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MARSHMALLOW- FINAL REVIEW SESSION

Posted: Mon Dec 02, 2019 12:38 pm
by Chem_Mod
The title is called "Marshmallow" so that you can search "Marshmallow" and easily find this post!

This is your favorite UA, Lyndon Bui, and I have created many practice problems for your final. The questions are modeled after previous test and exam questions, but it does not have everything you need to know. This covers only material after the midterm. We already covered pre-midterm material in a midterm review session.


Please complete these problems before my review session. My review session this quarter (FALL19) will be Friday, Dec 6, 7:30-10:30pm, in Haines 39.
I will go over each concept and problem in detail during the review session. The answers, but not full solutions or work, will be posted here at this post after the review session. Any errors in the test will be posted below as well.

Please complete the problems or attempt them before coming to the review session. This review session will feature Hannah Chew, Matt Tran, and Kate Santoso as well!

Link to Download Problems:
Marshmallow_FinalReviewFall19.pdf
(191.21 KiB) Downloaded 1524 times

***This is not indicative of the structure, length, or format of the actual final. Treat these as extra practice problems. ***

Extra practice:
Mini Marshmallows XD.pdf
(35.49 KiB) Downloaded 937 times


Errors: 1. Mini Marshmallows Q2A should be [Ni(NH3)3O]Br2, not [Ni(NH3)2O2]Br2
2. Mini Marshmallows Q2B should be dihydroxooxalatocobaltate (III) ion, not Dihydroxyoxalatocobalt (III) ion

Link for Answers:
Marshmallow_Answers.pdf
(559.39 KiB) Downloaded 579 times
Mini Marshmallows Answers.pdf
(40.41 KiB) Downloaded 725 times


Happy Studying and Good Luck!
-Lyndon Bui, UA

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Mon Dec 02, 2019 3:54 pm
by Jingyao Chen 4H
For number 41(c), it asks which pair of atoms on thymine are most tightly bounded and why, between C=C, C=O, and C=N. However, O don’t see a C=N bond in the structure. Is there a mistake?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Tue Dec 03, 2019 2:12 pm
by KBELTRAMI_1E
For number 4 how does the hybridization become sp2 if there are 4 p electrons and 2 s electrons?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Wed Dec 04, 2019 12:43 pm
by Tiffany_Chen 2K
For #31 should the name be ...nickel(III) ion? The complex has a 2+ charge.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Wed Dec 04, 2019 3:54 pm
by Julia Mazzucato 4D
KBELTRAMI_4I wrote:For number 4 how does the hybridization become sp2 if there are 4 p electrons and 2 s electrons?


Because you need three hybrid orbitals for this compound with three areas of electron density, there are 6 electrons to place in total.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 1:55 pm
by Jingyao Chen 4H
For #17, what does it mean by the “hybridization of each lone pair”? Is it supposed to be the hybridization of each central atom?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 2:11 pm
by Jingyao Chen 4H
For 21, how do we know oxidation number of Fe?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 3:15 pm
by serenabirkhoff_1K
KBELTRAMI_4I wrote:For number 4 how does the hybridization become sp2 if there are 4 p electrons and 2 s electrons?


If you draw the lewis structures you will see there are 3 regions of electron density around S, one lone pair and 2 bonds with 0. (remember a double bond still counts as one region of electron density). There are 3 regions and therefore it is sp2.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 3:40 pm
by Marty Hockey
For number 20 how do we know whether the expected geometry of the compound is square planar or tetrahedral?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 4:36 pm
by Rishika Yadav 3D
Marty Hockey wrote:For number 20 how do we know whether the expected geometry of the compound is square planar or tetrahedral?

I think that because there are no lone pairs on the Fe, it will be tetrahedral

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 8:30 pm
by Jessica Tejero 3L
For number 21 what is the oxidation state of iron?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 9:05 pm
by Alex Chen 2L
Rishika Yadav 3D wrote:I think that because there are no lone pairs on the Fe, it will be tetrahedral


It's different for coordination compounds. Since the porphyrin ligand binds to Fe four times at the corners of a square, the shape is actually square planar.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 10:35 pm
by kevinchang_4I
Will the answers to the Minimarshmallows be posted? Thanks!

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 10:37 pm
by Hannah Romano 4D
for 2b of mini marshmallows is the name spelt correctly? shouldnt it be Dihydroxo and not Dihydroxy ? maybe im just confused lol.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Fri Dec 06, 2019 10:38 pm
by kevinchang_4I
Jessica Tejero 3L wrote:For number 21 what is the oxidation state of iron?


The oxidation state of iron will be 2+ because two of the nitrogens have lone pairs making their formal charges -1 each.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:34 am
by Paige Lee 1A
For #1c on mini marshmallow, how do you know to choose NH4+ and not NO3- for the net ionic equation? Since they're both weak acids and bases

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:39 am
by JOtomo1F
Jingyao Chen 4H wrote:For number 41(c), it asks which pair of atoms on thymine are most tightly bounded and why, between C=C, C=O, and C=N. However, O don’t see a C=N bond in the structure. Is there a mistake?


I believe you're correct in saying that there is no double bond between carbon and nitrogen. You can still understand the point of this question though, in that the C and O are most tightly bound since oxygen is the smallest atom out of carbon, nitrogen, and oxygen.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:41 am
by JOtomo1F
Tiffany Chen 1K wrote:For #31 should the name be ...nickel(III) ion? The complex has a 2+ charge.


Yes, tonight Lyndon mentioned this was an error in the final review packet.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:42 am
by JOtomo1F
kevinchang_4I wrote:Will the answers to the Minimarshmallows be posted? Thanks!


I was also wondering how soon the answers would be posted.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 1:13 am
by Nikki Razal 1L
for question 40c, how do you know whether o2 or o3 has the stronger bond and why?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 1:33 am
by Matthew Chan 1B
For the Mini marshmallow worksheet, for problem 2, we are asked to write the name/formula for the coordination compound, etc.

in problem 2a, the coordination compound is [Ni(NH3)2O2]Br2. However, in the answer key, the compound is something completely different. I just wanted to check to see that given this coordination compound, the name would be: diamminedioxonickel(II) bromide. Thanks!

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:58 am
by Rebecca Remple 1C
Hi there! Thank you so much for sharing these practice problems. I was wondering if the answer key to the regular worksheet will be posted soon? I was not able to make the session but have been working on the problems, so I would love to be able to refer to it. Thank you!

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 11:15 am
by Ashley Osorio
How would one phrase number 36C?? Also, 36B is both Amphoteric and amphiprotic, right?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 11:38 am
by Haley Dveirin 1E
When will the marshmallow answer key be posted?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 11:59 am
by zfinn
Ashley Osorio wrote:How would one phrase number 36C?? Also, 36B is both Amphoteric and amphiprotic, right?


" the atoms that give glycine these properties are the N, with a lone pair that can accept a proton, and the -COOH, which can donate a proton." and for 36b it is both!

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:00 pm
by Aprice_1J
For mini marshmallows 2c, why is it cupperate instead of copper? Isn't it a +1 oxidation state?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:50 pm
by Joanne Kang 3I
min marshmallows 1c... why isn't it neutral?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:51 pm
by Jared Khoo 1G
Aprice_1J wrote:For mini marshmallows 2c, why is it cupperate instead of copper? Isn't it a +1 oxidation state?


The coordination complex has a 1- charge, so it is cuprate. This is shown because it forms an ionic bond with potassium which has a +1 charge, so you know the coordination complex must have a -1 charge. The transition metal will always have a positive oxidation state so don't look at that.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:52 pm
by Lauren Haight 1E
for mini marshmallow 2b, why is the coordination number for Dihydroxoyoxolatocobalt (III) 4? Is it because oxalato is bidentate and can attach to cobalt at two places?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:52 pm
by Joanne Kang 3I
Ashley Osorio wrote:How would one phrase number 36C?? Also, 36B is both Amphoteric and amphiprotic, right?

Yes.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:52 pm
by Jared Khoo 1G
Joanne Kang 3I wrote:min marshmallows 1c... why isn't it neutral?


ammonium is a conjugate acid of a weak base, so it will lower pH by giving a proton (H+) to water to form hydronium.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:53 pm
by Jared Khoo 1G
Lauren Haight 1E wrote:for mini marshmallow 2b, why is the coordination number for Dihydroxoyoxolatocobalt (III) 4?


Oxalate is BIdentate, so it will form 2 coordinate covalent bonds. Add this to the two bonds made to hydroxide and the coordination number is 4.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 12:55 pm
by Joanne Kang 3I
For mini marshmallows 2b, why is the coordination number 4?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 1:05 pm
by Joanne Kang 3I
Paige Lee 1D wrote:For #1c on mini marshmallow, how do you know to choose NH4+ and not NO3- for the net ionic equation? Since they're both weak acids and bases


NO3- is the conjugate base of a STRONG acid, so NO3- is very stable/does not affect the pH.
The only thing affecting pH then would be NH4+ producing H3O+

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 1:21 pm
by Deana Moghaddas 3E
when will original marshmallow practice's answers be posted

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 1:45 pm
by MeeraBhagat
Tiffany Chen 1K wrote:For #31 should the name be ...nickel(III) ion? The complex has a 2+ charge.


Yes I think it should be "ion" since its a positively charged molecule

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 1:49 pm
by kim 2I
Joanne Kang 3I wrote:For mini marshmallows 2b, why is the coordination number 4?


Oxalate is a bidentate so it would bind to the central TM in two places making the coordination 4 (2 binding spots for oxalate and 2 from the hydroxide ions).

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 1:54 pm
by MeeraBhagat
Lauren Haight 1E wrote:for mini marshmallow 2b, why is the coordination number for Dihydroxoyoxolatocobalt (III) 4? Is it because oxalato is bidentate and can attach to cobalt at two places?


Yes, it is because oxalato is bidentate.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 2:08 pm
by MeeraBhagat
Nikki Razal 4E wrote:for question 40c, how do you know whether o2 or o3 has the stronger bond and why?


o3 has resonance, which is stabilizing because the electrons are delocalized and makes the bonds stronger.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 2:08 pm
by Ruby Richter 2L
For number 21) you need to essentially "give back" an electron pair to the ligands bonded to the central atom to find their formal charge. Does this apply to all ligands and coordination compounds? Like B12 for example?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 2:18 pm
by TimVintsDis4L
Does anyone know where the answers to the practice are since its well over the time they were supposed to be posted?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 2:28 pm
by Celena Kim 2I
When will the answers for the final review packet be posted?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 2:31 pm
by Aadil Rehan 1D
Ruby Richter 4G wrote:For number 21) you need to essentially "give back" an electron pair to the ligands bonded to the central atom to find their formal charge. Does this apply to all ligands and coordination compounds? Like B12 for example?


I would assume so, but for the dashed-line bonds. For B12, a few websites have mentioned that the most common state is cobalt (III), and if you observe the structure of B12 and "take back" those dashed-line bonds, you're left with an oxidation state of 3+. For chlorophyll, the central magnesium atom usually prefers magnesium (II), and if you "take back" its two dashed-line bonds you have an oxidation state of 2+.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 2:47 pm
by mayarivers3I
Jingyao Chen 4H wrote:For #17, what does it mean by the “hybridization of each lone pair”? Is it supposed to be the hybridization of each central atom?

Can someone answer this please! I am wondering the same thing.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:01 pm
by Hannah Romano 4D
when are the answers for marshmallows being posted???

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:07 pm
by Annie Chantasirivisal_4G
mayarivers3I wrote:
Jingyao Chen 4H wrote:For #17, what does it mean by the “hybridization of each lone pair”? Is it supposed to be the hybridization of each central atom?

Can someone answer this please! I am wondering the same thing.


Hybridization of lone pairs can be determined by looking at the atom that the lone pairs are attached to. Thus, for example, the lone pairs of oxygen at the top where there's one double bond and two lone pairs would have a total of 3 regions of electron density, and its hybridization would be written as O(sp^2), while the oxygen at the bottom right attached to C-O-CH3 would have two single bonds and 2 lone pairs for a total of 4 regions of electron density, and its hybridization would thus be written as O(sp^3).

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:17 pm
by Kaitlynn Tran 3F
Nikki Razal 4E wrote:for question 40c, how do you know whether o2 or o3 has the stronger bond and why?


O3 is polar because the dipoles do not cancel out, so there are dipole-dipole intermolecular forces. The resonance due to the double bond also would cause it to have a stronger bond than O2.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:24 pm
by Jedrick Zablan 3L
Lyndon, I want to see the video you were trying to show during the review. Pls post it king.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:28 pm
by ZevMarx-Kahn3C
Hannah Romano 4D wrote:when are the answers for marshmallows being posted???


I'd also love to know!

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:43 pm
by Ashley R 1A
For number 21, how would you find the oxidation state for the central Fe atom, when it should typically only be around +1 to +3, when there are so many negatively charged anions around it?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:44 pm
by Grecia Velasco 4D
ZevMarx-Kahn3C wrote:
Hannah Romano 4D wrote:when are the answers for marshmallows being posted???


I'd also love to know!


Fellas, i gotta feeling it's either gonna be really late at night or tomorrow morning. Fluoride ion (F-) in the chemistry community thread.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:45 pm
by Julieta Serobyan4D
Lauren Haight 1E wrote:for mini marshmallow 2b, why is the coordination number for Dihydroxoyoxolatocobalt (III) 4? Is it because oxalato is bidentate and can attach to cobalt at two places?

Yes for bidentate ligands there are considered two separate binding sites.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:45 pm
by Junxi Feng 3B
Where is the answer for the Marshmallow Practice???

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 3:51 pm
by Annie Chantasirivisal_4G
Hey guys, he just posted marshmallow answers rn. posting in case anyone has it bookmarked/subscribed.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 4:16 pm
by Rishika Yadav 3D
For number 21, why is Fe 2+? I remember him saying in the review that it was because of the nitrogen bonds, but I don't remember why.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 4:18 pm
by Jacey Yang 1F
Nikki Razal 4E wrote:for question 40c, how do you know whether o2 or o3 has the stronger bond and why?


o2 has double bonds that are shorter and therefore stronger than the o3 bonds, which is between a single and double bond due to resonance.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 4:19 pm
by ZevMarx-Kahn3C
Annie Chantasirivisal_4I wrote:Hey guys, he just posted marshmallow answers rn. posting in case anyone has it bookmarked/subscribed.


Thank you!

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 4:24 pm
by Jacey Yang 1F
For mini marshmallow 2c, why is the coordination number for K[Cu(en)2(CN)2] 6?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 4:25 pm
by Adam Kramer 1A
kevinchang_4I wrote:
Jessica Tejero 3L wrote:For number 21 what is the oxidation state of iron?


The oxidation state of iron will be 2+ because two of the nitrogens have lone pairs making their formal charges -1 each.


Which two nitrogens have this formal charge? I am having trouble seeing this.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:01 pm
by Kayla Maldonado 1C
Joanne Kang 3I wrote:min marshmallows 1c... why isn't it neutral?

NH4+ donates a proton and H20 accepts a proton, therefore NH4+is acidic.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:04 pm
by TimVintsDis4L
Can someone please explain how to do #34. I know that you find the moles then use the excess moles and find the pH using that, but my math doesn't add up.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:06 pm
by Hannah Romano 4D
for question 41d) Doesn't thymine have 10 atoms that could form hydrogen bonds? all 6 hydrogens, both nitrogens, and both oxygens. Technically if the question was asking for how many HYDROGEN BONDS can form not just how many ATOMS, wouldn't it be 12 h-bonds because each oxygen can for 2 h-bonds?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:13 pm
by Hannah Romano 4D
TimVintsDis3C wrote:Can someone please explain how to do #34. I know that you find the moles then use the excess moles and find the pH using that, but my math doesn't add up.


When HCl and CaO are accidentally mixed in the flask, they will react to form salt and water making the following equation: 2HCl + CaO ---> CaCl2 + H2O. Knowing this, find the limiting reactant that was poured into the the flask. (Its CaO) so that means that HCl will be in excess in the solution. Use the previous equation to find how much HCl was consumed (remember that the stoichiometric ratio of CaO to 2HCl) then subtract the consumed HCl from the total HCl. Then you will have the concentration of the excess HCl which is then full dissociated in the solution because HCl is a strong acid so you can just take the negative log of this excess concentration and you will get pH=2.28.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:21 pm
by TimVintsDis4L
Hannah Romano 4D wrote:
TimVintsDis3C wrote:Can someone please explain how to do #34. I know that you find the moles then use the excess moles and find the pH using that, but my math doesn't add up.


When HCl and CaO are accidentally mixed in the flask, they will react to form salt and water making the following equation: 2HCl + CaO ---> CaCl2 + H2O. Knowing this, find the limiting reactant that was poured into the the flask. (Its CaO) so that means that HCl will be in excess in the solution. Use the previous equation to find how much HCl was consumed (remember that the stoichiometric ratio of CaO to 2HCl) then subtract the consumed HCl from the total HCl. Then you will have the concentration of the excess HCl which is then full dissociated in the solution because HCl is a strong acid so you can just take the negative log of this excess concentration and you will get pH=2.28.


I end up with .005248 mol of HCL and .002648 mol of CaO, which equates to an excess of .0026. Once I plug that in I get 2.7. So which of these numbers is wrong?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:32 pm
by Hannah Romano 4D
TimVintsDis3C wrote:
Hannah Romano 4D wrote:
TimVintsDis3C wrote:Can someone please explain how to do #34. I know that you find the moles then use the excess moles and find the pH using that, but my math doesn't add up.


When HCl and CaO are accidentally mixed in the flask, they will react to form salt and water making the following equation: 2HCl + CaO ---> CaCl2 + H2O. Knowing this, find the limiting reactant that was poured into the the flask. (Its CaO) so that means that HCl will be in excess in the solution. Use the previous equation to find how much HCl was consumed (remember that the stoichiometric ratio of CaO to 2HCl) then subtract the consumed HCl from the total HCl. Then you will have the concentration of the excess HCl which is then full dissociated in the solution because HCl is a strong acid so you can just take the negative log of this excess concentration and you will get pH=2.28.


I end up with .005248 mol of HCL and .002648 mol of CaO, which equates to an excess of .0026. Once I plug that in I get 2.7. So which of these numbers is wrong?


Okay so what you've found is when the 0.0026 mol of CaO are completely consumed along with 0.0052 mol of HCl. Because you originally had 0.0104 mol of HCl poured into the flask: 0.0104total-0.0052consumed=0.0052excess HCl. Then -log(0.0052)= 2.28. Hope this helped.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:37 pm
by TimVintsDis4L
Hannah Romano 4D wrote:
TimVintsDis3C wrote:
Hannah Romano 4D wrote:
When HCl and CaO are accidentally mixed in the flask, they will react to form salt and water making the following equation: 2HCl + CaO ---> CaCl2 + H2O. Knowing this, find the limiting reactant that was poured into the the flask. (Its CaO) so that means that HCl will be in excess in the solution. Use the previous equation to find how much HCl was consumed (remember that the stoichiometric ratio of CaO to 2HCl) then subtract the consumed HCl from the total HCl. Then you will have the concentration of the excess HCl which is then full dissociated in the solution because HCl is a strong acid so you can just take the negative log of this excess concentration and you will get pH=2.28.


I end up with .005248 mol of HCL and .002648 mol of CaO, which equates to an excess of .0026. Once I plug that in I get 2.7. So which of these numbers is wrong?


Okay so what you've found is when the 0.0026 mol of CaO are completely consumed along with 0.0052 mol of HCl. Because you originally had 0.0104 mol of HCl poured into the flask: 0.0104total-0.0052consumed=0.0052excess HCl. Then -log(0.0052)= 2.28. Hope this helped.


That makes so much more sense, thank you very much!

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:48 pm
by Ashley R 1A
for marshmallow 41d) which six atoms can form hydrogen bonds? for this problem, are we supposed to not include the hydrogens that could bind to the lone pairs on other molecules. Or are we supposed to count two lone pairs (like how there's two lone pairs on the double bonded oxygen) as two atoms?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:49 pm
by Annie Chantasirivisal_4G
Jacey Yang 3I wrote:For mini marshmallow 2c, why is the coordination number for K[Cu(en)2(CN)2] 6?


It is six because en is a bidentate, so it will bind at two areas; since there are two en, that would mean 4 binding sites, in addition to the 2 cyanides, for a total of 6 bonds bound to copper, thus coordination number 6.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 5:52 pm
by Diana Chavez-Carrillo 2L
Jacey Yang 3I wrote:
Nikki Razal 4E wrote:for question 40c, how do you know whether o2 or o3 has the stronger bond and why?


o2 has double bonds that are shorter and therefore stronger than the o3 bonds, which is between a single and double bond due to resonance.


So then is the stronger bond O2 because in a way O3 has like an average bond strength between a single and double bond since it has resonance? So the double bond in O2 is stronger than that average? I'm just confused because some people were saying it was O3 that was stronger because it was more stable with its resonance.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 6:03 pm
by Diana Chavez-Carrillo 2L
In the marshmallow packet, for question 28, for example, would it be acceptable to write (en) instead of the full name: ethylenediammine or do we need to write out the full name to get credit?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 6:03 pm
by Ariana Iranmahboub1G
For number 22 why can myoglobin bind to two O2 molecules?
In my notes from the lecture, Fe binds to only 1 02 since the heme complex and a protein results in Myoglobin, so how would myoglobin bind to two O2?

Re: MARSHMALLOW- FINAL REVIEW SESSION  [ENDORSED]

Posted: Sat Dec 07, 2019 6:19 pm
by Rebecca Remple 1C
Hi all,

I was going through the final review packet and have been having trouble understanding part of problem 17. In the problem, it asks us to draw C5H5NO2 and label all of the sigma and pi bonds. I understand most of the question, but one of the pi bonds is troubling me. Near the top of the molecule, a carbon is bonded to an oxygen which has two lone pairs. The sigma bond notation makes sense, but the pi bond says it is (O2p, C2sp2). In all other pi bond examples, both molecules' hybridization is just "p", such as (C2p, N2p). What makes this oxygen and carbon different? Why does this carbon break the trends? I would appreciate your feedback. Thank you for reading this and good luck on the final!

-Rebecca

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 6:59 pm
by Johnathan Smith 1D
Can someone explain how to get the pH for 34. I got the moles of each compound but can’t seem to get the overall pH.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 7:15 pm
by Rebecca Remple 1C
Johnathan Smith 1D wrote:Can someone explain how to get the pH for 34. I got the moles of each compound but can’t seem to get the overall pH.

Hi Jonathan,

Using the moles for CaO and HCl, you can determine how many moles of OH- and H+ are produced. You need to write out the equations in water to do so. Note that 2 moles of OH- are produced per molecule of CaO. Using these measurements, you can determine the net change in protons. H+ and OH- cancel out, so you can subtract [H+] - [OH-]. This will give you a smaller value for [H+], which you can plug into the equation for ph (-log[H+]). This will give you your final answer. I hope this helps! Good luck tomorrow :)

-Rebecca

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 7:59 pm
by Chem_Mod
Rebecca Remple 1J wrote:Hi all,

I was going through the final review packet and have been having trouble understanding part of problem 17. In the problem, it asks us to draw C5H5NO2 and label all of the sigma and pi bonds. I understand most of the question, but one of the pi bonds is troubling me. Near the top of the molecule, a carbon is bonded to an oxygen which has two lone pairs. The sigma bond notation makes sense, but the pi bond says it is (O2p, C2sp2). In all other pi bond examples, both molecules' hybridization is just "p", such as (C2p, N2p). What makes this oxygen and carbon different? Why does this carbon break the trends? I would appreciate your feedback. Thank you for reading this and good luck on the final!

-Rebecca


You are correct Rebecca, it should say 2p insteaed of 2sp2

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 8:03 pm
by Chem_Mod
Jedrick Zablan 3L wrote:Lyndon, I want to see the video you were trying to show during the review. Pls post it king.


It was baby groot dancing! Opening scene of guardians of the galaxy. Love it. I actually played it at the end once most people had left, it was quite fun. Next time maybe!

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 8:04 pm
by Chem_Mod
Ariana Iranmahboub 3G wrote:For number 22 why can myoglobin bind to two O2 molecules?
In my notes from the lecture, Fe binds to only 1 02 since the heme complex and a protein results in Myoglobin, so how would myoglobin bind to two O2?

It only binds 1 O2 molecule!

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 8:11 pm
by Rebecca Remple 1C
Hey again,

In Mini Marshmallows 1C, why does the NO3- in NH4NO3 not participate in the reaction with water, but NH4+ does? I just want to make sure I understand this conceptually before the final. Thank you!

-Rebecca

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 8:15 pm
by Elizabeth Harty 1A
How do you do number 34?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 8:17 pm
by Andrea_Torres
In number 34 in the packet to get the molOH we multiplied the Mol of CaO times 2 mol OH why was it 2 mol of OH but H+ was only one?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 8:35 pm
by Rita Chen 1B
Wait how do you know whether a coordination compound is a chelate? For example, how do you know that [Ni(NH3)2O2]Br2 is not a chelate?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 8:49 pm
by Grecia Velasco 4D
Are we supposed to know how to hybridize lone pairs? Because during class, Lavelle said no but its in marshmallows so im not sure.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 8:51 pm
by Labiba Sardar 2A
For 20, why is the expected geometry tetrahedral and square planar?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:03 pm
by Chem_Mod
Rebecca Remple 1J wrote:In Mini Marshmallows 1C, why does the NO3- in NH4NO3 not participate in the reaction with water, but NH4+ does? I just want to make sure I understand this conceptually before the final. Thank you!


Answer: HNO3 is a strong acid. Since its conjugate base is NO3-, that tells us that NO3- does not accept protons and therefore does not react with protons and will not affect pH.

Labiba Sardar 1C wrote:For 20, why is the expected geometry tetrahedral and square planar?


Answer: For coordination compounds, if the coordination number is 4, it can be either tetrahedral or square planar and you are not expected to know which it will be.

Rita Chen 1C wrote:Wait how do you know whether a coordination compound is a chelate? For example, how do you know that [Ni(NH3)2O2]Br2 is not a chelate?


Answer: Compounds with polydentate ligands will be chelates.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:11 pm
by MMckinney_4H
For number 34, why are two moles of OH produced for every mole of CaO?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:19 pm
by Connor Ho 1B
MMckinney_4H wrote:For number 34, why are two moles of OH produced for every mole of CaO?


CaO completely disassociates in water so:

CaO = Ca+ + O2-

If this were to further react in water, Ca+ would stay disassociated, however

O2- + H2O = 2OH-

after the equation is balanced.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:22 pm
by Annie Chantasirivisal_4G
MMckinney_4H wrote:For number 34, why are two moles of OH produced for every mole of CaO?


CaO separates into Ca^2+ and O^2-, and O^2- can be added with H2O to form 2OH-, thus 1 mole of CaO ends up producing 2 moles of OH-.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:23 pm
by AndreiRekesh1I
Paige Lee 1D wrote:For #1c on mini marshmallow, how do you know to choose NH4+ and not NO3- for the net ionic equation? Since they're both weak acids and bases


H + NO3 becomes HNO3, which is a strong acid and would be more inclined to dissociate completely rather than be put together (the equation would make more sense going the other way).

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:35 pm
by SarahSteffen_LEC4
On question number 21 of the Marshmallow review. Why does iron have a +2 charge if two of the nitrogens on the porphyrin ligand have a +1 charge?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:37 pm
by Connor Ho 1B
SarahSteffen_LEC4 wrote:On question number 21 of the Marshmallow review. Why does iron have a +2 charge if two of the nitrogens on the porphyrin ligand have a +1 charge?


The two nitrogens actually have a -1 charge, not +1.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:43 pm
by Naren_Ramesh_4F
On question 2b of the mini marshmallow, does the order of the ligand in the coordination complex matter?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:47 pm
by Grecia Velasco 4D
Naren_Ramesh_4D wrote:On question 2b of the mini marshmallow, does the order of the ligand in the coordination complex matter?


I don't think so BUT its good to go in order just in case :)

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 9:49 pm
by Kayla Maldonado 1C
#16 why is the trigonal planar shape considered nonpolar, how did we determine this ?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 10:05 pm
by CNourian2H
Naren_Ramesh_4D wrote:On question 2b of the mini marshmallow, does the order of the ligand in the coordination complex matter?


I dont think so

order of ligands matters in writing the name- alphabetical order
not in writing formula

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 10:27 pm
by Kayla Maldonado 1C
CHo_3I wrote:
SarahSteffen_LEC4 wrote:On question number 21 of the Marshmallow review. Why does iron have a +2 charge if two of the nitrogens on the porphyrin ligand have a +1 charge?


The two nitrogens actually have a -1 charge, not +1.


How is the charge for the nitrogens -1?

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 10:43 pm
by 205150314
For mini marshmallow 2c why does Potassium dicyanobis(ethylenediamine)cuprate (I) have a coordination number of 6? doesnnt it only have 4 atoms around it? or does the chelating ligand add more.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 10:46 pm
by 205150314
Kayla Maldonado 1A wrote:
CHo_3I wrote:
SarahSteffen_LEC4 wrote:On question number 21 of the Marshmallow review. Why does iron have a +2 charge if two of the nitrogens on the porphyrin ligand have a +1 charge?


The two nitrogens actually have a -1 charge, not +1.


How is the charge for the nitrogens -1?


I believe its -1 because of the 4 Bonds (2 single, 1 double) plus the lone pairs (2) make it be 5-6 for the formal charge .
I heard the dotted line counts

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 10:51 pm
by 205150314
could someone explain #34 on marshmallow to me? Is the solution basic or acidic and why? How do we know whether it'll be acidic or basic

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 11:34 pm
by MeeraBhagat
Kayla Maldonado 1A wrote:#16 why is the trigonal planar shape considered nonpolar, how did we determine this ?


The problem mentioned that the "X" in the AX3 were all the same atoms. Their dipole moments would therefore cancel and the molecule would be nonpolar.

Re: MARSHMALLOW- FINAL REVIEW SESSION

Posted: Sat Dec 07, 2019 11:36 pm
by Sofia Barker 2C
Joanne Kang 3I wrote:For mini marshmallows 2b, why is the coordination number 4?


The coordination number is 4 because C2O4 is bidentate, which means that it will bind to the transition metal at two sites. These two binding sites along with the bonds formed by the two OH- molecules add up to four total bonds.