: 2
Views: 140

### Re: Rotation from Sigma and Pi bonds

The condition for double bonds is to be stable and rigid. A combination of a pi and sigma bond (forms a double bond) has restrictions on how the bond can rotate. If this bond rotates past its range of motion, the double bond would break.
Sun Nov 11, 2018 11:32 am
Forum: Resonance Structures
Topic: bond lengths of resonant atoms
Replies: 4
Views: 281

### Re: bond lengths of resonant atoms

Resonance structure of atoms all exist at the same time, so each bond would technically be the same length as they are all the same bond in different resonance structures.
Sun Nov 11, 2018 11:26 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Angles of Shapes [ENDORSED]
Replies: 4
Views: 300

### Re: Angles of Shapes[ENDORSED]

VSEPR structures require a certain amount of memorization in order to remember the bond angle. For example, a Trigonal Pyramid has bond angles of <109 degrees. Dr. Lavelle hasn't mentioned whether we are required to memorize the angles yet or not, but I would assume so.
Sun Nov 11, 2018 11:22 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Dipole-Induced Dipole [ENDORSED]
Replies: 2
Views: 103

### Re: Dipole-Induced Dipole[ENDORSED]

A dipole-induced dipole is a force of attraction between two molecules that occurs when an attractive force is induced on a molecule by the presence of another polar molecule. For example, when a polar molecule nears another, say non-polar molecule, the partial charges of the polar molecule causes a...
Sat Nov 03, 2018 5:46 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 5
Views: 209

### Re: Electron Affinity

Can someone explain why C has a higher electron affinity than N in more detail plz? It’s confusing having said that N is closer to the right of the periodic table... Carbon has a higher electron affinity because a half-filled p sub-shell is more stable, giving Carbon a higher electron affinity than...
Sat Nov 03, 2018 5:38 pm
Forum: Lewis Structures
Topic: Lewis Acids and Bases
Replies: 5
Views: 161

### Re: Lewis Acids and Bases

Lewis acids are compounds that accept electrons, whereas Lewis bases are compounds that donate electrons. The covalent bond between the two is formed when the Lewis base donates an electron to the Lewis acid and a coordinate covalent bond is simply a type of covalent bond in which one reactant gives...
Sat Nov 03, 2018 5:33 pm
Forum: Octet Exceptions
Topic: Octet exceptions
Replies: 8
Views: 453

### Re: Octet exceptions

S, P, Si, and Cl are common elements that can form an octet because they can utilize the d-orbital found in the 3rd energy level. Elements generally will only want to fill their octet and only go over and expand their octet if they have to, with these 4 elements being able to have an expanded octet.
Sun Oct 28, 2018 5:45 pm
Forum: Properties of Electrons
Topic: Coulomb
Replies: 4
Views: 430

### Re: Coulomb

It is a natural attraction between positive and negative charges, and a natural repulsion between similar charges. For example, electrons in orbital around a hydrogen atom would have a coulombic attraction to the protons within the nucleus.
Sun Oct 28, 2018 5:42 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: when 4s goes after 3d??
Replies: 2
Views: 136

### Re: when 4s goes after 3d??

Dr. Lavelle wants us to place the 4s sub-shell after the 3d sub-shell because the notation is more accurate in telling us that the 4s sub-shell is the valence shell and is a higher energy level. Traditional notation places the 3d sub-shell after the 4s sub-shell when listing electron configuration, ...
Sun Oct 28, 2018 5:37 pm
Forum: Quantum Numbers and The H-Atom
Topic: Degeneracy
Replies: 5
Views: 247

### Re: Degeneracy

Degeneracy refers to the equal energy states within a certain orbital. The p-orbital would have a degeneracy of 3 because there are 3 different energy states:2px, 2py, and 2pz.
Sun Oct 21, 2018 3:52 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Shielding
Replies: 5
Views: 230

### Re: Shielding

Shielding works to reduce the pull outer electrons feel from the nucleus. In an element like Na, the one electron in the third outer shell is "shielded" from the effective nuclear charge. This outer electron does not have the same interactive forces and experiences weaker interactive force...
Sun Oct 21, 2018 3:44 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: "Energy can't be negative"
Replies: 1
Views: 87

### Re: "Energy can't be negative"

Energy itself can never be negative, but in Chemistry and Physics, we often use a negative sign in front of an energy value in order to indicate whether energy is lost or gained. A negative sign in front of an energy value simply states that energy is lost from the system.
Sun Oct 21, 2018 3:37 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Velocity +/- Values
Replies: 3
Views: 186

### Re: Velocity +/- Values

From what I can tell, the delta-v value would be 61. In your first example, delta-v, or change in velocity, is a total of 10 because the velocity ranges from -5 to +5. So going from -4 to +57, there would be a delta-v of 61.
Sun Oct 14, 2018 5:23 pm
Forum: Properties of Light
Topic: Visible Light Spectrum
Replies: 3
Views: 98

### Re: Visible Light Spectrum

I doubt we would have to know specific numbers associated with colors, just know that 700 nm is red and 400 nm is violet.
Red has a long wavelength and low frequency, and violet has a short wavelength and high frequency.
Sun Oct 14, 2018 5:22 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: HW 2 CH 1 1.39
Replies: 2
Views: 70

### Re: HW 2 CH 1 1.39

You would first convert ounces into kilograms.
Then, using De Broglie's equation we solve for wavelength with the equation:
λ = h / mv
h= Planck's constant
m= kgs
v= 92 mph converts to about 41 m/s
Sun Oct 14, 2018 5:19 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: E(n)=-hR/n^2
Replies: 3
Views: 110

### Re: E(n)=-hR/n^2

As electrons fall from orbitals (for example, n=2 to n=2), the electrons lose energy, hence the negative sign within Bohr's Equation. The negative sign basically signifies energy being lost in the system.
Mon Oct 08, 2018 11:19 am
Forum: Significant Figures
Topic: Formula sheet?
Replies: 5
Views: 317

### Re: Formula sheet?

I would assume that we should have the basic formulas memorized, we will only get a periodic table to test with.
Mon Oct 08, 2018 11:16 am
Forum: SI Units, Unit Conversions
Topic: Fahrenheit, Celsius, Kelvin
Replies: 3
Views: 245

### Re: Fahrenheit, Celsius, Kelvin

I think the temperature measurement of Fahrenheit is so ingrained into the US standard of measurement that it would be inconvenient and awkward for the US to suddenly change their standard of measurement for temperature.
Mon Oct 08, 2018 11:11 am
Forum: Empirical & Molecular Formulas
Topic: Converting Units
Replies: 5
Views: 237

### Re: Converting Units

I think it is best to convert units as you solve the problem because units cancel out as you solve the problem. Converting units at the end of the problem could lead to confusion and error.

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