CHEMISTRY COMMUNITY

Jade Hinds 2B

what a wild way to end winter quarter! thank you all for working so diligently in order to support our continued academic success. Stay safe everyone.

Jade Hinds 2B

these are all great suggestions. but now i'm feeling very nervous about the undecided plans for our final exam now that classes are cancelled. Who thinks it will still go as scheduled for Sunday?

Jade Hinds 2B

due to classes now being cancelled, will step-up/review sessions presume as scheduled or are those all cancelled as well?

Jade Hinds 2B

thank you everyone!

Jade Hinds 2B

Can someone tell me an idea of what all will be on test 2??

Jade Hinds 2B

consider the cell Ag I Ag+ (aq. 5.0 mmol.L^-1)II Ag+ (aq 0.15 mol.L^-1)I Ag. can this cell do work? if so, what is the maximum work that it can perform (per mole of Ag)?

Jade Hinds 2B

predict the standard potential of each of the following galvanic cells:
(a) Pt I Cr^3+, Cr^2+ II Cu^2+ I Cu

(b) Ag I AgI I I^- II Cl^- I AgCl I Ag

(c) Hg I Hg2Cl2 I Cl- II Hg2 ^2+ I Hg

(d) C I Sn^4+, Sn^2+ II Pb^4+, Pb^2+ I Pt

Jade Hinds 2B

(a) write balanced half-reactions for the redox reactions of an acidified solution of potassium permanganate and iron (II) chloride. (b) write the balanced equation for the cell reaction and devise a galvanic cell to study the reaction.

Jade Hinds 2B

calculate the standard reaction gibbs free energy for the following cells:
(a) 2 Ce^4+ (aq) + 3I^- (aq) > 2 Ce^3+ (aq) + I3^- (aq), Ecell = +1.08V
(b) 6 Fe^3+ (aq) + 2 Cr^3+ (aq) + 7 H20 (l) > 6 Fe^2+ (aq) + Cr2o7^2- (aq) + 14 H+ (aq), Ecell = -1.29V

Jade Hinds 2B

What is the initial reaction quotient when 3.2g of NH4HS is placed in a 2.0L vessel along
with 1.47 mol of NH3 and 2.85 mol H2S?

Jade Hinds 2B

very random, but can someone please tell me where broad is??? I have never been there before!

Jade Hinds 2B

will all the sections of thermodynamics be on the midterm exam? Just need some clarification.

Jade Hinds 2B

Air in a bicycle pump is compressed by pushing in the handle. The inner diameter of the pump is 3.0 cm and the pump is depressed 20 cm with a pressure of 2.00 atm. (a) how much work is done in the compression? (b) is the work positive or negative with respect to the air in the pump? (c) what is the ...

Jade Hinds 2B

I would say it won't hurt to just get the extra practice, especially since everything will be a fair shot on the midterm/final

Jade Hinds 2B

The pH of several solutions was measured in research laboratories of a food company; convert each of the following pH values into the molar concentration of H3O+ ions: (a) 3.3 (the pH of sour orange juice); (b) 6.7 (the pH of the saliva sample); (c) 4.4 (the pH of beer); (d) 5.3 (the pH of a coffee ...

Jade Hinds 2B

just realized this as I was going through the class website! thanks!

Jade Hinds 2B

would anyone be willing to give me a brief rundown of what lavelle covered in lecture on friday? I was out of town traveling for a competition and was not able to attend.

Jade Hinds 2B

does anyone know what problem set we are supposed to choose homework problems from for week three?? is it outline 2 or are we still focusing on chemical equilibrium?

Jade Hinds 2B

Not sure if this was covered in section, but are there specific equations/formulas we should for sure now for test 1??

(e.g. pH + pOH = kw)

Jade Hinds 2B

Honestly ice tables are just a quick to check your work, but from what I understand it is required that you use one to solve such questions on tests/exams

Jade Hinds 2B

whoever finds out this information first, please feel free to post it here!

Jade Hinds 2B

A drink contains 1.2 * 10^-10M of hydroxide ions, what is the pH of this drink?

Jade Hinds 2B

what do you all think are the MOST important constants/equations we should memorize for the exam? (e.g. DeBroglie)

Jade Hinds 2B

A cup of water is sitting at 25 degrees C. What is the molar concentration of hydronium ions in the cup? How about hydroxide ions?

Jade Hinds 2B

If 100KJ of energy was absorbed by the gas sample, how many photons in total caused electronic excitations? How many moles of hydrogen were excited assuming one photon interacted with one unique hydrogen atom?? Even though I already looked over the solutions to the exam, I'm still quite confused abo...

Jade Hinds 2B

Correct, the shape for SO2 is bent

Remember that the VSEPR formula is: AXnEm
A= central atom
X= attached atom
E= lone pair

Jade Hinds 2B

always remember the first bond must be a sigma bond which makes the rest pi bonds

Jade Hinds 2B

so does this mean that when you are naming metals, you just add -ate to the end? when is it -ite or -ide?

Jade Hinds 2B

Do some yoga/meditation, take study breaks as needed (maybe try and get off campus for a little if you can)
The best thing to do before an exam is not cloud your mind. We retain information best when we study refreshed and with a good mindset.

Jade Hinds 2B

In a way, some of the concepts can be considered stoichiometry because we do deal with the products and reactants of chemical reactions... but in a broader sense no, not really it is much more!!

Jade Hinds 2B

Can someone please explain how they solved this question? because i got it wrong on the midterm :/

Jade Hinds 2B

if you look at questions 27-32 on the final exam review it asks you to either name the compound or give the molecular formula. so id assume that for the exam Lavelle wants us to know both

Jade Hinds 2B

pretty sure to get the answer completely correct you have to write it out fully (so your 2nd answer would be right)

Jade Hinds 2B

actual study tip:
-do both the final review and the mini one that was posted!! rumor has it that Lavelle sometimes pulls questions from them and uses them as test questions

Jade Hinds 2B

unless you are good at math in your head, I suggest you bring one with you the final (non graphing only of course)

Jade Hinds 2B

What's the step to step process on how to solve this problem? because I am lost

I get that that you have to first convert from grams to moles... but what do you do next?

Jade Hinds 2B

if the charge distribution of the shape is symmetrical it is nonpolar
if the charge distribution of the shape is asymmetrical it is polar

Jade Hinds 2B

YES. Pretty the same concepts we will be learning, just expanding upon. Hold on to those textbooks people! :)

Jade Hinds 2B

note: as for the midterm and final exam we are only given a periodic table, NOT the list of equations/constants. we just have to know them.

Jade Hinds 2B

Honestly doing both practicing problems and studying old test questions would be best. Who knows, past questions could be reused on the final :/

Jade Hinds 2B

I'm gonna assume you mean "conjugated"???

Jade Hinds 2B

Are we supposed to convert to nm when solving problems using the DeBroglie equation??? or can we just leave our answers in meters?

Jade Hinds 2B

by definition: "a more stable conjugate base means a stronger acid"

Also, the size and difference in electronegativity of HCl makes it a stronger acid

Jade Hinds 2B

I would suggest you just go ahead and memorize them. That may make things much easier if you already know them! What about coming up with a fun mnemonic to help memorize them?

Jade Hinds 2B

amphoteric= means that the compound reacts as both as a base and as an acid
some examples-
1. lead oxide
2. zinc oxide

Jade Hinds 2B

Heres a fun way to memorize the three (OH)2 strong bases:

"drink your milk (Ca (OH)2) so you can be a strong (Sr (OH)2) baller (Ba (OH)2)"!!!

Jade Hinds 2B

when naming a compound, the roman numeral serves to represent the charge and oxidation state of the metal ion!

Jade Hinds 2B

if anyone has some tips/tricks on how to easily identify strong/weak acids and bases, please share!!!

Jade Hinds 2B

in a tetrahedral the central atom is surrounded by 4 substituent atoms vs in a square planar the central atom is surrounded by any amount of substituent atoms

Jade Hinds 2B

Well since most discussion sections are cancelled this week due the thanksgiving break, we will more than likely get test 2 back either in class monday or wednesday (11/25 or 27) or not until week 10 in section. But i'm not sure if the TA's will just post grades in Myucla before handing them back......

Jade Hinds 2B

ligands have at least one donor atom with an electron pair used to form covalent bonds with the central atom
3 types:
1. monondentate (e.g. chloride ion)
2. bidentate (e.g. oxalate ion)
3. polydentate (e.g. EDTA)

Jade Hinds 2B

Talk to your TA for sure, either in section or go to their office hours. Also go over the solutions to the exam on the class website so you can see the point distribution for each question. I did that and actually ended getting 7 points added to my total grade!

Jade Hinds 2B

Suggestions to study:
-VSEPR models
-dipoles
-molecular shape names... MEMORIZE (e.g. trigonal planar)

we honestly have not learned much since after the midterm

Jade Hinds 2B

We can all agree that based upon what we've recently learned in lecture, VSEPR and molecular shape naming is basically all that will be on test 2!

Jade Hinds 2B

anyone have an example of this? I'm still practicing drawing the structures

Jade Hinds 2B

Amphiprotic= a substance that can both accept and donate a proton (has characteristics of both an acid and a base)

amphiprotic vs. amphoteric:
-a substance is amphoteric when its reaction acts as an acid and as a base
-amphiprotic only applies to protic compounds

Jade Hinds 2B

I tell bad chemistry jokes, because all the good ones "Argon"...

Jade Hinds 2B

VSEPR= valence shell electron pair repulsion theory

*p.s. not quite sure on how to determine formula yet

Jade Hinds 2B

adding to that, resonance means that some lewis structures have multiple bonds in different equivalent locations

(e.g. from lecture NO3^-)

Jade Hinds 2B

going to be honest, I only use the textbook to get homework/practice problems. to me, too much reading makes it confusing, so I mainly utilize my lecture notes and do lots of practice.

Jade Hinds 2B

does anyone have any tips for making sure that you have enough valence electrons drawn when accounting for double bonds?

Jade Hinds 2B

by definition: a delocalized electron is an electron that is not associated with a single atom/covalent bond

however, I'm also not quite sure why the lewis structure doesn't capture this effect???

Jade Hinds 2B

QA: Why can't you trust an atom?
A: They make up everything!

Jade Hinds 2B

Are you made of copper and tellurium?
because you're Cu Te

lol

Jade Hinds 2B

Good question!!! Chemistry is strange... this calls for an answer from Dr. Lavelle

Jade Hinds 2B

what equation?

Jade Hinds 2B

step 1= convert nm to m 1nm= 10^9m so... 194nm = 1.94 x 10^-7m step 2= use speed of light formula: c=(wavelength)(frequency) 3.10 x 10^8= (1.94 x 10^-7m)(frequency) frequency= 1.546 x 10^15 Now you can plug the frequency into the formula for kinetic energy: E=hv E= (6.626 x 10^-34)(1.546 x 10^15)= 1...

Jade Hinds 2B

honestly, just know the rules on how to find them!

Jade Hinds 2B

All I would say, is that for test 1 don't worry about having constants or unit conversions memorized (as they will be given), but for future reference (e.g. the midterm and final) to know and understand them.

Jade Hinds 2B

PSA: don't forget a calculator for the test!!

Jade Hinds 2B

Khan Academy definitely has some helpful videos that can help with practicing sig figs!

Jade Hinds 2B

Random question, but does anyone have any advice/suggestions on things to post on here in for future weeks???
(Besides just posting homework questions)

Jade Hinds 2B

I know for a fact that all constants and equations are given. But as for the molecular vs empirical formula section, just in case I would practice finding them when it is not given!

Jade Hinds 2B

Yes, to find the net ionic equation, start by balancing the equation first... -i don't believe we've gone over this in lecture yet, but the second step is to break all of the strong electrolytes into the ions they form -last step= any that are aqueous on both sides of the chemical equation get cance...

Jade Hinds 2B

I agree with what most people have posted... i think its best that you try and practice problems for a variety of sections just as preparation for exams. In Dr. Lavelle's syllabus he even notes that 1 out of 8 homework questions are used in exams, so there's a possibility that you know some answers ...

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