CHEMISTRY COMMUNITY

Kristina Rizo 2K

KBELTRAMI_1E wrote:Does anyone know how to scan from an at home wireless printer?

If you have an iphone i know you can scan a document through the notes app, but unfortunately i do not know how to scan from your specific printer since they are all different.

Kristina Rizo 2K

Yes, they'll post the solutions on the same post they posted the worksheet link.

Kristina Rizo 2K

Does anyone know if we could only do the take home final on Sunday?

Kristina Rizo 2K

My TA updated my grades on myUCLA for test 2, they might email their sections as to how they will hang back the tests.

Kristina Rizo 2K

Does anyone know anything about how to go about with lecture tomorrow? Will it be online or???

Kristina Rizo 2K

Kaitlyn Ang 1J wrote:
Abigail Sanders 1E wrote:Will this review session still be held now that all classes are cancelled? Lyndon's sessions are normally the most helpful thing before the finals/midterms.

Facts! If not hosted in person, maybe livestreamed...?

I will actually fail this test if this session gets cancelled :(

Kristina Rizo 2K

I think the s should always be on the outside since it signifies the electrode, but I don't think it matters for g or aq.

Kristina Rizo 2K

When doing basic and acidic redox reactions, the only difference is placing the H+/OH- and H20 on the correct sides when comparing to "regular" redox reactions right?

Kristina Rizo 2K

can someone explain why it is important to know whether k is < or > 1.

Kristina Rizo 2K

yes you obtain n by calculating the number of moles of electrons transferred.

Kristina Rizo 2K

This is a silly question, but could someone please explain to me the differences between [A] and [A]o?

Kristina Rizo 2K

A platinum electrode is needed when there is no solid metal conductor as an electrode already present. If there are already a metal anode and a metal cathode, then the platinum electrode is unnecessary. Whenever an inert electrode is needed, it is usually the platinum electrode, and I am unsure if ...

Kristina Rizo 2K

The reaction potentials are found on pg A16-17 for the seventh edition book.

Kristina Rizo 2K

when i looked at the solutions manual, it said the cell reaction was H+ (aq) -> H+ (aq) so n=1. However, I am not sure why the H2 is not included.

Kristina Rizo 2K

Isn't this just the table of all the E naught values? I am pretty sure we will be given these values for our future tests.

Kristina Rizo 2K

I got the same answer. I checked the solutions manual and tried to work backwards to see if I take the ln of 1.0x10^6 what would I get, and i got 13.8, not 15. Sorry, but i don't really know either.

Kristina Rizo 2K

What is the numeric value for the faraday constant? I didn't write it down during lecture.

Kristina Rizo 2K

Ami_Pant_4G wrote:I kind think of it as the word cathode has a "t" in it, which looks like a "+" sign so we know it gains electrons (which is what happens in reduction), and then anode is the opposite. Hope this helps.

This was really helpful thank you!!

Kristina Rizo 2K

These values will be given to us for future tests rights?

Kristina Rizo 2K

We are still dealing with concentrations like Al and Al3+ or Zn and Zn2+. Therefore, the same principles we learned in the equilibrium unit apply here. If there's too much concentration of one of these ions, the equilibrium will shift to satisfy LeChatelier's. This would then affect Q in the Nernst...

Kristina Rizo 2K

You can use platinum or graphite whenever there isn't a conducting metal present.

Kristina Rizo 2K

Would this also be related to the equation delta S= q/T? And q = delta H?

Kristina Rizo 2K

Looking at the graph that lavelle made on Friday helped me understand more by visualizing how -delta G is spontaneous while + delta G is non-spontaneous.

Kristina Rizo 2K

Lauren Tanaka 1A wrote:The naught sign means that the conditions are under STP or standard temperature and pressure. If the delta G has the naught symbol then so does the delta S and H.

STP is 1 atm and 273.15K right ?

Kristina Rizo 2K

Yes it is a state function.

Kristina Rizo 2K

Lauren Tanaka 1A wrote:You use this equation when you want to see the change in gibbs free energy relative to when the K value changes in the equation (products and reactants ratio).

So we are comparing the delta G to the equilibrium constant?

Kristina Rizo 2K

I don't have my book with me right now but I would look at the thermodynamics outlines and objectives that we need to know for the midterm. Because he also lists what sections he wants us to read and understand.

Kristina Rizo 2K

This is kind of irrelevant to the question but will the question always say if it is reversible or irreversible? Or is there another way we will know which equation to use?

Kristina Rizo 2K

I would know why the equation exists. It exists in irreversible conditions (temperature constant, P and V changing at infinitesimally small intervals, so dw = -PdV. P becomes nRT/V, and if you take the integral of both sides you're left with w = -nRTln(V2/V1). It's just helpful to know in terms of ...

Kristina Rizo 2K

I don’t think this will be on the midterm

Kristina Rizo 2K

The question asks to calculate the work for an irreversible expansion against a constant external pressure of 1.00atm to find the final volume of 6.52L. I used the equation w=Pex * delta V and got -2.23L atm, but the answer is 226 and in the SSM it multiplied the -2.23L atm by 101.325. Does anyone k...

Kristina Rizo 2K

ayushibanerjee06 wrote:Why are bonds that are formed negative in bond enthalpy calculations?

It represents an exothermic reaction.

Kristina Rizo 2K

The three methods are Hess's Law, using bond enthalpies, and delta H = Σ delta Hf of products - Σ delta Hf of reactants. Using the bond enthalpy method is the least accurate so if you can use other methods that's preferred. This was extremely helpful thanks! But do you know which is more accurate (...

Kristina Rizo 2K

I’m not sure there is an equation to figure it out but you can also mentally think about the Lewis structure.

Kristina Rizo 2K

dtolentino1E wrote:yes!

the change in internal energy (delta U) is usually calculated as heat (q) + work (w), but at constant pressure, q = delta H and w = -P(deltaV)

So when P is not constant we go back to delta U= q +w?

Kristina Rizo 2K

Can someone explain to me what Hess’ Law is exactly and what equations pertain to it please.

Kristina Rizo 2K

I know that the change in pressure doesn't effect the equilibrium constant. According to my lecture notes from week 1 Friday, Lavelle stated that when there is a change in pressure there is no effect on the reaction or in reactant and product concentrations. However if volume decreases, and there ar...

Kristina Rizo 2K

I know the units for Kc is molarity, but could someone give the units to know if it is partial pressure.

Kristina Rizo 2K

There is also a chart on page F75 in the seventh edition. It is in Fundamentals J, the table is Table J.1.

Kristina Rizo 2K

Nawal Dandachi 1G wrote:pKa + pKb = 14, so solve for pKb. After finding pKb, use pKb = -log(kb) to find Kb

I thought by doing the -log, you would get pKb? Wouldn't you need to 10^pKb to get Kb? Or did I switch it?

Kristina Rizo 2K

What would happen if a temperature is given? Would I not be allowed to use the equation?

Kristina Rizo 2K

Kristina Rizo 2K wrote:I remember in 14A we were given a table from the book and I found it best to just memorize that table.

I would look at pg F75 in the 7th edition book for table J.1

Kristina Rizo 2K

I remember in 14A we were given a table from the book and I found it best to just memorize that table.

Kristina Rizo 2K

Adding on to this, does the Le Chatelier's Principle only apply for the partial pressures or do I need to know how to apply it for concentrations?

Kristina Rizo 2K

I thought Kp was used for gas only? Can someone clarify this please.

Kristina Rizo 2K

This is irrelevant to the stated question, but does anyone know if we can still turn in chemical equilibrium hw questions for week 2? Or does it have to be acids and bases?

Kristina Rizo 2K

I thought the Professor said we won't be expected to completely solve a cubic equation, only a quadratic equation?

Kristina Rizo 2K

Jacey Yang 1F wrote:You would convert the partial pressures to concentration using the ideal gas law equation.

Just to clarify, you are converting them all with PV=nRT before you create the K expression correct?

Kristina Rizo 2K

when a question gives the pressures of gases, but asks for the molar concentration do we just convert the equilibrium constant or do we convert all the pressures to molarity? Were you asking about a hw question? If so could you tell me which question so I can see an example of when/how to do this p...

Kristina Rizo 2K

The pressure doesn't affect the equilibrium constant. However, I think the professor stated that it does alter the overall reaction.

Kristina Rizo 2K

The question states to balance the following equations and then write the expression for K.
Part b) I2 (g) +F2(g) <--> IF5 (g).

I just want to clarify that when we use gases in the K expression we use partial pressure correct?

Kristina Rizo 2K

You have to look at how many atoms in the ligand have lone pairs, because the lone pairs are potential binding sites to the central metal. The ligand in part (a) has three nitrogen atoms that have lone pairs. Thus there are three binding sites so the ligand is tridentate. The ligand in part (b) has...

Kristina Rizo 2K

As far as I can tell from doing a bit of research, polydentate is always synonymous with chelating and monodentate with nonchelating. Reading through this page led me to that conclusion. https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Coordinat...

Kristina Rizo 2K

just count the number of things around the transition metal complex. Lone pairs count towards coordination numbers but there are never lone pairs around the transition metal complex (at least as far as I've seen). So your best bet will be to ask: "how many atoms are bonded to the transition me...

Kristina Rizo 2K

An amphiprotic substance is one which can both donate hydrogen ions (protons) and also accept them like water. Amphoteric means that they have reactions as both acids and bases. So does the amphiprotic substance mean it can be a Bronsted acid and base? While the Amphoteric substance relates to Lewi...

Kristina Rizo 2K

I also had a question for this hw problem. For b) BF3, why is it an acid, I thought it couldn't accept anymore electrons because b valence electrons is 3 and its already filled by 3 F's?

Kristina Rizo 2K

If my discussion was cancelled last week, can I still do hw problems on coordination compounds? Or does it have to be on acids and bases?

Kristina Rizo 2K

Kristina Rizo 3K wrote:Ya I don't think we need to know this for the final.

I don't think it will be heavily tested, if at all, but it would be good to understand the concept anyways.

Kristina Rizo 2K

I would still look at Clara Cho's two question's titled "Dimagnetism" and "Paramagnestism." People explained the difference between the two and why they were relevant.

Kristina Rizo 2K

Ya I don't think we need to know this for the final.

Kristina Rizo 2K

Does anyone know if the grades will be posted before next Friday? My discussion is on Friday, so I won't be able to receive my grade until next Friday.

Kristina Rizo 2K

Don't they cancel each other out when the molecule is symmetrical?

Kristina Rizo 2K

You can tell by the location of the atoms on the periodic table. Be, Al, Ga, Sn, Pb, and Sb form amphoteric compounds. Anything to the left of them on the period table forms bases, and anything to the right forms acids. Was this the diagonal line on the periodic table he was trying to explain in le...

Kristina Rizo 2K

They mean the same thing, I think he said something in lecture about using bent, but the TA's won't mark it incorrect if you use either one.

Kristina Rizo 2K

I know the bonds (sigma and pi), molecular shapes, bond angles and the intermolecular forces will be on test 2. I'm not sure if that is all though.

Kristina Rizo 2K

O3 has a bond angle of <120 degrees since it has a lone pair, but I thought O2 is linear with 180 degree bond angles. Is this from a specific hw question?

Kristina Rizo 2K

Also, another way the book states bent is angular. You'll be fine if you just say bent or angular.

Kristina Rizo 2K

The question asks to "State the relative orientations of each of the following hybrid orbitals: a) sp^3; b) sp; c) sp^3d^2; d)sp^2."
I don't really understand how to go about this question, could someone explain how to get the answer please.

Kristina Rizo 2K

Can someone also explain the difference between dipole-dipole and induced dipole-induced dipole.

Kristina Rizo 2K

The dipole moment is basically when a partially negatively charged atom in a polar covalent bond is attracted to another positively charged thing (usually the positively charged atom of another polar covalent bond or a cation). This isn't like a bond, but there is a very weak, but still significant...

Kristina Rizo 2K

VLi_1L wrote:Although CH2Cl2 is symmetrical, the differing polarities of the C–H and C–Cl bonds means the effect of the polar bonds is not cancelled, so the molecule is polar

SF4 has 4 bonds with one lone pair which makes it polar.

Is it because the C-H bond is stronger than the C-Cl bond?

Kristina Rizo 2K

Mariepahos4D wrote:The name is determined only by the bonding regions, but the lone pairs influence the shape.

When you say bonding regions, you mean the actual atoms bonded together right?

Kristina Rizo 2K

I don't think it matters which resonance structure you use since bonds don't really matter when making the structure in 3D.

Kristina Rizo 2K

Can someone explain how d isn't a radical. The structure should be of HOCO. I did it and i got H-O-C-O with 2 pairs of electrons on each O and with one lone pair on C, which should make it a radical right?

Kristina Rizo 2K

If asked to draw resonance structures, I am sure they are asking for all of them, so I would write them all just in case. If you don't and they explicitly asked for all resonance structures you could possibly lose partial credit.

Kristina Rizo 2K

You want the most electronegative atom to carry any extra negative charge and the least electronegative atom to carry any extra positive charge. So this means that any atom closer to the top right of the table should be the ones to carry the negative charge since they have a stronger pull on electr...

Kristina Rizo 2K

Formal charge: # ve- a neutral atom of the element would have - (sum of unpaired electrons + bonds) Note: a. count each unpaired electron attached to the atom as a single value b. count each bond as a single value For example, say that Nitrogen was surrounded by 1 double bond and 2 unpaired valence...

Kristina Rizo 2K

Electronegativity is the electron pulling power of an atom. As you move to the right of the periodic table, the electronegativity increases because atoms get closer and closer to having a full octet. As you move up the periodic table, electronegativity also increases because there is less shielding...

Kristina Rizo 2K

Does anyone know if for the test we are supposed to write out p as p^3 or px^1, py^1, pz^1?

Kristina Rizo 2K

For a, the question is asking for the configuration of Cu+. The normal configuration for Cu is [Ar]3d^104s^1. The + charge on Cu means you are taking off one electron, so you would take off the electron from the furthest shell from the nucleus. In this case, it would be from the s-block, which would...

Kristina Rizo 2K

Do you have a question regarding how to figure out the ground-state electron configurations?

Kristina Rizo 2K

Yes, they do not notate 4s in the configuration because they took 2 electrons out, to give it a 2+ charge. As stated earlier, they took the electrons out of 4s because it is farther from the nucleus compared to 3d. So it would be harder to take 2 electrons from the d-block compared to the s-block.

Kristina Rizo 2K

Doesn't the octet rule mean that there must be 8 valence electrons on each element?

Kristina Rizo 2K

It does correspond to the group but make sure you skip over the transition metals in the middle when looking at elements toward the right. For example, Boron has 3 valence electrons, not 13. So we normally skip over the d-block unless stated otherwise? For example, hw problem 2A.1a asks to give the...

Kristina Rizo 2K

2B.7 "The following Lewis structure was drawn for a Period 3 element. Identify the element." The Lewis structure given was an Oxygen double bonded to E (the unknown element) and 3 Chlorine elements that have a single bond with E. I was wondering if I am supposed to use the formal charge to...

Kristina Rizo 2K

Give the ground-state electron configuration expected for each of the following ions: a. Cu^+ b. Bi^3+ c. Ga^3+ d. Tl^3+ For a, I got [Ar]3d^9 4s^2, which becomes [Ar]3d^10 4s^1. I don't understand why the answer is just [Ar]3d^10? As for b, the answer is [Xe}4f^14 5d^10 6s^2. I'm not sure how to g...

Kristina Rizo 2K

I just want to clarify that we can still turn in quantum world hw questions as the 5 questions due in section? I have them done and don't want to find out later that I won't get credit.

Kristina Rizo 2K

An orbital is a subsection under a subshell. A subshell is recognized based off of the l value: 0=s, 1=p, etc. Then within these, each sub shell has certain orbitals with s having 1, p having 3, d having 5, and f having 7, where each orbital has 2 electrons paired based on their spin state. Could y...

Kristina Rizo 2K

I had the same confusion, but no the given range had nothing to do with the calculation you were supposed to do. I think they put it in to confuse the students (and they are doing a pretty good job at it too).

Kristina Rizo 2K

Adding on to this question, does anyone know if we will be given a chart of mass values for future tests? Because in the question, we were only given the wavelength and not the mass of a neutron.

Kristina Rizo 2K

As William has stated before, the electrostatic potential energy is significant to understand how an outer electron can be "taken" from an atom to result in a different electric charge. Professor Lavelle stated that this background information will be more useful in the future when we lear...

Kristina Rizo 2K

After the 4s state/orbital is occupied and electrons enter the 3d state, the 3d state would be lower in energy than the 4s state. This occurs for multi electron atoms after the atomic number 20 (Calcium). For Scandium (z=21), you would put 3d1 before 4s2 because the 4s state is higher in energy tha...

Kristina Rizo 2K

the "ml" quantum number gives the relative orientation of the electron in the specific sub-shell. We derive the "ml" number from the "l" number, by following the given values "ml" can be, which are "l","l-1",or "-l". This means t...

Kristina Rizo 2K

Also, does someone understand how Lavelle labeled which axis were used in the second to last example in today's lecture?
The example was:
n=2, l= 1, ml=-1 and he said the answer was that the electron was in 2px state. How did he know it was x?

Kristina Rizo 2K

Can someone explain how we are supposed to get ml quantum numbers (the third quantum number) again, I don't really understand how I know which number it is, especially if i am given l already.

Kristina Rizo 2K

what does Chem_mod mean? Is that the professor?

Kristina Rizo 2K

Can someone further explain what exactly De Broglie's Equation is used for. Also, I am unsure when I am supposed to use it. Thanks.

Kristina Rizo 2K

I think it is also helpful to visualize graphs or images when trying to learn the differences. For example, the graph of energy levels for Atomic spectra and the photoelectric experiment (the electron bouncing off the metal) because when you see a visual image it will help you understand the differe...

Kristina Rizo 2K

The relationship between the intensity and frequency of light is that as frequency increases, intensity increases- so essentially, they are proportional. This is because intensity is generally gauged as the energy per some unit of time and according to the energy equation of light where E=hv, as fr...

Kristina Rizo 2K

The answer for self-test E.2B part a. was 2.0 x 10^2 using scientific notation and with that ended up getting sig figs of 2. I didn’t use scientific notation so my answer was 200.1, which I then used for part b. My question is if I were to do that on the test, would I still get credit since my answe...

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