Search found 86 matches

by Ruby Tang 2J
Sun Feb 23, 2020 6:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6M.5a Cell diagram
Replies: 1
Views: 8

Re: 6M.5a Cell diagram

Usually the ions must be in the solid state in order to conduct electrons, but mercury is an important exception because it is the only liquid that can act as an electrode. Therefore, you don't need an inert electrode on the left side of the cell diagram.
by Ruby Tang 2J
Sun Feb 23, 2020 6:29 pm
Forum: Balancing Redox Reactions
Topic: 6K.3 Part D
Replies: 3
Views: 39

Re: 6K.3 Part D

This one was very confusing for me as well, but I think since Cl2 has to serve as both the oxidizing and reducing agent, if Cl is getting oxidized in Cl2 --> HClO, then the Cl2 also needs to get reduced somehow. The easiest way for this to occur would be to make the other half reaction Cl2 --> 2 Cl-.
by Ruby Tang 2J
Sun Feb 23, 2020 6:23 pm
Forum: Balancing Redox Reactions
Topic: 6K.3 b)
Replies: 2
Views: 20

Re: 6K.3 b)

The oxidation numbers for the hydrogen and oxygen present in each side of the reaction are the same, so hydrogen and oxygen specifically are not oxidized or reduced in this reaction. Therefore, you don't need a separate half reaction for them, since there is no oxidation or reduction of either the h...
by Ruby Tang 2J
Sun Feb 23, 2020 6:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum
Replies: 4
Views: 13

Re: Platinum

You only need an inert electrode when the half-cell does not have a solid substance to conduct electrons. In the case of Cu(s), it is in the solid state and therefore can serve as the electrode itself, which is why you only put Pt(s) on the right side of the cell diagram and not the left.
by Ruby Tang 2J
Sun Feb 23, 2020 6:04 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cell diagrams
Replies: 1
Views: 16

Re: cell diagrams

I believe the convention is different when there is a gas involved. For H2(g) --> 2H+ + 2e-, it is convention to put the H2(g) before the H+, since the anode is where oxidation occurs and in this case, H2(g) is the chemical species getting oxidized. You also generally put the electrodes on either th...
by Ruby Tang 2J
Thu Feb 13, 2020 6:37 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4F.11
Replies: 1
Views: 19

Re: 4F.11

I think you have to calculate the ΔS due to change in temperature and change in volume separately for this problem
by Ruby Tang 2J
Thu Feb 13, 2020 6:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Mean bond enthalpies
Replies: 3
Views: 17

Re: Mean bond enthalpies

When we are given mean bond enthalpy values, those values do not directly represent a change in energy coming about as a result of a specific reaction, unlike when we use the standard enthalpy of formation of a substance, which is by definition the change in energy resulting from the formation of a ...
by Ruby Tang 2J
Thu Feb 13, 2020 6:20 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U
Replies: 5
Views: 18

Re: Delta U

Technically, ΔU is only truly 0 in the case of an ideal gas. ΔU can be thought of as the gas's internal energy, comprising both potential and kinetic energy. By definition, an ideal gas does not have any interactions between particles, so potential energy is 0. That leaves kinetic energy. Temperatur...
by Ruby Tang 2J
Thu Feb 13, 2020 6:15 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Delta S
Replies: 4
Views: 16

Re: Delta S

ΔS of the system is the same regardless of whether the process is reversible or irreversible. However, ΔS of the surroundings and ΔS total are different depending on the reversibility of the process. In a reversible process: ΔS of the surroundings = -ΔS of the system ΔS total = 0 In an irreversible ...
by Ruby Tang 2J
Tue Feb 11, 2020 8:22 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: constant p & v
Replies: 1
Views: 26

Re: constant p & v

In an isothermal reversible compression, volume is decreased while pressure is increased. The opposite is true for an expansion, where volume is increased, and pressure is decreased. Whenever the process is reversible and isothermal, ΔH = 0. In contrast, for an isobaric process, ΔH = qp, and in an i...
by Ruby Tang 2J
Tue Feb 04, 2020 11:34 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: enthalpy equations
Replies: 1
Views: 9

Re: enthalpy equations

ΔH is equal to q whenever the reaction is occurring at constant pressure, a condition which is specified in the problem. I think you may be referring to the fact that there has to be no expansion in order for ΔH to be equal to ΔU (internal energy). Hope this helps!
by Ruby Tang 2J
Tue Feb 04, 2020 11:30 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4C.3
Replies: 3
Views: 59

Re: 4C.3

These values are all included on Dr. Lavelle's "Constants and Equations" sheet! The sheet can be found on the 14B website and is the same one that we will receive during any test or midterm.
by Ruby Tang 2J
Tue Feb 04, 2020 11:27 pm
Forum: Phase Changes & Related Calculations
Topic: supercooling
Replies: 1
Views: 21

Re: supercooling

Supercooling is when a liquid is cooled below its standard freezing point without crystallizing. In order for crystallization (i.e. formation of a solid) to occur, generally a nucleus of some sort is needed around which a crystal will form. Thus, supercooling can occur when there are no nuclei of th...
by Ruby Tang 2J
Tue Feb 04, 2020 11:17 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Negative Work Equation
Replies: 1
Views: 24

Re: Negative Work Equation

The equations for work all have a negative sign at the beginning in order to define the energy associated with doing work relative to the system rather than its surroundings. If the work equation did not have a negative sign (ie. w = PΔV), then when the volume of the gas increases (ie ΔV is positive...
by Ruby Tang 2J
Mon Feb 03, 2020 6:15 pm
Forum: Phase Changes & Related Calculations
Topic: 4B. 3 part b
Replies: 1
Views: 15

Re: 4B. 3 part b

I'm pretty sure the answer key in the textbook for this problem is incorrect. If you copy and paste the problem into Google you will see many solutions to the problem that all say w = 490 J.
by Ruby Tang 2J
Wed Jan 29, 2020 11:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D.3
Replies: 2
Views: 25

Re: 4D.3

The change in temperature should be proportional to the amount of carbon monoxide being reacted. First, convert 1.40 g of CO to moles, and you get roughly 0.0500 mol of CO. If you set up a proportion, then you get 0.0500 mol/1.00 mol = 0.636C/xC, with 0.636 being the change in temperature when 1.40 ...
by Ruby Tang 2J
Wed Jan 29, 2020 12:46 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Cpm vs. Cvm
Replies: 2
Views: 23

Re: Cpm vs. Cvm

Cp is higher than Cv, because when pressure is constant, volume is not, so the gas is doing work via expansion. Therefore, you must account for the fact that for Cp, not all of the heat will be used toward increasing the temperature of the substance; some will be lost to work. To answer why pressure...
by Ruby Tang 2J
Wed Jan 29, 2020 12:40 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4C.3
Replies: 3
Views: 59

Re: 4C.3

In the relevant section of the textbook, it is explained that for a monatomic ideal gas, Cp = 5/2R, while Cv = 3/2R, where R = 8.3145 J*K-1*mol-1.
by Ruby Tang 2J
Mon Jan 27, 2020 10:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acid and Bases
Replies: 2
Views: 41

Re: Acid and Bases

Sodium hydroxide
by Ruby Tang 2J
Mon Jan 27, 2020 4:10 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Expansion work
Replies: 2
Views: 23

Re: Expansion work

When heat is added at constant volume, all of the heat is used to increase the temperature of the substance. However, when heat is added at constant pressure, the volume is changing and therefore more heat is needed to achieve the same temperature when volume is constant. This is because not only is...
by Ruby Tang 2J
Sun Jan 26, 2020 1:28 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Kw Equations
Replies: 9
Views: 30

Re: Kw Equations

[H3O+][OH-] = Kw, and [Ka][Kb] = Kw. Keep in mind however that Kw will be different depending on temperature. We just tend to use 1*10^-14 b/c this is what Kw is equal to at the standard state temperature (25C)
by Ruby Tang 2J
Sun Jan 26, 2020 1:25 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 6C.13
Replies: 3
Views: 19

Re: 6C.13

The stronger the base, the weaker the conjugate acid. A weaker conjugate acid is denoted by a higher pKa, since pKa is the negative log of Ka (which is very small for a weak acid). Therefore, you would put them in order of increasing pKa. From weakest to strongest base, the answer should be aniline,...
by Ruby Tang 2J
Sun Jan 26, 2020 1:20 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpy vs. Standard Enthalpy of Formation
Replies: 2
Views: 16

Re: Bond Enthalpy vs. Standard Enthalpy of Formation

1. Bond enthalpy is the amount of energy required to break one mole of the given bond (ex. if the bond enthalpy of an O-H bond is 464 kJ/mol, then it would take 464 kJ to break 6.022*10^23 O-H bonds). 2. Standard enthalpy of formation of a substance is defined as the change in enthalpy when 1 mole o...
by Ruby Tang 2J
Sun Jan 26, 2020 10:59 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: state property
Replies: 1
Views: 9

Re: state property

A state function can describe a particular state without knowing the path that was taken to reach this state. For example, it is possible to say that a system has a certain amount of internal energy, enthalpy, entropy, etc. given a set of specified conditions. However, for a path function (ex. work ...
by Ruby Tang 2J
Wed Jan 22, 2020 4:57 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 6D.5
Replies: 2
Views: 28

Re: 6D.5

I believe for (a)-(c), there is a table in the relevant section of the textbook that has the Kb values of common weak bases. If you look at the solutions manual, there are no calculations made for Kb, which seems to indicate that they assumed Kb was meant to be given for the problem.
by Ruby Tang 2J
Thu Jan 16, 2020 6:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Autoprotolysis
Replies: 1
Views: 10

Re: Autoprotolysis

Autoprotolysis can occur with other molecules as well; not just water. For example, in some cases ammonia can undergo protolysis (2NH3 --> NH2- + NH4+) too. You are correct that water just happens to be the most common example.
by Ruby Tang 2J
Thu Jan 16, 2020 5:49 pm
Forum: Ideal Gases
Topic: ph
Replies: 10
Views: 49

Re: ph

Yes! pH can definitely be above 14 or below 0. An example is 12 M HCl, which has a pH of about -1.08. If we consider mathematically that pH=-log[H+], then we know that if [H+] is greater than 1, pH has to be below 0.
by Ruby Tang 2J
Wed Jan 15, 2020 5:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6A 21
Replies: 2
Views: 30

Re: 6A 21

Since the water is neutral (neither acidic nor basic), we know that [H3O+] must equal [OH-]. Normally, when we are assuming that temperature is 25C, Kw = 1*10^-14. This is why the pH of neutral water is said to be 7: at 25C, [H3O+]=[OH-]=1*10^-7; thus [H3O+][OH-]=1*10^-14. In the problem we are give...
by Ruby Tang 2J
Mon Jan 13, 2020 8:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework 5l. 29
Replies: 2
Views: 20

Re: Homework 5l. 29

For this problem, you can set up an ICE table, but instead of using the concentrations of the compounds, you use the partial pressures instead. You get: 2HCl (g) --> H2(g) + Cl2(g) I 0.22 0 0 C -2x +x +x E 0.22-2x x x We know that Kp = PH2*PCl2/(PHCl)^2, which we can then plug our equilibrium expres...
by Ruby Tang 2J
Mon Jan 13, 2020 8:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework 5.35
Replies: 3
Views: 28

Re: Homework 5.35

In the graph shown, the partial pressures of the gases gradually change until they eventually plateau. This plateau corresponds to the equilibrium concentrations of A, B, and C.
by Ruby Tang 2J
Thu Jan 09, 2020 1:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Self-test 5G.3A
Replies: 2
Views: 26

Re: Textbook Self-test 5G.3A

The net ionic equation would be 2Ag+(aq) + 2OH-(aq) <-> Ag2O (s) + H2O (l). Na+ and NO3- are the spectator ions and do not directly participate in the reaction. We don't use solids or liquids in the expression for the equilibrium constant, so we end up with Kc = 1/[Ag+]^2[OH-]^2.
by Ruby Tang 2J
Thu Jan 09, 2020 1:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5G. 3
Replies: 5
Views: 34

Re: 5G. 3

In addition, generally when you have a choice between Kp and Kc, Kp is assumed to be the default (ex. if you look at table 5G.2 which you had to use for many of the hw problems, they have a separate column for K and Kc. The K is assumed to be the same thing as Kp)
by Ruby Tang 2J
Wed Jan 08, 2020 7:28 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Module 4 Q17
Replies: 1
Views: 35

Re: Module 4 Q17

Everything you've done so far should be correct; x should be equal to either 0.0828 or 0.126. It can't be 0.126 because then that would mean that the equilibrium concentration of CO and H2O are negative, so that means that x has to be equal to 0.0828. Therefore, [CO]=[H2O]=0.0172, and [CO2]=[H2]=0.0...
by Ruby Tang 2J
Wed Jan 08, 2020 7:19 pm
Forum: Ideal Gases
Topic: Units for Pressure
Replies: 6
Views: 44

Re: Units for Pressure

They are both units of pressure, with 1 atm being approximately 1.01325 bar. As previously mentioned, you can use either unit as long as you ensure that the units cancel, but when dealing with the ideal gas law PV=nRT, we generally use atm instead of bar because we conventionally say that the gas co...
by Ruby Tang 2J
Wed Jan 08, 2020 3:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: partial pressure
Replies: 2
Views: 17

Re: partial pressure

Whenever there is more than one gas involved, we use the term partial pressure to refer to the pressure that the gas would exert if it were by itself. The sum of the partial pressures of all of the gases involved is the total pressure. We can rearrange the ideal gas law, PV=nRT, to solve for the par...
by Ruby Tang 2J
Sat Dec 07, 2019 4:58 pm
Forum: Identifying Acidic & Basic Salts
Topic: homework question 6D.11
Replies: 2
Views: 49

Re: homework question 6D.11

A salt with an acidic ion in it will produce a solution with pH < 7, and a salt with a basic ion in it will produce a solution with pH > 7. For each compound you would want to look at each ion in the compound and check whether it would affect pH. For example, with NH4Br, Br- would NOT have an effect...
by Ruby Tang 2J
Mon Dec 02, 2019 7:23 pm
Forum: Lewis Acids & Bases
Topic: Salts containing conjugate acids/bases
Replies: 2
Views: 21

Re: Salts containing conjugate acids/bases

Additionally, if the conjugate acid is the conjugate acid of a strong base, then it will have no effect on pH. The same is true for the conjugate base of a strong acid.
by Ruby Tang 2J
Mon Dec 02, 2019 7:20 pm
Forum: Lewis Acids & Bases
Topic: 6.13
Replies: 2
Views: 35

Re: 6.13

pKa is not the same as the pH scale. While pKa is also an indicator of the strength of the acid, it does not follow the 0-14 pH scale. pKa values can be as low as -5 and as high as 50, so knowing that the pKa value is greater than 7 has no significance (you can't know whether a compound is an acid o...
by Ruby Tang 2J
Mon Dec 02, 2019 7:10 pm
Forum: Amphoteric Compounds
Topic: 6A.17
Replies: 5
Views: 46

Re: 6A.17

In general, metal oxides tend to act as bases while nonmetal oxides tend to act as acids. The oxides of elements on or near the diagonal metalloid line going down the periodic table have relatively equal acidic and basic character, so they are considered amphoteric.
by Ruby Tang 2J
Mon Dec 02, 2019 7:07 pm
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: 6C.17
Replies: 2
Views: 43

Re: 6C.17

Additionally, BrO- is the conjugate base of a weak acid (hypobromous acid HBrO), so it must be a pretty strong base. Another thing to consider is that the defining basic characteristic of morphine is the N atom with its lone pair, and compounds like these generally make for relatively weak bases.
by Ruby Tang 2J
Mon Dec 02, 2019 7:01 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Anion stability
Replies: 6
Views: 52

Re: Anion stability

The Ka value is the equilibrium constant for the reaction involving the dissociation of an acid. It is equivalent to ([H+][A-]/[HA]). The higher the Ka, the higher the [H+] and therefore the stronger the acid. Normally you will only be given the Ka if the acid in question is weak, because a strong a...
by Ruby Tang 2J
Sat Nov 30, 2019 10:18 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6b.9
Replies: 3
Views: 41

Re: 6b.9

If you have pH, [H3O+] is 10^-pH. For example, if pH is 3, [H3O+] is 10^-3. The same is true for pOH and [OH-]. It's also useful to know the relationship between pH and pOH and [H3O+] and [OH-]: pH + pOH = 14, and [H3O+][OH-] = 1*10^-14.
by Ruby Tang 2J
Sat Nov 30, 2019 10:14 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Calculating pOH
Replies: 2
Views: 24

Re: Calculating pOH

Dr. Lavelle might go over it during lecture at some point; but either way it'll probably be useful information to know that pOH=-log[OH-], pOH = 14-pH, and [H3O+][OH-]=1*10^-14.
by Ruby Tang 2J
Sat Nov 30, 2019 10:09 pm
Forum: Conjugate Acids & Bases
Topic: Product of Acid and Base
Replies: 5
Views: 43

Re: Product of Acid and Base

In a neutralization reaction, an H+ ion is given off by the acid while an OH- ion is given off by the base. These two ions will combine to produce water. The remaining ions while combine to form a salt, which is the general term for any ionic substance that doesn't have H+ as the cation or OH- as th...
by Ruby Tang 2J
Fri Nov 29, 2019 4:54 pm
Forum: Lewis Acids & Bases
Topic: Homework 6A 17
Replies: 2
Views: 27

Re: Homework 6A 17

For this question, I believe the main concept they want you to understand is that nonmetal oxides tend to act as acids, whereas metal oxides tend to act as bases. The classification of oxides as acids or bases is more ambiguous when the other element is a metalloid, so As2O3 and Bi2O3 would be class...
by Ruby Tang 2J
Tue Nov 26, 2019 12:22 am
Forum: Bronsted Acids & Bases
Topic: Equlibrium Constant Expression for Strong Acids/Bases
Replies: 3
Views: 15

Re: Equlibrium Constant Expression for Strong Acids/Bases

Ka and Kb are meant to be used to calculate equilibrium concentrations of weak acids and bases only, because generally only a very tiny fraction of the acid/base is dissociated in water if it is weak. Strong acids and bases will have very large Ka and Kb, because they are generally assumed to comple...
by Ruby Tang 2J
Sun Nov 24, 2019 6:35 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelate Complex
Replies: 1
Views: 17

Re: Chelate Complex

A chelate is just a compound containing a ligand bonded to a central metal atom at multiple points. You can also think of it as any coordination compound that contains polydentate ligands. There is no such thing as a chelate shape, and since chelates are just a special type of coordination compound,...
by Ruby Tang 2J
Sun Nov 24, 2019 6:29 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Sphere Clarification
Replies: 1
Views: 16

Re: Coordination Sphere Clarification

A coordination sphere is just the array of molecules and ions directly attached to the central metal atom. It's just a grouping of the central metal atom and all of the ligands attached to it; shape is separately determined. Coordination spheres aren't visual aids, but knowing which metal ion and li...
by Ruby Tang 2J
Sun Nov 24, 2019 6:25 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination compound vs covalent compound
Replies: 1
Views: 17

Re: Coordination compound vs covalent compound

The atoms in a coordination compound are held together by coordinate covalent bonds, while covalent compounds are not. Recall that a normal covalent bond is one in which 2 electrons are shared between 2 atoms. Usually each atom contributes one electron to the covalent bond, but in a coordinate coval...
by Ruby Tang 2J
Sun Nov 24, 2019 6:18 pm
Forum: Naming
Topic: Order in Naming
Replies: 12
Views: 56

Re: Order in Naming

For coordinate compounds, the order of the atomic symbols does matter. The ligand names would be in alphabetical order (either using their prefixes or the name of the element), followed by the name of the transition metal cation name. I think the question was about going from the name of the coordi...
by Ruby Tang 2J
Sun Nov 24, 2019 6:14 pm
Forum: Naming
Topic: HW problem 9C.3(d)
Replies: 2
Views: 34

Re: HW problem 9C.3(d)

When writing the formula of the coordination compound, there is no single correct way to order the ligands as long as they are all written after the central metal ion. However, there is only one right way to name a coordination compound. The central metal ion should come first, with the ligands list...
by Ruby Tang 2J
Sun Nov 24, 2019 6:10 pm
Forum: Naming
Topic: Oxidation Number
Replies: 3
Views: 28

Re: Oxidation Number

If you were just given the ion, you would first find the total charge of the ligands and identify the overall charge of the ion. The charge of the metal + the total charge of the ligands should add up to the overall charge of the ion. For example, if you were given [Co(CN)6]-3, you would identify th...
by Ruby Tang 2J
Sun Nov 24, 2019 6:05 pm
Forum: Naming
Topic: Trans and Cis
Replies: 8
Views: 53

Re: Trans and Cis

Yes, you wouldn't be able to tell if you were just given the molecular formula. Cis-trans isomerism is when there is a double bond and therefore restricted rotation, since pi bonds can't be rotated without being broken. Cis indicates that the functional groups appear on the same side of the double b...
by Ruby Tang 2J
Sun Nov 24, 2019 5:54 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Definitions
Replies: 1
Views: 25

Re: Definitions

From the textbook: Complex: a species consisting of a central metal atom or ion to which a number of molecules or ions are attached by coordinate covalent bonds Coordination compound: electrically neutral compound in which at least one of the ions present is a complex Ligand: Lewis base attached to ...
by Ruby Tang 2J
Wed Nov 20, 2019 8:05 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Problem 3F.3c
Replies: 2
Views: 30

Re: Problem 3F.3c

Generally when there is a carbon atom in the molecule it is in the center. You would arrange H and Cl around it tetrahedrally. It technically does not matter how you arrange the 2 H and 2 Cl atoms around the C atom in the Lewis structure, since in a tetrahedral molecular geometry it is impossible fo...
by Ruby Tang 2J
Wed Nov 20, 2019 8:03 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Section 2E #27a
Replies: 1
Views: 29

Re: Section 2E #27a

If you're referring to the question that asks you to predict whether C5H5N would be polar, you technically don't need to draw the Lewis structure to figure it out. The C-H and C-N dipole moments are different, and there is a difference in electron pull between all of the atoms (N is more electronega...
by Ruby Tang 2J
Sun Nov 17, 2019 1:39 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: vapor pressure
Replies: 4
Views: 16

Re: vapor pressure

I don't believe that we have to know what vapor pressure is for Test 2. But essentially, when a liquid is heated and the molecules begin to accumulate enough energy to escape into the gas phase, it results in a layer of gaseous molecules on top of the liquid that exerts a pressure (hence the term va...
by Ruby Tang 2J
Sun Nov 17, 2019 1:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Strength of Repulsion
Replies: 4
Views: 23

Re: Strength of Repulsion

The electron cloud of a lone pair is dispersed over a larger area than that of a bonding pair, because while a bonding pair is held in place by two atoms, a lone pair is only held in place by one. This means that there is only one nucleus's positive charge drawing in and localizing the electron clou...
by Ruby Tang 2J
Sun Nov 17, 2019 1:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Interactions
Replies: 3
Views: 19

Re: Interactions

Yes to both questions!
by Ruby Tang 2J
Sun Nov 17, 2019 1:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polarity 2E.25
Replies: 2
Views: 18

Re: Polarity 2E.25

For CH2Cl2, recall Dr. Lavelle's explanation of the molecular geometry of water during lecture. In lecture, he drew a Lewis structure of water with the lone pairs and hydrogen atoms on opposite sides of the oxygen atom, explaining why it was a misleading representation of the molecular geometry. In ...
by Ruby Tang 2J
Sun Nov 17, 2019 12:39 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: Dipoles
Replies: 2
Views: 16

Re: Dipoles

Additionally, dipoles can cancel each other out. For example, in a carbon dioxide molecule, even though there is a difference in electronegativity between the carbon atom and each of the two oxygen atoms, the dipoles are pointing in the opposite direction (each pointing toward an oxygen atom) and th...
by Ruby Tang 2J
Sun Nov 03, 2019 7:57 pm
Forum: Electronegativity
Topic: memorizing tables
Replies: 9
Views: 41

Re: memorizing tables

I think it's dependent on the question. For example, if the question is asking about the numerical value of the electronegativity difference between two atoms of different elements, you probably wouldn't be expected to know this off the top of your head. However, it is pretty reasonable to be expect...
by Ruby Tang 2J
Sun Nov 03, 2019 7:48 pm
Forum: Lewis Structures
Topic: 2.B.11
Replies: 2
Views: 19

Re: 2.B.11

Generally, when you see a molecular formula given like that (instead of say C2H5NO2), the formula is a structural formula and can give you a clue about how to arrange the atoms in the Lewis structure. H2C, NH2, and COOH are all segments of the actual Lewis structure, with H2C in the center and NH2 a...
by Ruby Tang 2J
Sun Nov 03, 2019 7:41 pm
Forum: Lewis Structures
Topic: structure stability
Replies: 2
Views: 11

Re: structure stability

To add on, if you know that one of the atoms has to carry a nonzero formal charge (ie. the overall charge of the molecule is nonzero) but aren't sure which atom to put it on, put the more negative formal charge on the more electronegative atom
by Ruby Tang 2J
Sun Nov 03, 2019 7:36 pm
Forum: Lewis Structures
Topic: expanding an octect
Replies: 5
Views: 43

Re: expanding an octect

Generally, you would expand an octet if it would make the molecule's formal charges more favorable. For example, the Xenon atom in XeF4 has an expanded octet because 1) F cannot accommodate an expanded octet as it is in the 2nd period and therefore does not have any d orbitals that could hold additi...
by Ruby Tang 2J
Sun Nov 03, 2019 7:26 pm
Forum: Sigma & Pi Bonds
Topic: Versus
Replies: 3
Views: 22

Re: Versus

Every molecule has sigma bonds, but not every molecule has pi bonds. Molecules with double (1 sigma and 1 pi bond) or triple (1 sigma and 2 pi bonds) bonds will have pi bonds, which are the result of the overlapping of p orbitals.
by Ruby Tang 2J
Sat Oct 26, 2019 9:24 pm
Forum: Trends in The Periodic Table
Topic: Electron affinity of Chlorine vs Fluorine
Replies: 1
Views: 31

Electron affinity of Chlorine vs Fluorine

Why is the electron affinity of chlorine greater than that of fluorine? I understand that electronegativity and electron affinity are different, with electronegativity being the tendency to attract electrons and electron affinity being the amount of energy released when an electron is gained, but th...
by Ruby Tang 2J
Sat Oct 26, 2019 9:19 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Stability
Replies: 9
Views: 73

Re: Stability

It's all about charge distribution. The closer to 0 the formal charge is, the more evenly distributed the electrons are about the molecule. If the absolute values of the formal charges of the atoms in a molecule are high, this will lead to the molecule having regions that are more negatively or posi...
by Ruby Tang 2J
Sat Oct 26, 2019 9:09 pm
Forum: Lewis Structures
Topic: Resonance and lower energy levels
Replies: 2
Views: 14

Re: Resonance and lower energy levels

In resonance, the electrons are delocalized and therefore aren't fixed to a particular atom or bond. Because delocalization allows for the charge of the electrons to be distributed over a larger amount of space, the overall energy of the molecule is lowered and thus more stable.
by Ruby Tang 2J
Sat Oct 26, 2019 9:04 pm
Forum: Sigma & Pi Bonds
Topic: orbitals
Replies: 3
Views: 258

Re: orbitals

A simple trick to solve for the number of orbitals in the nth shell of an atom is to know that it is equal to n^2. So the 1st shell has 1 orbital, 2nd shell has 4, 3rd shell has 9, etc. You can also adjust this equation to 2n^2 to solve for the number of electrons that a given shell of an atom can h...
by Ruby Tang 2J
Sat Oct 26, 2019 9:00 pm
Forum: Sigma & Pi Bonds
Topic: Pi bonds
Replies: 3
Views: 39

Re: Pi bonds

The number of pi bonds in a molecule can be easily determined by looking at its Lewis structure. Every single covalent bond has 1 sigma bond, every double bond has 1 sigma and 1 pi bond, every triple bond has 1 sigma and 2 pi bonds, etc. For example, ethane (C2H6) has 7 single bonds, so it would hav...
by Ruby Tang 2J
Sat Oct 19, 2019 10:20 pm
Forum: DeBroglie Equation
Topic: Deriving the DeBrogile Equation
Replies: 8
Views: 76

Re: Deriving the DeBrogile Equation

It is probably fine that you have a basic understanding of what it does, but I guess the main takeaway in deriving the DeBroglie Equation is that you can combine E=pc and E=hv to get hc/λ = pc --> h/λ = p --> h/λ = mv --> λ = h/mv
by Ruby Tang 2J
Sat Oct 19, 2019 10:15 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Frequencies
Replies: 7
Views: 59

Re: Frequencies

You should definitely memorize that UV is from 10-400 nm and that visible is from 400-700 nm in case you get a question about the Lyman or Balmer series, respectively.
by Ruby Tang 2J
Sat Oct 19, 2019 9:57 pm
Forum: *Black Body Radiation
Topic: Applying Wein's Law
Replies: 3
Views: 49

Re: Applying Wein's Law

The most basic concept of Wien's law is that the wavelength of peak emission is inversely proportional to temperature on an object's blackbody radiation curve. Therefore, the higher the temperature, the shorter the wavelength (aka the hotter it is, the bluer it appears), and vice versa (aka the cold...
by Ruby Tang 2J
Sat Oct 19, 2019 9:44 pm
Forum: Properties of Electrons
Topic: 1B. 7 Homework help
Replies: 3
Views: 58

Re: 1B. 7 Homework help

For a) You can combine E=hv and c=λv to get E=hc/λ to find the amount of energy emitted. You know planck's constant (h), the speed of light (c), and wavelength (λ), so you just have to plug the numbers in to get the amount of energy emitted. For b) You have to first find how many moles of Na are in ...
by Ruby Tang 2J
Sat Oct 19, 2019 9:34 pm
Forum: Properties of Light
Topic: 1A. 15
Replies: 3
Views: 36

Re: 1A. 15

1), First, you need to know that the ultraviolet spectrum of atomic hydrogen corresponds to the Lyman series (defined as a transition between n=1 and n>=2). For this class, I would remember this in addition to the fact that the visible spectrum corresponds to the Balmer series (transition between n=...
by Ruby Tang 2J
Sat Oct 12, 2019 11:14 pm
Forum: Properties of Light
Topic: Rydberg constant
Replies: 7
Views: 60

Re: Rydberg constant

The Rydberg equation is used in instances in which we want to calculate the energy of a given energy level (n) in a Hydrogen atom. We use the second equation you listed, ΔE=Ef-Ei, when we want to find the energy difference when an electron transitions from one energy level to another. However, the v...
by Ruby Tang 2J
Sat Oct 12, 2019 11:06 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect and Photons
Replies: 6
Views: 40

Re: Photoelectric Effect and Photons

A photon is an elementary particle representing a unit or quanta of light. The photoelectric effect suggested that light exhibited the behavior of a particle (ie photon), because a change in the intensity of light did not result in a change in the kinetic energy of the electrons emitted from the met...
by Ruby Tang 2J
Sat Oct 12, 2019 10:58 pm
Forum: Properties of Light
Topic: Equations We’ve Learned So Far
Replies: 11
Views: 104

Re: Equations We’ve Learned So Far

A good rule of thumb is that any equation with mass (m) as one of the variables CANNOT be used for light, as light particles (aka photons) have no mass!
by Ruby Tang 2J
Sat Oct 12, 2019 10:28 pm
Forum: Properties of Light
Topic: 1A 15
Replies: 2
Views: 35

Re: 1A 15

The Lyman Series is defined as an electron transition from any n greater than or equal to 2 to n = 1 (or vice versa). You would want to use the Rydberg equation in this case: E = -(hR)/n^2. You can substitute E for hv, and then the h's on both sides of the equation cancel out and you're left with v=...
by Ruby Tang 2J
Sat Oct 12, 2019 10:04 pm
Forum: *Black Body Radiation
Topic: Black Body Radiation
Replies: 12
Views: 113

Re: Black Body Radiation

Blackbody radiation is essentially thermal EM radiation. The reason why it is called "blackbody" is because an ideal blackbody (which does NOT exist in nature -- the closest thing would probably be a black hole) absorbs all radiation (and thus reflects none) and appears to be black because...
by Ruby Tang 2J
Sat Sep 28, 2019 3:07 pm
Forum: Molarity, Solutions, Dilutions
Topic: HW Question: G5 (Part A)
Replies: 3
Views: 58

Re: HW Question: G5 (Part A)

Once you find the molarity of sodium carbonate solution (should be 0.07967 M), you can write out the following equation to find the amount of solution you need to get 2.15 mmol (or 0.00215 mol) of Na2CO3: 0.07967 mol/L * x L = 0.00215 mol. Once we solve for x, we get 0.02699 L. This is the amount of...
by Ruby Tang 2J
Sat Sep 28, 2019 2:50 pm
Forum: SI Units, Unit Conversions
Topic: Formula units vs molecules vs atoms? [ENDORSED]
Replies: 7
Views: 124

Re: Formula units vs molecules vs atoms? [ENDORSED]

46 g of NaCl * (1 mol of NaCl/58.44 g of NaCl) = 0.787 mol of NaCl (6.022 * 10^23 formula units/1 mol of NaCl) = 4.7 * 10^23 formula units of NaCl. You would essentially solve it the same way as you would for any molecular compound; you are just substituting the word "molecule" for "f...
by Ruby Tang 2J
Fri Sep 27, 2019 11:34 pm
Forum: SI Units, Unit Conversions
Topic: Formula units vs molecules vs atoms? [ENDORSED]
Replies: 7
Views: 124

Re: Formula units vs molecules vs atoms? [ENDORSED]

A formula unit is the empirical formula of any ionic solid (or covalent network solid). Since these solids (ex. NaCl or SiO2) don't exist as individual molecules, we use the term "formula unit" instead. In the example you stated, alumina is an ionic compound so the technically correct unit...
by Ruby Tang 2J
Fri Sep 27, 2019 8:52 pm
Forum: Significant Figures
Topic: How does Significant Figures work? [ENDORSED]
Replies: 12
Views: 140

Re: How does Significant Figures work? [ENDORSED]

Wanted to add: sig fig rules are different if you're adding or subtracting. With adding or subtracting, your answer would have the same number of decimal places as the least precise measurement. So 4.8-3.96 would be 0.8 (not 0.84 like it would be if following multiplication/division sig fig rules), ...
by Ruby Tang 2J
Fri Sep 27, 2019 3:25 pm
Forum: Limiting Reactant Calculations
Topic: HW1 M19
Replies: 4
Views: 132

Re: HW1 M19

You don't need to know the elemental composition of caffeine off of the top of your head. The way to figure out caffeine has oxygen in it is: 1) Due to the law of conservation of mass, if there are 0.376 g of caffeine reacting, and 0.966 g of product being produced (0.682 g CO2 + 0.174g H2O + 0.110 ...

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