## Search found 60 matches

Sat Mar 16, 2019 11:04 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Porous Disk vs Salt Bridge
Replies: 3
Views: 320

### Porous Disk vs Salt Bridge

Why is the notation for a porous disk a single line (|) but for a salt bridge it is double lines? (||)
Sat Mar 16, 2019 10:32 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Steady State Approximation
Replies: 3
Views: 381

### Steady State Approximation

Do we have to know how to use steady state approximations? I remember that in lecture it was mentioned but not really covered?
Sat Mar 16, 2019 2:20 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6N.3c Cell Potential
Replies: 1
Views: 114

### 6N.3c Cell Potential

Hi, I am stuck on problem 6N.3c in the 7th edition textbook. Predict the potential of the following cell: Pt(s)|Cl2(g,250 Torr)|HCl(aq, 1.0M)||HCl(aq, 0.85M)|H2(g,125 Torr)|Pt(s) I am trying to figure out the half reactions and I am a little confused on which side is the cathode and anode. Any help?
Fri Mar 08, 2019 10:02 pm
Forum: First Order Reactions
Topic: half-life for second order
Replies: 1
Views: 106

### half-life for second order

How do you derive the half life equation for a second order reaction?
Thu Mar 07, 2019 6:47 pm
Forum: Zero Order Reactions
Topic: Zero Order Reaction- how to identify
Replies: 2
Views: 150

### Zero Order Reaction- how to identify

So by definition, a reaction is a zero order reaction if the rate is independent of the concentration of the reactant. I am slightly confused on how you would be able to identify if a reaction is zero order? Are there specific examples?
Thu Mar 07, 2019 6:42 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units of k
Replies: 4
Views: 212

### Units of k

Why do the units of k change depending on the overall order of the reaction?
Sun Mar 03, 2019 2:19 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E° is 0 for Concentration Cells
Replies: 3
Views: 174

### E° is 0 for Concentration Cells

Why does E°= 0 for concentration cells?
Sun Mar 03, 2019 2:16 pm
Forum: Van't Hoff Equation
Topic: K value- Temp
Replies: 6
Views: 517

### K value- Temp

Why does the value of K change when the temperature changes?
Wed Feb 27, 2019 12:03 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.5 7th ed
Replies: 3
Views: 113

### Re: 6L.5 7th ed

Also note that in the reaction, its says HCl(aq)

Since we know that HCl is a strong acid, it fully dissociates in water. So when it says HCl(aq) it really means H+(aq) + Cl-(aq)

We can rewrite the unbalanced reaction as: Cl2(g) + H2(g) -> H+(aq) + Cl-(aq)
Sun Feb 24, 2019 7:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Reduction Potential - Intensive
Replies: 1
Views: 64

### Standard Reduction Potential - Intensive

Why is it significant that the standard reduction potential is an intensive property?
Sun Feb 24, 2019 7:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Endothermic Reactions Spontaneous
Replies: 2
Views: 136

### Endothermic Reactions Spontaneous

Is it ever possible that a endothermic reaction can be spontaneous? If so, under what circumstances?
Sun Feb 24, 2019 7:07 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Temperature's Effect on Gibbs Free Energy
Replies: 2
Views: 96

### Temperature's Effect on Gibbs Free Energy

How does temperature affect whether a reaction will be spontaneous or not?
Sun Feb 17, 2019 5:27 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Enthalpy
Replies: 4
Views: 372

### Re: Enthalpy

Entropy is defined as ΔS=q/T. Based off the equation, the magnitude of change in entropy is greater when the value of T is lower. This is because temperature is in the denominator so the heat added to the system will have a greater effect on the change in entropy. Thinking about it intuitively, this...
Sun Feb 17, 2019 5:21 pm
Forum: Calculating Work of Expansion
Topic: work
Replies: 2
Views: 122

### Re: work

We need to calculate work when there is expansion work done. So firstly, there must be a change in volume.

Under constant pressure:
W=-Pdelta V

Under constant temperature: (isothermal, reversible)
W=-nRTln(V2/V1)
Sat Feb 16, 2019 4:31 pm
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: Degeneracy
Replies: 4
Views: 382

### Re: Degeneracy

Yes, the lowest level of degeneracy is W=1.

Thus when we plug W=1 into the equation S = klnW, S=0. (ln1 = 0)

There is no residual entropy when the degeneracy is 1
Sat Feb 09, 2019 4:00 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 4A.9 7th Edition
Replies: 3
Views: 194

### Re: 4A.9 7th Edition

The specific heat capacity of copper is 0.38 J/C.g. This value is a known calculated value thats specific to copper.

A list of specific and molar heat capacities of common materials, including copper, are listed under Table 4A.2 (its on page 252 in my textbook.)
Sat Feb 09, 2019 3:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 3/2R and 5/2R
Replies: 5
Views: 300

### 3/2R and 5/2R

Hi,

I am a little confused on calculations having to do with 3/2R. When would we use this when calculating heat capacities?
Sat Feb 09, 2019 3:44 pm
Forum: Calculating Work of Expansion
Topic: Reversible Work and Maximum Work
Replies: 5
Views: 187

### Reversible Work and Maximum Work

Why does reversible expansion do more work than an irreversible expansion?
Sun Feb 03, 2019 1:33 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Expansion Work and Nonexpansion Work
Replies: 2
Views: 103

### Expansion Work and Nonexpansion Work

Hi,

Can someone explain the difference between expansion work and nonexpansion work? Also, how does this relate to reversibility?
Sun Feb 03, 2019 1:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Why Bond Enthalpies are the least accurate
Replies: 3
Views: 352

### Why Bond Enthalpies are the least accurate

I remember in lecture that Dr. Lavelle said that out of the three methods, using bond enthalpy to calculate ΔH is the least accurate. Can someone explain why this is?
Fri Feb 01, 2019 8:50 am
Forum: Phase Changes & Related Calculations
Topic: U and its relations to work
Replies: 8
Views: 301

### U and its relations to work

What does the variable U stand for and what is its relation to work?
Fri Jan 25, 2019 12:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: increasing pressure, what happens to concentration?
Replies: 10
Views: 570

### Re: increasing pressure, what happens to concentration?

According to Le Chatelier's Principle, a change in pressure will result in an attempt to restore equilibrium by creating more or less moles of gas. For example, if the pressure in a system increases, the equilibrium will shift to favor the side of the reaction that involves fewer moles of gas. Simil...
Fri Jan 25, 2019 12:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE BOX and coefficients
Replies: 4
Views: 235

### Re: ICE BOX and coefficients

Using the equation N2(g) + 3H2(g) <--> 2NH3(g) as an example. The coefficients in front of the reactant and product affects the change in concentration. If you started with 0.1M of N2 and H2, in the ICE box you would put the initial concentration as: N2 = 0.1 H2 = 0.1 NH3 = 0 Next for the change in ...
Wed Jan 23, 2019 4:52 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE Table Clarification
Replies: 4
Views: 162

### Re: ICE Table Clarification

We can approximate when the Ka or Kb value is less than 10^-3. A small Ka or Kb value means that the acid or base is very weak so not much is ionized during the reaction, which is why we can approximate when we solve for x.
Wed Jan 16, 2019 4:20 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pure Solids and Pure Liquids
Replies: 4
Views: 215

### Re: Pure Solids and Pure Liquids

Unlike gases and aqueous solutions, pure liquids and solids do not change in molar concentration in a reaction. So, we do not need to include them in equilibrium constant expressions. Also, solvents (ex: water) are omitted from equilibrium constant expressions because the change in solvent concentra...
Wed Jan 16, 2019 4:05 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Inert Gases
Replies: 5
Views: 219

### Re: Inert Gases

When an inert gas is added to the system in equilibrium at constant volume, the total pressure will increase. But the concentrations of the products and reactants will not change. So, the equilibrium does not change. The number of moles per unit volume remains the same.
Wed Jan 16, 2019 2:17 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework question
Replies: 1
Views: 166

### Re: Homework question

In this question, the reaction occurring is : HClO2(aq) + H2O(l) ---> H3O+(aq) + ClO2-(aq) The reason why the H3O+ conc. and ClO2- conc. are the same is because of the stoichiometric coefficients are both one in the balanced equation. HClO2 is actually not a strong acid. For the second question, Ka ...
Thu Jan 10, 2019 6:47 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Homework 5G.11 7th edition
Replies: 1
Views: 99

### Re: Homework 5G.11 7th edition

Notice that Hg, B2Cl4, and Hg2Cl2 are either solid or liquid. The molar concentration of pure substances (solids or liquids) do not change. So, when you are writing the reaction quotient for this reaction, only BCl3 will be included because it is a gas.
Wed Jan 09, 2019 8:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 7th ed. 5G.5 decomposition??
Replies: 1
Views: 105

### Re: 7th ed. 5G.5 decomposition??

Partial pressure is proportional to the number of molecules. At equilibrium, 5/11 X2 molecules remain. This means that 45.56% of the molecules in the flask are X2 molecules. Using this, we can calculate the partial pressure of X2 by multiplying the initial pressure by 0.4556. We do this because the ...
Wed Jan 09, 2019 8:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5G.5 pt.c
Replies: 1
Views: 64

### Re: 5G.5 pt.c

For this problem, the diatomic molecule X2 is dissociating. This means they are separating into the individual element X. So, the reactant is X2 and the product is X.

We need to balance the equation because of conservation of matter so there is a coefficient of 2 in front of X. Hence, X2 ---> 2X
Sat Dec 08, 2018 2:21 pm
Forum: Lewis Acids & Bases
Topic: Lewis acids and bases vs. Bronsten
Replies: 2
Views: 108

### Re: Lewis acids and bases vs. Bronsten

Its actually the opposite...

A lewis acid is an electron pair acceptor.
A bronsted acid is a proton donor.

Lewis base: electron pair donor
Bronsted base: proton acceptor
Fri Dec 07, 2018 9:48 pm
Forum: Amphoteric Compounds
Topic: Amphoteric compounds
Replies: 2
Views: 142

### Re: Amphoteric compounds

Amphoteric oxides have similar locations to where the metalloids are in the periodic table. I think you just have to memorize what elements form amphoteric compounds.
Fri Dec 07, 2018 9:42 pm
Forum: Conjugate Acids & Bases
Topic: Oxoacids
Replies: 2
Views: 316

### Re: Oxoacids

Examples of oxoacids include carbonic acid (H2CO3), nitric acid (HNO3), sulfuric acid (H2SO4). In all of these acids, the H atom is bonded to an oxygen atom. These acids dissociate in water by breaking the bond between the oxygen and hydrogen. The product of oxyacids and water is hydronium ions and ...
Thu Dec 06, 2018 10:17 pm
Forum: Properties of Light
Topic: Midterm Question 3B
Replies: 1
Views: 151

### Re: Midterm Question 3B

We can use the equation I = hv - 1/2mV^2 to solve this problem. Since hv= hc/λ and λ = 58.4 x 10^-9 m we can calculate the energy of the incoming photon. The mass we use in this equation is the mass of an election. m= 9.109383 x 10^-31kg The velocity is given but we need to convert it to SI Units: 2...
Wed Dec 05, 2018 8:37 pm
Forum: Einstein Equation
Topic: Midterm Question 6 part A
Replies: 1
Views: 350

### Re: Midterm Question 6 part A

You can use equations such as E = h ν, E = hc/ λ and c = λ ν ONLY for light. De Broglie's equation: λ = h/mv can be used when the object has mass. Microscopic objects like electrons have wavelike properties since it has momentum and mass. HOWEVER, light does not have mass so you cannot use De Brogli...
Wed Dec 05, 2018 8:13 pm
Forum: Bond Lengths & Energies
Topic: How to Predict Bond Lengths
Replies: 1
Views: 1079

### Re: How to Predict Bond Lengths

You can predict the bond length of each bond because NO2 has resonance. Resonance occurs when you can draw multiple lewis structures of the same molecule just by moving where the double bond occurs. In reality, if a molecule has resonance, the actual bond length will be a combination of all of the l...
Sat Dec 01, 2018 9:31 pm
Forum: Lewis Acids & Bases
Topic: Lewis/Bronsted acids and bases
Replies: 2
Views: 135

### Re: Lewis/Bronsted acids and bases

There are two different definitions of acids and bases: 1) Lewis acid and base 2) Bronsted acid and base By definition, lewis acids and bases are defined in terms of being able to accept or donate electron pairs. In comparison, Bronsted acids and bases are defined in terms of being able to accept or...
Sat Dec 01, 2018 9:25 pm
Forum: Naming
Topic: Ion Placement in Name
Replies: 1
Views: 103

### Re: Ion Placement in Name

Typically, if there is an anion in the coordination compound, that means that the atoms inside the square brackets form a cation. Conventionally, the part listed inside the square brackets consists of ligands and the central metal they are bonded to and outside of the brackets is the counter-ion. Fo...
Sat Dec 01, 2018 9:12 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination #
Replies: 2
Views: 100

### Re: Coordination #

The coordination number is the number of atoms, ions, or molecules that a central atom holds. To answer your question, yes the total number of ligands is equal to the coordination number. Knowing the coordination number is useful when writing the molecular equation of a coordination compound and nam...
Sun Nov 25, 2018 8:38 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: Visualizing a Dimer
Replies: 1
Views: 119

### Re: Visualizing a Dimer

No, dimers can be linked together by bonds other than hydrogen bonds. There are two types of dimers: covalent and non-covalent. Non-covalent dimers such as water are held through hydrogen bonds. Covalent dimers form bonds that are covalent with other monomers. A good example of a covalent dimer is d...
Sun Nov 25, 2018 8:20 am
Forum: Hybridization
Topic: Figuring out the number of sigma and pi bonds in a molecule
Replies: 2
Views: 119

### Figuring out the number of sigma and pi bonds in a molecule

How are you able to determine the number of sigma bonds and pi bonds there are in a molecule?

In 2F.3 in the 7th edition, it asks this question for H2S and SO2. I don't know where to start to figure this out.
Sun Nov 25, 2018 7:59 am
Forum: Sigma & Pi Bonds
Topic: Which bond would break first.
Replies: 15
Views: 1096

### Re: Which bond would break first.

When a double bond breaks, pi bonds will always break first. Pi bonds are weaker than sigma bonds. This is because sigma bonds have head-on overlapping while pi bonds only have lateral overlapping. The end-to-end axial overlap of electrons attracts the nuclei to form a strong bond. On the other hand...
Sat Nov 10, 2018 7:30 pm
Forum: Dipole Moments
Topic: Hydrogen Bonds
Replies: 20
Views: 646

### Re: Hydrogen Bonds

Hydrogen bonds are strong bonds and they are one of the strongest intramolecular attractions. It takes a considerable amount of energy to break hydrogen bonds. Water has a high boiling and melting point because they have strong hydrogen bonds. However, hydrogen bonds are still weaker than covalent b...
Sat Nov 10, 2018 7:19 pm
Forum: Electronegativity
Topic: Electronegativity
Replies: 3
Views: 187

### Re: Electronegativity

Electronegativity is the tendency of an atom to attract electrons to bond with it. Ionization energy is the energy required to remove the outermost valence electron from a neutral atom. They both have the same trends on a periodic table where they increase when going from left to right and down to u...
Sat Nov 10, 2018 7:11 pm
Forum: Quantum Numbers and The H-Atom
Topic: Degeneracy
Replies: 8
Views: 747

### Re: Degeneracy

Another thing to note is that when an atom only has one electron, the orbital energy only depends on the principle quantum number n. For example, in a hydrogen atom, a 2p orbital is degenerate with a 2s orbital.

However, this is not the case for multi electron atoms.
Fri Nov 02, 2018 5:14 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Valence Electrons in the d-orbitals
Replies: 2
Views: 169

### Re: Valence Electrons in the d-orbitals

Adding on, transition metals have incomplete d sub shells, which can actually be used for bonding. Since they can be used for bonding, they should be included as valence electrons. For example, the electron configuration of Manganese is: [Ar] 3d^5 4s^2 Although the outer shell is 4s, the electrons i...
Fri Nov 02, 2018 5:03 pm
Forum: Lewis Structures
Topic: How to decide central atom?
Replies: 6
Views: 395

### Re: How to decide central atom?

The trend for electronegativity and ionization energy is the same on the periodic table. So the element that is the central atom should have both the lowest ionization energy and be the least electronegative. Electronegativity and ionization energy increases as you go up and to the right.
Tue Oct 30, 2018 11:13 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity of Gallium and Indium
Replies: 2
Views: 325

### Electron Affinity of Gallium and Indium

I noticed that the electron affinity of Gallium and Indium are exactly the same. They are both +29. Can someone please explain why this is? I thought that typically the electron affinity should decrease as you go down a group.
Sun Oct 28, 2018 9:01 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: electron configuration of tungsten
Replies: 1
Views: 2447

### Re: electron configuration of tungsten

First, we need to find the closest noble gas on the periodic table to tungsten, which is: Xenon (Xe) So, the first part of the electron configuration is : [Xe] Since tungsten's atomic number is 74 and xenon's atomic number is 54: 74-54= 20 electrons There are 20 more electrons to fill. Note Xenon's ...
Sun Oct 28, 2018 8:47 pm
Forum: Ionic & Covalent Bonds
Topic: elements with low ionization energies
Replies: 3
Views: 158

### Re: elements with low ionization energies

Note that ionization energies generally increase across a period. An increase in atomic number corresponds to an increase in the number of protons in the nucleus. So, electrons are held tighter by the higher effective nuclear charge since there are more protons in the nucleus. So, elements with low ...
Sun Oct 28, 2018 8:25 pm
Forum: Ionic & Covalent Bonds
Topic: 2A.6 7th Edition
Replies: 1
Views: 57

### Re: 2A.6 7th Edition

Hello! So, first we need to figure out the ground state electron configuration of a neutral atom of phosphorus, which is: 1s^2,2s^2,2p^6,3s^2,3p^3 We can figure this out because its in group 15, period 3. But, since we need to figure out P^3-, we have to add three electrons to the outermost shell be...
Fri Oct 19, 2018 9:47 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum number M [ENDORSED]
Replies: 7
Views: 433

### Re: Quantum number M[ENDORSED]

The quantum number ml is the magnetic quantum number. It indicates the orientation of an orbital around the nucleus. The values of m depend on l.

For example, if l=1, then m = -1,0,1

There are three possible values for m, which means that there are 3 different orientations. (px, py, pz)
Thu Oct 18, 2018 2:21 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Homework Question 1D.15 7th Edition
Replies: 1
Views: 82

### Homework Question 1D.15 7th Edition

What are the principal and orbital angular momentum quantum numbers for each of the following orbitals:

A) 6p
B) 3d
C) 2p
D) 5f

I can figure out the principal quantum number; however I am confused about how to find the angular momentum quantum number. Is there an equation to calculate it?
Thu Oct 18, 2018 12:35 am
Forum: Photoelectric Effect
Topic: Intensity
Replies: 2
Views: 91

### Re: Intensity

In the photoelectric effect, the intensity of light is proportional to the number of photons. Higher intensity just means that there is a greater number of photons present. Electromagnetic waves have both particle and wave properties! You shouldn't think of light having only particle properties or o...
Tue Oct 09, 2018 11:56 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E15 homework problem
Replies: 2
Views: 255

### Re: E15 homework problem

In this problem, the metal M is unknown and you need to figure out what it is. You know that the molar mass of the molecule is 74.1 and you can calculate the molar mass of the hydroxide, which turns out to be 34.02 g/mol. So to find the mass of the metal you do: M = 74.1 g/mol - 34.02 g/mol = 40.08 ...
Tue Oct 09, 2018 11:47 pm
Forum: Limiting Reactant Calculations
Topic: HW M.7 B
Replies: 1
Views: 181

### Re: HW M.7 B

Yes, you're right that magnesium is the limiting reactant. Are you referring to the solutions manual when you said that boron oxide is used to calculate the mass of boron produced? If so, I think the solutions manual was illustrating that if you calculate how much boron can be produced by boron oxid...
Tue Oct 09, 2018 11:38 pm
Forum: Limiting Reactant Calculations
Topic: How to determine the limiting reactant???? [ENDORSED]
Replies: 8
Views: 1978

### Re: How to determine the limiting reactant????[ENDORSED]

Hi Avery! A good place to start is to make sure that your chemical equation is balanced. Next, figure out how many moles you have for each reactant by dividing the known masses of reactants by the molar mass of each reactant. After you figure out the numbers of moles you have of each reactant, look ...
Thu Oct 04, 2018 2:07 pm
Forum: Empirical & Molecular Formulas
Topic: Molar mass and molecular weight
Replies: 3
Views: 296

### Re: Molar mass and molecular weight

The molecular weight calculates the mass of one molecule of a substance. In comparison, the molar mass refers to the mass per mole of a substance. The molar mass can be used to calculate the number of atoms, molecules, and other units. The two have different units. Molar mass: grams per mole Molecul...
Thu Oct 04, 2018 12:43 pm
Forum: Limiting Reactant Calculations
Topic: Fundamentals 7th Edition M1
Replies: 2
Views: 175

### Re: Fundamentals 7th Edition M1

Hello! To calculate the percent yield, you use the equation: percent yield = (actual yield/theoretical yield) * 100. In this problem, the question gives you the information that the actual yield is 25.2g of hydrazine. All that's left to calculate is the theoretical yield of N2H4 and plug it into the...
Wed Oct 03, 2018 3:58 pm
Forum: General Science Questions
Topic: Finding Molecular Formula, Mass Percentage
Replies: 2
Views: 179

### Re: Finding Molecular Formula, Mass Percentage

I believe that the first step you need to do is notice that the sample size has a mass of 1.78 mg. You need to convert mg into g. For example: 1.78 mg = 1.78 x 10^-3 g After converting all of the units from mg to g, find the mass percentage composition by dividing each element's mass by the mass of ...

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