Help with 4 subjects

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Well I'm going through the 4th week in IB! (yihaa) and I'm writing 4 tests !

Maths Hl

Economics HL

Chemistry Hl

Biology SL

I'm not worried about the first and the last because I'm sure I'll get a 7

But the problem is in the other two.

Well I'm studying Economics, I've learnt everything by heart, and what I mean by everything is the teacher's notes, the book and the companion.

I don't know what else to study! Any ideas of course are welcome!

Last but NOT least is my chemistry test.

I'm sure I know everything. I've solved 30 exercises that the teacher gave us and also did about 36-40 question from old chemistry past papers.

But STILL there is something that I don't really get well.

What is the thinking if we want to solve the exercises that have to do with Avogadro's constant. *Max helped me with an exercise yesterday and I'm grateful!

Such as : Analytical chemists can detect amounts of amino acids as small as 2 .0 × 10–21 mol of molecules.

How many molecules does this represent?

A. 2.0 × 10^–21

B. 1.2 × 10^3

C. 6.0 × 10^23

D. 3.0 × 10^44

I really don't get it.

And also something else, I know that mol is a LOT bigger than molecule, but where in between are grams and atoms?

*By the way I didn't know where to post this question as it has almost everything in it. But since there where 2 G4 subjects I posted it here

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Analytical chemists can detect amounts of amino acids as small as 2 .0 × 10–21 mol of molecules

Each mol is 6 x 10^23 (basically Avogadro's constant which I may or may not have just remembered right ) worth of molecules. So 2.0 x 10-21 worth of mols means 2.0 x 10-21 worth of 6 x 10^23 molecules

If that makes any sense! Basically to get the answer you say that you have 2.0 x 10-21 worth of Avogadro's constant. So to get the answer you should divide 2.0 x 10-21 by Avogadro's constant to get how many molecules there are in total.

A mol is Avogadro's constant worth of molecules, you see. Grams have to do with the physical mass of whatever it is you have - a mol of oxygen will weigh more in grams than a mol of hydrogen as you have exactly the same number of molecules of each (avogadro's constant worth of molecules) but oxygen has a greater molar mass (which you can read off a periodic table, it's 16 which is equal to the protons + neutrons in an oxygen atom).

Atoms are what molecules are comprised of

I think you're confusing different sorts of units. Grams are physical weight, atoms are literally just the individual blobs of hydrogen, oxygen or whatever, molecules are two or more atoms joined together and a mol is Avogadro's constant worth of anything. You can have a mol of atoms or indeed a mol of molecules because all a mol is is a particular number of molecules, just like you can have 5 apples and 5 oranges which both have totally different weights, properties etc. but which all have in common the number 5. It's just that molecules are so crazy small we've gone for "mol" instead of writing out Avogadro's number every time.

Dunno if that helps, but I think you're probably confused by trying to merge them all together. They're not all units for measuring the same thing!

EDIT: LOL sorry, confused multiply and divide

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Analytical chemists can detect amounts of amino acids as small as 2 .0 × 10–21 mol of molecules

Each mol is 6 x 10^23 (basically Avogadro's constant which I may or may not have just remembered right ) worth of molecules. So 2.0 x 10-21 worth of mols means 2.0 x 10-21 worth of 6 x 10^23 molecules

If that makes any sense! Basically to get the answer you say that you have 2.0 x 10-21 worth of Avogadro's constant. So to get the answer you should divide 2.0 x 10-21 by Avogadro's constant to get how many molecules there are in total.

A mol is Avogadro's constant worth of molecules, you see. Grams have to do with the physical mass of whatever it is you have - a mol of oxygen will weigh more in grams than a mol of hydrogen as you have exactly the same number of molecules of each (avogadro's constant worth of molecules) but oxygen has a greater molar mass (which you can read off a periodic table, it's 16 which is equal to the protons + neutrons in an oxygen atom).

Atoms are what molecules are comprised of

I think you're confusing different sorts of units. Grams are physical weight, atoms are literally just the individual blobs of hydrogen, oxygen or whatever, molecules are two or more atoms joined together and a mol is Avogadro's constant worth of anything. You can have a mol of atoms or indeed a mol of molecules because all a mol is is a particular number of molecules, just like you can have 5 apples and 5 oranges which both have totally different weights, properties etc. but which all have in common the number 5. It's just that molecules are so crazy small we've gone for "mol" instead of writing out Avogadro's number every time.

Dunno if that helps, but I think you're probably confused by trying to merge them all together. They're not all units for measuring the same thing!

So you are saying that the right answer to the chemistry question above is A. (if I'm correct)

But the markscheme says that it is B. 1.2 x 10^3

I'm getting the whole Avogadro thing but this question is really strange

It's from a Past Paper! (November 2008)

* So because they are saying that it is mol of molecules you should multiply it with 6.023 x 10^23 and you have found it

Oh my God I finally understand it

Edited by Watermelon

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I have 2 tests in Biology and Maths HL. You're probably doing a test on cells in Biology right? But my curiosity arises as to what you are doing your maths test on. I have one on Trig1,Quadratics and Inequalities, Functions. What is yours on?

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Yeap my bio test is on cells(piece of cake ) *My bio is SL

My maths teacher was in the hospital for 2 weeks so we had only 3 lesson with him so far (he is so awesome though!)

So he is giving us a test on quadratics, inequalities and functions which are already known from last year !

Both of these tests are tomorrow!

When are yours?

Edited by Watermelon

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All that kind of maths I've done expect the absolute value function which is easy really and then some stuff in trig1. My maths test is on the 16th, the day before we break up and then Bio is on the 14th. But remember it's the easy things that people do silly mistakes in Maths and then Bio is just a matter of learning the stuff.

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