http://orgo.curvedarrow.com/punbb Curved Arrow Press Forum en http://backend.userland.com/rss http://orgo.curvedarrow.com/punbb/viewtopic.php?pid=377#377 377@http://orgo.curvedarrow.com/punbb Topic: Why are potassium salts soft soaps and sodium salts hard soaps? Message: Yahoo Answers wrote:Q: Why do potassium salts yield soft soaps while sodium salts yield hard soaps?i have been searching relentlessly for weeks trying to find an answer to this. it was a part of my organic lab assignment from a while back and i never found the answer to it. A: This is an interesting question. I had to do a little research to learn what this meant. From searching the internet for hard and soft soaps. Hard soaps are physically hard, in this case meaning they contain little water. Sodium chloride may be added to help salt out the soaps and make them hard. The problem with hard soaps is that they are less effective. Sodium salts are more easily isolated as hard soaps. Potassium soaps are soft soaps, meaning they are softer due to more water being present in their isolation. From what I can gather, the key difference is due to the solubility of the salts. Potassium salts are more soluble in water than their equivalent sodium counterparts. I found a journal reference in the www here. There are several chemistry experiments that essentially repeat this experiment on a practical scale and compare the temperature at which different salts dissolve, for example. This is my opinion of the chemistry involved. As one goes across and down the periodic table, more and more protons are introduced into the nucleus of each atom. That increases the Coulombic attraction for electrons. Additional electrons will encounter a repulsion by the inner and outer shell electrons as well. Since the differences are in the metal cations, we need only look at how sodium, potassium, lithium, magnesium, and calcium might differ. Lithium might be predicted to be less soluble as lithium only has a single pair of electrons to interfere with any attraction to the nucleus of 3 protons. Sodium has more protons and an additional completed shell of electrons to interfere with an attraction to the nucleus. That completed shell of electrons will diminish the force of attraction for another electron at it will be at a much greater distance than those electrons of a halogen. The distance of an electron that completes a shell will be much closer to the nucleus than an electron that will start the next outer shell. It is difficult to predict the effect a priori. It is easier to look at data and rationalize what has happened. Since the reactivity decreases K>Na>Li, potassium is the most reactive and the lowest affinity for its outermost electron. Logically, it should also have a low affinity for the electrons of the carboxylate (the more basic component present). However, by entropic arguments, in solution, no charge localization will exist. Thus the soap anion and potassium cation will become surrounded by water molecules. If sodium (calcium or magnesium) has a higher affinity for the carboxylate, that increased force will decrease the ion separation and solvent insertion. Presumably, this increases the affinity between the hydrocarbon ends of soap for each other and exclude water. This will lead to a harder soap. Wed, 03 Dec 2008 09:42:32 -0500 http://orgo.curvedarrow.com/punbb/viewtopic.php?pid=375#375 375@http://orgo.curvedarrow.com/punbb Topic: Can anyone recommend me some good Organic Chemistry books Message: Yahoo Answers chemistry wrote:Q: I'm taking an Organic Chemistry class and we use most of the time McMurry's textbook. It is overall a great book, but it's weak in some aspects (reaction mechanisms, few examples, etc.). Can anyone recommend me some good Organic Chemistry books for a future chemist? (aid books are ok too) I wish I had the notoriety to have others recommend our book. However, until that occurs, I must pump it up myself. The book is "A Guide to Organic Chemistry Mechanisms" (Amazon.com, Barnes and Noble or http://www.curvedarrowpress.com... ). You can see classroom results at the website. The book is a guided inquiry style book. You will find a series of examples present that I guarantee you can solve. They are then repeated at a greater level of difficulty and by doing so, everyone can succeed in learning reaction mechanisms. You can learn more about guided inquiry at the POGIL website, www.pogil.org. Compare their results with our results. Yahoo Answers chemistry wrote:A: Instead of a book, take a memory course. Organic is so much memory. Once you have mastered several hundred to several thousand items, then you can start to be good in organic. Been there, done that. I sucked at organic because I didn't have a good memory for the thousands of compounds and methods for making them. *edit*I just noticed another post in which a good memory was suggested. That strategy is one of the two common ways to learn ochem. Use your memory if logic doesn't apply. Use reasoning to avoid rote memory. That is precisely why I have been trying to promote my book. My class average on the ACS ochem exam improved by 20+ percentile points. That is like everyone being given a full letter grade increase, but I didn't do this through generosity. Compared to other classes, these students knew more. The development of the book came from learning why students were not answering mechanism questions when given the answers two weeks before the exam. Simply, the mechanisms are too complex to just memorize. However, they are linked by logic. Getting students to follow the logic markedly improves the scores. This book succeeds in doing that. Sun, 30 Nov 2008 08:49:50 -0500 http://orgo.curvedarrow.com/punbb/viewtopic.php?pid=306#306 306@http://orgo.curvedarrow.com/punbb Topic: Gasssoline Message: I would think that determining the brand of gasoline and searching for its chemical composition could be the way to go. Most suppliers of products in today's awareness of health issues etc - do in fact often supply this sort of information. Sometimes it is about contacting the supplier directly and stating that I am in a high degree of contact with this product, and need to know its ingrediants. I haven't tried this myself with gasoline.I think unleaded may contain a degree of aromatic compounds (benzene-toluene)that I think improve its rating. I dont believe it would be in high percentages as these compounds are somewhat valuable in other contexts rather than for combustion reactions. I am not a chemist by trade so I may be misinforming you here. Your question makes me think that you are looking perhaps in a specific target compound that can be separated from gasoline. I dare say a question such as this, if really explored, one could learn alot of chemistry.Finaly, I am new to this forum and not sure if indeed me responding as I have, is the norm. I dare say I will find this out. Wed, 16 Jul 2008 21:14:15 -0400 http://orgo.curvedarrow.com/punbb/viewtopic.php?pid=305#305 305@http://orgo.curvedarrow.com/punbb Topic: Gasssoline Message: Your question is outside my area of expertise. Wed, 18 Jun 2008 12:01:40 -0400 http://orgo.curvedarrow.com/punbb/viewtopic.php?pid=304#304 304@http://orgo.curvedarrow.com/punbb Topic: Gasssoline Message: Hellowhere can i find what are the ingredients of gasoline(without lead) 95 octan? and what is the percent of each ingredient?thank you Wed, 18 Jun 2008 10:18:19 -0400 http://orgo.curvedarrow.com/punbb/viewtopic.php?pid=156#156 156@http://orgo.curvedarrow.com/punbb Topic: Why is organic chemistry so hard? Message: ParkingCycloheptatriene has 6 pi electrons, but it does not fulfill the rules for aromaticity. You must be able to draw resonance structures using all the atoms in the ring. The CH2 group cannot be used, therefore cycloheptatriene is non-aromatic. The radical can use all of the atoms in resonance structures, but it does fit the Huckel rules for aromaticity, namely 6 or 10 pi electrons (2n+2 rule). Therefore, it is also non-aromatic. The anion also can use all atoms to form resonance structures, therefore could also be aromatic, but again the Huckel rules for aromaticity do not fit. It does fit for an anti-aromatic system with 8 pi electrons (2n, n=4). I don't know whether this will be truly anti-aromatic or not. There are many systems that could be consider anti-aromatic, but are able to adopt a conformation such that the electrons do not interact as needed to be aromatic or anti-aromatic. That is, if changing conformations blocks all electrons from becoming part of a higher energy system, it will do so. An example that is often cited is cyclooctatetraene. It forms a puckered shape so it is not planar (one rule for aromaticity) so the electrons do not interact in forming the resonance structures. I would guess that such an anion has been prepared and if the hydrogen were parallel to the pi electrons, then that atom would block resonance with it. The non-bonded electrons could then be orthogonal to the pi system and should not be counted as part of the aromatic system. The effect would be the same as pyridine with its lone pair of electrons being orthogonal to the pi system also. Thu, 06 Mar 2008 01:47:18 -0500 http://orgo.curvedarrow.com/punbb/viewtopic.php?pid=90#90 90@http://orgo.curvedarrow.com/punbb Topic: Why is organic chemistry so hard? Message: I expect you will get a lot of answers for this. Those that found it easy and those that found it hard. Even the instruction is geared for those sentiments. I have helped students who had very difficult problems and those that had very easy problems. Let me distill it down. For those that find it easy, they focussed on the principles. There are only a few patterns that are varied to explain most of the reactions. On the other side is the camp in which if you can't understand it, memorize it. Some of the books and websites serve this line of thinking. I can't speak for your school, but the course and expectations can vary quite widely. From my experience, most students succeed with stereochemistry, conformational analysis, nomenclature, etc. They describe static things. If given enough practice, students know what sp3 or axial mean.Reactions are a different matter. You start with something and end up with something else and the variations are endless. I used reaction mechanisms or mechanistic thinking as a staple of my teaching activities. I also introduced a mechanism workbook to supplement the class. By doing so, I raised my class average on the ACS organic exam by 20 percentile points.I find it interesting that mechanism based textbooks are in the minority while functional group based books are the majority. A mechanism based book focusses on how you get to the answer and a functional group based book focusses on where you are going. Many students (and professors) resist a mechanism approach. A mechanisms is a logical explanation of the electron movements that lead to the products. I like it. That kind of thinking appeals to me and has worked well with my class. At the other extreme, some schools emphasize retrosynthesis and can even be rigid in how it is to be formatted. I have tutored some students in schools like that. I mention this because it strikes me as being extremely challenging to try to use reactions you do not know. It is like translating from English with a foreign language dictionary. I would expect organic chemistry to be extremely challenging at those schools.I cannot predict which type of instruction you will encounter. If you have the ability and have good instruction, you shouldn't have any problem. On the other hand, I had just answered a question in which I explained that organic chemistry has some inconsistencies. Those inconsistencies coupled with a "memorize it" approach to learning can make for a long course. If you want to learn reaction mechanisms, use "The Language of Organic Chemistry; A Guide to Organic Chemistry Mechanisms" at http://www.curvedarrowpress.com. (Incidentally, I had a summer high school student learning reactions from the book without taking organic chemistry. The book makes the reactions accessible and I believe my results are a reflection of that.)Answers Yahoo.com post Sun, 17 Feb 2008 13:07:26 -0500 http://orgo.curvedarrow.com/punbb/viewtopic.php?pid=89#89 89@http://orgo.curvedarrow.com/punbb Topic: Why is organic chemistry so hard? Message: I see this question or something like this posted quite frequently. Below are some of my answers. Sun, 17 Feb 2008 13:07:18 -0500