CHEMISTRY COMMUNITY

AustinMcBrideDis3L

If you don't want to understand why: just remember we always leave out solids and liquids, molecules with the (s) and (l) subscript. If you want to know why, its because the reaction is happening in a solution of water, that means there are TREMENDOUS amounts of water compared to the other molecules...

AustinMcBrideDis3L

Yes you are correct, don't forget the relationship between the two: Ka x Kb = Kw = 10^-14

AustinMcBrideDis3L

Think of this question like it came from last week (the Ka is your K value... which you will use in your k expression. Set up your ice table by using the concentration given to you for the initial acid concentration. And calculate from there!

AustinMcBrideDis3L

Can someone explain the reasoning behind why comparing the Pka and pH values will determine whether the solution is charged or neutral such as that in the last two questions of our sapling hw?

AustinMcBrideDis3L

Taylor Newville 1C wrote:Can someone who had Lavelle last quarter for 14A explain what his midterms are like?

A lot of the questions are quite similar to the tougher textbook problems so definitely brush up on those!

AustinMcBrideDis3L

Hi, I have followed the textbook and I believe it has been using molarity. I find just staying in molarity easier because most answers want molarity anyways, so just convert from the very beginning and you should be good!

AustinMcBrideDis3L

I've always struggled to picture the relation between what an exothermic/endothermic reaction means with relation to a system and to whether the DeltaH is positive or negative, does anyone have mnemonic strategies or ways of thinking to clear that up?

AustinMcBrideDis3L

Im confused on when you can neglect the x component in the denominator sometimes. In example 5I.3, the textbook says approximate x<3.21 & 6.21 So in the solving for x in the equation equal to K, the x's in the denominator are just crossed out? When can we do this/when can we not? Because I'm sur...

AustinMcBrideDis3L

In an experiment, 0.020 mol NO2 was introduced into a flask of volume 1.00 L and the reaction 2NO2(g)⇌N2O4(g) was allowed to come to equilibrium at 298 K. (a) Using information in Table 5G.2, calculate the equilibrium concentrations of the two gases. (b) The volume of the flask is reduced to half it...

AustinMcBrideDis3L

So in a lot of the equilibrium calculations we end up using the quadratic formula/or polysmlt on the calculator to find the two roots.
My question is how do we know which one to pick when they are both positive? Is it always the one closer to 0? (when both are positive?)

AustinMcBrideDis3L

I doubt every single question will be from the textbook but I would assume a decent chunk of them will be.

AustinMcBrideDis3L

Can someone explain part B... why formic acid is actually stronger than acetic acid.

Suggest an explanation for the different strengths of (a) acetic acid and trichloroacetic acid; (b) acetic acid and formic acid.

AustinMcBrideDis3L

Can someone explain the reasoning behind why the answer is hypobromite?

Which is the stronger base, the hypobromite ion, BrO−, or morphine, C17H19O3NC17H19O3N? Justify your answer.

AustinMcBrideDis3L

Can anyone explain the steps to solve this problem? 6B.3 A careless laboratory technician wants to prepare 200.0 mL of a 0.025 M HCl(aq) solution but uses a volumetric flask of volume 250.0 mL by mistake. (a) What would the pH of the desired solution have been? (b) What will be the actual pH of the ...

AustinMcBrideDis3L

Im a little confused on where to start for this question

The molar concentration of HCl in hydrochloric acid is reduced to 12% of its initial value by dilution. What is the difference in the pH values of the two solutions?

AustinMcBrideDis3L

I heard that there is really no chance of a curve in this class. I really hope he doesn't consider a downcurve.

AustinMcBrideDis3L

So Bronsted acids and bases are taking with respect to proton donating/accepting. Lewis acids and bases are with respect to donating/accepting electrons.

AustinMcBrideDis3L

I actually have decided I will be switching majors after knowing a bit more about my major this quarter. Currently I am a biology major however, I was looking at the upper division classes that I would need to take and I do not think I would be particularly interested in those so I'm thinking of swi...

AustinMcBrideDis3L

In textbook problem 9C.5b it asks whether CO₃^2- is polydentate or not. The answer keys states that it can be mono dentate or bidentate, how can this molecule have two options... I especially do not see how bidentate is possible.

AustinMcBrideDis3L

I was wondering what you would use for Fe when the complex does not have a negative charge. All the textbook problems end up having that complex with a negative charge for iron so it becomes ferrate, but if the complex was positive it wouldn't be ferr would it?

AustinMcBrideDis3L

I just use flashcards or just memorize them straight up because many of them are used so often in all STEM based classes.

AustinMcBrideDis3L

Im confused because I've started the textbook problems for this section but many of them require us to come up with the names for the compounds. Are we required to learn the nomenclature rules for this section, I simply assumed we didn't because Lavelle didn't cover it in his lectures (at least for ...

AustinMcBrideDis3L

I reflect everything everyone has said above, but also be wary the coordination number is for every bond that attaches to the central atom (make sure you don't ever count the bonds between say the C and N.

AustinMcBrideDis3L

I struggled with this one so I ended up just submitting the answer and looking for the hints. Im sure you found the first one, the second one has a triple bond and is still linear, the last one is super tricky because is forms a triangular ring. Hope that guides you in the right direction!

AustinMcBrideDis3L

Degenerate orbitals are defined as orbitals that have the same energy.

AustinMcBrideDis3L

Professor Lavelle referenced in his lecture that repulsion strength goes in this order (LP-LP, LP-atom, atom-atom) thus the lone pairs will exert a bigger repulsive force on the other atoms making the other atoms get closer together (becomes less than 120 degrees or 109.5 what have you) so the LP ca...

AustinMcBrideDis3L

All molecules exhibit LDF forces, many molecules have other forces as well such as ion-ion!

AustinMcBrideDis3L

Axial is referring the axis position (the vertical axis), and equatorial are the ones surrounding the middle (think the equator of a globe) and the north and South Pole are the axes.

AustinMcBrideDis3L

Linear arrangements seem pretty easy but there are some specifics where I get confused. In I 3 - , the molecule is linear however the central atom has 3 lone pairs, is the reason why it is still linear because they are all I atoms and have the same electronegativity and thus any L.P's will arrange s...

AustinMcBrideDis3L

Regarding your first question, yes you can tell if bonds will be polar covalent bonds if you determine there is a difference in the electronegativities of the two atoms involved. However, the MOLECULE may be non-polar even if all the BONDS-WITHIN are polar because sometimes the shape can be symmetri...

AustinMcBrideDis3L

Yes, if you are unable to attain a structure with 0 formal charge on all the atoms you generally should draw the lewis structure in a formation that puts negative formal charges on the more electronegative atoms (typically the non-central atoms).

AustinMcBrideDis3L

I relate to a lot of you on this. I will calculate how many more points I can miss altogether or even on my next midterm before I lose my chances of getting an A. Its especially worrying when the midterms have such few questions that one question can make you lose a lot of points. I think the best t...

AustinMcBrideDis3L

I do not believe that there is a subtitle feature for these bruin casts. However, like many people have pointed out you can speed or slow down Professor Lavelle's lectures which can be really helpful.

AustinMcBrideDis3L

Cations are typically found on the left side of the periodic table (Alkali metals/Alkaline earth metals -groups 1&2) Anions are found on the right side (Halogens/Chalcogens - groups 16&17) Note that towards the middle of these two groups the lines get more blurry and you start seeing element...

AustinMcBrideDis3L

Can someone explain the reasonings for part b and c?

3F.5 Suggest, giving reasons, which substance in each of the following pairs is likely to have the higher normal melting point (Lewis structures may help your arguments): (b.) C2H5OC2H5(diethyl ether) or C4H9OH (butanol) (c.) CHI3 or CHF3

AustinMcBrideDis3L

Can someone explain why the answer is (b)? 2D.3 Which of these compounds has bonds that are primarily ionic? (a) BBr3; (b) BaBr2; (c) BeBr2. I understand why its not Boron, but I don't know how we are supposed to know which will create to a more ionic bond (between Be and Ba) if we aren't given the ...

AustinMcBrideDis3L

There is no correct image representation of what electrons look like. However, by distorted he means that the paths of the electrons are shifted so that they are less "circular" you could say, and more like an egg because the positive pull of the cation will attract electrons to create an ...

AustinMcBrideDis3L

Can someone explain why part c is the answer that it is:

2A.23 On the basis of the expected charges on the monatomic ions, give the chemical formula of each of the following compounds: (c) aluminum hydride

Answer: AlH3

AustinMcBrideDis3L

I also was wondering this, I'm pretty sure from what I keep hearing from others (who have gone to Lavelle's Office Hours) is that he will give us the formulas for things that we wouldn't typically know. But I'm also not sure if soon he would expect us to know formulas such as nitrate because they ar...

AustinMcBrideDis3L

Because as you go across a period you are not only just increasing in electrons you are increasing in protons. The positive central charge of the nucleus is becoming very big. As a result, the electrons in that outer shell will be pulled closer to the center due to the positive-negative attractions ...

AustinMcBrideDis3L

Ionic bonds typically occur between a metal and a non-metal. One atom "donates" or "loses" electrons and the other atom snatches them up and completes the bond. In covalent bonds the electrons are shared amongst the atoms involved.

AustinMcBrideDis3L

I feel like I remember him saying it's useful to write it the long way because its more specific but its also not wrong to write it the shorter way. I think he will be explicit on whether it needs to be in the long form on midterms. Also I doubt he will ask us write out the ml quantum numbers for d ...

AustinMcBrideDis3L

I have a decent understanding of the three terms: shells, subshells, and orbitals but I have a lot of trouble visualizing the complete relationships between them all for the periodic table and for atoms. I know that these are just models and we don't know what things look like but is there any way o...

AustinMcBrideDis3L

I believe the Sapling explanation is using different units. To be safe for midterms and the final just use the number and units given on the equation sheet we are allowed to use.

AustinMcBrideDis3L

ħ is just some chemistry technical term/jargon for h/2π. Thus when its (1/2)*ħ it equals the h/4π in the other equation. Also the equations should both have a greater than or equal to sign, so I don't know why there is a discrepancy there.

AustinMcBrideDis3L

The 4th quantum number is found by determining the spin of the electron. A spin up electron will have the quantum number +1/2 and a spin down electron will have the quantum number -1/2.

AustinMcBrideDis3L

Professor Lavelle mentioned in his lecture on Friday that technically there are math models for an angular momentum of 4 and above but there are no elements that are on the periodic table for which that would apply to.

AustinMcBrideDis3L

Ive worked out the problem here:

AustinMcBrideDis3L

Not sure, but you should know which answer is correct if that's the case if you know all the sig-fig rules, Lavelle has a whole document dedicated to sig-figs and rounding on his website and I would definitely recommend that.

AustinMcBrideDis3L

I would definitely recommend doing the post-assessment modules as well as go over any textbook problems you struggled with. Also review the outlines of what we are expected to know on Lavelle's website.

AustinMcBrideDis3L

I think you should be able to use the most common conversions such as km to m and kg to g as well as picometers and nanometers as they have been in many practice problems.

AustinMcBrideDis3L

How I see it is that when talking about "intensity" with regard to the wave model of light, intensity refers to amplitude. When we talk about "intensity" with regards to the particle model of light, intensity refers to number of photons. So I like to think of there being two defi...

AustinMcBrideDis3L

I completely agree, I thought they were very effective for review (because it covered the lectures again) and sometimes Prof. Lavelle would have different things to add to each lecture and that would be helpful to my understanding.

AustinMcBrideDis3L

We will have to be careful if the exams are proctored. My friend told me that she studied super hard for an exam and while she was taking it she read out loud the questions to herself to better comprehend it. The instructor watching her thought that she was reading the questions out loud to a frien...

AustinMcBrideDis3L

Can someone explain what the letter c (the answer) means? Which of the following happens when the frequency of elec- tromagnetic radiation decreases? Explain your reasoning. (a) The speed of the radiation decreases. (b) The wavelength of the radiation decreases. (c) The extent of the change in the e...

AustinMcBrideDis3L

diegomartinez1F wrote:Mass of electron is given:

Me= 9.10938 x 10^-31 kg

Do we need to convert this to grams or can we keep it as kg?

AustinMcBrideDis3L

Typically in cases of chemistry you will have some type of multiplication or division in your problem and as a result you will just use the smallest amount of sig figs in the givens as the amount in your answer. (but follow the rules others have given above if your problem happens to only include ad...

AustinMcBrideDis3L

I'm not too sure, I remember Lavelle told us this class does not focus on memorization but he never specified on this topic. Generally this type of naming is easy because sometimes when the elements are both on the right side of the periodic table they follow as: prefix (di, tri, penta) element and ...

AustinMcBrideDis3L

No, The empirical formula should be the simplest ratio form of the molecular formula. If the empirical formula was larger than the molecular, the empirical formula must not be simplified to its simplest ratio.

AustinMcBrideDis3L

Can someone help with this problem, I'm not sure where to start.

F. 27) A mixture of NaNO3 and Na2SO4 of mass 5.37 g contains 1.61 g of sodium. What is the percentage by mass of NaNO3 in the mixture?

AustinMcBrideDis3L

Does anyone know how many sig figs we should take from the molar masses on the periodic table for our homework and problems? Also which is preferred: rounding or truncating?

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