CHEMISTRY COMMUNITY

Anna_Mohling_1D

HClO is a weak acid ( Ka=4.0×10−8 ) and so the salt NaClO acts as a weak base. What is the pH of a solution that is 0.081 M in NaClO at 25 °C?

Could someone walk me through this problem? I solved for Kb by doing 1x10^-14 / Ka but I am unsure what my next steps are.

Anna_Mohling_1D

After converting the mol/3L into molarities, you will get that, initially, there were .133 mol/L H2 and .533 mol/L of I2. Since the problem says that 60% of the H2 had reacted at equilibrium, then at equilibrium, there is 40% of the original H2 concentration left. .4 X .133= .0532 mol/L H2. Now we ...

Anna_Mohling_1D

For the pH of row (i) in the problem, how did they get 0.176? In general, how do you find the pH of concentrations over 1? I don't know what the answer to your question is but as far as I know, this problem was not assigned on the syllabus! Maybe finding the pH of concentrations over one isn't cove...

Anna_Mohling_1D

You would use the Kw given in the problem because you only use neutral water's Kw when the temperature is at 25 degrees Celsius. To find the concentrations for hydronium and hydroxide you would take the square root of the given Kw. I was also confused on this question but your answer makes sense! I...

Anna_Mohling_1D

My number one thing is that if I'm going to study I want to make sure it is productive study time. I ensure this by leaving my phone somewhere else, looking at the time I start studying and promising myself that I will work hard for ___ amount of time. This helps me keep myself accountable and makes...

Anna_Mohling_1D

Hi! For this question I basically manipulated the given equations to get the equilibrium constant for the equation the questions asks about. So, I took the inverse of the K for N2(g)+3H2(g)↽−−⇀2NH3(g) and then raised K to the power of 3 for this equation H2(g)+I2(g)↽−−⇀2HI(g). Then I multiplied thos...

Anna_Mohling_1D

I also would appreciate clarification on this! From my knowledge, I think to minimize the effects refers to the equilibrium constant the system will adjust to make sure it stays the same? However, I am not completely sure.

Anna_Mohling_1D

I think for this one it's saying that 60% has reacted by equilibrium, so your initial concentration is still what they gave you in the first sentence but your equilibrium concentration should be 40% of your initial (because that's what's left). Your change is the 60% of the initial concentration. O...

Anna_Mohling_1D

I think this varies for most students! I personally like to go to at least 2 UA sessions/week (I usually go to 1 step-up and 1-2 workshops). Sometimes I would go to more before exams because the UA's oftentimes provide review questions. During the week before finals, I went to about one per day beca...

Anna_Mohling_1D

Like a lot of the students above me mentioned, I recommend doing the textbook problems along with actually reading and taking notes on the assigned textbook sections! This helped me understand concepts in addition to just solving problems. I also highly recommend going to UA learning sessions. I spe...

Anna_Mohling_1D

5I.19 A reaction mixture that consisted of 0.400 mol H2 and 1.60 mol I2 was introduced into a flask of volume 3.00 L and heated. At equilibrium, 60.0% of the hydrogen gas had reacted. What is the equilibrium constant K for the reaction H2(g)+I2(g)⇌2HI(g) at this temperature? Could anyone explain to ...

Anna_Mohling_1D

Hi! For this question you'll use the equation m\Delta v\Delta x\geq \frac{h}{4\prod } ! So first, I make sure everything is in the correct units (mass in kg, velocity in m/s, position in m). So first convert the given velocity from km/s to s. Then, you know the mass of a proton is 1.693 x 10 ^ -27 k...

Anna_Mohling_1D

As far as I am aware, it is as simple as that! 1 bond = 2 electrons and 1 dot = 1 electron.

Anna_Mohling_1D

I'm not completely sure what the reasoning is but HBr is a strong acid so I would just memorize all of the strong acids because then it's easy to do the process of elimination!

Anna_Mohling_1D

Hi, they are not the same! See saw has 1 lone pair and 4 bonding pairs and trigonal pyramidal has 1 lone pair and 3 bonding pairs.

Anna_Mohling_1D

I think it's because C is more electronegative so it has greater electron-withdrawing power and is able to stabilize the anion after it donates a proton!

Anna_Mohling_1D

Hi! The negative charge is just part of the formula but make sure to take it into account when drawing your Lewis Structure! So the total number of valence electrons is 26 (6 from O for a total of 18 + 7 from I + 1 from the negative charge). Then, when you draw the Lewis Structure you'll notice ther...

Anna_Mohling_1D

I believe electron arrangement just looks at the regions of electron density but then molecular shape takes lone pairs into account. So for a molecule with 2 bonding pairs and 2 lone pairs, the electron arrangement would be tetrahedral but the shape would be bent.

Anna_Mohling_1D

It also really helps me to separate the given salt/ion before I even consider ranking them! I do this because then it's easier to identify which may come from strong bases or acids!

Anna_Mohling_1D

I was also confused about this. Should we just memorize whether these are basic/acidic/neutral?

Anna_Mohling_1D

I don't think the order matters when writing the formula as long as the TM is first and the ligands follow. However, the order is alphabetical when writing the name!

Anna_Mohling_1D

I think most people suggest taking 14BL after 14B but I have a friend who took both simultaneously and said it was very doable!

Anna_Mohling_1D

2.45 Consider the bonding in H2C=CHCHO. (a) Draw the most important Lewis structure. Include all nonzero formal charges. (b) Identify the composition of the bonds and the hybridization of each lone pair -- for example, by writing sigma(H1s, C2sp^2) Hi! I am confused about how to write the compositio...

Anna_Mohling_1D

Name each of the following complex ions and identify the oxidation number of the metal. C. [Co(CN)5(OH2)]2- Could someone explain how to name this. So usually I first look at the TM which in this case is Co (TM listed first). Since the overall charge is 2-, the charge of Co has to be +3 (CN is 1- a...

Anna_Mohling_1D

Could someone help me figure out the coordination number of [Pt(en)Cl2] and explain why it is not 2? I thought that the number of bonds is equal to the coordination number. Is that not true in this case? Also, what does the en indicate? Thanks! Hi! the en signifies ethylenediamine which is NH2CH2CH...

Anna_Mohling_1D

When they ask about relative positions, I think they are talking about the positions of atoms in relation to one another in a 3D space, using the lewis structure to help create the model. Lewis structures are 2D, but the actual model of the molecule is in 3D. For instance, the lewis structure for C...

Anna_Mohling_1D

I usually just think of it as a word rather than the 5 letters so I say it like Vespr which is in the wrong order for the acronym so I make sure to remain cognitive of that! Not sure if this makes a ton of sense but I hope it's a little bit helpful!

Anna_Mohling_1D

2E.1 Below are ball-and-stick models of two molecules. In each case, indicate whether there must be, may be, or cannot be one or more lone pairs of electrons on the central atom. Why isn't the answer for part b "cannot be one or more lone pairs"? If the bond angle is 180 degrees doesn't...

Anna_Mohling_1D

I am a little bit confused about how to tell when we are supposed to give the shape of the electron arrangement of the molecule. Is there a "default"? I also get confused with whether we account for lone pairs when giving shape or electron arrangement. If anyone could help explain this, I'...

Anna_Mohling_1D

The textbook uses the name angular to describe molecular shape but is angular the same as bent? Or if not, what is the difference between bent and angular?

Anna_Mohling_1D

There are 3 H-bonds in a GC pair and 2 h-bonds in an AT pair! Hope this helps!

Anna_Mohling_1D

For stronger intermolecular forces are you looking for the larger molecule because it has more electrons=stronger bonds while for intramolecular forces you would look for the smaller molecule so it can be pulled in closer? I believe that if we're talking about intermolecular forces you'd be analyzi...

Anna_Mohling_1D

In addition to what everyone else said, I find it really helpful to just know that polarizing power is related to cations and polarizability is related to anions!

Anna_Mohling_1D

I believe when we draw resonance structures we are already drawing the most stable structure according to the formal charges!

Anna_Mohling_1D

Hi! By draw do you mean drawing the Lewis Structure? I think the molecule is covalent because the difference in electronegativity between Al and Cl is not very significant.

Anna_Mohling_1D

hello! In some cases, we may be given the electronegativity values and we compare them to see whether or not the bond is polar or non-polar. Otherwise, we may need to just simply compare the polarity of two compounds. For example, we may be asked between HF and HI is more polar. Since I is less ele...

Anna_Mohling_1D

Hi everyone! I was wondering if anyone knows if there's a "threshold" or anything to determine whether a molecule is polar or non-polar from the Lewis Structure. I know that if an element is very electronegative compared to the other element, there will be a partial negative on the more el...

Anna_Mohling_1D

I am also unsure about this. I believe it has something to do with polarizability? Br and I are both larger than F and Cl so they have a larger/more easily distorted electron cloud and higher polarizability. I'm not sure if I have the correct thought process so if anyone knows, I'd really appreciate...

Anna_Mohling_1D

FionaHunter21 wrote:Between two anions in the same row, would an anion with a -2 charge be more or less polarizable than an anion with a -1 charge?

I think it is just by anion size. So whichever one is larger will be more polarizable even if the charge is a smaller magnitude. Someone, please correct me if I am wrong!

Anna_Mohling_1D

Give the ground-state electron configuration expected for each of the following ions: (a) Cu+ For this question I got the ground-state electron configuration of Cu: [Ar] 3d^9 4s^2 and then when I took the positive charge into account I got Cu+: [Ar] 3d^9 4s^1. Can anyone explain why this is incorrect?

Anna_Mohling_1D

A UA mentioned that we don't need to know how to write electron configurations involving the f-block however I have noticed that some of the assigned textbook questions involve the f-block. Does anyone know if this a mistake/if I should skip these questions? Or should I learn how to do it/ will we b...

Anna_Mohling_1D

Give the ground-state electron configuration and number of unpaired electrons expected for each of the following ions: (a) Ca2+; (b) In+; (c) Te2−; (d) Ag+ I am a little bit confused about part d. I got the configuration for Ag+: [Kr]4d^9 5s^2 and then since it's plus 1 I thought it would be Ag+: [K...

Anna_Mohling_1D

I have a friend who is in 14b and 14bl right now and she says it is very doable so I would do whatever works best with your schedule!

Anna_Mohling_1D

2A.9 Which M2+ ions (where M is a metal) are predicted to have the following ground-state electron configurations: (a) [Ar]3d7; (b) [Ar]3d6; (c) [Kr]4d4; (d) [Kr]4d3?

I am a little bit confused about what this question is asking for, does anyone know how to start/ interpret the question?

Anna_Mohling_1D

Hi everyone, could anyone explain how they understand or interpret questions that ask which orbital an electron would be removed from to create a +1 ion? I'm a bit confused because I originally assumed it would be removed from the orbital with the e- found furthest from the nucleus.

Anna_Mohling_1D

I just realized we are supposed to omit (e) so please disregard this!

Anna_Mohling_1D

Write the ground-state electron configuration for each of the following atoms: (e) tungsten Could anyone explain how to write the ground-state electron configuration for W? I know it begins with [Xe] however I don't understand how to write the correct configuration and am specifically struggling wit...

Anna_Mohling_1D

Write the ground-state electron configuration for each of the following atoms: (a) silver

Can anyone explain why the electron configuration for silver isn't [Kr]5s^2 2d^9?

Anna_Mohling_1D

If the wavelength of incident light on sodium metal was 810 nm, and the work function of sodium is 1.1 eV, what is the wavelength of the ejected electron? I converted the wavelength and work function to SI units. I then found the frequency and used that to find the energy of the photon (2.45x10^-19)...

Anna_Mohling_1D

5. (10 min) Light of wavelength 346 nm is shone on the surface of sodium, and the velocity of the ejected electrons is measured to be 6.73 x 105 m/s. What is the work function of sodium in eV? I am confused about this question because I'm not sure what equations to use. I was planning on using 1/2 m...

Anna_Mohling_1D

4. Zinc metal has a work function of 6.89 x 10-19 J. a. If UV light with a wavelength of 122 nm is shone on the zinc, what is the kinetic energy of the emitted electrons? b. What is the longest wavelength of light that will eject an electron from zinc? What is the smallest frequency of light that wi...

Anna_Mohling_1D

I noticed I have been struggling with identifying which equations to use and when (specifically when to use c=lambda(frequency), E=h(frequency), or De Broglie's). Does anyone have any tips or would be willing to share how they interpret problems and decide when to use what equation?

Anna_Mohling_1D

6. The work function for lithium is 4.6x10^-19 J. a) What is the lowest frequency of light that will cause photoelectric emission? b) What is the maximum energy of electrons emitted when light of 7.3x10^14 Hz is used? I understand part a and got the correct answer; however for part b I keep getting ...

Anna_Mohling_1D

I don't think the order is fixed but I just skipped all the questions involving quantum numbers and ended up answering 18 questions that I know we have covered in lectures!

Anna_Mohling_1D

Does anyone know how to turn off Sapling's randomization of the questions? I know Dr. Lavelle mentioned we should do this in one of his recent emails but I cannot figure out how and some questions before #19 involve material that we have not covered yet.

Anna_Mohling_1D

1D.11 How many orbitals are in subshells with l equal to (a) 0; (b) 2; (c) 1; (d) 3?

What does l refer to in this problem?

Anna_Mohling_1D

I think you are right as well! However, I was a little bit confused because I feel like the majority of 1D.2 covers information that wasn't covered in the lecture?

Anna_Mohling_1D

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6×10^3 km⋅s−1. (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50×10^16 Hz. How much energy is required t...

Anna_Mohling_1D

A college student recently had a busy day. Each of the student’s activities on that day (reading, getting a dental x-ray, making popcorn in a microwave oven, and acquiring a suntan) involved radiation from a different part of the electromagnetic spectrum. Complete the following table and match each ...

Anna_Mohling_1D

In one stage in the commercial production of iron metal in a blast furnace, the iron(III) oxide, Fe2O3, reacts with carbon monoxide to form solid Fe3O4 and carbon dioxide gas. In the second stage, the Fe3O4 reacts further with carbon monoxide to produce solid elemental iron and carbon dioxide. Write...

Anna_Mohling_1D

Calculate the amount (in moles) of (d) H2O in 2.00 g of Na2CO3⋅10H2O For this question, I found the molar mass of Na2CO3⋅10H2O to be 19100 g. mol^-1. I divided 2g by this molar mass to get 1.05x10^-4 moles Na2CO3⋅10H2O. I then multiplied this by 10 because there are 10 (molecules?) of H2O to get 0.0...

Anna_Mohling_1D

Adding on to what Tamara and Hannah explained, make sure to convert your calculated wavelength from m to nm by diving by 10^-9. I forgot to do this originally and kept getting the incorrect answer.

Anna_Mohling_1D

I got the right answer now, thank you! I did not realize that I was supposed to divide the total energy by the work function I initially solved for.

Anna_Mohling_1D

When a metal was exposed to photons at a frequency of 1.43×1015 s−1, electrons were emitted with a maximum kinetic energy of 3.70×10−19 J. a. Calculate the work function, Φ, of this metal. b. What is the maximum number of electrons that could be ejected from this metal by a burst of photons (at some...

Anna_Mohling_1D

Hi everyone,
I didn't know where else to ask this question but did anyone else receive an email from their TA about needing to get an external webcam (one that can be plugged into a computer)? I just want to clarify if this is necessary before buying one.

Anna_Mohling_1D

A great way to sort through all the STEM (and every other club) is to check out the @uclaeaf Instagram! They just highlighted every club on their page with details, application deadlines, and such.

Anna_Mohling_1D

I am also having trouble finding the empirical formula for this question. I wrote out the chemical reaction as C_H_O_ + O2 --> CO2 + H2O because I believe "burning" is the same as combustion. From there I calculated the moles of CO2 and H2O, but I don't know what my next step should be. An...

Anna_Mohling_1D

Hi everyone, I am confused about the Sapling week 1 homework, question 7, and was wondering if anyone could walk me through how to solve it. The question is as follows: A solution of CaCl2 in water forms a mixture that is 41.5% calcium chloride by mass. If the total mass of the mixture is 986.6 g, w...

Anna_Mohling_1D

Hi! Looking at the explanation for this question really helped me because it explained that all non-zero digits are significant, that zeroes between 2 non-zero digits are significant, and that trailing zeroes are not significant if there is no decimal point showing. So 950000 has only two sig figs a...

Anna_Mohling_1D

Thank you for posting and sharing this. It is very motivating hearing how important this class and material is not just now, but in the future as well.

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