Datasets:

personal006

/

khanq_ms_timestamp

like 0

At 13:17 Sal multiplies the numerator and denominator by Vsub-b/Vsub-d. Is this a valid operation and why?

sPz5RrFus1Q

Yes, it s valid. Note that you can multiply anything by 1 without changing it (1x = x), and also that dividing something by itself gives 1 (y/y = 1). Combining these, we have that multiplying anything by something over itself does not change the original value (x * (y/y) = x). This is the same as multiplying the numerator and denominator by any nonzero value, because x * (y/y) = (x * y) / y.

why does sal says at 1:19 that the process from C to D, took out less heat than the added in the process from A to B????

sPz5RrFus1Q

This follows from the previous video, but the argument goes like this. In the complete cycle the net change of the internal energy is zero. But delU = Q - W, so 0 = Q - W, or Q = W, where W, the work done in the cycle and represented by the area of the PV diagram inside the cycle, is positive. So Q = W > 0. Now Q = Q(AB) + Q(CD) where Q(AB) > 0 and Q(CD) < 0. Therefore, Q(AB) + Q(CD) = W > 0, or Q(AB) > - Q(CD), which is the questioned claim.

At 8:44, I do not understand how you find the direction the current flows. IF you do the right-hand rule for both of the possibilities, don't you get the same result. With each current, at one point, it creates magnetic field in the direction of magnetic flux and opposite direction of magnetic flux. If someone could explain this, it would be great. Thanks!

9q-T8o1HUcw

This may be a point of confusion for others too! With each current, try the right hand grip rule, only with your fist open and your palm in the direction of the field. You will find that you can trace the loop with your thumb, all the while your palm in the same direction. This means the current will also move in the same direction throughout. Can t understand? Search Right Hand Palm Rule .

At 11:36, Sal states that the enthalpy for the reaction is -74.8. When I calculated it, it came out to be -74.5. Please explain

8bCL8TQZFKo

Rounding errors most likely. Some people like to use intermediatary values for further calculations others prefer to use exact value.

At 2:23 when Sal flips the arrow so that CH4 is now a product, is there a specific rule that allows this?

8bCL8TQZFKo

No there is not a specific rule to do this. this is the requirement of the solution to flip the arrow so that we can get the CH4 on the product side where we need it.

At 9:54 Sal says " If the system does work it looses energy" , but shouldnt it gain energy according to the equation , we get that 10J of heat is ADDED to the system

aOSlXuDO4UU

If the system does work on something else, it gave energy to something else, and the principle of conservation of energy tells us the system must have less energy than it had before. If you add thermal energy to the system you can replace the energy it lost by doing work.

At 2:48, what is the meaning of "inherent macrostate of the system" ?

aOSlXuDO4UU

Inherent macrostate of the system just means The state of the system at the time of measurement in this case.

07:40 - Technically , If a balloon is expanding isn't work BEING DONE ON IT rather than it doing work ?? i mean gas molecules cant just automatically expand without an external force right ?? (e.g. I blow the balloon ) unless ur considering the gas molecules as a separate entity/system from the balloon wherein the gas molecules do work ... are you ??

aOSlXuDO4UU

The balloon expands because the gas molecules hit the inside of the balloon and push on it. That work is being done BY the gas molecules ON the balloon. Your intuition is that this can t happen all by itself, and you are right that a balloon in equilibrium wont just suddenly start expanding. But if heat is added to the balloon, the gas molecules would become more energetic and do work that expands the balloon.

At 5:55 why sal is comfortable with ∆E=Q+W and avoids using ∆E=∆Q+∆W? can you explain it ?

aOSlXuDO4UU

That is because heat and work actually alredy represent a certain change! You might know that work is defined as an integral, thus represents a change (you can easily look this up). Same goes for heat, which has as unit the Joule as well. So when you say Delta Q, you re referring to the change of something that designates change, and that isn t what we re trying to say here.

10:27 shouldn't the blood pressure increase, due to the increase of resistance, caused by the the decraese of blood vessel diameter?

qMaVLzWnS80

The pressure should rise at the site of narrowing but past the vasculitis the blockage reduces blood pressure in the rest of the vessel past that site.

7:56 (In video). So does the pair of Homologous Chromosomes only code for one thing such as hair color or can they code for multiple things? If so what?

dNp7vErqlaA

A pair of homologous chromosomes consists of one maternal chromosome and one paternal chromosome. Each homologous pair has copies of the same genes at the same loci. Since genes are the functional unit responsible for coding a characteristic like hair colour, chromosomes can have many genes that code for different things (any phenotypic characteristic you can think of). Some traits or characteristics are coded by multiple genes.

At 4:28 Is it necessary that m0ther wiII have X? If there is an XY c0mbinati0n what w0uId be the gender? Cant it be femaIe 0r is the X recessive f0r femaIe ?

dNp7vErqlaA

Females are XX, so yes, it is necessary for a normal, ferrite woman to have an X (two in fact!). XY combo is male. X chromosome from the mother, and Y from the father.

On 3:00 Sal calls the ovum a sperm cell. Isn't the sperm cell the "tadpole"? Also when is a cell called a gamete. I know the ovum is a gamete but I'm not exactly sure about the sperm cell. For male gamete is the "tadpole" a gamete or the unification of gamete and ovum?

dNp7vErqlaA

The unification of sperm and ovum is not a gamete, it is just a zygote, but the sperm or the ovum individually is a gamete.

In the beginning, around 1:17, you say that the sperm that reaches the ovum is a "winner" because he won the race, but isn't it true that many other sperm got to the egg as well but had to deteriorate the zona pellucida, and the sperm that was lucky enough to find a spot in the zona pellucida that had already been deteriorated "wins"?

dNp7vErqlaA

yes, I believe it s the first sperm to get through the zona pellucida that wins

In the video at about 7:11 Sal mentions the 23 homologous chromosome pairs that are present in the zygote's nucleus. He gives the example that on one chromosome pair each chromosome codes for the same things (proteins) and he uses hair color as an example. Do both traits get expressed in the offspring or does the sex of the offspring determine which genes are expressed?

dNp7vErqlaA

If you re asking if, for example, the offspring is male, all traits from the father are dominant and all traits are from the mother are recessive, then no. Offspring are very unlikely to get every trait from one parent and no traits from the other.

at 4:30 he talks about the pair of sex defining chromosomes, so if it's XX you are female, and if it's XY you are male. but can it be YY?

dNp7vErqlaA

No. While there are disorders that cause unusual numbers of sex chromosomes, the X chromosome has numerous genes on it that are not found on the Y chromosome but which are essential to forming a viable body during gestation. Thus in the extremely unusual situation that a zygote had a YY, then it could not form a functional body and the embryo would die during gestation, probably very early on.

At 5:22 what did Sal meant when he said " The cross product cares about the vectors that are perpendicular to each other" ? Please help!

NnlAI4ZiUrQ

Sal has videos about cross product, which is a way to multiply vectors. It s result is maximized when the vectors you are multiplying are perpendicular to one another. It is zero when they are parallel.

At 3:04 I wondered what is the precise equation for the field lines? And are they discrete, as in quantized?

NnlAI4ZiUrQ

I can t remember the equation by head, but you can find an approximate value by considering a magnet as two monopoles at a small distance apart... Whenever you work with fields, you assume a continuity to it, but they can be considered as the manifestation of virtual particles (thus quantum-like) that carry the information hey, there s a field there!

I don't understand what Sal means when he says "monopole" at 0:45; anyone care to explain simply?

NnlAI4ZiUrQ

Think of an electron or a proton, these are single points of electric charge which would make them electric monopoles. With magnets we have never found a single point charge of magnitism so you alwasy have a North and South on every magnet which is a dipole.

At 5:20, Sal says that the cross product only cares about vectors that are perpendicular to each other. How is that so? In the video where he introduced cross products earlier, he used vectors that had an angle that had less than 90 degrees between them, so they weren't perpendicular, so cross products do work between 2 vectors that aren't perpendicular. I'm confused! (Of course I understand that no result is obtained if they are parallel as sin(0) would just be 0).

NnlAI4ZiUrQ

Thanks :) Makes logical sense to me but just hoping you re right, it didn t seem that way when Sal explained it in earlier videos but maybe he felt he didn t need to, thanks again all the same!

at 1:00 Sal atarts to draw some lines , what are these lines called ? What is the distance between each of these lines ?

NnlAI4ZiUrQ

These are called field lines. They always point from North to South. There is no specified distance between the lines, but the closer together they are (the more dense the lines are), the stronger the field at that point - and vice versa.

At 7:45, Is Webber the SI unit or Tesla?

NnlAI4ZiUrQ

SI Unit of magnetic field is Tesla which is also equal to Weber/m^2

5:51 why does a magnetic field have to be perpendicular to exert a force? why wouldn't it accelerate a charge parallel to it?

NnlAI4ZiUrQ

This was determined by experiment and how the math worked. There is no consistent way of coming up with a mathematical definition of the magnetic field without having the force on a moving particle to be perpendicular to the direction of motion and the field.

At about 5:31 he says if the velocity is perpendicular to the magnetic field then we will get a number.So my question is that if its not perpendicular to the magnetic field then what? And can anyone help me what he says at 5:50 im really confused Thank You

NnlAI4ZiUrQ

If the velocity is not perpendicular, then you have to use some trigonometry to figure out what component of the velocity is perpendicular. If the velocity is parallel, then the answer is 0.

I'm having trouble with an initial concept Sal makes around 3:05 - Why does AC = 9.81m/s^2? The 9.81 is from the force to due gravity, not centripetal acceleration. The 9.81 is in effect on the car at all points around the circle, not just at the top.

4SQDybFjhRE

Only at the top of the loop is the pull of gravity maximally unopposed by the normal force that the track applies to the car.

At 5:26, Sal says something about the traction of the road. What does he mean by traction?

4SQDybFjhRE

Traction - maximum frictional force that can be produced by two surfaces without slipping

At 1:51 how did we get acceleration as 9.81 m/s^2?

4SQDybFjhRE

That is the acceleration due to gravity, it is usually a given in any problem involving gravity on earth. A = G * m/r^2 = ((5.9736 * 10^24 kg) * ((6.67398 * 10^-11 (m^3)) / (kg (s^2)))) / ((6.371 * 10^6 m)^2) = 9.82213342 m / s2

at 4:19 what is formal charge

yg0XJWHPqOA

Charge present on the individual atom in a molecule

At 3:00, there are 3 atomic orbitals, which means there are 3 atomic orbitals. If this is the case, why don't you fill the bonding molecular orbitals (with 2 electrons) AND assign 1 electron in the anti bonding orbitals in the Frost diagram? (which would give you a non positive integer)

yg0XJWHPqOA

The cyclopropenyl carbocation has only two π electrons. There is no third electron to put in an antibonding orbital.

At 6:17 it says that it is just 4n, not 4n+2 Why? How do we know when is it 4n+2 or just simply 4n?

yg0XJWHPqOA

To be aromatic it has to have 4n+2 pi electrons. Cyclobutadiene does not have 4n+2 pi electrons and so it does not meet the criteria for aromaticity. This is explained in the video.

How come "n" is equal to zero in a Huckel's rule ? at 3:05, he says that we have 0 pi electrons in the anti bonding MO and that's why 4n = 4*0 =0, but in the previous video on stability of benzene ring we also have 0 pi electrons in the anti bonding MO but instead of putting n as a zero he put n as one. Why is that? What does n represent in the Huckel's rule ? Thank you.

yg0XJWHPqOA

I think he should have paused in between these bits. Huckel s rule gives us the number of pi electrons that mean a ring could be aromatic, the solutions to Huckel s rule are 2, 6, 10, 14, etc. It has nothing to do with the number of electrons in only the antibonding MOs, just the total number of pi electrons. n is simply an integer value starting from 0, eg 0,1,2,3

@1:56 why does he draw the triangle like that and not turned? I mean why not 2 mo in the bonding part and 1 in the anti-bong part?

yg0XJWHPqOA

because while drawing the polygon in the frost circle u always start from a point at the bottom of the circle.Similarly he drew the square of cyclobutadiene in a tilted manner so that one of its vertices touches the circle at its bottom.

At 2:22 why did he draw the triangle inverted in the frost circle? pls answer...

yg0XJWHPqOA

According to the rule ,one of its vertices should point downwards . Therefore its drawn inverted such that one of its vertices is at the base of the circle.

At 6:23, what is a torroid?

eUF59jCFcyQ

Basically the shape of a donut or bagel is a torrid.

At 2:09 is space expanding all the time?

eUF59jCFcyQ

Space will always continue to expand because the initial explosion from the Big Bang (theoretically) gave it momentum .

At 6:14 he says that we know there is a slight curvature to space. I thought this topic was still up for debate and there have been tests indicating it is actually flat.

eUF59jCFcyQ

You are correct. Sal s video is a bit out of date. Our most recent observations indicate that the universe is almost certainly flat, to within about +/- 0.5%.

At 0:16, if all the 'space' and 'matter' we know today was in that speck, what was this speck sitting in prior to the Big Bang? Nothing?

eUF59jCFcyQ

We don t know anything about the universe before the big bang. It s not even clear that there was a before the big bang. Time itself may not have existed until the big bang.

4:49 a sphere is a 3D object if it is 2D it would also be 4D and the 4D is time 5D is a tesser; tesser is the act of a tesseract which is going to one different point in an infinite small time

eUF59jCFcyQ

infinite 3d… look at my answer to cameron.norton under Sweep N Clear s question

At 5:03, Sal mentioned having a 'profound' brain might enable you to see in more than 3 dimensions. Is this actually possible for a human being? Might evolution ever get us there? Thanks!

eUF59jCFcyQ

It s possible, but improbable. More likely scientists will develop technology for seeing more dimensions.

Wait, I thought at around 4:17, that the universe is constantly expanding. If it is constantly expanding, and assuming it always will, how is the area still finite?

eUF59jCFcyQ

When you expand a finite area by a finite amount it never becomes infinite.

At 6:20 sal mentions a toroide i am sure of misspelling it but what is it?

eUF59jCFcyQ

Think of a donut.

At 2:22, Sal talks about a two-dimensional space. Isn't a sphere three-dimensional?

eUF59jCFcyQ

The surface of a sphere is 2d. The sphere itself is 3d.

At 5:50, Sal said there is a four dimensional sphere , that means there is four dimensions, what is the fourth dimension?

eUF59jCFcyQ

It is simply a fourth spatial dimension. As we only intuit three spatial dimensions in our everyday life, it is difficult to describe a fourth spatial dimension aside from pointing to analogy. So, as a two dimensional surface of a sphere is to the three dimensional sphere, our current three dimensional universe can be thought of as the surface of a four dimensional hypersphere.

at 1:40 sal starts talking about what the matter is expanding into and the edge of the universe. how is it possible that we're not expanding into something else? doesn't everything need to be within something larger?

eUF59jCFcyQ

No, it doesn t. If the universe is inside something larger, then why isn t that thing part of the universe? THe universe is everything. What s happening is that space itself is expanding, everywhere. It s not that there s some outer boundary that s moving farther and farther into some new territory.

I'm slightly confused at 2:18 . He says he has a 2-dimensional space with a finite area and no edges, and he draws a sphere. If it's a sphere, you can keep walking in one direction and come back to where you started, hence having no edges, but it's not a 2D space if it's a sphere. Thanks for your help.

eUF59jCFcyQ

For something to be N dimensional means that any point that is part of that object requires N coordinates identify its location. Even through a sphere occupies 3 dimensions any point on its surface can be specified by 2 coordinates therefore it is 2 dimensional.

At 00:46 Sal said that all the matter exploded and started to condense? Why after explosion matter started condense?

eUF59jCFcyQ

As the universe expanded, it got cooler. As it got cooler, matter could condense. Sort of like steam becomes water as it cools. Not exactly the same, but that s the idea

When a 2-dimensional space is mentioned in 2:20, I'm confused. Isn't a 2-dimensional space impossible?

eUF59jCFcyQ

I understand some of what you re saying, but those things are 3-dimensional, so it would make sense that they form very flat 3-dimensional disks.

At 10:50, aren't some galaxies travelling towards other galaxies?

eUF59jCFcyQ

yes but at the same time some galaxies are actually spreading apart.

at 0:15 Sal said that the universe was infinitely small but if Einstein made the equation E=mc^2 then if practically had no mass how did it get energy to explode?

eUF59jCFcyQ

You are mistaken in assuming that because the universe was small it no mass/energy. It had enormous mass/energy.

At 10:41 it says the universe is expanding everywhere. HOW IS THE POSSIBLE?

eUF59jCFcyQ

Why do you think it is not possible? The expansion and contraction of space is part of what Einsteins theory of Relativity describes.

0:09 Why is the Big Bang called the Big Bang? The name seems a little odd to me.

eUF59jCFcyQ

Georges Lemaitre called the theory big bang as a joke when it was first proposed because he disliked it.

At 9:47 sal said more dimensions. Can their be any more dimensions than the 3 we know?

eUF59jCFcyQ

Basically in String Theory, M Theory and even supersymmetric quantum theories have dimensions in addition to the usual 3 spacial and 1 time dimension. The extra dimensions are either to small to detect or not accessible.

At 1:33 if space itself was expanding, is it nothingness its expanding into (not even space, just the absence of matter) or is it just growing and there is nothing else around it, or nothing else had ever been there before? (I know this is a confusing question, sorry.)

eUF59jCFcyQ

At 1:33 if space was expanding that means that there is more space. Space is not nothing. It s space as in a continuous area or expanse that is free, available, or unoccupied. .That is why space is called space.Sort of like continuous free area.

At 6:24, Sal mentions something called a toroid, what is that? Also when speaking of the 4th dimension, what does it look like? Theoretically, I mean.

eUF59jCFcyQ

A toroid is a geometrical shape, similar to a doughnut, that is generated if you revolve, for instance, a circle around an axis that lies outside the circle itself. An o-ring has a toroidal shape.

At 00:16, Sal talks about how the universe started from an infinitely small point. How did this point exist, according to the Big Bang Theory?

eUF59jCFcyQ

Well, if you think of black hole theory, then it shows that these infinity small objects can exist. Since the universe is expanding, then if you turn the clock back, it should begin with everything coming from an infinitely small point.

At 0:42, Sal says that the point exploded outward. That made me wonder, could the universe implode?

eUF59jCFcyQ

It s one possible eventual fate of the universe, but we think we have ruled it out.

Hi, I'm not sure if Khan's statemant at 6:15 that "we know it has a slight curvature" is correct. I read that the universe is flat with only a very small margin of error and although it might mean that the curvature is so small that the universe appears to be flat, we can't be sure because there is no proof for this statement, or is there?

eUF59jCFcyQ

The measured curvature is so slight that it is within the margin of error of the measurements. So, it could very well be flat, or it could be curved and very big.

At 7:30 Sal says that light might not be able to ever 'go around' the universe, and that it is continually expanding. My question is, does that mean that the universe is expanding faster than the speed of light? If so, isn't the big bang and all that contradictory?

eUF59jCFcyQ

Expansion allows parts that are far enough away to recede from each other faster than the speed of light. This in no way contradicts the big bang theory.

At 7:26, Sal says that even if light were to travel around the universe, it would take an unbelievably large amount of time - so does that mean that light actually bends with a really small curvature?

eUF59jCFcyQ

If the universe is curved, then light would follow a curved path through it. Our best current evidence indicates that the universe is not curved, or if it is, the curvature has to be very, very small.

At 9:11 is there there space beyond the small sphere if not, how does it keep expanding?

eUF59jCFcyQ

There is currently no reason to think otherwise.

at about the 3:00 minute mark in the video you talk about a curved 2D finite space as a shpere... well how can a 3D object be 2D or vise versa?

eUF59jCFcyQ

the only possible way i can see this happening is if a 3D shape was sucked into a black hole the technically speaking it is a 3d shape the just looks like a 2D shape

At 1:25, I am confused. Can someone explain expanding space to me? I don't get it at all...

eUF59jCFcyQ

Space IS everything. It HAS everything. But even the best scientists don t know it completely. So, don t worry.

At 5:17, why can't you move diagonally?

eUF59jCFcyQ

that s just a combination of the other two perpendicular directions

at 3:03 sal said about 2 dimensional space but he gave the example of a sphere which is 3 dimensional

eUF59jCFcyQ

He is referring the the surface of a sphere. You can uniquely specify any point on the spheres surface with only 2 coordinates making it 2 dimensional.

At 0:23 seconds Sol as I see the speaker being called that in various comments, anyway, what is a singularity?

eUF59jCFcyQ

Of course, we re not even sure about that yet; a number of experts have doubts on the matter.

At around 6:23. he mentions something like a sphere. Can someone tell me how to spell that name, because I want to see a visual of that shape.

eUF59jCFcyQ

I believe Sal uses a sphere for a 3-D surface on a 4-D sphere to illustrate how we know space can curve. However, this is simply analogous with Earth s finite area yet no boundary idea. There is no picture that can describe 4-D because we live in a 3-D reality. Its just as abstract as asking for a picture of time. Luckily we can create mathematical models to draw these ideas and abstractions.

As Sal mentioned at 8:20 that everything in the universe goes in the same direction and follows it. So if fire a gun in the space and we are also in space, there are no limitations and blockade, will the bullet hit us back?

eUF59jCFcyQ

If the universe is curved in that way, yes. WE don t know if it is.

4:10 isn't a sphere a 3 dimensional space and a circle a 2 dimensional space? right...

eUF59jCFcyQ

Yes you are correct! Sphere 3D Circle 2D

In 3:36 , why is he finding the mole?

NM0WycKCCDU

Because that will let us find the molar ratio between the atoms which will give us the empirical formula (which is the entire point of the video)

At 6:04 shouldn't it be Hg2Cl? For every one mole of Hg we have 2 moles of Cl. Why is it HgCl2?

NM0WycKCCDU

HgCl2 means 1 Hg atom and 2 Cl atoms Hg2Cl means 2 Hg atoms and 1 Cl atom.

This may have been answered in another video, but if you got a ratio of let's say exactly 1:1.5, would you round up or round down in the empirical formula?

NM0WycKCCDU

Good question. Multiply them both by 2 so you get a ratio of 2:3.

At 5:18, where does the number .3639 come from?

NM0WycKCCDU

It is the number of moles of Hg. It is written on the right of the calculator as a rounded number (0.364)

Why do we assume that the percent compositions are in given in mass rather than in volume or numerically? Why can't the percents be saying that we have a mole ratio just over 3:1?

NM0WycKCCDU

Because atoms tend to differ widely in terms of mass. If all atoms weighed the same then we could indeed use weight percentages to determine empirical formulas (formulae?), but, as Sal showed us in this video, there are two Cl atoms for each Hg atom, instead of the one Cl atom to each three Hg atoms that the percentages seemed to indicate. In other words: There are six times fewer Cl atoms than it seemed. This is because Cl atoms are about six times LIGHTER than Hg atoms.

If the ratios aren't exact and he just rounded to 2:1, how exactly do these non-whole ratios work out in the real world? Do chemists just round the way he did to find the formula since you can't have a fractional molecule?

NM0WycKCCDU

If the ratios are reasonably close to integers (say, within a few percent), they round off as in the video. If the ratios aren t close to integers, they repeat the analysis one or more times.

At around 5:14 why did he divide it by .3636 where did he get that number from?

NM0WycKCCDU

.3639 came from the finding the number of moles in 73 grams of Mercury.

In aluminium chloride (AlCl3) the ratio of chlorine to aluminum (2.25mol:0.749mol) is about 1:3. Can someone help explain why the empirical formula is different from sal's example where in this senario the chlorine is greater in mass yet three Cl atoms are used for each Al atom in the compound.

NM0WycKCCDU

The ratio of chlorine to aluminium is 3:1, not 1:3. So the empirical formula of aluminium chloride is AlCl₃.

Why was it necesarry to change into mole form? 27% to 73% is roughly a 2:1 ratio, is it just luck that the percentage ratio and the mole ratio were similar or will this always be so?

NM0WycKCCDU

73%27% is closer to a 3:1 than 2:1 ratio. You convert it into moles so that you can get a closer estimate.

At 2:15, what is episodic memory?

45qlm6cfHgg

It is the collection of past personal experiences that occurred at a particular time and place.

Does IQ mean intelligent at 1:35?

45qlm6cfHgg

IQ itself stands for intelligence quotient. It is based off a person s score on a standardized test. Often IQ is used to measure a person intelligence. So for example a person with an IQ of 100 would have an average intelligence. I m sure Wikipedia has a much more comprehensive explanation, if mine was not helpful.

If an ion is the loss/gain of electron(s) and isotope involves the collective numerical value of protons and (sometimes changed) neutrons, is there ever an atom that can lose a proton?? How come when you have a cation, like at 6:21 with Pt+4, it doesn't add 4 of those to protons? Is it because they're electrons and it wouldn't make sense to add electrons to become protons?

zTUnjPALX_U

Atoms only gain or lose protons during radioactive processes, not during chemical reactions. If a proton is gained or lost, then the atom changes into a different element, because an element is defined by the number of protons that it has. Pt4+ is a platinum atom that has lost 4 electrons to give it a 4+ positive charge. There is no change in proton number, otherwise it wouldn t be platinum any longer.

At 3:00, a practice question is given. The problem was solved easily as the periodic table was right there, and Sal could find out the atomic number of platinum by referring to the periodic table. But, what if the same question is asked in an exam, and a periodic table is not given? How do we find out the number of protons then?

zTUnjPALX_U

You should be given a periodic table in any exam, check with your teacher. It is a silly idea to memorise the periodic table but you may have to...

at 1:12, how did you get 5 electrons instead of 6 electrons?

zTUnjPALX_U

If it lost an electron, as in some other element stole an electron from carbon. Don t overthink it too much.

At 1:12 why don't you also include the ethyl and propyl group when naming the alkene? Should you have to include the methyl, ethyl, and propyl?

GFiizJ-jGVw

Those aren t groups, they are already accounted for by saying the main carbon chain is heptene

At 1:02 how do you know if it's a methyl group or not? Why doesn't the lone hydrogen count

GFiizJ-jGVw

CH3 by itself is a methyl group

at 3:23 Sal only named the 4-methyl constituent ... you don't have to name the two big priority groups on either side of the double bond? Just saying "Z" is sufficient?

GFiizJ-jGVw

The name of the compound is 4-methylhept-3-ene. The Z specifies the configuration of the double bond. No more information is needed to completely identify the compound. Just saying Z is sufficient.

At 5:31, where the second example of an Alkene is named using the E-Z naming Scheme, would it be the same thing as 3-Bromo-Trans-Oct-3-ene?

GFiizJ-jGVw

Strictly speaking, you can use the cis/trans nomenclature only for disubstituted alkenes. Without the Br group, this would be cis-oct-3-ene. With the Br group, you have to use the E/Z notation.

At 7:20, what does LH do specifically in the male and female body? I don't think they went over that every well

f_Z1zsR9lFM

The luteinizing hormone in females stimulates ovulation. In males it stimulates testosterone production.

At 2:58,in the example of (N) ,oxygen is having a partial charge and it turns to (N) then why hydrogen with a positive charge didn't turn to a (E) and what happens when both charges come together

Z4F88tTx9-8

Sorry I m having trouble understanding your question. Could you please try rewording it?

At 0:19, what is a prime carbon?

jUUJSOM1ihU

The carbons in the sugars are given the little dashes so that they can be distinguished from any numbers given to atoms in the other rings :)

At 0:15 why does Sal say that we can look at the 5' carbon to tell if the molecule is DNA or RNA? Isn't the 5' carbon connected to a phosphate group in both RNA and DNA? The carbon he refers to later at 0:26, that distinguishes RNA from DNA, is the 2' carbon that lacks an -OH group, therefore, making the sugar deoxyribose instead of ribose.

jUUJSOM1ihU

I have not seen the video, but the ribose-deoxyribose differentiation is based on the -OH group on the second carbon only. Hence, the deoxyribose sugar, is actually named 2-deoxyribose.

At 1:20 what makes or defines that it is higher concentrated?

qbCZbP6_j48

Hi Jasmine, Concentration is defined as the amount of the constituent per unit volume of solution. Therefore, if the volume is held constant and the amount of the constituent is raised, the concentration becomes higher. Similarly, if the amount of the constituent is held constant and the volume is decreased, the concentration also becomes higher. Hope that helps :)

At 1:28-1:30, Sal says 'shining at a wavelength of light that is specifically sensitive to the solute'. What does that mean ?

qbCZbP6_j48

Depending on what is in a solution, it will absorb light at only some of the wavelengths of light. We usually choose a wavelength where the component we are studying absorbs most strongly and where other components of the solution do not absorb.

At 9:25, what is that symbol next to the "A" and what does that mean?

qbCZbP6_j48

It means is proportional to

At 10:20, he seems to be indicating that if you know the concentration and absorption of the solute, you can figure out the chemical composition? Or am I just totally off?

qbCZbP6_j48

Perhaps. If every solvent has a unique constant variable (epsilon) in the beer-lambert formula, then yes. However, this is usually not the way spectrophotometry is used; there are better ways to find composition.

So molecules can absorb light? @ 2:00

qbCZbP6_j48

Yes they can. If they do, an electron gets promoted to a higher energy level. Some (or all) of this extra energy can be transformed into vibrational energy of the molecule. And the remaining part can be radiated away by giving off light (of a lesser frequency than the one that was absorbed).

Sal, at 2:02, I heard you say "...some of this light at certain frequencies is going to be absorbed..." Did you mean wavelength instead? I know that in the analysis of DNA or RNA concentration, DNA and RNA have a maximum absorption at 260 nanometers, which explains why this technique is called UV spectrophotometry since 260 nm is within the UV range.

qbCZbP6_j48

Frequency and wavelength are sometimes used interchangeably because they can both describe the energy of a light source. Energy = (constant) * frequency = (constant) * 1/wavelength.

At 11:00, is there a unit that absorption is measured?

qbCZbP6_j48

Assuming you mean absorbance, the answer is no. There is no unit. To avoid confusion, we sometimes use abs to indicate that it is an absorbance, but there is no actual unit. The reason that there is no unit is that the units all cancel out when the computation is done.

About Absorbance at 7:57. When Sal says "The negative log of T" does he mean you take the logT and multiply it by negative 1 (-1), or does it mean 1 over the log of T (1/logT)? Like how 10^-1=1/10.

qbCZbP6_j48

He means either (-1)×logT or log(1/T). Note: log(1/T) = log1 - log T = 0 - log T = -logT. They both mean the same thing.

Nearly At 7:56, Sal said that Absorbance is equal to the negative log of T. What does log mean ?

qbCZbP6_j48

Its a logarithm. That is typically covered in Algebra II. You need to know how to work with logs and exponential functions in order to be able to do General Chemistry.

at like 5:50ish when he's finding the percent of hydrogen, can you just subtract the percentage of carbon to find the percent of hydrogen?

UPoXG1Z3sI8

Of course, but it s always good to have a double check which you would have by calculating both independently.