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At 06:34, you mentioned that the the carbon on the right is a partial carbocation. I'm a little confused on how that carbon, as well as the one on the left, have partial positive charges. | FaOOx6IZxV8 | The Br atom has a formal positive charge. Also, it is a fairly electronegative atom. The Br wants electrons! Is gets some of this electron density by drawing the electrons in the C-Br bonds closer to itself. This decreases the electron density around the two carbon atoms and gives them a partial positive charge. |
At 6:40, How is a tertiary carbon electrophile undergoing an SN2 reaction? Wouldn't the other 3 Carbons block it with Sterics? If there were a Hydrogen present instead of that Methyl group I would see no problem. Thanks for the videos! | FaOOx6IZxV8 | Don t forget that that at point, the bonds are highly strained.The tertiary carbon is almost trigonal planar, so it s easy for a nucleophile to attach. |
At 4:34, Hank says some of the pollen may find its way to a female cone.
Isn't the chances of this happening very low? How are there so many pine trees when the chances of fertilization are low? | H3XT-YU2n0c | Yes, the chances are very low. But they have large numbers on their side. Something may only happen 0.01% of the time, but if you try it a million times, you re likely to achieve the result. |
at 13:25 does Sal mean to write conformation? | I6LsWSXx8fg | He does, well spotted! |
This may be a "which came first- chix or egg" question, but it really is sincere:
at 13:22 is the molecule considered "anti-configuration" primarily because it is 1) in the most stable position? or 2) because a methyl group forms a 180 degree angle with another methyl group?
P.S. please don't say both | I6LsWSXx8fg | I promise not to say both. . Oops, I just said it. Anyway, 2 is correct. Anti means opposite . The anti configuration happens to be the most stable. |
at around 13:15 you say, "... so it's further away from other methyl groups..." when you were referring to the other carbons in the ring. They aren't technically called methyl groups right? | I6LsWSXx8fg | yea you re right, he meant CH2 groups. remember the ending -yl only refers to groups off the main chain |
4:5. If the molecules spread from one corner of the box into the whole box, no increase in entropy happens? So, the fact that the molecules very rarely gather together back into the corner has nothing to do with the second law? | dFFzAP2OZ3E | Sal states that entropy is only defined for systems in equilibrium. Surely, a box with all particles in a corner is not in equilibrium. If so, it doesn t makesense to say that the particles spreading into the entire box increases entropy. Still, that the particles won t surely reduce themselves back to the corner may have a relation to the second law: if the particles did, you could perhaps put a wall and get two systems whose added entropy is lower than thhe original s. |
At 3:30 why is the pressure upwards at the bottom of the cube greater than the pressure at the top? | vzID7ds600c | If the body submerged in the liquid is a 3 dimensional object, the object clearly has a height. We know that the liquid pressure is directly proportional to depth. Since the depth at the top is lesser than the depth at the bottom, the pressure at the bottom of the cube is greater than that at the top of the cube. |
At 8:00, to summarize Archimedes principle- for every submerged object the weight of water displacement equals the object's weight? Is that right? Thanks. | vzID7ds600c | No. Nothing was talked about the object s weight. It summarizes saying that the buoyancy force acting on the submerged object is equal to weight of displaced liquid, which depends only on the volume of the object. That is not the only force acting in the object though, there is also the object s weight but it was not mentioned so far. |
Refer 00:34 & 02:25 sec in Fluids(Part 5). We know pressure varies as (density*g*h) for a jar with liquid to level h (and no objects). Please educate me on how the pressure at each point of the jar will be effected if a cube denser than the water is suspended (and immersed) in the water using a thread. Is the profile of pressure in the jar w.r.t the height of the jar going to remain unaffected with the introduction of objects into the liquid. If so why? Please explain me mathematically.Thank you | vzID7ds600c | what IS Archimedes Principle?? i dont understand |
7:24: When Sal shows that the volume of the cube is also the amount of liquid displaced, is this true with any/every object or does this just so happens in this example? Please answer, Thank you! | vzID7ds600c | Yes, whatever is the volume of object immersed in liquid ( be it the whole object or a part of it) , that is the amount of liquid displaced. Its true for any object of any shape. |
Hi, I think that the pressure is scalar. So that the pressure has no direction. He should to say "force of pressure" (at 1:46)? Is it right? Thx, P. | vzID7ds600c | pressure is a tensor quantity ; neither scalar or vector , a coordinate-independent geometric quantity. |
At 8:08, Sal says the net upward force of submerged objects equals the weight of liquid displaced. Would it be accurate to say this applies to gases too since we're talking about weight, and possible compression wouldn't change weight? | vzID7ds600c | That is correct. Archimedes principle is a law of ideal fluids. Fluids aren t just liquids, they also include gases. |
At 0:50, Sal says that even though the pressure is dependent on depth, it acts in all directions. How does this make intuitive sense? Also, if pressure is dependent on acceleration due to gravity, it shouldn't exist in the upwards direction at all (since gravity acts downwards). | vzID7ds600c | WHen you are standing on the ground do you feel pressure against your feet? This is because you are being pulled down by gravity but the ground is pushing up with an equal force. In liquid you have the same thing, the liquid above the depth is being pulled down by gravity but the liquid below it has to have provide enough pressure to hold it up. |
at 6:42, would it be the density of the fluid instead of saying the density of the liquid ? or is it arbitrary ? | vzID7ds600c | It would be a little more correct to say fluid instead of liquid , but it s a very minor distinction. After all, all liquids are fluids, but not all fluids are liquid. And the main difference between liquids and other fluids is that liquids are incompressible. But that particular characteristic has no impact on this example, so there really is no problem in using one or the other. |
at 1:10 u said that on every particle of water equal force is exerted cos of which it doesnt move. but arent the molecules of any fluid always in motion? | vzID7ds600c | They are in Brownian motion, but that motion is random (and very small) so it cancels out and doesn t really matter for a problem like this. |
at 6:37 when (dpg)d^2, it should be equal to d^3pd^2gd^2. why it is only d^3 pg | vzID7ds600c | He s multiplying and not adding and that s why the distributive property that you are talking about won t work. For eg-when I say 2^2(5*4*2)=2^2(20*2)=4*40=160 160 is actually 8 multiplied by 20 ie 2 cubed multiplied by 5*4 That s what he s doing when he says d^2(dpg).He s actually multiplying d*d*p*g*d ie d^3pg. I hope this helps.:):):) |
At 6:33, why does sal keep on saying p instead of rho? | vzID7ds600c | Because he doesn t want to say rho |
At 2:26, so a volcano or a mountain would form at a subduction zone? | Y0eWnOZpSpQ | Yes, volcanoes form at the subduction zone because its like a the mid ocean ridge. When two plates collide and one subducts below the other there is usually a small space that magma can squeeze through, thus creating volcanes |
Although Jay points out only one beta Carbon at 01:28, actually there is another beta Carbon left to the alpha Carbon in the drawing, but since it doesn't matter which one to take, the other one is not mentioned, right? | uCW6154hPkc | Yes, there is another beta carbon in the ring, and the methyl group is also a beta carbon. It does matter which one you choose. You could remove H atoms from any of these, but you would get a different product in each case (actually, you get a mixture of all three products). Jay just showed you the mechanism that gives the most stable, and therefore the major, product. |
Why is there no stereochemistry for isopropyl group at 06:33? I don't understand Jay's explanation about the reason. | uCW6154hPkc | There is stereochemistry. He is really saying that the isopropyl group is no longer pointed up or down. Since it is on a double-bonded (sp2 hybridized) trigonal planar carbon, it is neither up nor down but in the plane of the ring. |
7:50, the preference depends on the base right, if it is sterically hindered or not? And here, we are just assuming the base is not sterically hindered? | uCW6154hPkc | The base is ethoxide ion, so it is not sterically hindered. However, the preference comes from the requirements of the E2 mechanism The important point of this video is that E2 eliminations must be anticoplanar. In cyclohexanes, E2 eliminations must be trans-diaxial even if the cyclohexane ring has to assume an unfavourable conformation to do this. |
At 7:06 Why does the isopropyl group become flat and planar and no longer pokes out at us? | uCW6154hPkc | Because the location of the double bond has changed. The carbon that has the isopropyl substituent is now involved in a double bond, so is sp2 hybridized and trigonal planar. That is, the isopropyl substituent will now be in the plane of the page. The cyclohexene on the left has the isopropyl group coming out of the page because in that structure the carbon with the isopropyl substituent is not involved in a double bond so is sp3 hybridized and has tetrahedral geometry. |
at 9:21, jay said the leaving group should be axial. Why must it be axial? | uCW6154hPkc | For the chlorine group to form anti peri-planer position with the hydrogen it must be in axial position.Also since in the equitorial position the co planerity is not achieved by the chlorine and the hydrogen atom.hence the axial position is required. |
At 11:20, is the product from the reaction with the minor conformation of menthyl chloride. This means that the minor conformation is being used up to make the product. This puts stress on the equilibrium between the minor and major conformations, so that equilibrium should shift toward the left. Does this continue to the point where there is no longer any of the major conformation? | uCW6154hPkc | Essentially, yes. This is an example of Le Châtelier s priinciple in action. As you remove one component in an equilibrium, the system responds in such a way as to relieve the stress by producing more of that component. |
At 10:00, I thought that the cells couldn't live without mitochondria because they wouldn't get the energy to do stuffs. | 1aJBToJrlvA | anaerobic cells can live without mitochondria because they need no oxygen for respiration they get energy from the glycolysis process which occur in cytoplasm not in mitochondria. |
refrence to 1:00 aren't there a membrain AND a cell wall? | 1aJBToJrlvA | In plant cells, there is both a cell membrane and cell wall, but in animal cells, there is only a cell membrane. |
Referenceing 10:55, if it is true that all mitocondrial DNA can be traced back to a single "Eve" mitocondria and it doesn't combine with "father" mitocondrial DNA, does that mean that all mitocondria in the world are the same? How do variances occur? | 1aJBToJrlvA | Variances occur through mutation |
At 10:00-10:05, if cells didn't have mitochondria before, then how did they produce energy? | 1aJBToJrlvA | I am not an expert but I think they might have used glycolosis before cells had mitichondria. I have read about glycolosis and it produces a net 2ATP without mitichondria. It is possible they used another method of course. |
At 8:50what is rRNA? | 1aJBToJrlvA | rRNA is ribosomal RNA, essentially RNA specifically generated to produce ribosomes. It is produced and stored in the nucleolus, a region within the nucleus. |
seedless vascular plants? what are they 5:00 | 1aJBToJrlvA | They are mainly ferns and horsetails, but most people aren t very familiar with them. They have vascular tissue so can transport nutrients more efficiently than the non-vascular plants (mainly mosses) so typically grow larger. They tend to be in wet environments because they have swimming sperm instead of pollen which is more common in plants with seeds (gymnosperms and angiosperms). |
At 4:00, what about Pseudopods? | 1aJBToJrlvA | There two arm-like projections of an amoeba which they can use to consume food and move. |
what was that thing at around 0:50? | 1aJBToJrlvA | That was a basic diagram of a animal cell |
At 4:25 Hank references City. What exactly is he referring to by city?
And aren't the centrosomes involved in cell division, so are they not a separate organelle altogether? | 1aJBToJrlvA | He means that the cell is like a city, with sewage, roads and stuff. Symbolically |
The probability function that Sal demonstrates around 1:47 gives me the impression that electrons constantly change energy levels "sharing" the energy that moves them from each shell for an extremely sort period of time. Is that true? I read similar questions in the comments section but i don't really get the answers... thx! | FmQoSenbtnU | The electrons stay within their own orbital unless they get energy from outside. |
Why doesn't Sal use 1s1 when he has doing the electron configuration for carbon on 7:20 | FmQoSenbtnU | There are 6 electrons in carbon, so 1s2 is necessary. Because carbon is in the 2nd energy shell, it fills up the 1st. 1s1 wouldn t fill up the first energy shell. |
If we looked at the electron configuration for Boron (1s2 2s2 2p1), would the single electron in the 2p orbital occupy both sides of the "dumbbell shape" or only one side? I looked at the chart at 6:00 and noticed the two sides of the orbital don't seem to actually touch. | FmQoSenbtnU | The 1 p electron would occupy both sides of the dumbbell shape. As these shells are probability distributions in which we can most probably find the electron, that means that there is a very small probability in which the electron is not found within the volume of the orbital. This is when the electron could move from one side of the dumbbell to the other. |
What is Sal doing at 6:22? | FmQoSenbtnU | He fills in the electrons in each p orbital. Each orbital can consist of maximum two electrons, and the lines represent the electrons, I suppose. If you didn t understand my meaning, please write a more specific question, maybe I can answer it. Hope I could help. |
11:50. why did you put 2p³ ? | FmQoSenbtnU | period block^group |
At 2:30 ,how can we know that electrons don't orbit around, but they jump, without seeing them? | FmQoSenbtnU | Indeed, we do not actually know for sure that it even jumps! Most of people only believe what they perceive with their eyes... However, the most accepted theory today is quantum mechanics (an abstract theory I would undoubtedly say), but I am not an expert myself so I don t want to give you false inclines. If you are interested, do some research by your own, because this truly is a bemusing topic! |
Given what has been talked about in this video (up to 5:30) and the last video, if you added more electrons (making it a negatively charged "atom"/without adding more to the nucleus) would you increase its mass? Considering you are expanding the orbital field and its 99% of the atoms mass. | FmQoSenbtnU | If you are adding more electrons to an atom, you are increasing its mass, because electrons have mass. If, for example, you added an electron to an oxygen atom, the mass of the atom would increase by only 0.003 %. This is such a small change that, for ordinary measurements, we can say that the mass of the ion is the same as that of the atom. |
AT 9:30
How do you know when to stop with the electron configuration? | FmQoSenbtnU | You stop adding electrons to the configuration when you have accounted for all of the electrons in the atom. |
At 0:08, Sal says "newtonian" or something similar sounding. What does that mean? | FmQoSenbtnU | Newtonian = according to the laws of motion as understood by Newton. |
At 4:55, at the table that the atomic orbitals are depicted, there are f orbitals only for n 4 and there are d for n5, p for n6 and only s for n7. Other depictions that i have seen, presen n5 with f, n6 with d and n7 with p, Why is that? Are there different opinions? Are they both correct? | FmQoSenbtnU | The issue is that there are no elements massive enough to actually have f orbitals occupied in the n=6 or n=7 shells. These orbitals still exist, they re just empty -- though they might have an electron in them if the element is in an excited state. |
At 3:54, why can't there be three electrons there? Why is there only two? | FmQoSenbtnU | Each atom can only hold a certain amount of electrons due to molecular structure and what-not. |
At 12:14, how are you able to check if you have done your electron configuration correctly? | FmQoSenbtnU | when you add the digits of your configuration u will get the atmic number of the element. for example- 2,4 check=2+4=6 which is the atomic number of carbon |
At around 2:40, how do we know the probability of finding an electron in a given orbital? I thought we couldn't ever know EXACTLY where an electron is. So how would we collect data to get, say, "90%"? | FmQoSenbtnU | The laws of quantum mechanics tell us how to calculate the probability. The orbital is just a graphical display of that probability function. We never do know exactly where an electron is. We don t develop any of the probability data by checking a random sample of electron locations. It s all math. |
At 6:30, ok so in the case of p orbitals, how would you identify say p sub x in comparison to y when you could observe it from a different angle and see the other | FmQoSenbtnU | To add to Just Keith s great answer, when an atom is bonded it is common to define the line connecting the two atoms as the z axis. |
At 11:25 how do we know that nitrogen has 3 orbitals in the P block? No explanation at how Sal arrives at that because he is going backwards in calculating that? Also for Silicon totally confused at how he arrived at the solution. What is the maximum electrons in a P shell? | FmQoSenbtnU | N is atomic number 7. Start filling the orbitals 1s2. That leaves 5 to go. Next is 2s2. Now there are 3 to go. Next comes p. So 2p3. Max in the p shell is 6. Max in d is 10. |
at 9:20, what happens to the electrons from the 1s subshell? Do they become part of the dumbbell shape of the p subshell, or are they still in the original sphere position? | FmQoSenbtnU | They stay where they are |
In 10:00, Sal moved Helium from group #18 and moved it beside Hydrogen under group #2 , I understand that he moved it to give us a closer idea, but what is the correct group for Helium? | FmQoSenbtnU | He only moved it there because it has the same electron configuration as group 2 (s2), but helium behaves as a noble gas not as a metal, so it is in group 18. |
At 04:44, in the column heading, shouldn't it be - s, px, py, pz? pz came first. | FmQoSenbtnU | Thank you for clarifying my doubt! :) |
at 2:55, what makes electrons go close to the nucleus sometimes, but sometimes far away? | FmQoSenbtnU | what I think Sal is trying to say is that the electrons fill up a cloud and that if we want to map the area where the electrons are 90% of the time, that they would be within a certain regions. In that region of around 90% probability, you will find electrons close to the nucleus and those that are not so close. As we advance in the course, we will later learn about Electron Shielding, and other effects that explain such positioning, but that will be explained later. |
At 13:30, when he is giving the electron configuration for Silicon (Si) how does he know to put 6 for 2p? Do you have to just guess or is there something that can indicate this? | FmQoSenbtnU | Its actually the highest number of electrons that can go into p orbital. There is a rule for that. |
At 3:49, I still do not get the fact of putting and what does it mean when you put 1s2? | FmQoSenbtnU | In 1s², the 1 is the number of the energy state and s is the type of orbital in that state So, 1s tells you that you have an s orbital in the lowest energy state. The superscript tells you how many tells you how many electrons are in that orbital. So 1s² tells you that you have two electrons in an s orbital in the lowest energy state. |
@6:10, why are P-sub-z orbitals in the vertical direction? I thought that was the y-direction. | FmQoSenbtnU | When looking at a coordinate plane it appears that the y axis is going up and down but in reality it is flat so it is going back and forth. and the x axis is going side to side. the z axis comes in when talking about 3 dimensional things. z goes up and down. |
What is Tetris? (3:10) | FmQoSenbtnU | It s a game. Shapes fall from above and u hav 2 make it fall in such a way that a row is completed. If that happens, the row vanishes. the game is over when the stacked shapes touch the top |
at 10:38 IS Helium in the s or p block and whats the definition of a shell. | FmQoSenbtnU | s block- only 2 electrons fill the 1st energy level (1s2). A shell is the energy level that the electrons fill. |
At 5:50, when he is naming the orbitals, what do the S, P, D, and F stand for? | FmQoSenbtnU | s , p , d and f are names for orbitals. They were originated from descriptions of the spectral lines resulting from electron spectroscopy experiments on atoms within each of the blocks of the periodic table. They stand for sharp, principal, diffuse and fundamental |
At 12:35 in the video, I have a question about the periods. I understand the 1s1 and 1s 2. I don't understand Li since its in period 2 why would it not be 2s3? Thanks! | FmQoSenbtnU | Because s shells can only hold two electrons. p shells hold 6, d shells hold 10, and f shells hold 14. |
@ 8:53, sal says that the first electron goes into the Pz orbital. doesnt it go into the Px orbital or does that matter? | FmQoSenbtnU | The electron can t tell the difference between Px, Py, and Pz. It can go into any of them. |
@8:03 why is it 2p^3 isntead of 1p^2? | FmQoSenbtnU | There are no 1 p shells due to the space about the atom s nucleus. Similarly, there are no 2 d or 3 f sub-shells. |
I saw the periodic table many times in the lecture and I observed and element(Dont know its name) with symbol Tc being put with a dashed square on it. Look in at 04:21. It's got 43 atomic number.
I dont understand. Is it an exceptional element or something that was discovered very much later on? | FmQoSenbtnU | Tc is Technetium , and was only discovered with the help of technology. so yes, it was discovered much later than the elements around it, and, strangely enough, very much radioactive and used in medicine. |
at 1:15, sal says that the first orbital, that is the one nearest to the nucleus has the lowest energy. but wont the closest orbital have the highest ? | FmQoSenbtnU | This is the potential energy of the electron. The electron is electrostatically attracted to the nucleus, just as you are attracted by gravity to the centre of the Earth. It takes energy to pull an object away from something that is attracting it, so the potential energy is higher as the distance increases and lower as the distance decreases. Electron energies are zero when the electron is at infinite distance from the nucleus and become more negative as the distance decreases, |
at 7:10, why are electrons designed to be with specific orbitals? | FmQoSenbtnU | How can we answer why questions like that? This is how our universe is. Why is it that way? There s no way to know. |
At 2:00 you say that the electron could be anywhere but they appear to be bounded by these non-overlapping orbitals. Can an electron really be anywhere or is there a limit to how far it can be from the nucleus? | FmQoSenbtnU | There is no limit to how far it can be, but the odds of it being very far away are so infinitesmally small that you can ignore them because it will basicially never happen in the lifetime of the universe. It s like asking is there any limit to the number of consecutive times you can roll a 6 on a die. There s no limit, but you aren t going to roll 20 in a row in your lifetime. |
At 1:22, Sal says Helium has two electrons, but doesn't he mean two protons? | FmQoSenbtnU | In a neutral atom, (i.e. one that does not have an overall positive or negative charge) the number of protons and electrons are the same. Sal was correct to say that Helium has two electrons. The neutral Helium atom has two protons and thus also two electrons. |
Why are Carbons electrons configured - 1s2, 2s2, 2p2.... Why is it 1S2? Isnt the 1 orbital just for period 1... I am talking about 8:31 in the video. | FmQoSenbtnU | You forgot about Helium from right-side of table with 1s2 configuration. You also may write like this [He]2s2 2p2 |
At 4:08 why is Sal plotting the 2s orbital(green dots) on top of the 1s orbital? They have the same diameter? Shouldn't it be bigger in diameter? | FmQoSenbtnU | Finding an electron is all about probability. If you re-watch the video, Sal mentioned that the probability of finding an electron in the 1s orbital is near to the center of the atom is very high. The 2s orbital is farther away from the center. There might be overlap between electrons in the 1s and 2s orbitals. However, the probability of finding a 2s electron near the center is very low. |
At 11:58, what is the difference 2s1 and 1s1? | FmQoSenbtnU | He is describing the electron configuration of lithium: 1s²2s1. In 1s², the 1s shows that we have an s orbital at energy level 1, and the superscript 2 tells us that there are two electrons in this orbital. In 2s1, the 2s tells us that we have an s orbital at energy level 2, and there is one electron in this orbital. |
I was still a little confused about P-orbital filling order, like with carbon and nitrogen.
Shouldn't carbons electron configuration be 1s2, 2s2, 1p2. (see 8:00)
I just wanted a little clarification on how this should be written.
(same thing with nitrogen, is it actually supposed to be 1s2, 2s2, 1p3)
*also, does it matter whether you specify x, y, or z position of the orbital? | FmQoSenbtnU | There is no 1p orbital, p orbitals start from the second shell on, so that s why they are 2p. If you need the specifics of why I can go into this but the quantum numbers videos go over this too. If you wanted to be specific you could do 2px1 2py1 2pz0 for carbon and 2px1 2py1 2pz1 for nitrogen, but generally we don t bother. Doing this would get very long and complicated around where we get to the transition metals. |
At 12:30, when you write out the electron configuration for nitrogen, why must you write 1s^2 2s^2 then 2p^3? Wouldn't just writing 2p^3 imply that all the all the electron shells underneath are "filled up"? | FmQoSenbtnU | No. Because when you go for higher configurations(more number of electrons), the electrons in the lower orbitals are not always filled before the electrons in higher orbitals. e.g. the 4s orbital. After 3s you fill 3p but after that you fill 4s and then 3d. For example, the electronic config. of titanium is 1s^2,2s^2,2p^6,3s^2,3p^6,3d^2,4s^2. |
I do understand how there's the 90% chance of finding the electron in a certain area (2:32), but there is eventually a point where it can't be right? I mean you can't have that electron be 5 light-years away, but you can have it in it's shell. Is there a defined area where the electron physically cannot be? | FmQoSenbtnU | No, there is not eventually a point where it can t be. There s only a point where it is very improbable to be. The probability of being 5 light years away is infinitesimally small. The probability of being even a few inches away is infinitesimally small. |
At 1:10, I thought there were multiple electrons in the first shell? I mean i am not the chemistry type but that's what I thought. Is that true? Cant there be at least 2 electrons? | FmQoSenbtnU | Shell n=1 holds a maximum of 2 electrons. |
At 6:59, why do you not put a three in front of the name? (i.e. 3-propanal.) Are Aldehydes not considered substituents? | oeyBfrx5RJY | The aldehyde is always going to be assumed as being on carbon 1, otherwise it wouldn t have the -al suffix. |
At 7:46 can we name the aldehyde as isohexanal .. ? help me ! | oeyBfrx5RJY | Also, iso refers to a branched carbon group (forming a Y-shape) and does NOT apply to hydrogens. Don t confuse the hydrogen on the aldehyde with a carbon - it s not a methyl group! (If it were, it would be a ketone instead of an aldehyde.) If this is difficult to see just by looking at a structure, it might help to draw C s or dots at each carbon while counting to ensure you re not including any hydrogens. |
At 7:45 why is it called 2-methyl pentanal instead of 2-methyl pentenal because it has double bond with oxygen so alkene? | oeyBfrx5RJY | An alkene is only a double bond between two carbon atoms. Because this molecule has a double bond between a carbon and an oxygen atom (and there is a hydrogen attached to the double bonded carbon), the functional group is called an aldehyde. The presence of the aldehyde is indicated in the suffix -al. |
Hi, at 2:50 can you correct my answer please ? IUPAC for "Cinnamaldehyde" will be: 3-Benzyl prop-2-eneal m I right ? :D | oeyBfrx5RJY | No. Your first answer is totally wrong (benzyl=/=phenyl) The name requires a sterochemical prefix and so is (E) 3-phenylprop-2-enal or (E) 3-phenyl-2-propenal. |
At 1:08, Sal says that sweat is mainly made up of water, so what are the rest of the constituents of sweat? I know that since sweat tastes salty, it has a salt content (NaCl), but what else it has along with water and salt, no matter how small the quantity? | _eEONOJHnEs | i found this at Chemistry.about.com... hope it helps! Perspiration consists of water, minerals, lactate and urea. On average, the mineral composition is: sodium (0.9 gram/liter) potassium (0.2 g/l) calcium (0.015 g/l) magnesium (0.0013 g/l) Trace metals that the body excretes in sweat include: zinc (0.4 milligrams/liter) copper (0.3â0.8 mg/l) iron (1 mg/l) chromium (0.1 mg/l) nickel (0.05 mg/l) lead (0.05 mg/l) |
At 2:34, Sal says that it becomes it's gassiest state. Are there more or less gassy states then? | _eEONOJHnEs | I think he might have meant gaseous instead. |
At 7:36 Sal says that 65% of us is oxygen and at 7:54 Sal then says that 18% of us is Carbon, if you add those percentages up that equals 83%. So what is the remaining 17% of us made out of? | JgYlogdtJDo | Well the building blocks of life are CHNOPS (Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur). So the other parts would be the other things I listed but I believe that hydrogen is right up there with oxygen since the human body is mostly water. Also there is going to be a tiny amount of other elements like gold and iron and other things but they would be a tiny tiny amount. |
At 0:36, what does Sal mean by "Kilojoules per mole?" Is it referring to the amount of energy that was released during the chemical reaction that broke off the phosphate group from the triphosphates? | -KE7jTXwNYs | Joules is the unit of energy. Kilojoules is [the unit of energy multiplied by 1,000]. |
what does he mean by phosphorylate a molecule at 3:45? | -KE7jTXwNYs | Phosphorylate means to add a phosphate group to the molecule, example adenine di-phosphate to tri-phosphate: ADP --> ATP |
At 14:27, you said the speed is 7.23m/s. Isn't that wrong because you are using only the height of the ramp, you did not add the radius for the cylinder. gh would be (4+2)*9.8? | 5eX5WnPDnvs | When the cylinder gets to the bottom, the center of mass will still be 2m above the ground. 4m is the change in height. |
02:56; At the split second in time v=0 for the tire in contact with the ground. How is it, reference the road surface, the exact opposite point on the tire (180deg from base) is exhibiting a v>0? Surely the finite time snap would make the two points on tire equal in v? Unless the tire is flexible but this seems outside the scope of this problem... | 5eX5WnPDnvs | Relative to the ground, the contact point has no velocity. If it did, it would be slipping, not rolling. Relative to the ground, the point 180 degrees opposite the contact point has big velocity, because the ball is rolling. Relative to the CENTER OF THE BALL, the contact point and its opposite have velocities that are equal in magnitude but opposite in direction. But we are not looking at the velocity compared to the center of the ball. We re looking compared to the ground. |
At 5:47 'r' being the radius of the ball,isn't 'rw'= tangential velocity of the a particle on the surface of the ball?And how is that equal to the velocity of center of mass? | 5eX5WnPDnvs | Watch the video again, carefully, from 3:22 to 4:28. David explains the relationship between the tangential velocity of the surface of the ball and the velocity of the center of mass. |
At 14:17 energy conservation is used which is only applicable in the absence of non conservative forces. However, isn't static friction required for rolling without slipping? | 5eX5WnPDnvs | Not if the object is already rolling. Static friction is required to apply a torque. (Also, total energy is ALWAYS conserved. MECHANICAL energy (PE + KE) is conserved in the absence of non-conservative forces. ) |
Ok Im confused, at 3:00, when discussing how cannon-bard felt that james-lange theory was inconsistent because you can experience a physiological response of increased heart-rate from running and an emotion not be triggered, Isn't that the same thing as cannon-bard theory saying that physiological response and emotion happen at the same time. My heart racing after running a mile doesn't simultaneously trigger an emotion. | FkDVucEoJpU | What he is saying is Cannon-Bard believed that you experience raised heart rate and other things without having to have an emotion to back it up, though if you do have an emotional trigger it will happen at the same time though, I m with you he could have been a little more thorough about the whole physical activation and separating it from the emotional activations. |
At 11:26, how do we calculate the pH of original buffer solution, ie : 9.33? | lsHq5aqz4uQ | We know, pH = pKa + log [A-]/[HA] kA of NH4+/NH3 = 5.6 X 10Ë-10 Therefore, pKa= -log(5.6 X 10Ë-10)= 9.25 Given, [A-] = NH3 [HA] = NH4+ So, for the given buffer solution, pH = pKa + log [NH3]/[NH4+] pH = 9.25 + log [0.24]/[0.20] pH = 9.25 + (7.9x10^-2) pH = 9.25 + 0.079 pH = 9.329 = 9.33 |
At 8:48, why is the reaction written out as NH4 reacting with H3O instead of HCL and NH4? How would I know in future problems to first react HCL and water to form H3O and then react the H3O with NH4?
(In the first example, you were able to react NH4 directly with NaOH instead of reacting the NAOH with H2O first, so why is it different with this example?) | lsHq5aqz4uQ | HCl in water exists almost exclusively as HâO⺠and Clâ», so it is chemically more correct to write the equation using HâOâº. In practice, it doesn t matter which equation you use. What matters are the concentrations of NHâ and NHââº, not the equations you produce these species. |
At 1:04, 5:48 and 10:25 why do we use the pka of NH4Cl and not NH3 in the calculations. In other problems, how would we know which pka to use? | lsHq5aqz4uQ | NH4+ and NH3 are a conjugate acid-base pair, with NH4+ being the acid. The HendersonâHasselbalch equation that is being used is defined in terms of pH and pKa. pKa refers to the acid, and hence the pKa for NH4+ is used. |
at 8:13 he says that "this is all in water", but i thought he said it was in the buffer solution (0.20M NH3 and 0.24M NH4+)? | lsHq5aqz4uQ | the brackets indicate that it is in an aqueous sol n., although the proper labeling of NH3 and NH4Cl would be NH3 (aq) and NH4Cl (aq). For practicality, it is assumed in this case, that when there are brackets around a compound (ex. [x] , [y+] ) that they are in sol n.. |
How do you know which is the acid and which is the base at 0:29 ? | lsHq5aqz4uQ | The acid will usually have one more proton (or H) than the base - this allows it to donate that proton and fit the definition of an acid. |
I am trying to solve the problem presented at 7:16 without using the Henderson - Hasselbalch equation. as I understand, I am supposed to divide the end concentration of the products by the end concentration of the reactants, and equal the result to Ka, then solve for [H+]. but the concentration of [H+] at the end of the process is 0. what am I doing wrong? | lsHq5aqz4uQ | Hi there, I m not sure where you went wrong but here is a step by step working out using that method: NH4+âH+ + NH3 Ka=[H+][NH3]/[NH4+] 5.6x10-10=[H+][NH3]/[NH4+] Original moles NH3=0.12 Original moles NH4+=0.1 New moles NH3=0.09 New moles NH4+=0.13 Conc NH3= 0.18 Conc NH4+=0.26 (5.6x10-10)/(0.18/0.26)=[H+] [H+]=8.09x10-10 -log[H+]=9.09=pH |
At 4:35, how come the initial concentration of OH- is 0.01M? If the buffer system is NH4+ +OH-->NH3 + H2O, shouldn't there already be some OH- before the sodium hydroxide is even added? | lsHq5aqz4uQ | This is the concentration of OHâ» before it reacts with the buffer. The concentration of OHâ» before the buffer is added is 2.1 à 10â»âµ mol/L. This is negligible compared with 0.01 mol/L. |
At 5:56 how do we know we put NH3 over NH4+. I thought the henderson-Hasselbaclch equation was pH=pKa +log [Conjugate base] / [Conjugate acid]? Is it because the OH- was the limiting so it has run out? | lsHq5aqz4uQ | The log term you have isn t correct, it should be log([conjugate base]/[acid]) NH3 is the conjugate base of NH4+ Does that make sense? |
At 2:49 it is said nitrogen fixing bacteria are on legumes... Are they only found on legumes? | 6rwoktPmqpY | No, that s just one example. Beans are great, though. |
At 0:51
If we are 65% Oxygen and only 19% Carbon, why are we called Carbon-based organisms? | 6rwoktPmqpY | even though we have more oxygen, carbon does more. |
@ 3:00 Did he say kudzu? Whats that? | 6rwoktPmqpY | Kudzu is a group of plants in the genus Pueraria, in the pea family Fabaceae, subfamily Faboideae. They are climbing, coiling, and trailing perennial vines native to much of eastern Asia, southeast Asia, and some Pacific Islands. |
2:10
He said a triple bond. So if the plants need it how does it break apart? does it ever break apart? | 6rwoktPmqpY | A. It s like three steel ropes in tug of war. They are strong, but put a crazy lot of people on each side or just cheat and throw acid. and they break. B. Yes, refer up to A. |