Q&A for 30AL

Question:

will you be posting the answers to the final, and if not can you? thank you

Answer:

I am not posting th answers to final exam since there is NO Regrade for Final.

Question:

Professor, will you give us all the tables we need for IR and CNMR?

Answer:

Yes I will

Question:

Professor Henary, would studying your review sheet, and lab techniques for the labs we have done this quarter be sufficient enough to do extremely well on your final exam, or is there some other material I may be overlooking. Thank you.

Answer:

Yes, I think so.

Question:

Will error analysis/calculation be covered on the final?

Answer:

No

Question:

I was doing the practice final and I had a quick question. For the balanced equations of problem 14 the answer provided does not balance the chromium ions. Is that an error or correct? If correct, could you please explain why. Thank you! :)

Answer:

I think this is an error and the correct answer should be 2 Cr(3+) and not Cr(3+)

Question:

When trying to purify the nickel in the soil lab, the nickel did not disslove when added to 6M HCL and water (forming Nickel Chloride). We tried to run a UV-vis but the solution was not reddish, it was tan. The result came back very dilute. I can't figure out why the nickel wouldn't dissolve in the water and HCL.

Answer:

The nickel did not dissolve because it has lower affintity for the Chloride ion.

Question:

Hello Professor. For the final, will you give us the main equations (like you did on the midterm)?

Answer:

Yes I will in most casses.

Question:

i was wondering how i can check with you to see if my labtop is compatible with the stuff you have for projecting the powerpoint, do i bring my labtop to you?

Answer:

I have a connection to your lab top.

Question:

How much are we getting grading on in terms of accuracy of the quantitative results? Is it going to hurt our grade if we used the right technique but didn't really get accurate results?

Answer:

Really not much, may be 8 points max. for quantitative results.

Question:

Professor, knowing we have two different inorganic compounds in our soil sample, how would we separate the two in order to determine the number of moles metal ion per gram of soil sample?

Answer:

You can use precepitation reactions with Ba chloride, ba hydroxide, and so on

Question:

For the dectection of cobalt in the ion exchange experiment, we used KNO2, a 1:1 ration of K+ to NO2-, and the manual says that the precipitate should be K3CO(NO2)6, a 1:2 ratio of K+ to NO2-. How does this work? Also, to balance the charge, is Co oxidized from 2+ to 3+?

Answer:

The balanced equation is as follow: Co(+3) + 6KNO2 === K3CO(NO2)6 + 3K(+) CO is CO(III) and not CO(II)

Question:

When setting up the sublimation apparatus for isolating the organic compounds, does the soil sample itself (before the separation of inorganic and organic compounds) go at the bottom of the flask below the "cold finger"?

Answer:

Sublimation only if you know that you have camphor or naphthalene. If you look at p. 116 of the lab manual you will see how sublimation works. Dried compound should be at the bottom of a clean, dry filter flask.

Question:

What is the chemical formula for dimethylyglyoxime? Thanks

Answer:

The formula for dimethylyglyoxime is C4H8N2O2

Question:

Hello Professor, I was just wondering what was the average on the midterm?

Answer:

Midterm Average was 80%

Question:

In Lecture today, you mentioned we may have Iron in our soil samples but in the handout we got for the soil samples, only Co, Cu, and Ni are listed as possibilities. Are we really only looking for 3 inorganics and 5 organic components in our soil? I was also wondering if every sample has 2 inorganic and 3 organic compounds in their soil as many have been saying. Or does the number actually vary from sample to sample? Thanks!

Answer:

Yes we really looking for only 2 inorganic in your soil unknown. Your unknown may have Co,CU or Cu,Ni, OR Co, Ni

Question:

In the copper test we conducted for the Ion Exchange lab, is the ammonia neutral? If it is, how does the copper bond with it to form Cu(NH₃)₆ ²⁺?

Answer:

Yes NH3 is neutral. Cu(2+) + 6NH3 = Cu(NH3)6 (2+)

Question:

For the Ion Exchange Chromatography post lab you told us to write the balanced equations for the tests. For these,s hould we worry about the atoms oxidizing? We're wondering because we can't seem to balance the equation for the iron test properly.

Answer:

You will write the equations for the metal ions, Ni(2+) , Cu(2+), Fe(3+) withe the reagents you added for the test.. for example: Fe(3+) + KSCN= K(+) + FeSCN(2+) and so on.

Question:

i have the same problem as the previous question. Does the student have to specifically say the formula of the fragment? or, can the student say something like, it is the mono substituted benzene ring attached to a carbon double bonded to an oxygen? So in other words, does the formula need to be specifically stated, or can it be implied through words?

Answer:

If you have teh fragments, it is easy to specify which fragment you have for example for m/z=77 corresponds to a phenyl ion;[C6H5]+ and so on.

Question:

I was grading some of the responses from the CPR. On 2 of my reviews, the individuals described portions of fragments IE "the benzene ring by itself" or "the benzene ring with the chlorine, attached to a carbonyl". I'm not quite sure whether to grade those as accurate or not because technically some of those descriptions are short hydrogens( in benzene's case C6H6 isn't the fragment C6H5+). Any thoughts? Thanks!

Answer:

It should be peak at m/z=77 due to [C6H5]+, M/7=111 due[ClC6H4]+ ion and another peak at m/z 139 due [ClC6H4 CO]+ and so on.

Question:

Hi professor, for part 3 of analysis of the iorn oxalate complex, how do we calcualte the experimental molecular weight of our prodcut. Thank you

Answer:

The experimental mol weight can be calculated as follows; From beer's Law we can calculate the moles of iron Expt mol wt= wt of product/mol of Iron

Question:

for the error analysis in concentration for one of the standards are we supposed to include the error of the 5mL plastic syringe? If so, what is the error of the 5mL syringe because we were only given the error for a 1mL syringe.

Answer:

Yesx you should include this error which is +(-) 0.05mL

Question:

Hi Professor, Do you know the last day we can turn in regrade requests. Thanks.

Answer:

It was yesterday (Monday 11/14) by 2pm

Question:

for iron III postlab, for finding inherent error for the concentration of the standard, how do we do this? do we use any error in the buffer or the bipyridal or only the error for the graduated cylinder used for those two? thanks.

Answer:

I think you measured the quantity of buffer and bipy using a graduated cylinder. the error for any graduated cylinder is 5% of vol you have added.

Question:

What is the ion exchange post lab due?

Answer:

Ion exchange post lab due on 11/29 and 30 depending on when your section meets.

Question:

My lab partner and I used a 10ml Volumetric Flask in Iron Lab III. What numerical value should we use its error? Thank you!

Answer:

The error in 10mL volumetric falsk = + (-) 0.008

Question:

Professor, for the Iron Oxalate lab part III what is the difference between the error in concentration for "solution B" unknown and the % inherent error for unknown solution B

Answer:

You can calculate the error in Conc in solution B as follows: Calculate Amax and Amin for the unknown soln "B" (same as what you did for the standard). *Project Amin to the max. slope and project Amax to min. slope. * the range on the x-axis will give you Cunk. The absolute error in the unknown can then be approximated by finding îCunk/2. The % inherent error measures the maximum tolerance of the uncertainties in the experimental.

Question:

Professor, how do we calculate the gram of product for question 4 under data analysis.

Answer:

you calculte the experimental molecular weight in #4 from Beer's law as follows: Weight of product / moles of iron. you can calculate for moles of iron from beer's law as I did last Monday in lecture. If you have any question come to my office or any TA office hour.

Question:

RE: Post lab Iron analysis part 2 Do we calculate %RAD for more than one of our titration trials?

Answer:

You should calculate moles of oxalate / g sample for each trials and then calculate the %RAD. review Page 24 and 25 in lab manual

Question:

FOr the Iron Oxalate Part two postlab, to calculate the moles of oxalate per gram we just take the answer calculated in part (i) and divide it by the weight of the sample we used in the titration? Ex. 3.3moles C2O4 divided by .05g ?

Answer:

Yes

Question:

Hi Professor, for the second part of the oxalate lab, i was wondering how you figure out the % RAD? Thank You

Answer:

Just review page 24 and 25 in lab manual

Question:

for the nmr prelab question 2 it asks how many non-identical carbon atoms there are. is "non-identical" the same thing as "magnetically unique"? meaning that the number of non-identical carbons is simply the number of lines there are?

Answer:

Yes the # of non-identical carbons is simply the number of lines there are and each line represent 1 carbon. For CH, CH2 and CH3 you can identifies these C's from the DEPT spectra.

Question:

Hi professor, i was wondering when are we getting our midterms back?

Answer:

Tomorrow and in Wednesday in lab

Question:

For iron oxalate part 2 post lab, are we supposed to write about the UV spectrum like it says in the guidelines eventhough we took the UV spectrum in part 3? Thanks.

Answer:

Yes you should do this part since you have all infos. I alraedy answer the UV question before.

Question:

Professor, one more question about the Iron Oxalate lab part II. For our data, do we only use our two titrations or do we use our two titrations as well as our lab partner's (total of 4)?

Answer:

combine your 2 titratyions with your partner's titrations in order to calculate the moles of Oxalate

Question:

Professor, one more question about the Iron Oxalate lab part II. For our data, do we only use our two titrations or do we use our two titrations as well as our lab partner's (total of 4)?

Answer:

You must use 4 titrations(combine the titrations)

Question:

Professor, for the Iron Oxalate Post-Lab Part II, does the amount of 3M H2S04 and 25mL de-ionized water affect the inherent error for moles of oxalate / gram of sample?

Answer:

You can us ethis amounts when you calculate for the IE. for 25ml of DIwater the error is 5% of the graduated cylinder you used.

Question:

Hello Professor Henary, I was told that the due date for one of the postlabs has been extended. Please confirm which one it is and when is it due? Thank you

Answer:

Iron oxalate part #3 has been extended to 11/15 & 16 instead of 11/8&9

Question:

When is the Iron postlab pt 2 due?

Answer:

Iron post lab part 2 is due next Tuesday and Wednesday depending on when your section meets.

Question:

Professor, in the post lab #2 for iron oxalate, what does it mean "expected wavelength"? Is it the wavelength we use for UV spect on lab3 of the iron oxalate? Thanks.

Answer:

The maximum absorption of the iron-oxalate complex should occur at the wavelength corresponds to the complementary color of green. This should be around 700nm or so.

Question:

For the prelab question, isnt the volume of each concentration of HCL give in the procedure?

Answer:

I already answerd this question, you have to write a procedure for that dilution as follows: You will use M1V1 =M2V2 if you need to make for example 10mlof 2.5F HCL from 6M HCl M1=2.5F , V1=10, M2=6F, V2=? you can find V2 and so on

Question:

professor, in the cpr, if someone calls peak A a "alkane C-H stretching" is that good enough or do they need to specifically say alkyl or sp3? Thanks

Answer:

You need to spicify all stretch that is have same wavenumbers.

Question:

hello prof, how do we determine the volume of each concentration of HCl? (prelab question #2 pg. 127)

Answer:

You will use M1V1 =M2V2 if you need to make for example 10mlof 2.5F HCL from 6M HCl M1=2.5F , V1=10, M2=6F, V2=? you can find V2 and so on

Question:

For the Iron Part 2 post lab, do we only use the data for the 2 titrations that each member in the group did or data for a total of 4 titrations each group did?

Answer:

You should use the data for the 4 titrations that each group did.

Question:

Dear Professor For exp 15, prelab, the lab manual speaks of 6 F HCl. I don't understand what unit is F. Can you clarify? Thank you very much.

Answer:

For HCL, it has only 1 proton so 1M=1N=1F M=Molarity, N= Normality and F=Formality

Question:

Professor, what happened to the Br that shows up in the formula for the salt but is not present when it is shown in the chemical equation?

Answer:

You do not need Br in the chemical equation but you do need it in formula for calculation in quastion #4

Question:

you said we can bring one sheet of notes with anything on it correct? Both sides of an regular sheet of paper?

Answer:

Yes you will be using a cheat sheet and you can write any thing on both sides of the cheat sheet.

Question:

Will we be given dielectric constants on problems that ask us to calculate matters of solvent use?

Answer:

Yes I will give you dielectric constant on problem if I ask you any quastion dealing with polarity

Question:

Hi Professor, I was wondering if specifics from the iron oxalate lab were going to be on the midterm. Thanks.

Answer:

Only parts 1 and 2. I answered this question before

Question:

I was wondering if you could explain 'salting out' in terms of the caffeine experiment that we did. In this particular case, was the polarity of the water increased or decreased? how were the tanic acid and the caOH affected by the addition of NaOH to the solution?

Answer:

The polarity of water should increased when you added a salt and at this point caffeine will not be soluble in salted water. It will be soluble in propanol.

Question:

Will iron oxalate pre/post lab be covered on the midterm?

Answer:

Only parts 1 prelab and post lab and part 2 prelab only

Question:

what do we need to know about the theory behind the iron oxalate lab for the midterm? for example will we need to be able to solve for the variables if you gave us experimental numbers?

Answer:

For the iron oxalate lab you should know only parts 1 and 2.

Question:

will we be getting a chart with all the IR bond vibraiton types and wavenumber ranges or should we copy one onto our cheat sheet?

Answer:

I will give you a nice table for the IR that has all streching vibration you will use. You do not have to write any numbers in your cheat sheet

Question:

Hi professor, I was wondering if you could upload the handouts from lecture. I seemed to have misplaced the second and third weeks handouts and I know they are very important to study from. THank you so much.

Answer:

You can come to my office in 1072 and pick up the ones you have misplaced.

Question:

Professor: For the cafeeine post-lab you said that for the TLC, both stages are polar, but in the Mohrig text it says that one one stage is polar, i.e. the silica gel plate, and one is non-polar, the ascending solvnt. So how does the TLC work if both phases are polar? Also, for the midterm...how much is going to be covered from the Iron lab we are doing now? Thanks a lot

Answer:

For caffeine we use water as a solvent which is polar

Question:

hi Professor Henary, will the midterm cover 1)UV/MS Spectroscopy, 2)Iron Oxalate Prelab/Postlab, and 3) Error Analysis using Beer's Law?

Answer:

Midterm will not cover error analysis of Beer's Law but it will cover simple Beer's Law questions(review my lecture notes and 20L) also will cover UV-visible . Mass spectra (MS) will not be covered

Question:

Professor Henary, what time is your office hour tomorrow? (on this coming Friday, Oct 28th)

Answer:

On Friday extra office hour at 10 am

Question:

Hi Dr. Henary, my question was regarding the post lab of extraction of caffeine. More specifically how do determine the molar extinction coefficient. I know the equation is molar extinction coefficient = A/LC; however, how do we determine A, the absorbance, and C, the concentration. Thank you.

Answer:

You will use A=eCL; e=molar extinction coefficient. A is the max absorbance for your caffeine absorpton spectrum, L= 1cm cell, and you can calculate the concentration,C, from weight of your sample and molecular weight of caffeine which is 194g/mole as follow: moles = wt sample(g) 194 (g/mol). You dissolve your sample in 50mL DI.water then C= moles / L ; L= 0.05L

Question:

Professor, when/where do you have extra office hours?

Answer:

I have extar office hours today from 10-11 am in 1336 and on Monday I have 2 hours office hours from 10-12(noon)

Question:

For the caffeine post-lab, I had a question about the TLC that was performed. In the other TLC we performed for caffeine, the stationary phase was polar and the mobile phase was non-polar. However, for the mobile phase this time, we use H20 which is very polar, but we still used the same plate. Which phase in this TLC for caffeine was polar and which was non-polar?

Answer:

For the caffeine TLC lab both phases are polar. like dissolve like.

Question:

professor for question 1 for the prelab for week one of the iron lab, what volumes do we use for oxalic acid? You say to use the first chemical equation but we will use oxalic acid for both rxns. Thanks

Answer:

You will use 6-mL of 1M oxalic acid 9P. 100 in lab manual)

Question:

How do we calculate % yield of caffine? Also, what is the Landgrebe that we are supposed to compare it to?

Answer:

% caffeine in tea = (g of crude caffeine / Initial weight of the tea bags ) x 100% OR % caffeine = (g of crude caffeine / Final weight of DRIED tea bags after brewing) x 100%

Question:

For caffeine post-lab the part where you ask us to explain our observations with equations, do you mean write out chemical reactions or use equations like the extraction equation?

Answer:

•The only "real" chemical reaction here is the reaction of Ca(OH)2 with the tannic acid. •You should mention the reason why you added NaCl. •You need to explain the purpose of acetone in the experiment

Question:

For Aspirin Post Lab #2, do we need to account for error in the indicator we used and if so, what values do we use? Also, is there any other errors that should be accounted for besides the error in the base concentration ,buret,and balance?

Answer:

Yes, the indicator error is +/- 0.05 . Nothing besides the error in the base concentration ,buret,and balance?

Question:

In the Caffeine Pre Lab Question #4 d) What does it mean by "using one to four extractions"? Do you calculate the %compound that can be removed from each extraction?

Answer:

It means you will do extraction 1 time, 2 times,3, times and 4 times. In order to answer this problem you have to use parameters for multiple extraction which are: n=1,2,3,4 and 2v2 = v1 and k=2 and assume Wi = 1gm. then apply that to the equation for multiple extraction in lecture notes. If you can not get it please stop by my office or go to any TA office hour.

Question:

Professor, For the caffeine prelab, what substances do we have to find MSDS information for? It's not listed on the guidelines.

Answer:

NONE

Question:

I'm a little confused about the calculation of the yield. In the first postlab of Aspirin synthesis, it says to calculate crude yield, and %corrected yield, and in the second postlab it says to calculate recrystallized yield. Does that mean that % crude yield is before recrystallization? But it sounds like %corrected yield should be done with the data after recrystallization. Which weight should we use for each of the following yields: %crude, %corrected, and %recrystallized?

Answer:

yes, % crude yield is before recrystallization. After recrystallization you have weighed your pure Aspirin, then find moles of pure aspirin and divide moles of pure aspirin by max theoritical moles of aspirin (which is moles of salicylic acid)

Question:

For the Postlab for part1 of the aspirin lab, how are we supposed to find the % corrected yield? i did not understand how to use the info the lab manual gave us.

Answer:

I just answer this quastion before, pease review the question / answer .

Question:

I'm confused about what eaxactly is in the abstract, do we just basically summarize the techniques and processes and tell you the final calculated result or the data we got from the experiment?

Answer:

For the abstract -2 -3 sentence about the what you are going to make or analyze. Just read how to write a prelab report from teh web.

Question:

In regards to the post lab for part one of the aspirin project, I was wondering how to exactly calculate the second part of the numerator for the % corrected yield. I am not sure if what we do is add up all of the volumes of water we used, and base it off of that, or if there is a different amount we are supposed to take. I tried doing it with adding all of the water up and the change was very insignificant, about +0.01% difference. Also, I have another question about that part. For those calculations I am assuming we are using the product we retreived after recrystallization and I was wondering if we are assuming that it has the molecular weight of pure aspirin to take calculations. Thanks a lot.

Answer:

% corrected yield= moles of Aspirin recovered + moles left in solution / theoritical moles of product To calculate moles of product left in solution as follows: you suppose to know how mnny mL of water and ethanol used in the synrhesis and ewcrystallization. I think you added ~ 50mL of water and 10 mL of ethanol. grams of product left in soln= ml of solvent used(water + ethanol) times 0.025 g/100 mL. Then moles left= grams/180.3g x 1mol

Question:

In calculating the % corrected yield for Post-lab #1, how do we calculate the moles of product left in solution? Are we supposed to know how many mL of water are in the solution?

Answer:

Yes you suppose to know how mnny mL of water and ethanol used in the synrhesis and ewcrystallization. I think you added ~ 50mL of water and 10 mL of ethanol. grams of product left in soln= ml of solvent used(water + ethanol) times 0.025 g/100 mL. Then moles left= grams/180.3g x 1mol

Question:

1. What is the % inherent error required for post-lab #2: Aspirin Analysis. How do we calculate this %. 2. Is the purity given by the following equation: moles of SA in solution % PURITY ----------------------- theoretical moles of aspirin in sample

Answer:

Inherent error in % yield is relative error in wt of Salicylic acid, in weight of repirin recovered and in vol of solution Inherent error in purityy is relative error in Molarity of NaOH, Vol of NaoH and wt of aspirin % Purity = actual moles of acid /theoretical moles of asp in sample

Question:

For the pre-lab, do we complete both week 1 and week 2 by our first lab section of the week? Or do we turn in week 1 on the first day and week 2 on the second??

Answer:

Wek 1 is period 1 and is due today and tomorrow. Week 2 is period 2 for aspirin and is due on Thursdsay and Friday depending on when your section meets.

Question:

is the formation of aspirin an exothermic or endothermic reaction?

Answer:

When heat is given off by a reaction the reaction (dH is -ve) is said to be exothermic (giving off heat). Reactions in which heat is taken up (dH is +ve) are called endothermic Ttaking uo heat from surroundings).

Question:

Professor, When doing our prelabs is it necessary to make data tables in our lab book before doing the experiment. I have always found that it is better to collect the data on scratch paper and then make the tables accordingly to make the data look nicer. Is this possible? Thanks

Answer:

When you make data tables always start new page in your notebook and leave tables blank. Fill data table during experiment.

Question:

Dear Prof. Henary Do we have lab on Thursday (09/29) before our first lecture? Thank you very much.

Answer:

Yes we will have a lab this Thursday on 9/29 and every one must attend his/her assigned section.

Question:

Do we go to lab on the first day of instruction this thursday even though we havent had lecture yet?

Answer:

Yes wee will have a lab this week (week 0) on Thursday.

Question:

I was wondering if we have lab on the first day instruction for Fall Quarter (9/29/05) even though we havent had lecture yet?

Answer:

Hi, Yes we will have lab on the first day (Thursday) week 0 this week. Every one should attend the lab this week.