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At 3:45, since Sal used atomic weights in his calculations and not the specific atomic masses, shouldn't it be the molecular weight of benzene, and not the mass?

UPoXG1Z3sI8

Yes, he should really have referred to the molecular weight of benzene.

What was the word he said at 7:33 when he was talking about the diabetic person? "I've drawn for you now someone with a ( ), which is diabetes, meaning they have some medical condition."

6vy5CX6vK0I

Comorbidity. Comorbidities are any other conditions that a person has at the same time as the one you re interested in.

At 2:52 he talks about RNA. What is RNA?

6vy5CX6vK0I

RiboNucleic Acid

Why would an elderly person be higher risk? 8:08

6vy5CX6vK0I

They are weaker than young men or women.

At 12:09, David says we have to break up the diagonal vector in order to substitute it into the horizontal and vertical equations. Couldn't we just solve the horizontal and vertical equations - at which point we would have a diagonal vector - and add the 45N vector to the sum of all the Forces?

24vtg9Ehr0Q

As far as I have understood your question, No you cannot do that because Force is a VECTOR QUANTITY and it must follow the vector laws of addition. To do that we have to take suitable axes and break the diagonal vector into FcosTheta and FsinTheta accordingly and proceed further.

At 9:22 what does the a in the graphic represent? I understand ay and ax but a?

24vtg9Ehr0Q

a is the overall acceleration not the horizontal or vertical acceleration.

at 13:50. Instead of using sin and cosine to find the portion of force which acts upon each axis, can we divide 45 Newtons by 90 and multiply by 30 for the x axis and by 60 for the y axis? 45N/90 times 30 = force in the x direction 45N/90 times 60 = force in the y direction does this work? It seems simpler that using cos/sin. thanks :)

24vtg9Ehr0Q

It might work in this problem, but if the angle was something a little harder, you would need to use sin and cos.

2:34. So if we have negative force, which would be negative? Mass or acceleration?

24vtg9Ehr0Q

which one of those is a vector?

Why are the Horizontal and vertical accelerations not squared when using pythagorus equation? At 9:20

24vtg9Ehr0Q

Eventually, the total horizontal force and total vertical force will be squared and added and then square rooted (it that is a word) to equal the total force in a diagonal direction, but he was not going to go through the whole problem yet.

I know that it is a long question but PLEASE PLEASE PLEASE ANSWER...🙏🙇🙏🙇 If we replace the balloon Sal draws in around 5:50 with a round glass flask and make holes in it in different levels and insert tubes with the one open side facing upwards and then we press the piston, the water spurting out of the tubes will rise upto the same level. Why?

lWDtFHDVqqk

Because when an external pressure is applied to a fluid the pressure is transmitted throughout the fluid undiminished. Hence when you press the piston the fluid or in this case water spurts out of the holes and all reach the same level.....

At 0:49 you divide F1 by A1. I do understand P=F\A but I don't understand how you can 'just' divide F1 by A1? Can you please explain this.

lWDtFHDVqqk

Thanks Lucas, I was considering A1 x D1 as a given (volume) and couldn t understand how you could divide F by A and not doing anything on the otherside but obviously Sal is considering, which he also says, F1 x D1 and he is re-writing this one. Makes sense. Thanks for the explanation.

0:37, how can the Dinput equal to Doutput?

lWDtFHDVqqk

They aren t equal. The volume input and volume output would be the same. Area x Distance = Volume. In this case, the area changes between the two, therefore so does the distance. However, volume stays the same. Pressure also stays the same. What changes is the force.

At around 3:25, he establishes that P1V1=P2V2. I was just wondering if this had anything to do with Boyle's gas law?

lWDtFHDVqqk

PV = nRT. If T is constant, then the ideal gas law becomes PV = constant, which we can say another way as P1V1 = P2V2. In other words, Boyle s Law and Charles Law are both special cases of the ideal gas law.

In 6:55, Sal draws that pipey thingy. What is it?

lWDtFHDVqqk

It is a U -shaped tube filled with a fluid.The diameter of the right-hand section is greater than the diameter of the left-hand section.

why at 9:10 does the iniatial force divided by the initial are ( 10 / 2) become 20n? Shouldn't it be 5n?

lWDtFHDVqqk

initial force by initial area is pressure(given as 10 Pa). pressure is force /area therefore force =pressure x area =10 Pa x 2 m^2 =20N

At 1:47, why does Sal multiply and divide by A1 and A2?

lWDtFHDVqqk

The left side of the equation is multiplied and divided by A1 (keeping the same value) and the right side of the equation is multiplied and divided by A2 (also keeping the same value). This is just to convert the relation to another kind of dimension, changing force by pressure.

At around 9:58 the denominator is 4m when it should be 4 m^2, but I suppose it doesn't matter since we all get it anyway.

lWDtFHDVqqk

You are right. Thank you for pointing out this mistake because it might help other confused people

At 7:36, Sal mentions area in and area out. How does the area change throughout?

lWDtFHDVqqk

The area depends on the container. Here Sal has shown a kind of a U-tube which has different areas at the ends. Thus the area is different in the in and out conditions.

At 10:01 we calculated f2 to b 40n nd f1 to b 20n...my doubt is shouldn't a larger surface area hav smaller force as compared to that of a smaller surface area have large force...or mayB im confused...what's the right way??

lWDtFHDVqqk

perhaps you just feel it that way (actually i felt it in a similar way) but there is no reason why it should be correct. See just remember one thing, the pressures at the same level should be equal and that gives that you get a larger output force where the area is larger.

at 5:00 when you discussed that water in a single container could not be compressed butt is int there oxygen in water.

lWDtFHDVqqk

yes, there is oxygen in water, but it is at a concentration of about 10 ppm (million). by the time those oxygen molecules have any noticable effect on the pressure, you d have more problems with the container breaking or stretching due to the pressure. Also, since there is no such thing as a perfect incompressible fluid in the first place (only almost perfect), the oxygen gets lost in the rounding.

At 6:00 what if the structure above the balloon is not rigid and is made up of a rubbery substance? What changes will take place in the balloon?

lWDtFHDVqqk

Well, like he said. The pressure are size in the balloon will increase uniformly.

At 6:22 Sal says that the liquid is not compressible .but what happens when we are filling the balloon with water and is trying to squeeze it.is it not becoming compressed?

lWDtFHDVqqk

No, it s not. The water moves around but its total volume does not change.

at 8:03, for l=1 ml has 3 values(-1,0&1) and has 3 kinds of orientation(on x-axis,y-axis & z-axis).Does any of the 3 values of ml correspond to any specific orientation?

KrXE_SzRoqw

No, x, y, and z are all relative. Since they end up being symmetric in the end, it doesnt matter. It just makes it easier to picture.

at 4:30 in the video it says that for n-1 of 1, l=0 which makes sense but if l=0,1,2,3........n-1 then if n=0 can l=-1 ?

KrXE_SzRoqw

No, n can only be equal to 1 or higher, so l can only be zero or a positive integer up to n-1

At 2:20, Jay says that the higher energy level has higher energy associated with it. However, in another video, Sal said that the farther the electron from the nucleus, the weaker the force on it that's why they're the ones to get pick off first. Aren't these 2 statements conflicting with each other?

KrXE_SzRoqw

No, they are consistent with one another. Energy and force are not the same thing. You need to review the concepts of work and potential energy.

At 10:00,is only p-orbital possible??What do the different axes signify?What difference does it make?

KrXE_SzRoqw

The different axes depict the spatial arrangement of the electron clouds. The arrangement of these orbitals actually dictates the orientations and angles of the bonds. To have covalent bonds, the orbital clouds need to overlap, sort of like how Legos can only be connected in certain ways.

at 3:02 , how does l represent the shape of an orbital?

KrXE_SzRoqw

If you are talking about physically, to help you understand, you can use balloons :)

At 3:10: The values of l are dependent on n. And they go on up to n-1. Why not till n?

KrXE_SzRoqw

This is just a rule that we have to accept. I don t think there is any explanation for it but limiting l to n-1 fits the experimental data. It explains why, at the n = 1 level, there is only one orbital (an s orbital) whereas as at the n = 2 level, there is an s orbital plus p orbitals. If l went up to n, rather than n-1, then there would be two types of orbitals at the n = 1 level.

At 1:51 Jay says that n is also called energy level or shell. But we cannot simultaneously determine the velocity and position of an electron, so that should rule out the existence of any well defined trajectories of the electron. Then how can we define these shells as the path the electron follows around the nucleus?

KrXE_SzRoqw

The shells are not paths. They are energy levels. Also, it s not true that we can t simultaneously determine velocity and position. What the uncertainty principle says is that there is a limit to the precision with which both of those quantities can be known simultaneously. Measurements that are less precise than that limit are no problem.

At 2:27, why does energy increase away from the nucleus ?

KrXE_SzRoqw

The electron is attracted to the nucleus. It takes energy to pull an electron away from the nucleus. The further you have to pull the electron from the nucleus, the greater the energy you have to put into the system.

at 1:17 he says that the first quantum number is called principal quantum number and this is symbolized by n which can be 1,2,3 and so on. if n symbolizes first quantum number how can it be 2,3 and so on. what does n symbolize and what is principal quantum number?

KrXE_SzRoqw

It s essentially the shell that an electron is in

At around 5:30 minutes when sir refers to the shape of p-orbital (bow tie shape), should we consider it in vertical form or can it be taken in horizontal form also?

KrXE_SzRoqw

yes obviously the answer is right

At 6:29, what is meant by the word 'Orientation"?

KrXE_SzRoqw

The word orientation refers to the physical location of a subshell for a given atom. In the example with the p orbital there are 3 different subshells, (p x , p y , and p z ) each of these subshells occupies a different space surrounding the atom. If you think about it from the perspective of the electrons, they want to be spread out as far as possible in the space they have because likes repel likes. Thus, the orbitals are spread out as much as possible and oriented in the the x, y and z planes respectively.

At 2:23 khan says abt electron having higher energy level associated with it. how does an electron have an higher energy level associated with it?

KrXE_SzRoqw

The electron by itself does not, but the atom does, and the way it does is by having the electron move against the electrical attraction of the positively charged nucleus.

What does "quantum" mean in "quantum mechanics"? Jay referred to Bohr model as "classical mechanics" (@0:40).

KrXE_SzRoqw

The quantum in quantum mechanics means that some things come in discrete amounts called quanta. In classical theories values like position and energy need to be able to take on continuous values. In classical physics there is no mechanism to describe why the Bohr model of the atom exists, there is no reason that you couldn t have electrons in any orbit and not just in the ones defined in the Bohr model. When you introduce the idea of quanta of energy this starts to make sense.

at 10:21, the whole explanation of the mag quantum is finished. But I'm still wondering, how do the integers correlate to px, py, and pz? How does that relate to -1,0, and +1?

KrXE_SzRoqw

The orbitals that come from the Schrödinger equation with m = -1, 0, -1 are impossible to graph, because they contain complex terms like e^(imφ), where i = √(-1), m is the quantum number, and φ is an angle. But certain mathematical combinations of these orbitals remove the complex terms and give the familiar px, py, and pz orbitals.

At 7:30 - 10:15 it's determined that there is the s orbital and three p orbitals. What does this imply about the location of the electron? Is the electron going to be found in one orbital or is it found in any of those p-orbitals and s-orbital?

KrXE_SzRoqw

You can have one electron on each side. For example, in the s orbital you can have 2 electrons, 2 on each side, and for the p orbital you can also have 2 on each side, but you have to keep in mind that when you are writing the electron configuration, there are 3 sets of p orbitals.

At 11:14 Why does the electron spin quantum number has 1/2 value and not 1?

KrXE_SzRoqw

All fermions have an spin of integer + 1/2. Quantum spin is a measure of the intrinsic angular momentum of a particle.

At 9:12, how do I know which axis to draw the orbital on? Does it matter?

KrXE_SzRoqw

It doesnt matter.

At 4:43 he says that n=2 therefore l= 0, 1 . I understand how he got 1 (n-1) but I don't understand why it can be both 0 and 1? Also, at the part where he is talking about Magnetic Quantum Number, I also don't quite understand how he came to the conclusion of : if l=0 then ml=0 and if l=1 then ml= -1, 0, +1. Please help

KrXE_SzRoqw

l can be any integer from 0 to n-1. It is telling you which orbitals are present for that n value. So if n = 2, l can be both 0 and 1 which correspond to 2s and 2p orbitals. ml can be integers from -l to +l including 0. If l = 0 the only possible value for ml then is also 0. If l = 1 then now ml can be -1, 0 and +1 It s more a matter of this is just how the quantum numbers are defined.

At 4:38, he says that if n is equal to two, then l is equal to 0 AND 1. Before that, he said that if n is equal to one, then l is equal to just 0. So would I be correct if I say, "If n is equal to two, then l is equal to n and 1?" I am sorry if it sounds confusing.

KrXE_SzRoqw

If n=2 its not equal to 0 and 1, it just means that the principal quantum number n=2 contains subshells that are named l=0 and l=1. n=1 contains a subshell named l=0. Its important to remember that the l=0 subshell that is WITHIN the n=1 shell is not the same as the l=0 subshell WITHIN the n=2 shell or any other shell

1:55? What in the world is that sound?

XQTIKNXDAao

Coffee maker taking apart.

7:40 when the metal expende he stop the circuit, whow do the circuit come back again ?

XQTIKNXDAao

The metal expands due to heat and since its in the bimetallic strip it bends and opens the circuit. With the circuit open it stops producing heat and allows the bimetallic strip to cool down again which un-bends the bimetallic strip allowing contact again.

At 3:01 you began discussing homologous structures as evidence for evolution. My biology teacher said that these structures are controlled by different DNA. How does that work?

Q-aGAX27SIo

You d have to elaborate on what your biology teacher said, because that s pretty vague. All DNA on everything living on this planet is different. There is not a single pair of living organisms that have identical DNA... So please elaborate on your teacher s wordage.

@ 3:28 Sal says we will go into the math for this a little bit later. Where is the video where he does go into the math for this?

ITA1rW5UraU

He might of forgotten to finish off the math. Managing and creating this whole site is hard and takes alot of time. Keep going on Sal!!!

I`m sorry but just to recap, Force is equal to acceleration multiplied by mass? "3:28"

ITA1rW5UraU

You can refer to Newton s Second Law of Motion whcih states that the Force applied to an object is proportional to the rate of change in momentum; F=(mv-mu) / t F=m(v-u) / t and since a=(v-u)/t you simply get F=ma Hope i helped!

How is the fourth quadrant (shown at 11:15) not defying the second law of thermodynamics as it is a reaction in which entropy is decreasing and takes energy. If this were possible then the entropy of the universe would be fluctuating, no? It would mean that somethings could happen that lower the entropy of the universe

J2L-X2sUigs

The fourth quadrant is not defying the second law of thermodynamics because it is using up free energy. A spontaneous reaction that decreases the entropy of the universe is not possible, as it violates the second law. Remember that the entropy of the system can decrease, as long as it compensates for that by increasing the entropy of the surroundings (universe). One way of doing so is by sucking up free energy. :)

At apx. 4:20, shouldn't this proceed via Sn1 since it's a secondary alcohol?

KPh60w6McPI

We aren t given enough information to make a good decision. The tosylate is an excellent leaving group, so I could predict SN1. But Br⁻ is a fairly good nucleophile, so I could predict SN2. If we knew the solvent, we could make a better prediction: polar aprotic = SN2; polar protic = SN1. Overall, I would predict SN1 based on the excellent leaving group.

At 3:30, unlike reactions involving primary alcohol and tertiary alcohol, the secondary alcohol first reacted with TsCl and pyridine to make it a better leaving group. Is it possible to remove the hydroxyl group without first reacting the alcohol with TsCl?

KPh60w6McPI

It is not possible to remove the OH group itself. You have to react the OH with something to make it a better leaving group, but it doesn t have to be TsCl.

At 2.35 Sal wrote delta U + P delta V = 0 which is true for adiabatic expansion only, not for adiabatic compression. Using this equation he obtained another expression at 10:44 which should again be true only for adiabatic expansion. Then at 12:54 how could it be applied for process D to A which is adiabatic compression ?

ixRtSV3CXPA

Why is it true for expansion but not compression? The only difference between the two is the sign of delta v.

Is it fair to say that 1/T * deltaT has no unit? Same goes for 1/V * deltaV Because at 6:51 Sal claims that the sum of those to zero but if they do have a unit one would be a unit of volume and one would be a temperature, adding those to up and expecting them to be 0 would be weird right?

ixRtSV3CXPA

Because the units of delta T and the T are same,if you put the units in 1/T*delta T then the units will cancel themselves.So,it has no unit.Same goes for the 2nd expression!

From about 13:02 I didn't understand how Sal changed the Ts and Tf to T1 and T2. Please help.

ixRtSV3CXPA

Yeah, S stands for start and F stands for finish, so in the segment he was working with (B to C), the start value is T1 and the finish value is T2, and in the other segment (D to A), the start value is T2 and the finish value is T1. Check the graph yourself to confirm that (at 11:30)

Could someone explain to me why at 5:56 Sal is able to divide the 'work done' term by nRT, specifically by T? If it were an isothermal process then I would understand how since T isn't varying we can just cancel it but in an adiabatic process such as this, T is a variable so it is not erroneous to divide through by it in this way ? (He has written pressure as a function of volume AND temperature NOT just volume, as would be the case when dealing with work done in an isothermal process).

ixRtSV3CXPA

I believe he can divide throughout by a constant or variable, as long as he does it equally on both sides of the equation (which he does) There is no physical significance to what he is doing, it is simply a mathematical way of rearranging the equation to make the integeration possible (seperating V and T terms) Make sense OK??

At 2:07 time, it was glazed over that P is considered to be constant in the quasi-static process. Why is obvious that P needs to be kept constant? What about the system makes it clear that pressure has be considered constant, except to allow the proof to work out? I am noting that when adiabatic systems were originally discussed in an earlier video, pressure was shown to vary, thus these approximations have been difficult to conjure for the purposes of making thermodynamic proofs. Much thanks.

ixRtSV3CXPA

Although in an infinitesimal change P is almost constant , when Sal substituted P as a function of V and T he was not keeping P constant. So, when integrating the equation the functionality of P is brought in through P = nRt/V. P is not constant in the total adiabatic process. Over an infinitesimal interval deltaP approximately equals (nRT/(V+deltaV)-nRT/V) which is much smaller than deltaV

At 1:36 he says, that pH= -log[H3O+]. Can someone explain why?

JoGQYSTlOKo

In an aqueous solution (i.e. when water is the solvent), each of the H+ (protons) donated by an acid will combine with a water molecule to form H3O+. Consequently, in water H+ and H3O+ are used interchangeably.

at 8:25 why do we add the volume of the base to the volume of the acid for the new volume??

JoGQYSTlOKo

Because the reaction occurs in an aqueous solution, the volume is additive.

at 8:36, why is the new volume of H3O+ 30ml?? I dont understand y r v adding the volume of the base?

JoGQYSTlOKo

Because this is an aqueous solution, volume is additive.

at 7:30, is that an ICE Table?

JoGQYSTlOKo

An incomplete one, but yes.

At 6:22, "3d electrons have higher energy than 4s". Could you define energy more clearly? I thought that in general the further away an electron is from the nucleus the more energy it must have, in order to resist attraction from the positive nucleus (as described in earlier video). Are we talking about kinetic energy here? Do the electrons in 3d move faster than the ones in 4s, even though electrons in 3d are closer to the nucleus?

qkLzAXUP_K0

Attraction to the nucleus is not the only factor at play in determining the energy. There is also repulsion by the electrons that are already there. The 3 shell is crowded by the time you are ready to start filling the d subshell. It s easier to go to 4s first.

At 6:14, Sal says that the outermost electrons will be in the (4S^2) sub-shell, and the electrons with the highest energy will be in the (3D^6) sub-shell, so I am unable to understand that, first of all, why aren't the outermost electrons in the last sub-shell (ie. 3D^6), and secondly, how come the electrons with highest energy in different sub-shell than the outermost electrons?

qkLzAXUP_K0

4s fills before 3d. That s just how it is. There is no rule that says 3 has to fill up completely before 4 starts. Nature does it the way nature wants to do it, not the way that seems simple to us. Nature fills the lower energy levels first. 4s is lower energy than 3d.

at 0:40 what is a S subshell?

qkLzAXUP_K0

In every electron shell electrons are further organised into subshells. The very first (innermost) shell only holds 2 electrons, and they belong to the S Subshell you asked about; there are no other subshells in the first main shell. However, the other shells can contain more than 2 electrons. The first 2 still go into the S subshells, but they re called S-2, S-3 etc. to make the names different from the first one. The extra electrons in every electron shell go into subshells other than the S.

At 5:15, why doesn't Sal write the configuration for iron like this? 1s2, 2s2, 3s2, 4s2, 2p6, 3p6, 3d6

qkLzAXUP_K0

We list the orbitals in increasing energy

At 7:33, I don't understand what Sal means by saying kilometers per second per mega parsec.

1V9wVmO0Tfg

If two points are a megaparsec away from each other, they will be moving away from each other at about 70 km/s. So, if they are 5 megaparsecs away from each other, they will be moving away from each other at 350 km/s. So, the further they get from each other, the faster they move away from each other.

At 3:09 Sal says something about a 4 dimensional sphere. What are the four dimensions and are there more dimensions after that?

1V9wVmO0Tfg

You know of the three spatial dimensions. Try to imagine one more added on top of those three. That is the 4th dimension Sal is referring to in this video. There may be even more spatial dimensions than four, but we currently have no way to test that.

If I took an inflatable balloon with some dots on it and blew some air into it, would that be a good visualization of the expansion of the universe like Sal talks about at around 2:45? Thanks ;) !

1V9wVmO0Tfg

That is the most common experiment to help people visualize the expansion of the universe. It shows that not only is the universe expanding, but also how that expansion is accelerating.

at 8:57 what is a mega parsec

1V9wVmO0Tfg

Mega means one million. So that s a million parsecs. A parsec is a measure of distance, equal to a little more than 3 light years.

At 11:15, the resonance structure of the sulfur compound looks like it has 10 electrons in its octet instead of 8 (double bonded to an oxygen, a lone pair, and two methyl compounds). Why would this happen?

bFj3HpdC4Uk

Sulfur doesn t have to follow the octet rule, lots of elements in the third period and below don t have to follow it.

At 8:30, shouldn't the electrons from the lower-left oxygen be attacking the carbon, and the pi bond going to the oxygen? Jay has it set up so that the pi bond goes straight to the C-O sigma bond.

bFj3HpdC4Uk

No, it must be the π electrons that move. Otherwise the upper right carbon would be pentavalent.

at 9:01, what keeps that negative oxygen from the already cleaved intermediate from earlier from just forming DMSO earlier on? It would seem counter intuitive to cleave, then reform, then cleave again. Not that nature always follows the easiest path given, but is there any specific reason that extra oxygen bonds to the carbon at 6:50 rather than just leaving to form DMSO?

bFj3HpdC4Uk

There is no DMS present during the reaction. The usual solvents is a mixture of methanol and dichloromethane. DMS is added for reductive workup only after the molozonide has formed.. It is easily oxidized to DMSO by the molozonide and any excess ozone.

My prof mentioned that the first step of the reaction that forms molozonide at 2:55 is a 1,3 dipolar cycloaddition. Can someone elaborate on the 1,3 dipolar part?

bFj3HpdC4Uk

The 1,3-dipolar part is referring to the ozone (O3). A dipole is a compound that is neutral overall, but carries a positive and a negative charge (like O3). The 1,3 part is because, if you number the oxygens in ozone, it is oxygens 1 and 3 that react in the cycloaddition.

At 8:51, why does sulfur attack oxygen?

bFj3HpdC4Uk

Oxygen-oxygen bonds are weak and therefore unstable, which is why they can be attacked by the sulphur (from DMS).

At 3:50, why would that happen?

bFj3HpdC4Uk

Any arrangement with three O atoms in a row is unstable. That is why ozone, :O-O=O:, is so reactive in the first place. The five-membered ring formed by the reaction of ozone with the ring, called a molozonide , is still highly unstable, because it still has 3 O atoms in a row. It could decompose back into ozone and the original alkene, but if it decomposes as in the video, we get more stable products — carbonyl groups and only two adjacent O atoms.

At 13:28 can we produce an alkane from wolf kishnerr reduction or clemensen reduction

bFj3HpdC4Uk

Yes, but the point of the reaction is to produce carbonyl groups from the alkene product.

How are the those resonance structures at 1:33 if they are the same structure just flipped, doesn't a resonance structure have to be a different configuration of electrons?

bFj3HpdC4Uk

They haven’t flipped. The O atoms are still in the same place. Only the positions of the electrons have changed. That’s why they are resonance structures.

At 12:25, Jay skips writing out the whole mechanism for the reaction again, understandably. However, he fails to mention how the side attached to only one oxygen would 'flip' over to repel the partial negative and formal negative charges on the oxygen. How could the 'flip' occur if all the carbons are connected? Do they break off and then reattach to the ring or is there another mechanism? Thanks.

bFj3HpdC4Uk

What needs to happen is that the negative charged oxygen needs to attack the other carbonyl, nothing really needs to flip there s free rotation around the single bonds.

The wave arcs drawn at around 1:30 are constantly bending up towards the surface. In the video on refraction, Sal showed how increasing density caused a bend toward the surface. However, once the wave is moving parallel to the curvature of the earth, why doesn't the angle decrease or stop? On the second half of the arc, while it is moving closer to the surface of the earth, the density is decreasing, so why doesn't the wave start curving the other direction?

yAQSucmHrAk

If the wave started curing in the other direction it would mean the layers of density would have reversed, the layers would be getting more dense. But they don t. Going up, the wave would be traveling into less dense material, thus, turning toward the left. At first I didn t get it either, but I drew it out the way Sal did in Refraction of Seismic Waves. You should also try it!! It all made sense to me after that. Good luck!!

Shouldnt the waves in a "uniform earth" move in straight lines? Why are they curving back to the surface at 1:30? I understand why they curve when they change a medium.

yAQSucmHrAk

i think he meant, uniform as in with no liquid core tho made with the same material that would still get denser as we go down

why are the waves travelling in arcs from one point to the other? Why don't they travel in a straight line? aka see time stamp 2:11.

yAQSucmHrAk

disregard again! Should ve just watched the vid previous to this!

Would it be possible, to use the equation in its form at 1:33, to get the cell potential with a temperature different to 25 °C/298K? So not under standard conditions.

QaOtsYouet0

Yes. You just have to replace the temperature (in Kelvin) and since F and R are constants they stay the same

At 6:44, does the leading strand use a RNA primer too? Or is it just DNA polymerase that comes in and starts working 5' to 3'?

eM7arWJJ3zk

Yes, the leading strand uses a RNA primer to start off the new DNA chain, and then DNA polymerase will come in.

I know that we also have a polymerase I and polymerase III. How is polymerase I different than polymerase III mentioned at 7:02?

eM7arWJJ3zk

DNA pol 1 has 5 to 3 polymerase activity in addition it has 5 to 3 and also 3 to 5 exonuclease activity. it can read and correct errors in both direction while DNA pol has only 5 to 3 exonuclease activitty. further, DNA pol 33 is the main enzyme for replication while DNA pol 1 used for replacement of RNA primer added by primase enzyme by DNA nucleotides.

Around 6:36, Sal says an RNA primer binds to the 5' end of the leading strand. Why is this RNA primer involved in DNA replication?

eM7arWJJ3zk

The DNA-polymerase can only add nucleotides on an existing strand of DNA, so the primer (located at ori - origin of replication) fakes a DNA strand with a couple of RNA nucleotides. It s just to get things going. The primer is always broken down and replaced by DNA at the end of the replication process.

At 1:38 in the video, the instructor says to leave the LED lights OFF to just test the motor. I have watched this whole series of videos over and over, and as far as I can tell the ONLY connection to the positive pole of the battery When the DPDT switches are not pressed) is THROUGH the LEDs. If that part of the circuit is interrupted (lights off) how can any current flow through the motors? Please indicate how the motors get positive current without the LEDs getting current.

VIdvlSFDl2c

maybe they are separate moters.

shouldn't sal wrote, 4p6 4d10 5s2 5p6 at 2:03 instead of 4p6 5s2 4d10 5p6 for the xenon configuration ?

L-0FkEPPdXE

The way that Sal wrote the configuration is the standard order to right the configuration. However, many chemists would be fine with your order, too, since both describe which electrons are where. If you re taking a chemistry class you should double check with your teacher, though, to see if they re okay with you using a different order.

Sal writes at about 4:00 Nd: [Xe]6s^2 4f^4. Could you write Nd: [Ba] 4f^4 too? Or do you just substitute in a noble gas and then start at the beginning of the next period? Thanks in advance!

L-0FkEPPdXE

When using this shortcut, you must start with a noble gas and work from there.

1:58, Im sorry, what does the "d" stand for, I haven't seen the equation that way before.

Bt0mz4mGddk

The d is the sign of the derivative. In this case, the d is part of the d/dt , which means change of ___ with respect to time . In this case, since it is d[A]/dt, it means the change of the concentration of A with respect to time, or the rate of how fast the concentration of A is changing as time goes on.

At 6:20, What is the centromere made of?

VXLSTd_dlKg

Centromere is the central (in case of metacentric chromosomes) part of the chromosome which is made up of: An Electron dense material in centre and two kinetochores which surround the electron dense material

At 5:09, why does Sal refer to the strand of DNA as a chromosome? I thought it was still in chromatin form? And if it hasn't formed a chromosome yet, would the duplicated strand still be called a sister chromatid?

VXLSTd_dlKg

He is correct but inside genetics there chromosomes and inside chromosones theres dna and im not 100% sure what is inside dna :) Hope this helps :)

At 5:41, are chromosomes and chromatids the same thing?

VXLSTd_dlKg

A chromatids are just pairs of chromosomes. If they split, then they would be called separate chromosomes.

At 3:01 to 3:06 of the video I have a question: Does the number of chromosomes determine the complexity of the organism?

VXLSTd_dlKg

No, not at all. Adders-tongue, a plant, has 1260 chromosomes whereas humans have 46. A few more examples; pineapples 50, elephant 56, potato 48. We wouldn t consider potatoes more complex than we are at all. Chromosome count has nothing to do with complexity, intelligence, or any other way we try to rate ourselves and other species.

Is it actually called 2,3-DPG? The notation at 6:18 says that it's called bisphosphoglycerate, so wouldn't it be BPG?

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The prefixes bis- and di- are often used interchangeably. Bisphosphoglycerate seems to be more common, but diphosphoglycerate would also be correct and both abbreviations would be correct.

At 4:23, how did carbon suddenly get another proton and become Nitrogen. Without an electron, it should Stay a Carbon isotope and become an ion (+1), right?

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In beta decay, one of the down quarks that composes a neutron (two down and one up quarks) in C-14 decays via the weak interaction into an up quark, leaving a proton (two up and one down quarks). The W⁻ boson from the weak interaction quickly decays into an electron and an anti-neutrino.

At 6:51,why did he put *"-"* before J?

enr7JqvehJs

The pattern for calculating the determinate is +,-,+. Because J is the second component, you subtract it from the determinate. The other two components (I, K) are added to the determinate.

At 1:25 the i unit vector comes up. It is a silly question - but why does it have like half a triangle on top of it...soon the j, and k have it too. (I bet I've missed something somewhere.)

enr7JqvehJs

That s just how we indicate that it is the unit vector. As opposed to, say, the square root of -1.

at 7:57 where did that minus come from

enr7JqvehJs

This comes from the definition of a determinant for a 2x2 matrix, if you have a matrix | a b | | c d | then the determinant for that matrix will be ( a*d - b*c )

Sal said at 5:08 in the video that he is going to do a proof can some one tell me where is it?

enr7JqvehJs

It s in the linear algebra playlist.

At 1:59, why does the bromine have a formal charge of +1 after it bonds with the two carbons? It has 8 valence electrons doesn't that make it negative?

FaOOx6IZxV8

No, formal charge = valence electrons - non bonding electrons - bonding electrons/2 7 - 4 - 4/2 = +1 Think about it another way, a neutral bromine has 7 electrons. This one has 2 bonds and 2 lone pairs. If the bonds were broken equally and we gave 1 electron to each atom of each bond, bromine would now have 6 electrons (2 from the 2 broken bonds and 4 from lone pairs) 7 - 6 = 1

4:02 Why the halide ion formed won't act as a nucleophile and attack the hydrogen from the H2O added to the compound?

FaOOx6IZxV8

The halide ion formed can act as a base and attack the hydrogen from the H2O added to the compound. But H2O is more likely to attack because: 1. The H2O molecules vastly outnumber the X- ions. 2. H2O is a much stronger base than X-.

I'm pretty sure I understand this, but I just want to make sure. 2:12, Jay says that the halogen attracts the magenta electrons closer to it. Wouldn't it attract both sets of electrons closer to it and you would have a choice of which carbon the water would attach. If I'm wrong and for some reason the magenta electrons are more attracted to the halogen than the other set, then why?

FaOOx6IZxV8

You are correct. In this case the substrate is symmetrical, so the halogen attracts both electrons equally.

3:00 Why wont Br- attack the partially positive C instead of H-OH?

FaOOx6IZxV8

It can. Indeed, Br- is a stronger nucleophile than water, because of its negative charge. But there are so many more water molecules present than bromide ions that the chances of attack by a water molecule are much greater than by a bromide ion. For example, the concentration of water may be about 55 mol/L The concentration of Br2 may be about 0.1 mol/L. and only a very small fraction of these exist as Br- ions at any given instant.