CHEMISTRY COMMUNITY

Ben Rolnik 1D

There was another question just like this which I just answered :) hopefully that helps!

Ben Rolnik 1D

yeah this is a tricky log based question! Essentially, once you understand that the question is basically saying "X" initial HCL and ".12X" change in HCL then you SECOND molarity will be log(.12x) .... and the principle of logs is: log(A * B) = Log(a) + log(b). therefore, log(.12...

Ben Rolnik 1D

yes For this equation: pH = -log( square root ( kA * molarity HA ). That's not always true, but it works here... and also usually where you're not given much more info. This works because from your icebox the equation can be rounded to: kA = X^2 / [Molarity HA] //// pOH is always "14 - pH"...

Ben Rolnik 1D

This is a really good question.... The truth is that the Henderson-Hasselbach Eq is actually just a manipulation of the basic equilibria equation.... therefore, instead of thinking about it in terms of its limitations and usefulness, it's more important to think about the general equation itself and...

Ben Rolnik 1D

I don't think we need to memorize these values. They should be given.

The most important thing is that you understand what they mean and how to use them to solve the equations (especially for the conjugates...)

Ben Rolnik 1D

This question is really tricky (unless you actually go through the Toolboxes and examples given in chapter 13 in the book). but for (a) basically you know that for the equilibria equation, "HA - X" and "A + X" (from your ice box) is basically going to be the same as HA and X.... ...

Ben Rolnik 1D

Can someone show me how they set up problem 13.11 -- the book skips a step and I'm not sure how they got their initial pH.

Thanks!

Ben Rolnik 1D

Yes :)

Ben Rolnik 1D

Hey everyone,

I'm getting started on Self-Test 2 -- but seeing as the test is coming up on Tuesday, I wanted to start a thread for us to compile all the right answers to study.

If you have answers, post them here and we can compare notes.

Happy studying!

Ben Rolnik 1D

Got it! Will do :) Thanks!

Ben Rolnik 1D

Can someone explain why the solution for the balanced equation is 2A <-> B + 2C ?

Thanks!

Ben Rolnik 1D

Can someone please explain when we actually use the ideal gas equation? It seems like most of the problem in the book let you set up the ICE box using pressure without needing to convert it into a concentration... so I'm a bit confused about when we will need to convert partial pressure to molarity ...

Ben Rolnik 1D

Can someone help me understand the difference between Exothermic and Endothermic (as well as how we use this to make chemical equilibrium calculations). For some reason, it reads like a brain teaser to me!

Thank you!
Ben

Ben Rolnik 1D

Why is the the lewis structure for CLO2 "O-Cl-O" (with 3 electrons around Cl) and not "O = Cl = O" (with 3 electrons around Cl).... both have FC of 0 and 19 electrons... in fact the one with 2 double bonds actually has the lower formal charge.

Thanks!

Ben Rolnik 1D

just to add onto this -- since there were no homework problems which required performing electronegativity calculations, then you can be pretty sure questions like these won't show up on the tests. In general, I would suggest focusing on the specific questions that arise from the homework problems. ...

Ben Rolnik 1D

so here's the formula. 1. count the valence electrons for each atom in the molecule 2. place the least electronegative atom in the center (or the atom with the lowest ionization energy... or the atom farthest away from Fluorine). 3. arrange all the other atoms around it symmetrically (this will also...

Ben Rolnik 1D

It's been very helpful for me to think about your question in terms of this: all elements C N O F Ne want to form an octet. Period.... but elements after & including Phosphorus want to minimize their formal charge (even if that ends up forming more than an octet). So if you've formed a good lewi...

Ben Rolnik 1D

This is very helpful -- and I think it gets confusing especially if you aren't looking directly at the #'s .... with that said I think the rule of thumb that Chem_Mod made, is great.

Ben Rolnik 1D

After learning a bit about quantum physics, I'm wondering if someone can define the problem with creating a unified field theory to bridge the gap between quantum physics and classical physics. Does this have to do with the "continuous" vs. "quantum particle" dimensions of light ...

Ben Rolnik 1D

I'm really curious about the history of the Einstein equation... what's the difference between E = HV and the famous equation E = mc*2?

Ben Rolnik 1D

Wanted to start a thread sharing thoughts / feedback after Test 1. For me... my biggest "not to self" is to PACE MYSELF WAY BETTER NEXT TIME! The time seemed to shoot by in an instant. I could have easily used 30 more minutes so the biggest piece of feedback for myself I have is to move MU...

Ben Rolnik 1D

Hey guys! Here are my answers for Self Test 1 -- What do you get? 1a. 24.0 g NaOH 1b. 81.3 mL 2a. 2AL + 6HCL --> 2AlCl3 + 3H2 2b. 9.51g AlCl3 3a. Dx >= 3.2 E -32 3b. 1.3 E -31 m 4. 3.61 E -19 J 5. CH4O 6. 2.98 J 7. 2CH3OH + 3O2 --> 2CO2 + 4H20 8. 1.86 E -6 m 9. C5H12O5 10. (drew a sine wave graph) A...

Ben Rolnik 1D

Okay... I think C1H4 has to be the answer because I actually solved this a completely different way. Still, it would be great to get a TA to explain this more succinctly. Here's how to solve the problem using the 6.4 g CxHx information... 1. 6.4g X + O2 --> 8.8g CO2 + 7.2g H2O 2. factor out the weig...

Ben Rolnik 1D

You can also think about it in terms of the way the shape of the wave changes as frequency decreases. If frequency goes, down, this means wavelength goes up, and the wave of light flattens. The wave of light actually describes the oscillation of the electric and magnetic fields as light travels thr...

Ben Rolnik 1D

Yeah... this is pretty tricky... I got C1H4. I'm not sure if my method was correct but here's how I thought about it. Would be great if one of the TA's checked this.... 1. 6.4g X + O2 --> 8.8g CO2 + 7.2g H2O 2. With this in mind, I'm assuming we're trying to finding the empirical for a CxHx compound...

Ben Rolnik 1D

This is due to the photoelectric effect. The idea is that the energy per photon is a function of h*v (frequency). So if frequency goes DOWN, wavelength goes UP -- and hence the electric field has less potential energy to influence electrons. Think about it like this: as wavelength decreases (e.g. th...

Ben Rolnik 1D

Dr. Lavelle mentioned that it will be information covered up to Wednesday's class (so it kind of depends on how much we cover until then)... This includes the fundamentals sections and all of chapter 1 (possible chapter 2). I'm sure he will also go over more detail on Monday! I would start studying ...

Ben Rolnik 1D

Thank you for the response!!

And I'm digging the sci-fi connection :)

Ben Rolnik 1D

Kyle!!

What an awesome response -- thank you so much for this!!! I totally understand it now. Thank you :)

Ben Rolnik 1D

Two men walk into a bar. The first says I'll get some H2O. The second man says, I'll get Some H2O too..... drinks it and dies!

H2O2 = Hydrogen peroxide

Ben Rolnik 1D

Can someone explain where Planck's constant comes from? I understand how to use it... but what exactly does it mean? I read in the book that the smallest quantity we study in chemistry is 10^-34 (where "space breaks down")... and since ( h = 6.698 x 10^-34 ) I'm very curious what this actu...

Ben Rolnik 1D

Can you go straight from cm to mm using (10^-3 / 10^-2)... without having to convert to 1meter first?... and if so, does this change at all if you're dealing with units like cm^3?

Are there any shortcuts for these sorts of conversions?

Thanks!

Ben Rolnik 1D

Problem G.25 says we start with .10M of Substance X.... so .10 = (n / v). I got that part! The next part of the problem seems to be saying something like: " .10M * (10 mL) = [2^90 * ( 10 mL) ] * [final molarity Molarity] At this point I get kind of lost... especially because the answer in the s...

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