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For those Chemists out there !!

Disquisition
Posts: 391
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9/6/2013 11:23:11 PM
Posted: 3 years ago
Help me understand the mole(mol)

I know that Avogadro's number is 6.02 x 10^23 which equals 1mol right?

Ok lets say we need to find the molecular mass of sugar (C12H22O11) which is
342 Daltons. But obviously we couldn't measure out each molecule so, we say 342g. With 1g = 6.02 x 10^23 Daltons and 1mol = 342g

I'm confused on why we say 342g/1mol of sugar in other words what do the grams represent.

I know this may be overly confusing but if you can understand me dilemma could you write out your answer in a detailed comprehensive fashion. If you can't understand just say so I'll try to reword.

I'd prefer people who hold a degree in chemistry/have already taken intro chem in college to comment or someone well versed in this subject.
Jack212
Posts: 572
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9/7/2013 3:01:48 AM
Posted: 3 years ago
1 mole of something is 6.02 x 10^23 of it.

So 1 mole of hydrogen is 6.02 x 10^23 hydrogen atoms.

And 1 mole of nitrogen is 6.02 x 10^23 nitrogen atoms.

In both cases, the number of atoms is approximately the same. However, nitrogen atoms are bigger and heavier than hydrogen atoms, so 1 mole of nitrogen atoms will obviously weigh more than 1 mole of hydrogen atoms. So for a given substance, we say it weighs X grams per mole (or X gmol-1), which simply means that 1 mole of it will weigh that many grams.

There's a formula that makes it simpler.

n = m/M

n = number of moles of X
m = mass of X
M = molar mass of X (mass per mole)

Beware, biologists and chemists use different units when talking about the same thing. If you see "M" in a biology textbook, they're talking about molarity, which is the number of moles per litre and referred to by chemists as concentration (represented by "c").

Hope this helps.
Bullish
Posts: 3,527
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9/7/2013 10:01:00 PM
Posted: 3 years ago
The average atomic mass (basically the number of protons + the number of neutrons) of one molecule of a substance is directly proportional to each mole of a substance. It was discovered that if you take the (atomic mass)*(6.022*10^23) molecules of any compound is equal to the (atomic mass) number of grams; This is want we refer to as a mole.

For example, (6.022*10^23) molecules of hydrogen is equal to 1.0079 grams of hydrogen. In other words, one mole of hydrogen is equal to 1.0079 grams of hydrogen.
0x5f3759df
Disquisition
Posts: 391
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9/8/2013 2:20:38 AM
Posted: 3 years ago
Alright thanks guys that cleared a few things up for me.

However, this also goes for the amount of molecules in something like sucrose right?
So if I find the molecular mass (being the sum of the atomic mass of each element in a molecule) of sugar, that is 1mol equaling 342 grams it's the same concept right?
Lordknukle
Posts: 12,788
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9/8/2013 12:03:03 PM
Posted: 3 years ago
At 9/8/2013 2:20:38 AM, Disquisition wrote:
Alright thanks guys that cleared a few things up for me.

However, this also goes for the amount of molecules in something like sucrose right?
So if I find the molecular mass (being the sum of the atomic mass of each element in a molecule) of sugar, that is 1mol equaling 342 grams it's the same concept right?

Yes. 6.02 * 10^23 molecules of sucrose are in 342 grams.
"Easy is the descent to Avernus, for the door to the Underworld lies upon both day and night. But to retrace your steps and return to the breezes above- that's the task, that's the toil."
Sidewalker
Posts: 3,713
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9/8/2013 12:56:54 PM
Posted: 3 years ago
At 9/8/2013 2:20:38 AM, Disquisition wrote:
Alright thanks guys that cleared a few things up for me.

However, this also goes for the amount of molecules in something like sucrose right?
So if I find the molecular mass (being the sum of the atomic mass of each element in a molecule) of sugar, that is 1mol equaling 342 grams it's the same concept right?

http://www.convertunits.com...

342.29648 Grams
"It is one of the commonest of mistakes to consider that the limit of our power of perception is also the limit of all there is to perceive." " C. W. Leadbeater
Andromeda_Z
Posts: 4,151
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9/8/2013 1:45:10 PM
Posted: 3 years ago
At 9/6/2013 11:23:11 PM, Disquisition wrote:
Help me understand the mole(mol)

I know that Avogadro's number is 6.02 x 10^23 which equals 1mol right?

Yep. I mole of anything is Avogadro's Number of that thing. So if you had 6.02*10^23 chairs, you'd have a mole of chairs. But nobody has that many chairs.

Ok lets say we need to find the molecular mass of sugar (C12H22O11) which is
342 Daltons. But obviously we couldn't measure out each molecule so, we say 342g. With 1g = 6.02 x 10^23 Daltons and 1mol = 342g

I'm confused on why we say 342g/1mol of sugar in other words what do the grams represent.

That means that 1 mole of sugar weighs 342 grams. When you express it as a fraction like that, it's usually so you can cancel units and such as a way to find out how many atoms of sugar are in an amount of sugar that *isn't* exactly 342g.

I know this may be overly confusing but if you can understand me dilemma could you write out your answer in a detailed comprehensive fashion. If you can't understand just say so I'll try to reword.

I'd prefer people who hold a degree in chemistry/have already taken intro chem in college to comment or someone well versed in this subject.

I don't have my degree yet, but I'm a Junior in college working on my Chem degree so i've taken a lot of these classes.
Andromeda_Z
Posts: 4,151
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9/8/2013 1:46:35 PM
Posted: 3 years ago
At 9/7/2013 3:01:48 AM, Jack212 wrote:
1 mole of something is 6.02 x 10^23 of it.

So 1 mole of hydrogen is 6.02 x 10^23 hydrogen atoms.

And 1 mole of nitrogen is 6.02 x 10^23 nitrogen atoms.

In both cases, the number of atoms is approximately the same. However, nitrogen atoms are bigger and heavier than hydrogen atoms, so 1 mole of nitrogen atoms will obviously weigh more than 1 mole of hydrogen atoms. So for a given substance, we say it weighs X grams per mole (or X gmol-1), which simply means that 1 mole of it will weigh that many grams.

There's a formula that makes it simpler.

n = m/M

n = number of moles of X
m = mass of X
M = molar mass of X (mass per mole)

Beware, biologists and chemists use different units when talking about the same thing. If you see "M" in a biology textbook, they're talking about molarity, which is the number of moles per litre and referred to by chemists as concentration (represented by "c").

From what i've seen, chemists just use brackets [ ] around a number to represent that it's in moles/Liter

Hope this helps.
Jack212
Posts: 572
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9/8/2013 3:07:35 PM
Posted: 3 years ago
At 9/8/2013 1:46:35 PM, Andromeda_Z wrote:

From what i've seen, chemists just use brackets [ ] around a number to represent that it's in moles/Liter

[H+] means "concentration of hydrogen ions". When using numbers, they write "mol dm-3" after it. When describing a generic relationship, they use "c" (e.g. c = n/v).