| (no subject) |
[Dec. 20th, 2009|06:04 am] |
I'm going to say upfront that I am the LEAST scientifically-minded person you'll ever meet. I never made it past basic biology in school and the idea of me trying something chemistry-related is well, laughable.
Having said that, I need some chemistry help! And please excuse any terminology errors I make, though you are free to snicker at my mistakes. :D
I'd like to make some wine charms for a friend who is very scientifically-minded. I thought of something he would get a kick out of, but I'm not sure how to make it a reality. I want to make wine charms that have the molecular formula for different... chemicals? in wine. A quick google search turned up this image of different wine molecules. It also turned up this charm, which is the "look" I'm going for. (I'm going to be using wire and beads for this project.)
So as a complete moron looking at those two images, I notice a few differences. The first image has areas where there are double lines, and some of the parts are O and some are HO or OH. (Is my ignorance giving you a headache yet?) The image of the necklace has balls in different areas and none of the lines are double. So I guess what I'm asking is, how do I turn the symbols in the first image into something more like the necklace charm, that can be replicated in simple wire and round beads? (For the record, I'm not attached to the specific molecules in the first image. Any molecules that are found in wine will do.)
If you are goodly enough to help me out, please act as if you are talking to a five-year-old and make your answers suitably simplistic. It would be amazingly fantastic if someone could just make a quick MS Paint image for me to go by, but I understand if that's too much trouble. Thanks for any help you can give! |
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| Biochemistry: Urea Cycle |
[Dec. 11th, 2009|08:39 pm] |
My prof has given the net rxn of the urea cycle to be:
NH4+ + HCO3- + Aspartate + 3 ATP + H2O ---> Urea + Fumarate + 2 ADP + 2Pi + AMP + PPi (+H2O = 2 Pi)
And in the notes she states that four ATP equivalents are required to synthesize urea.
...Where is this fourth "equivalent" coming from? I've been informed that it has to do with the higher energy phosphate bonds but i just can't quite put it together in an explanation that works for my brain.
Any insight would be appreciated! The final is on Monday so hopefully I figure it out before then. |
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| Alkali metal + water |
[Dec. 7th, 2009|07:55 pm] |
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What exactly is the reaction that takes place between alkali metals and H2O? What is the mechanism? I know it involves the highly exothermic loss of an unpaired electron from the metal and that the products are the metal hydroxide and H2. |
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| Probably a simple question with a simple answer. |
[Dec. 5th, 2009|11:43 pm] |
| [ | mood |
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Ok, so I'm an A level chemistry student, who has recently carried out my chemistry investigation. I'm still working on my research, and I realised that I actually don't have the order of the decomposition of Hydrogen Peroxide when catalysed with Manganese Dioxide.
I've tried finding it- google has failed me, as it seems to have done pretty constantly throughout my whole investigation, and I was wondering if anyone knew it? So far, the closest I've gotten is a pseudo-first-order rate, which doesn't overly help me.
Thank you in advance. |
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| Soliciting Sample Organic Qualitative Analysis Questions |
[Dec. 4th, 2009|12:13 pm] |
I have an organic lab test coming up next week that includes qualitative analysis. I expect questions to appear on it that look like those in the Mohrig Qualitative Analysis Prelab.
Here's one of those questions:
7. A compound of bp 152°–153°C is water-insoluble and insoluble in 2.5 M NaOH, 1.5 M HCl, and concentrated H2SO4. The original compound reacts negatively to a 2,4-dinitrophenylhydrazine test. The 1H NMR spectrum produces the following signals: 1.25ppm, 6H, d; 2.9 ppm, 1H, septet; 7.1–7.4ppm, 5H, m. The proton-decoupled 13C NMR spectrum shows singlets at 22, 34.5, 126, 127, 129, and 149 ppm. The IR spectrum shows four peaks between 2980–2800cm–1 and three peaks in the 3100–3000cm–1 region. Deduce the structure and name of the compound and assign all spectral absorptions.
I'm enjoying these, and I think I ought to do more of them. If you have questions like this accessible, I would appreciate it hugely if you'd post them. Or maybe we could all compose a few and bookmark them on the info page for other people looking for practice.
Good luck on incipient finals if you have them, and thanks! |
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| (no subject) |
[Dec. 2nd, 2009|06:47 pm] |
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If I'm asked what the major product of 1,4-dibromobutane in 1 eq. NaOH, how do I know if the major answer is 4-bromobutanol or if there will be an intramolecular reaction in 4-bromobutanol to form a cyclic ether? |
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| (no subject) |
[Dec. 2nd, 2009|08:50 am] |
For the synthesis problem above, the answer I'm given is:
1. 3 NaNH2, mineral oil, heat
2. MeBr, DMF
3. H2, Pd
I really don't understand the reasoning behind these steps. If anyone could explain how to do this synthesis, I'd be very grateful. |
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| Properties of Cholesterol in various solvents |
[Dec. 1st, 2009|04:11 pm] |
Okay, a few weeks ago I posted a question related to cholesterol's structure. Little did I know it, but the lab write up in question was a two parter, and this week we used Thin Layer Chromatography to characterize the cholesterol we isolated from a calf brain a few weeks ago.
My issue is, I love biochemistry, but not so much the chemistry part. What I am wondering is how to rationalize the results that I got on my TLC plates:
Plate #1 was placed in a chloroform/methanol/water (70:25:3) solvent
Plate #2 was place in a hexane/ethylether/acetic acid/methanol (90:10:1:5) solvent.
Solvent #1 is clearly more polar COMPARED to Solvent #2.
My knowledge of chemistry pretty much stops at "like dissolves like" which would imply that cholesterol, being largely non-polar aside from the one little -OH group would travel farther in the non-polar solvent. However, the results show quite the opposite. Cholesterol travelled WAY farther (pretty much all the way to the solvent front) in the polar solvent than the non-polar solvent, in fact it travelled even farther than the more POLAR phospho and sphingolipids that I was also characterising.
I can't wrap my head around this. How does one little -OH group get dragged all that way in a polar solvent when cholesterol is a big fat rigid set of rings? |
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| (no subject) |
[Dec. 1st, 2009|03:30 am] |
I need some serious help. I hate chemistry so much that I'm seriously considering switching over to some fluffy liberal arts major because I cannot stand the thought of another semester of it. I don't even know how to go about solving this problem:
A compound of carbon, hydrogren and oxygen was burned in oxygen. 1.000 g of the compound produced 1.418 g CO2 and 0.871 g of H2O. In another experiment 0.1103 g of the same compound was dissolved in 45.0 g of water. This solution had a freezing point of -0.0734C. What is the molecular formula of the compound?
I don't want the answer, I just don't understand how I'm supposed to piece these things together and come out with a molecular formula. Don't I need the freezing point constant? What am I supposed to do with how much CO2 and H2O was produced when the substance was burned in oxygen?? I've looked through all of my notes, my book, and online sources for a similar problem but I haven't figured it out. |
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| Single/Double Replacement Reactions Question(s). |
[Nov. 29th, 2009|06:08 pm] |
Hi,
I hope everyone had a nice Thanksgiving!
I need general clarity of Single Replacement and Double Replacement Reactions. Can anybody help?
Single Replacement:
Zn(s) + 2Hcl(aq)----> ZnCl2 + H2
IE: Double Replacement:
Na2SO4(aq)+BaCl2-------> BaSO4(s)+2NaCl
Thanks in advance!! |
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| Test for vinyl alkene |
[Nov. 29th, 2009|03:04 pm] |
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Would you expect a vinyl group conjugated to an aromatic ring to give a positive Br2 test for alkenes? Or does the extra stability make them less sensitive to the addition reaction? What about other common chemical tests for alkenes? I have to identify an unknown compound in my organic chemistry lab, and I'm pretty sure I have trans-cinnamaldehyde but I need to distinguish it form benzaldehyde. I'll be doing 13C and 1H NMR on Tuesday and of course this ought to be fairly conclusive, but I'm supposed to gather as much supporting data as possible, and I also need to fill up some time during lab. Also, I'm interested in the answer for chemistry's sake, regardless of how it applies to my class. Thanks. |
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| Question about entropy? |
[Nov. 28th, 2009|05:12 am] |
I feel stupid because I'm rubbish at the whole of physical chemistry. Especially anything to do with entropy. Anyway, this is my question:
Okay, this is just one question; I just want to know how to do it rather than straightforward what the answer is. I find entropy quite hard to deal with and can't really find any websites that help.
0.2889g N2O4 was introduced to an evacuated vessel of volume 500cm^3. After equilibration the total pressure inside was 21.460 kPa at 298 K and 24.130 kPa at 308 K. Find standard (delta)H for the reaction N2O4(g) (reversible arrow) 2NO2(g).
I think it's probably really simple but I just need to be shown how to do it really. Also if you want Yahoo Answers points you can answer here instead: http://answers.yahoo.com/question/index?qid=20091127205830AALJjB8 :) xx |
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| (no subject) |
[Nov. 20th, 2009|11:45 pm] |
Hi, im stuck on a question on a piece of homework. I've been wracking my brain trying to figure it out but i just keep getting stuck.
the question is:
"270ml of 0.244M Potassium Chloride is allowed to react with 50.0ml of .210M lead nitrate. If 7.7 x 10^-3 moles of lead chloride are recovered, what is the percent yield?"
Can someone please assist? This area was probably one of the hardest for me throughout the entire class. |
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| (no subject) |
[Nov. 20th, 2009|06:52 pm] |
The following is a post-lab question from my Orgo I lab on the resolution of enantiomers:
The formation of a white solid is often observed after alpha-phenylethylamine comes into contact with carbon dioxide in the atmosphere. What is the white compound? Give an equation that shows its formation.
I'm not really sure of the answer. This was what I came up with:
Is this correct? And it if is, what is this "white compound" that forms?
Thanks for your help. |
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| Cholesterol |
[Nov. 17th, 2009|07:53 pm] |
Okay, so I am actually working on a lab report for a biochemistry course, but I feel like this question relies on more general chemical concepts. I'm no good at chem, so here I am.
Anyways, in the lab we isolated phosphoplipids, cholesterol, and sphingolipids from a calf brain. I am wondering what is so special about the structure of cholesterol that gives it the nice white flaky crystal appearance while the phospholipid and sphingolipid fractions were relatively plain looking yellow or white clumps?
I know that cholesterol is important in maintaining the rigidity of cellular membranes, but I am really at a loss as to how to explain it's physical appearance as this is not something that we really focus on as part of this course and i haven't taken a chemistry course in a while. |
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| Hi there! |
[Nov. 14th, 2009|06:48 pm] |
I'm new to this community. :) Oxfordmuse is my academic journal, and I will be posting helpful chemistry info. on my journal. Please feel free to visit! I may also link things I write to this community, if I think that they would be especially helpful, as well as using this site to help myself with other chemistry concepts.
~ Hannah |
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| Where did my product go? |
[Nov. 2nd, 2009|08:38 pm] |
So I had a pretty bad lab day today. (<1% Yield) I'm super bummed. :(
I suspect that my product disappeared after using the rotary evaporator after collecting the fragments using column chromatography.
I used a eluent of Toluene:Et-Ac 20:1 (Rf value 0.25). Toluene's boiling point is 110 degrees and my product's boiling point was 83-85 degrees. Can I just assume that the bigger portion of my product disappeared in the rotary evaporator alongside toluene?
Probably should have used pentane as non-polar solvent for the eluent... |
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| Rate of reaction of NADH |
[Oct. 29th, 2009|02:20 pm] |
Hi guys,
I'm in biochemistry, but a lot of our problems deal with general chemistry concepts.
QUESTION
I have a mix of the following:
NAD+ = .04 ml of 5mM
G3P = .1 ml of .2M
phosphate = .1ml of .2 M
buffer = .46 ml
GAPDH = .2 ml, with a density of 9.7mg/ml
The absorbency is found to be at 340 nm.
Rate of increase of absorbency (delta(A)), is .17/min.
I need to calculate the rate of production of NADH in this reaction, in units of micromoles/min.
ANALYSIS:
The equation is as follows:
G3P + HPO4(2-) + NAD+ --------------> BPG + NADH + H+
So, there is a 1 mol : 1 mol ratio.
I converted all of the above reactants into moles:
G3P = 2e-5 mol
phosphate = 2e-5 mol
NAD+ = 2e-7 mol
Therefore, the limiting reagent is NAD+. I would then get 2e-7 mol of NADH, and thus, 2e-4 mmol of NADH. This is a part where I am stuck. There is a tip to consider the reaction volume.
There is a law that absorptivity is equivalent to the molar extinction coefficient times the concentration times the length, which is assumed to be 1, so it may be disregarded in this problem:
A = E x C
Since I have moles of NADH, I was considering placing that over the total volume of the mixture (this is where the volumes of buffer and GAPDH become quite useful) and then multiplying it by the molar extinction coefficient of 6,300 (which was given) to get a final absorption, but I feel like I'm just shooting in the dark with this.
Any direction is helpful. Again, the rate of absorption is .17/min.
Thank you!
EDIT: Actually, my problem said to "follow the absorbance at 340 nm" which is different from the absorbance being 340 nm. Absorbance does not have units.
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| Soluble only in concentrated H2SO4 |
[Oct. 28th, 2009|01:28 am] |
What sort of organic compound(s) would only be soluble in concentrated H2SO4?
I'm totally stumped by my organic lab problem set; I have some ideas based on other information, including spectral data, but everything I come up with looks like it should be soluble in at least some of the commonly used solvents like acetone, EtOH, methylene chloride, etc. The problem states: "The solubility tests show a compound that is insoluble in everything except concentrated sulfuric acid." I believe the compound contains an unsaturated ketone and it may be an organophosphorus compound. It is not an alkyl halide (failed the silver nitrate test) or an aldehyde (failed the Tollens test but formed red precip. with Brady's reagent). I appreciate any help! Thanks :) |
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| (no subject) |
[Oct. 27th, 2009|04:16 pm] |
I have a question I'm having problems answering. Can someone help?
If 25.0 mL of 0.100 M NaOH react with 25.0 mL of 0.100 M HCl, the resulting solution increases in temperature from 22.3°C to 24.7°C. What is the ∆H in kJ/mol for the reaction? (Assume the specific heat of the solution is 4.184J/(g°C), and the density of the solution is 1.00 g/mL.)
Here's the balanced equation: HCl(aq) + NaOH(aq) --> NaCl(aq) + H20(l) |
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