Thank you so much Dave sir, I couldn't understand this concept in my teacher's 1.5 hour lecture which I understood here with crystal clarity here in 4 minutes!! You have excellent teaching skills, I am a fan of your videos sir !!

Hello, Prof. Dave. I'm a science teacher at a high school in Tokyo. So I enjoy watching and learning your movies. I'm currently teaching organic chemistry, hydrocarbon first of all. I hope we can exchange some topics, or info. The thing is I did the lecture about this topic the other day. So I noticed the turn of the absorption of water and CO2 was different. They're usually removed, absorbed with CaCl2, and soda lime. The latter can absorb both ones, so water should be removed first of all. Of course your lecture has no problem in itself. Thank you.

That is superb Prof. If i keep on watching your videos i will never be the same again. God bless you

Explained 1/3 of a chapter in ~4 minutes which took my teacher to teach 4 weeks, LOL! Thank you Professor Dave

Good idea "check comprehension“ Physics videos so oftenly make u believe you get it... But not

Prof. Dave you are my hero!

Nice to meet you again proffesor dave Nice video

It can be like C = 1.2g = 0.1 mol H = 1.45-1.2 = 0.25 = 0.25 mol C : H = 0.1 : 0.25 = 2 : 5

I would like to know iw the general chemistry order playslist as the mathematics one ? ( Meaning it's going from 0 to 1000 ) ? Because I have a more hard time to understand the general chemistry one , there is so many things that we do not know but that are already appearing here . Exemple at 0:31 when professor daves talk about combustion but by learning chemistry only from this playlist we dont know what is it yet !

Thank you very much

What's the name of the method of separating carbon dioxide and water when hydrocarbons were burned?

Why are the percentages used to calculate the empirical formula and not the actual weight, as usual, to determine the moles?

Huge love n appreciation from India

At the end of the day you really have to know amu's to make any of this work.

At 3:15 in the top left, why did he multiply by 12.0g C/44.0g CO2? I thought the denominator and the nominator should be equal.

How can we count that there are x numbers of protons neutrons and electrons then we can't see atom it self ?

...st the end during checking comprehention, can someone PLEASE explain to me how 6.90:17.1 = 2:5 ??? ...and how to calculate it manually ? tY

Great videos! My chemistry days are well in the past but one thing that confused me... when specifying grams per mole why do you use whole number amu/s of 16 and 12 for O and C, but 1.008 for H. I must have missed something.

@carmenraad5293

3 жыл бұрын

I wondered the same exact thing. Maybe because you cant round hydrogen???

So I assume this is the old way of doing like Mass spectroscopy or I guess the precursor to it?

what if we have an inorganic Compound such as layered double hydroxide which has hydrocarbon inside. then, what happens to that inorganic compounds hydrogens. are they counted in the resulting percentages? tnx for your awesome channel.

@ProfessorDaveExplains

7 жыл бұрын

good question! i think this technique really only works for simple hydrocarbons and basic derivatives.

This lecture removed my confusion....

Hello Professor! I am so grateful for your videos. Content like this can have a big impact on society as the more students ***understand*** the basis of science, the more likely we are to reach further! I have a question as well, on min 2:40 you gave the molecular mass of benzene (78 a.m.u.) in order to get its molecular formula. My question is, how could one know the molecular mass without having the molecular formula first? that way seems to make more sense to me. Was it discovered with experiments as interesting as the one to discover the percent composition of benzene? The second question was whether the quotient of the molecular masses of the molecular and empiric formulas was always a whole number. It seems it will always be but, is there any instance it would not? can we say that when it is not a whole number, we have done something wrong? Thank you again and again!

@ProfessorDaveExplains

6 жыл бұрын

very good question! i know there are some clever ways to do it using analytical chemistry. freezing point depression, stuff like that. but i'm not really sure what technique we used for this kind of stuff initially! and second yes, the molecular mass will always be a multiple of the empirical formula mass, as the empirical formula is the lowest whole number ratio of the elements. otherwise there was an error!

@gabriels2395

6 жыл бұрын

Thank you for replying Professor Dave!

@blackpink5937

9 ай бұрын

​@@ProfessorDaveExplainsin checking comprehension how did you convert 6.90:17.1 into 2:5 ...what did you divide it with. My teacher taught me you divide both the ratios with the least quotient.

how did u find the ratio?

where did on the check comprehension for 6.90:17.1 = 2:5 come from? i just cant see it.

@suzaneoriordan4366

2 жыл бұрын

You divide by 3.45 and round off for 17.1

Prof. Dave, how do you know a molecular mass of an unknown sample? If you don't know empirical/molecular formula in the first place (as we need to do combustion experiment to find one). Thank you so much in advance!

@ProfessorDaveExplains

6 жыл бұрын

good question! these days the best method would be mass spectrometry. i have a tutorial on this in my organic chemistry series if you want to know more!

@julladalao4533

6 жыл бұрын

Thank you so much :)

@julladalao4533

6 жыл бұрын

Thank you Professor Dave. Will have a look at it!!

Professor Dave, do you know when you round off your values as I get the percent rounding wrong

@nelksper

2 жыл бұрын

Significant figures. I recommend organic chemistry tutor's vid on it. Consists of a simple rubric with additional separate rules in addition/subtraction, and multiplication/division.

If C is 6.9 and H is 17.1 then wouldn't the ratio be C5H2 instead of C2H5? since 6.9 is multiplied by 5 and 17.1 is multiplied by 2.

@ProfessorDaveExplains

7 жыл бұрын

but it's a ratio, we are looking at the moles of each element present. there is much more hydrogen present, so that should certainly have the larger subscript.

Hi Professor Dave! I was wondering how experiments like this can get a accurate answer on the chemical composition of something by reacting it with something and measuring the products since the expected yield and the actual yields are pretty much never 100% accurate.

@musicloverhayat8402

3 жыл бұрын

We are just looking at the theory so that it is acqurate

@fgnmghdshd6056

3 жыл бұрын

@@musicloverhayat8402 so in practice it won't work?

First let me say these videos are great, thank you for making them. I was just thinking though that the example for a molecular formula was a bit redundant in the sense that you need to know the molecular mass of the molecule to calculate its molecular formula. But to know the molecular mass, you must know the molecular formula to know how many times you multiply the atomic mass of the individual elements. So do you have another example that doesn't imply that we just know a molecule's molecular mass?

@ProfessorDaveExplains

6 жыл бұрын

but this is how it went in history! these are the data chemists had and the tools they used to derive molecular formulas. there are ways to calculate mass without knowing the formula.

@toothfairy430

6 жыл бұрын

Oh, I see. For the sake of knowing more, do you have a video showing a way to alternatively calculate molecular mass? I don't see in my notes from the previous videos in this playlist an alternative method. And high five for answering so fast!

@ProfessorDaveExplains

6 жыл бұрын

i don't have a tutorial on it, when we learn this concept we just sort of take it for granted that we know the molecular mass, but one day i hope to do a series recreating old experiments! show how we came to know all the stuff we know. but i'll need quite a bit of funding for that.

@toothfairy430

6 жыл бұрын

Good luck man, hope you can do that one day

But how do you get the molecular mass in the first place without knowing the actual number of each element in a molecule?

@ProfessorDaveExplains

4 жыл бұрын

to my knowledge mass spectrometry would be the best method

How did you get a ratio of 2:5 = 6.9:17.1??? I'm really confused. I need to pass my exam. T_T Thank you in advance Prof. Dave! ^_^

@ProfessorDaveExplains

7 жыл бұрын

17.1/6.9 = 2.5! it's the lowest whole number ratio.

@blinkeverlast718

4 жыл бұрын

use 1.20g instead of 82.8g; and 0.25g instead of 17.2g in getting the equivalent moles of C & H. you will get C=0.1mol & H=0.25mols and get the ratio - 1:2.5 or 2:5 (if u multiply it by 2) and u will get C2H5 as an empirical formula, then go proceed in getting molecular formula.

@rubenlg00

3 жыл бұрын

@@blinkeverlast718 To be honest, I still don't get the logic behind the ratios, but your solution makes sense mathematically. Thank you so much!

@sumaiyapervez647

2 жыл бұрын

@@ProfessorDaveExplains how does this make sense? 2.5 becomes 2 for the carbon and 5 for the hydrogen? i am really lost

@movieviewer6345

Жыл бұрын

@@ProfessorDaveExplains how did the answer 2.5 from the division of 17.1/6.9 becomes the 2 for Carbon and the 5 for hydrogen? please help i am confused. thank you.

But how we can calculate the molecular mass if we don't know the molecular formula yet ?!

wouldn't the ratio be 1:3 in the comprehension question? since 17.1/6.9=2.47=2.5=3 for hydrogen ? rounding up to 3? and 6.9/6.9=1 for carbon?

@ProfessorDaveExplains

8 жыл бұрын

well we need our ratios to be integer values, and 2.5 is just too far away to round up or down. we need it to be extremely close to an integer in order for it to make sense.

@B.A.Gondal

8 жыл бұрын

oh i got it, so you multiply the whole formula by 2 to get the integer values since 2.5=5/2....thanks i got it now.....and btw i think we can use Euclidean Algorithm to get the integer which would give the nearest integer values for the whole formula. I know E.A is used for integer values only but i think we could use it for decimals too. When the remainder is about 0.01 we could take the quotient at that point and multiply through to get the whole number formula. Ofcourse it is for only complicated formulas....for this formula, it's a overkill....

@SaudiaTate

5 жыл бұрын

yeah this makes sense. isnt it CH3??

@SaudiaTate

5 жыл бұрын

and for the molecular formula I got C4H12

Hello sir nice lesson but in the "Checking Comprehension" I didn't understand on where you get the 2:5 ratio, please help thanks :)

@ProfessorDaveExplains

5 жыл бұрын

divide both by the smaller number, we don't have integers so we have to increase the values proportionately until we have a ratio with whole numbers

@aristonblaisekimruales8369

5 жыл бұрын

​@@ProfessorDaveExplains Oh, now I get it. Thank you very much, Professor Dave, for your subscriber from the Philippines :)

@movieviewer6345

Жыл бұрын

@@aristonblaisekimruales8369 can you explain how did he get the 2:5 ratio?

Hi dave, I son't understand why you burned 0.342 g. I also don't understand why you took 1.156 g of carbon dioxide. Can you please explain it to me?

@ProfessorDaveExplains

4 жыл бұрын

it's just random data to give an example

@ayansharma2460

4 жыл бұрын

@@ProfessorDaveExplains oh ok i thought you got that number because it was like an exact weight. Thanks!

Good

dear professor Dave, I didn't understand why we are assuming we have 100g of benzine when we find the ratios of both carbon and hydrogen knowing that we were already given a specific mass at the beginning of that substance?

@ProfessorDaveExplains

2 жыл бұрын

it's just a way of converting percentages to masses

@parvati27

2 жыл бұрын

@@ProfessorDaveExplains Thank you

Why is 12 amu being divided by 44 amu, why not subtracted?

@ProfessorDaveExplains

3 жыл бұрын

we are getting percentages

Just out of curiosity, would combustion only form CO2 and H2O? What if H2O2 or some other product was produced?

@ProfessorDaveExplains

6 жыл бұрын

hmm seems unlikely given that the O-O bond is unfavorable, i've never seen combustion producing anything other than H2O and CO2

@cooperbassham650

5 жыл бұрын

Professor Dave Explains Hi professor Dave, aren’t incomplete combustion’s possible where CO can also be produced

@azyle2104

4 жыл бұрын

@@cooperbassham650 yes , you're right

I don’t get it one bit, perhaps,take it slow

‏‪0:52‬‏ الرسم

why is this the first video that had me confused T.T

How in the ... do you weight hydrogen?

@ProfessorDaveExplains

Жыл бұрын

With a scale.

Sir we want to do extraction of ALKALOIDS TANNIN CAFFEINE ETC please make a video on extraction 🙏🙏❤️

1:02 just a bookmark