Search found 111 matches
- Sat Mar 14, 2020 5:49 pm
- Forum: Administrative Questions and Class Announcements
- Topic: UA Final Review - Kate, Riya, Matthew
- Replies: 13
- Views: 2332
Re: UA Final Review - Kate, Riya, Matthew
Regarding question 11: This is not representative of what would actually happen right? Because when temperature increased, K went up from 0.0177 to 0.0186, but isn't K supposed to decrease with increasing temperature?
- Sat Mar 14, 2020 4:07 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Determining if a reaction mechanism is feasible
- Replies: 3
- Views: 368
Re: Determining if a reaction mechanism is feasible
Remember that no matter the substitutions u may have to make for intermediates, the rate law will have the same order no matter what.
Can you explain what you mean by this?
- Sat Mar 14, 2020 3:50 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Determining if a reaction mechanism is feasible
- Replies: 3
- Views: 368
Determining if a reaction mechanism is feasible
Can someone tell me the conditions that we use to check if a proposed reaction mechanism is possible/feasible? i.e. the conditions it must meet
- Sat Mar 14, 2020 11:47 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Elementary Reaction Definition
- Replies: 3
- Views: 382
Re: Elementary Reaction Definition
As far as I can tell, an elementary reaction is defined by it having one transition state. But a chemical rxn (i.e. an overall reaction) can be made up of multiple steps of elementary reactions, thus having multiple transition states in its reaction profile.
- Sat Mar 14, 2020 9:12 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: reaction mechanisms
- Replies: 2
- Views: 230
Re: reaction mechanisms
In this class, we will always use the pre-equilibrium approach.
- Fri Mar 13, 2020 2:17 pm
- Forum: General Rate Laws
- Topic: ENDGAME 14f
- Replies: 2
- Views: 271
ENDGAME 14f
For the Endgame worksheet, how is 14f done? How do you get rid of the concentration of B? See the original ENDGAME post for the problem details.
- Fri Mar 13, 2020 12:14 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Relationship between work, cell potential, and delta G
- Replies: 6
- Views: 695
Relationship between work, cell potential, and delta G
Can someone please explain (conceptually, not with equations) the relationship between work, cell potential, and delta G? Like explain why wmax is = to delta G.
- Wed Mar 04, 2020 2:13 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Liquids in cell diagrams
- Replies: 2
- Views: 163
Liquids in cell diagrams
How do we know when to include liquids in cell diagrams? In problem 6L.7b, H2O liquid is not included in the cell diagram even though it is involved in both half reactions. But in problem 6M.5, Hg liquid is included.
How do we distinguish this?
How do we distinguish this?
- Mon Mar 02, 2020 9:30 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 6M.11
- Replies: 1
- Views: 205
Re: 6M.11
I believe that because there are solid metals included in the half reactions, you don't need to add an inert electrode as those solids will already conduct e-s (unless it's something like I2 that's not a metal and won't conduct e-s well).
- Mon Mar 02, 2020 9:25 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Test 2 Thermodynamics
- Replies: 4
- Views: 364
Re: Test 2 Thermodynamics
Are you referring to Outlines 4 and 5 from Lavelle's website? If so, the second page from the thermo outline (4) and everything on outline 5 including any thermo is fair game for Exam 2.
- Mon Mar 02, 2020 9:23 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Electrode
- Replies: 2
- Views: 233
Re: Electrode
I was really confused about this too, just wanted to point you and anyone else who is confused to the video "Redox reactions part 1: explaining the galvanic cell." It does a really good job conceptualizing Galvanic cells and helped me visualize how the cathode and anode change when current...
- Mon Mar 02, 2020 9:20 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Negative standard reduction potential
- Replies: 3
- Views: 300
Re: Negative standard reduction potential
Standard reduction potential means K<1, the reaction is not spontaneous, and the cell will be electrolytic rather than Galvanic.
- Mon Mar 02, 2020 9:19 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Reducing final equation to get n?
- Replies: 2
- Views: 269
Reducing final equation to get n?
Does anyone know if when balancing the redox reaction for an overall Galvanic/concentration/electrolytic cell, we are supposed to reduce the coefficients? I think my TA said in discussion not to in order to get the correct number of e-s to use in the equation for Ecell, but the solutions manual for ...
- Wed Feb 26, 2020 2:47 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Nernst at 25 degrees C
- Replies: 1
- Views: 175
Nernst at 25 degrees C
Can someone confirm the equation for calculating K at 25 deg. C for me?
The solutions manual says lnK=nE(stand)/0.02569
In lecture, Dr. Lavelle said to use logK = nE(stand)/0.0592
Can we use either? And are we expected to memorize these because they are not on the constants and equations sheet?
The solutions manual says lnK=nE(stand)/0.02569
In lecture, Dr. Lavelle said to use logK = nE(stand)/0.0592
Can we use either? And are we expected to memorize these because they are not on the constants and equations sheet?
- Tue Feb 25, 2020 6:48 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Where to find Ecell values
- Replies: 15
- Views: 916
Where to find Ecell values
Can someone point me to where to find a table of reduction potentials for common half reactions? Either in the book or on Lavelle's website...can't seem to find it
- Tue Feb 25, 2020 5:56 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Platinum electrode
- Replies: 4
- Views: 337
Platinum electrode
What is the rule for when we need to include a solid platinum electrode in our cell diagram?
- Tue Feb 25, 2020 4:26 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 6L.3b
- Replies: 3
- Views: 267
6L.3b
For 6L.3b, we are given the following cell diagram:
C(gr) | H2(g) | H+(aq) || Cl- (aq) | Cl2 (g) | Pt (s)
Can someone explain what the C(gr) part is and how we are supposed to use it when writing the half reactions?
C(gr) | H2(g) | H+(aq) || Cl- (aq) | Cl2 (g) | Pt (s)
Can someone explain what the C(gr) part is and how we are supposed to use it when writing the half reactions?
- Sat Feb 22, 2020 6:26 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Clarifying from textbook
- Replies: 2
- Views: 230
Clarifying from textbook
In the textbook, it says "In a galvanic cell, a spontaneous chemical reaction draws electrons into the cell through the cathode, the site of the reduction, and releases them at the anode, the site of the oxidation." Can someone explain the drawing of electrons through the cathode? Because ...
- Sat Feb 22, 2020 4:43 pm
- Forum: Balancing Redox Reactions
- Topic: oxidizing AND reducing agent
- Replies: 3
- Views: 278
Re: oxidizing AND reducing agent
I don't understand how to write out a reduction equation for chlorine in this case
I think that since in this case Cl2 gas is in liquid water, you assume that it dissolves into aqueous Cl- ions... That should be the product on the right side of your reduction rxn.
- Sat Feb 22, 2020 4:42 pm
- Forum: Balancing Redox Reactions
- Topic: oxidizing AND reducing agent
- Replies: 3
- Views: 278
Re: oxidizing AND reducing agent
I could be wrong, but I believe that since Cl2 gas is the only reactant, in this case it is both oxidized and reduced. It has products in both and oxidized and reduced state, making it both an oxidizing and reducing agent.
- Sat Feb 22, 2020 4:16 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 10
- Views: 644
Re: Salt Bridge
A salt bridge allows for the flow of the negative ions that aren't participating in the redox reaction. Remember that we cannot just put aqueous ions in solution, they must dissociate from a solid salt. Those ions can make the charge unbalanced, so having a salt bridge essentially corrects that.
- Sat Feb 22, 2020 4:14 pm
- Forum: Balancing Redox Reactions
- Topic: Basic/Acidic solutions
- Replies: 2
- Views: 208
Re: Basic/Acidic solutions
The main difference we discussed in my discussion is that for alkaline conditions (basic), you add the same number of hydroxides as you just added H+s to both sides. This is because conceptually, we know that for a basic solution, there will not be more H+ than OH- in solution.
- Sat Feb 22, 2020 4:12 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing charge when balancing redox reactions
- Replies: 1
- Views: 148
Balancing charge when balancing redox reactions
When we are balancing the charge at the final step of balancing redox rxns (when we combine the half rxns), if we need to multiply by a constant to balance the e-s, do only the substances from the half rxn that produced those e-s get multiplied by the constant? Or does the entire side of the combine...
- Tue Feb 11, 2020 7:57 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Cv vs. Cp?
- Replies: 3
- Views: 289
Re: Cv vs. Cp?
we assume that the volume isn't changing and therefore use Cp.
^How does this make sense because if volume isn't changing, isn't that assuming "constant volume" which points to using Cv, not Cp?
- Tue Feb 11, 2020 7:26 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Cv vs. Cp?
- Replies: 3
- Views: 289
Cv vs. Cp?
How do we know when to use Cv vs. Cp? I know one is for constant volume and one is for constant pressure, but what about for a sudden irreversible compression of gas where there is a temperature and volume change? For the temperature part of the entropy calculation, how would we know which c value t...
- Mon Feb 10, 2020 9:36 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy of surroundings and system [ENDORSED]
- Replies: 1
- Views: 102
Entropy of surroundings and system [ENDORSED]
How do we know when entropy of surroundings equals entropy of the system? Does this happen only when delta g = 0? I'm pretty confused about this..
- Sun Feb 09, 2020 8:26 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 4H.9
- Replies: 2
- Views: 191
4H.9
In the solutions manual explanation for 4h.9, it says that container A has the highest entropy because it has the "most particles". Can someone explain why this is because all the containers have 1 mole of gas?
- Sun Feb 09, 2020 6:20 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: Residual Entropy
- Replies: 5
- Views: 114
Re: Residual Entropy
What causes there to still be some energy, allowing it to have some disorder? I thought that at 0 Kelvin, all particles stop moving, therefore there wouldn't be any disorder. At 0 K, there is no contribution to entropy from rotational/thermal motion. However, there is, for most molecules, residual ...
- Sun Feb 09, 2020 12:12 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Hess's Law
- Replies: 10
- Views: 300
Re: Hess's Law
Enthalpy is a state function (state values can be added/subtracted without worrying how they got there).
- Sun Feb 09, 2020 11:20 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Intensive vs. extensive, state vs. non state
- Replies: 6
- Views: 271
Intensive vs. extensive, state vs. non state
Can someone give me a comprehensive list of the functions we have looked at so far that are intensive vs. extensive and state vs. non state? Also, are the two concepts related?
- Sun Feb 09, 2020 11:16 am
- Forum: Administrative Questions and Class Announcements
- Topic: memorizing things?
- Replies: 13
- Views: 667
Re: memorizing things?
Memorizing equations is not required as they will be given to us, but I would recommend memorizing the units for certain things (delta H, q, S, etc.) so you don't get points knocked off for mixing up units since those will not necessarily be given.
- Sun Feb 09, 2020 11:05 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy Change with both volume change and temperature change
- Replies: 2
- Views: 129
Entropy Change with both volume change and temperature change
How do we determine which equation to use when calculating entropy for a system for which there has been both a temperature change AND a volume change? (Refer to pizza rolls question 5)
- Sun Feb 02, 2020 6:22 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Test 1 #6
- Replies: 6
- Views: 370
Re: Test 1 #6
HF, unlike the other halogen acids, is not a strong acid due to the fact that Fluoride is highly electronegative and it has a small ionic radius, meaning the HF bond is more difficult to break and therefore does not dissociate easily like the other halogen acids (HBr, HI, etc.).
- Sun Feb 02, 2020 6:19 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Delta U vs Delta H
- Replies: 4
- Views: 136
Re: Delta U vs Delta H
Delta U is given by the energy supplied to the system by heat (q) plus the energy transferred by compression work (w). When the system is under constant pressure, q is equal to Delta H, so Delta H becomes a part of how Delta U is calculated.
- Sun Feb 02, 2020 6:17 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Ka approximation
- Replies: 6
- Views: 538
Re: Ka approximation
To check if the approximation is valid or not, you need to check if the percent ionization of the original substance is less than or equal to 5%. If it is greater, then you know that x will impact the original substance's molarity enough such that a quadratic must be used.
- Thu Jan 30, 2020 3:48 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond enthalpies
- Replies: 4
- Views: 250
Re: Bond enthalpies
I don't think so, I'm pretty sure if the energy of the bonds broken is greater than the energy of the bonds formed, then the reaction can be endothermic. But someone correct me if I'm wrong.
- Thu Jan 30, 2020 3:38 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Units for work
- Replies: 3
- Views: 147
Units for work
Does anyone know if it's okay to leave units for work as L x atm? Or do we have to convert to Joules?
- Wed Jan 29, 2020 10:32 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalphy of Combustion
- Replies: 2
- Views: 108
Enthalphy of Combustion
Can someone please explain how to use given enthalpies of combustion for compounds to find the total enthalpy of the reaction? (An example of a problem like this is 4D.15)
- Sun Jan 26, 2020 4:58 pm
- Forum: Phase Changes & Related Calculations
- Topic: Steam vs Water
- Replies: 4
- Views: 199
Re: Steam vs Water
So basically: considering the heating curve for water (you can google this), we can see that it takes a lot of energy/heat to convert 1000 degree liquid water to 1000 degree steam. So, when the steam comes into contact with a colder surface (skin), it has to release a lot energy in order to condense...
- Sun Jan 26, 2020 4:41 pm
- Forum: Phase Changes & Related Calculations
- Topic: What is a state function?
- Replies: 3
- Views: 177
Re: What is a state function?
A state function is one wherein the state of the system depends only on the final and initial states, not on the path taken in between. For example, displacement is a state function. If you walk 25 paces forward and then 15 back, your total displacement is still 10 (the same as if you had just walke...
- Sun Jan 26, 2020 4:36 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Order of homework for Thermochem unit
- Replies: 6
- Views: 359
Order of homework for Thermochem unit
Hi, does anyone know what the recommended order is to do the homework for the Thermochemistry unit? The problems for 4A and 4B don't seem to match up to what we've learned in class so far.
- Wed Jan 22, 2020 7:09 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 6B.9
- Replies: 5
- Views: 178
Re: 6B.9
Alexis Webb 2B wrote:Can you post a picture of the problem or your work for reference?
I didn't rlly write down any work, I just divided Kw (10^-14) by 1.5 M... I got 6.67 x 10^-15.
- Wed Jan 22, 2020 3:11 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 6B.9
- Replies: 5
- Views: 178
6B.9
This problem asks us to fill in a table for [h3o+] [oh-] pH and pOH. The given [h3o+] for the first one is 1.5 M, so I tried to use Kw=[hydronium][hydroxide] to get [hydroxide], but the answer I get (6.67 x 10^-14) is not what the solution manual says. Can someone tell me where I'm going wrong/how t...
- Tue Jan 21, 2020 9:53 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Autoprotolysis
- Replies: 1
- Views: 125
Autoprotolysis
Can someone please explain when to not use the concentration of H+ to calculate pH? It's something about the dissociation due to the autoprotolysis of water but I don't remember the exact threshold...
- Wed Jan 15, 2020 10:34 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Percent Ionization
- Replies: 11
- Views: 393
Re: Percent Ionization
Yes, because the change to the initial concentration of the acid or base will be essentially zero. But usually the percent ionization doesn't come first, and is a step to confirm that approximating was okay (which you would do based on the value of K being <10^-3).
- Wed Jan 15, 2020 8:38 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5J.11
- Replies: 4
- Views: 155
Re: 5J.11
It's not especially important. Focus on the fact that energy is required to break bonds, and since we can clearly see the breakage of bonds (and no formation of new ones), we know the reaction will be endothermic.
- Wed Jan 15, 2020 8:32 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5I.13 c
- Replies: 1
- Views: 87
Re: 5I.13 c
Cl2 is more thermodynamically stable because it has a lower relative concentration of Cl products to its Cl2 reactants than F to its F2 reactants. So, Cl2 is more likely to remain than F2, meaning it is more stable. This can also be determined from the fact that Cl2 is a smaller Kc: less products on...
- Wed Jan 15, 2020 8:12 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: concentration of H3O+
- Replies: 2
- Views: 85
Re: concentration of H3O+
^Yes, basically you have to account for the amount of H3O+ that already exists naturally due to autoprotolysis. Don't make the mistake of just calculating pH when [H3O+] is this small.
- Wed Jan 15, 2020 8:10 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5l.29
- Replies: 5
- Views: 885
Re: 5l.29
Hi, not sure where you might be going wrong but I can try to explain how I did it. I set up an ICE chart where HCl changes by -2x and the other two gases change by +x. Then, because K is very small (it is less than 10^-3), I set it equal to x^2/(0.22)^2. We can do this because because K is so small,...
- Sun Jan 12, 2020 3:33 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: What goes into Kc and K?
- Replies: 2
- Views: 136
Re: What goes into Kc and K?
Yes. Do not include solids or liquids.
- Sun Jan 12, 2020 3:32 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Rounding in K problems
- Replies: 4
- Views: 263
Rounding in K problems
In the solution for problem 5I.23, I noticed that the values for the equilibrium concentrations of the reaction were rounded according to sig figs before they were plugged into the equation to find Kc. Is this a universal rule for rounding? If not, how do we know when to apply sig figs?
- Fri Jan 10, 2020 9:35 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Problem 5i.11- using molarity in place of pressure?
- Replies: 3
- Views: 194
Problem 5i.11- using molarity in place of pressure?
So this problem basically asks you to calculate the reaction quotient given the amount of each substance in a container and the volume of that container. All of these substances are gases however, so don't we need to use partial pressures, not molar concentrations? The answer key just divides each n...
- Fri Jan 10, 2020 9:00 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: When to use Le Chatelier's
- Replies: 4
- Views: 207
Re: When to use Le Chatelier's
Le Chatelier's Principle essentially states that "chemical reactions will adjust to minimize the effects of changes." Therefore, you would use it if a change is applied to a system to determine how the system will react in order to try and bring itself back to equilibrium. Ex: If you sudde...
- Fri Jan 10, 2020 8:58 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Calculating the Equilibrium Quotient
- Replies: 3
- Views: 290
Re: Calculating the Equilibrium Quotient
Also, the equilibrium quotient basically tells you how the system is going to react next in order to move towards equilibrium (or if it already is at equilibrium, when Q equals K). Q tells us if we have "too few" products or "too many", allowing us to predict which direction the ...
- Sat Dec 07, 2019 1:35 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Diethylenetriamine Tridentate
- Replies: 1
- Views: 107
Re: Diethylenetriamine Tridentate
This, combined with the fact that there are spacer atoms between the N's and that there are sigma bonds allowing rotation, make it tridentate.
- Sat Dec 07, 2019 1:32 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: chelating vs. polydentate?
- Replies: 2
- Views: 176
chelating vs. polydentate?
What is the difference between the definition of a chelating ligand and a polydentate ligand? Doesn't being polydentate (bonding to the Tx metal at more than one place) automatically form a "ring" and make it chelating?
- Sat Dec 07, 2019 1:15 pm
- Forum: Biological Examples
- Topic: Chemotherapy drugs
- Replies: 7
- Views: 529
Re: Chemotherapy drugs
Cisplatin is one biological example of how coordination compounds are relevant. But I believe we should also know the biological functions of Cr, Fe, Co, Mn, Ni, Cu, Zn. The outline for this unit mentions knowing that Co functions in vitamin B12 specifically.
- Sat Dec 07, 2019 1:13 pm
- Forum: Biological Examples
- Topic: Porphyrin
- Replies: 1
- Views: 168
Re: Porphyrin
Yes. This is shown when it bonds to Fe at 4 points to form a Heme complex.
- Sat Dec 07, 2019 1:11 pm
- Forum: Student Social/Study Group
- Topic: midterm question 4B
- Replies: 1
- Views: 223
Re: midterm question 4B
Step 1: Convert kJ to J -> 100,000 J. Step 2: We know the energy per photon is equal to 1.936... x 10^-18 from part a of the question. That 100,000 J of incoming energy is the total energy of all the photons, so if we divide 100,000/1.936...x10^-18, we get the number of photons. This also makes sens...
- Fri Dec 06, 2019 2:07 pm
- Forum: Calculating the pH of Salt Solutions
- Topic: Marshmallow 34: how does CaCl2 affect pH?
- Replies: 1
- Views: 152
Marshmallow 34: how does CaCl2 affect pH?
This is the problem: Lyndon sees his crush and panics, accidentally dropping 382.7 mg of HCl and 147.1 mg CaO into a 1L flask. After filling that last with water up to the 1L mark, what is the pH of the resulting solution? I'm confused because HCl and CaO will form CaCl2, and I remember that the sal...
- Fri Dec 06, 2019 1:43 pm
- Forum: Photoelectric Effect
- Topic: kinetic Energy
- Replies: 2
- Views: 309
Re: kinetic Energy
I assume you are referring to kinetic energy of an electron ejected in a photoelectric effect problem? If you are, the KE is zero when the energy (E=hv) of the incoming light is equal to the work function. In other words, you don't have any excess energy to be released as KE or the wavelength of the...
- Fri Dec 06, 2019 1:41 pm
- Forum: Naming
- Topic: Naming coordinate compounds
- Replies: 1
- Views: 125
Re: Naming coordinate compounds
The chlorine inside the brackets is a ligand attached to the Co. So, since it is the first alphabetical ligand, it comes first. The suffix is not ate because you only add that if the charge of the bracketed part is negative. In this case, since it is bonding with Cl-, it is positive, so you do not n...
- Sun Dec 01, 2019 4:15 pm
- Forum: Bronsted Acids & Bases
- Topic: J9
- Replies: 3
- Views: 290
Re: J9
chari_maya 3B wrote:is the answer to part a CH3COOK?
Yes, that's the correct answer. Can also just be written as CH3CO2K or potassium acetate.
- Sun Dec 01, 2019 4:13 pm
- Forum: Naming
- Topic: Roman numerals
- Replies: 6
- Views: 519
Re: Roman numerals
You know this because you know the overall charge of the compound you are naming. For example, say you are naming [Co(NH3)6]3+. You know there is an overall plus 3 charge. You have 6 neutral ammonias and therefore that one cobalt must get all of the charge. Therefore, the name of this compound would...
- Sun Dec 01, 2019 4:10 pm
- Forum: Naming
- Topic: explain Coordination compound
- Replies: 5
- Views: 421
Re: explain Coordination compound
Coordination compounds form when neutral molecules or atoms (or anions) supply a central cation (usually a Tx metal) with an electron pair to form a coordinate covalent bond. These often form when Tx metals in solution first form complexes with water as the ligands, which are then replaced by more e...
- Sun Dec 01, 2019 4:06 pm
- Forum: Bronsted Acids & Bases
- Topic: Relative acidity
- Replies: 2
- Views: 121
Re: Relative acidity
Chlorine has a high electronegativity, meaning it has a high tendency to attract electrons. So, it stabilizes the molecule by drawing electron density away from the negatively charged oxygen in the O-H bond, which weakens that bond and makes it more likely to give off a proton.
- Sun Dec 01, 2019 3:59 pm
- Forum: Naming
- Topic: Order of ligands in formulas for coordination compounds
- Replies: 4
- Views: 244
Order of ligands in formulas for coordination compounds
When writing the formula of a coordination compound, does the order in which the ligands are written matter?
Ex: In hw 9c.3d, for the name tetraaminediaquacobalt (III) bromide, does it matter whether the OH2 or NH3 is written first in the formula?
Ex: In hw 9c.3d, for the name tetraaminediaquacobalt (III) bromide, does it matter whether the OH2 or NH3 is written first in the formula?
- Sun Nov 24, 2019 7:54 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Formation of coordinate covalent bonds
- Replies: 2
- Views: 150
Formation of coordinate covalent bonds
How does one determine how many coordinate covalent bonds a Tx metal can form when forming a coordination compound? i.e. how do we know how many ligands can/will attach themselves?
- Sun Nov 24, 2019 7:46 pm
- Forum: Biological Examples
- Topic: Cisplatin
- Replies: 12
- Views: 678
Re: Cisplatin
I don't fully understand the concept yet, but in lecture, Dr. Lavelle said we need to "know how cisplatin shuts down cell division." I'm assuming this means we need to understand that cisplatin (and NOT trans-diamine-dichloro-platinum" has the correct geometry to form a coordination c...
- Sun Nov 24, 2019 7:36 pm
- Forum: Lewis Acids & Bases
- Topic: Donor and Acceptor
- Replies: 6
- Views: 379
Re: Donor and Acceptor
The difference is between when you are talking about the species accepting/donating a proton or an electron. That is the difference between the Bronsted-Lowry definition of acids and bases versus the Lewis definition. In Lewis, acids are ELECTRON acceptors, whereas in Bronsted-Lowry, acids are PROTO...
- Sun Nov 24, 2019 7:29 pm
- Forum: Sigma & Pi Bonds
- Topic: Sigma and Pi Bonds
- Replies: 7
- Views: 455
Re: Sigma and Pi Bonds
Also: sigma bonds form when two orbitals interact end-to-end, whereas pi bonds form when 2 orbitals overlap side-by-side. Note that pi bonds have electron density on each side of the internuclear axis, whereas sigma bonds have electron density along it. This will change the rotatability of the atoms!
- Tue Nov 19, 2019 5:52 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 2E.21 d
- Replies: 1
- Views: 95
2E.21 d
In 2E.21 d, we are asked to determine the bond angles of N2H4. The Lewis structure gives trigonal pyramidal geometry about each of the N atoms, and the answer key gives the bond angle as 107 degrees... But why is it not just <109.5 degrees? In what case to we assign a specific bond angle to trigonal...
- Sun Nov 17, 2019 9:07 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular shape and lone pairs
- Replies: 2
- Views: 177
Molecular shape and lone pairs
How is it possible for a molecule to be linear if the central atom has lone pairs? Wouldn't those electrons repel the electrons of the bonded atoms like in a trigonal pyramidal molecule? Example: AX2E3
- Sun Nov 17, 2019 8:57 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 2E. 5 Question
- Replies: 4
- Views: 251
Re: 2E. 5 Question
So 120 degrees would be the bond angle for a trigonal planar molecule. You can think of the lone pairs as acting like another atom attached to the central atom, whose electrons repels the electrons of the other two. However, the repulsion due to the lone pairs is STRONGER than the repulsion due to b...
- Sun Nov 17, 2019 8:17 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 4
- Views: 306
Re: Bond Angles
I believe that we don't need to know exact bond angles for certain molecules, but we might need to know their relationship to the expected bond angle based on electron density arrangement. For example, a trigonal pyramidal molecule has tetrahedral electron density arrangement, but because the lone p...
- Sun Nov 17, 2019 8:06 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Radicals
- Replies: 5
- Views: 327
Re: Radicals
Yes, Dr. Lavelle mentioned in class that the lone electron is considered as one region of e- density.
- Sun Nov 17, 2019 8:06 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Polar vs non polar
- Replies: 5
- Views: 301
Re: Polar vs non polar
No, lone pairs may be a common indicator of polarity, but it is not a catch-all rule. For example, molecules like I3 that are linear with lone pairs present around the central atom are still non polar due to cancelling dipoles.
- Sun Nov 17, 2019 8:03 pm
- Forum: Hybridization
- Topic: Hydrogen Bonding
- Replies: 2
- Views: 105
Re: Hydrogen Bonding
Based on homework problems and what we've done in class, it seems like we may be asked to determine whether hydrogen bonding would be present based on a molecular formula, to draw the orientation to other molecules based on H bonding, or to identify it as the most significant intermolecular force pr...
- Sun Nov 10, 2019 7:19 pm
- Forum: Dipole Moments
- Topic: Dipole moment units
- Replies: 4
- Views: 258
Dipole moment units
The units of the dipole moment (C x m) have me somewhat confused. What does the calculation for a dipole moment (charge x distance) actually tell you? Is it the strength of the interaction?
- Sun Nov 10, 2019 7:16 pm
- Forum: Hybridization
- Topic: Why is hybridization necessary?
- Replies: 3
- Views: 136
Re: Why is hybridization necessary?
I believe I recall that hybrdization makes the orbitals suitable for electron pairing/bond formation, but I'm sure we will go into more detail on this in lecture this week.
- Sun Nov 10, 2019 7:14 pm
- Forum: Ionic & Covalent Bonds
- Topic: Interaction potential energy
- Replies: 1
- Views: 100
Interaction potential energy
In the slides from the last lecture, Dr. Lavelle wrote Ep is proportional to a1a2/r^6 and then 1/r^6. Are these both for interaction potential energy? Do they show different things?
- Sun Nov 10, 2019 7:08 pm
- Forum: Lewis Structures
- Topic: expanded octet
- Replies: 3
- Views: 244
Re: expanded octet
When n is greater than or equal to 3 and the element is in the p block, an expanded octet is possible. This is possible because of the presence of the d sublevel.
- Sun Nov 10, 2019 7:05 pm
- Forum: Dipole Moments
- Topic: Temporary Dipole Moment
- Replies: 3
- Views: 283
Re: Temporary Dipole Moment
A dipole moment refers to the presence of two charges (di-pole, two charges). A temporary dipole occurs when in a covalent bond, the electrons momentarily are distributed unevenly, such that the distribution is not perfectly shared between atoms. This creates temporary partial charges.
- Sun Nov 03, 2019 5:33 pm
- Forum: Coordinate Covalent Bonds
- Topic: example of coordinate covalent bond
- Replies: 2
- Views: 169
Re: example of coordinate covalent bond
A coordinate covalent bond forms when one atoms supplies BOTH of the atoms that are shared in a covalent bond. In lecture, the example was given of F- providing both of the electrons to fulfill B's octet in the Lewis structure of BF3 to form BF4. The bond between the F that came from the F- and the ...
- Sun Nov 03, 2019 5:29 pm
- Forum: Ionic & Covalent Bonds
- Topic: Induced dipole-induced dipole interactions
- Replies: 1
- Views: 91
Induced dipole-induced dipole interactions
Are induced dipole-induced dipole interactions different from dipole-induced dipole interactions? How so? Can an induced dipole then induce another dipole and is this a separate type of interaction?
- Sun Nov 03, 2019 5:26 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: polarizing power
- Replies: 3
- Views: 235
Re: polarizing power
The large distortion refers to the tendency of electrons in the anion to be pulled towards the cation, creating more covalent character to the bond. Small, highly charged cations like Al3+ have small enough ionic radii and great enough charge that they have high potential to create this distortion o...
- Sun Nov 03, 2019 5:22 pm
- Forum: Octet Exceptions
- Topic: Radical
- Replies: 6
- Views: 322
Re: Radical
Atoms have a tendency to want a full octet. A radical has an atom with unpaired electrons, therefore, they have a tendency to form bonds in order to complete their octet and pair their electrons. This is a more stable, lower energy state.
- Sun Oct 27, 2019 6:06 pm
- Forum: Properties of Electrons
- Topic: Determining Number of Valence Electrons
- Replies: 2
- Views: 195
Re: Determining Number of Valence Electrons
Magnesium is not a transition metal, it is an alkaline earth metal, so knowing how to find the number of valence electrons for transition metals is not needed for this problem.
- Sun Oct 27, 2019 6:04 pm
- Forum: Resonance Structures
- Topic: Ideal Lewis Structure
- Replies: 4
- Views: 201
Re: Ideal Lewis Structure
Because the molecule possesses resonance, each structure will be essentially identical, save for the placement of a certain double or triple bond. You can draw the most "correct" structure by representing all these structures as equal using a double-headed arrow. But they are all equivalen...
- Sun Oct 27, 2019 8:40 am
- Forum: Electronegativity
- Topic: Molecular Geometry
- Replies: 4
- Views: 227
Re: Molecular Geometry
I know that past midterms have included molecular geometry. I'm guessing this is something we will go over next week when we study hybridization, but it all depends on the pacing of the class for the particular year.
- Sun Oct 27, 2019 8:35 am
- Forum: Ionic & Covalent Bonds
- Topic: hybrid/line structure
- Replies: 2
- Views: 95
hybrid/line structure
In lecture, Professor Lavelle drew a structure for benzene that he called "hybrid/line structure" or a "resonance hybrid" that looked like a hexagon with a ring in the middle. He said it was a better representation than the Lewis structure because of the experimentally observed b...
- Sun Oct 27, 2019 8:30 am
- Forum: Ionic & Covalent Bonds
- Topic: Explaining periodic trends
- Replies: 3
- Views: 196
Explaining periodic trends
There are different factors (increasing/decreasing nuclear charge, electron shielding, increasing/decreasing distance of electrons from the nucleus) that affect periodic trends in ionization energy/atomic radius/electron affinity. I remember talking in high school chem about which of these factors a...
- Sun Oct 27, 2019 8:26 am
- Forum: Ionic & Covalent Bonds
- Topic: Double bond placement
- Replies: 15
- Views: 924
Re: Double bond placement
Double and triple bonds should be placed when the number of electrons does not allow for single bonds only + valence electrons for each atom, so electrons must be shared so they can be "counted twice" like he mentioned in lecture.
- Sun Oct 27, 2019 8:25 am
- Forum: Lewis Structures
- Topic: Drawing the structure
- Replies: 7
- Views: 442
Re: Drawing the structure
Yes, it is still a Lewis structure even though P breaks the octet rule because it uses the same notation (lines for bonds and dots for valence electrons) as other Lewis structures.
- Sun Oct 20, 2019 2:42 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: What is Z eff e?
- Replies: 3
- Views: 175
Re: What is Z eff e?
Z eff refers to the effective nuclear charge. In this case, Z eff e refers to the effective nuclear charge experienced by an electron. The equation for calculating it can be found in the textbook. Basically, it is asking you to evaluate how strong the attraction of the electron will be to the nucleu...
- Sun Oct 20, 2019 2:39 pm
- Forum: Properties of Light
- Topic: N levels
- Replies: 8
- Views: 511
Re: N levels
The "n levels" are the principal energy levels. The n is the principal quantum number, which tells you how far away from the nucleus the electrons are as well as how much energy those electrons have. Increasing n means that distance from the nucleus as well as electron energy is increasing.
- Fri Oct 18, 2019 5:09 pm
- Forum: Properties of Electrons
- Topic: "Exception" in Writing Electron Configurations
- Replies: 4
- Views: 283
"Exception" in Writing Electron Configurations
In class today, Dr. Lavelle discussed an "exception" in writing electron configurations... He said "Half full d5 and full d10 subshells have lower energy". So in the example of Cr, the configuration is written as [Ar]3d5 4s1. Can anyone explain this to me? Why does the 4s shell n...
- Fri Oct 18, 2019 5:03 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: How to Name Electron Configurations
- Replies: 5
- Views: 302
Re: How to Name Electron Configurations
You don't necessarily "know" when to use the previous element- it can just be more convenient if you are trying to write the electron configuration for an element with many electrons. Using noble gas configuration eliminates a lot of the writing and allows you to only write the valence ele...
- Fri Oct 18, 2019 5:01 pm
- Forum: Photoelectric Effect
- Topic: The Work Function
- Replies: 15
- Views: 1045
Re: The Work Function
The work function is the energy required to remove an electron from a metal. Each type of metal has a specific work function. Think of it as the threshold energy or minimum energy to remove the electron. When you say E=hv is equal to work function, I think you may be referring to how the kinetic ene...
- Fri Oct 18, 2019 4:57 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Atomic Spectra
- Replies: 5
- Views: 177
Re: Atomic Spectra
Note that the dark lines show that the atom can only absorb radiation at certain frequencies. Each element has a specific, characterizing absorption spectrum.