The Mole and Molar mass

[Christiano]

Hey peeps, I really need help understanding:

-What the mole is
-Avogadro's constant
-Molar mass

If someone could put it in simple terms it would be great.

My teacher cannot explain it properly because she is just a fill-in biology teacher 



-

[stonecold]

A mole is the unit of measurement in chemistry that allows you to compare one element to another.
For example, 1 mol of silver is equivalent to 1 mol of sodium in terms of the number of particles present.

It is however not correct to say that 1 gram of silver is equivalent to 1 gram of sodium in terms of the number of particles present.  Silver is heavier, and therefore, less particles, or atoms, are required to make up 1 gram compared to sodium.

Basically, the mol measures the number of particles.  Particles can be either individual atoms or molecules.

Avogrado's Constant is 6.02 x 10²³.  This basically means that 1 mol contains 6.02 x 10²³ particles.

The molar mass is the mass of 1 mol of any given element or compound. (pretty much what is on the periodic table.  MM sodium is 23, MM CO₂ is 44 etc.)

Conversions:
Mol to mass (multiply by molar mass)
Mass to mol (divide by molar mass)
Mol to particles (multiply by Avogrado's Constant)
Particles to mol (divide by Avogrado's Constant)

[Christiano]

A mole is the unit of measurement in chemistry that allows you to compare one element to another.
For example, 1 mol of silver is equivalent to 1 mol of sodium in terms of the number of particles present.

It is however not correct to say that 1 gram of silver is equivalent to 1 gram of sodium in terms of the number of particles present.  Silver is heavier, and therefore, less particles, or atoms, are required to make up 1 gram compared to sodium.

Basically, the mol measures the number of particles.  Particles can be either individual atoms or molecules.

Avogrado's Constant is 6.02 x 10²³.  This basically means that 1 mol contains 6.02 x 10²³ particles.

The molar mass is the mass of 1 mol of any given element or compound. (pretty much what is on the periodic table.  MM sodium is 23, MM CO₂ is 44 etc.)

Conversions:
Mol to mass (multiply by molar mass)
Mass to mol (divide by molar mass)
Mol to particles (multiply by Avogrado's Constant)
Particles to mol (divide by Avogrado's Constant)

Thanks, great sum up!

I am also confused about the empirical formula and molecular formula, what's the difference?

[superflya]

emprical is the simplest whole number ratio, molecular is the actual amount.

[stonecold]

Empirical formula is a formula in simplest form.
Molecular formula is the actual formula for a molecule.

Take glucose for example.
It has molecular formula C₆H₁₂O₆
Its empirical formula however is the simplified version of the molecular formula.  It just represents the ratio of atoms present relative to one another, not the actual number of atoms present. (CH₂O)

In some cases, E.F will equal M.F.
e.g. H₂O

[Christiano]

Awesome, these explanations are 10 times better than my teacher is giving, and the textbook has got a lotta mumbo jumbo that confuses the point.
Thanks!!

[Christiano]

When calculating the amount (in mol) of:

chlorine molecules represented by 1.0 x 10(to the power of 20)

How does this equate to 1.7 x 10(to the power of -4)?

Sorry, in a rush, didn't look up on how to make the numbers represent powers

[stonecold]

Basically.

n(moles) = n(molecules) / Avogrados Constant

[simonhu81292]

number of particles over avogadro's number gives you the mole
as stated by stonecold...
one mole = 6.02x10^23
therefore referring back to your question
1.0x10^20 over 6.02x10^23
will give you 1.7x10^-4
...
got beaten

[Christiano]

OH yeah, I got it, wasn't reading my CAS properly, because it came up with 0.000166. Is there a way to turn this into proper notation?

[stonecold]

yeah, go to the settings, and change some setting to say scientific.

best to do chem calculations with a scientific calculator though, as this is all you're allowed in the exams...

[vexx]

OH yeah, I got it, wasn't reading my CAS properly, because it came up with 0.000166. Is there a way to turn this into proper notation?

your calculator could have a button which does it, otherwise
0.000166=1.66x10^-4
(move the '.' however many either side.)

[Christiano]

yeah, go to the settings, and change some setting to say scientific.

best to do chem calculations with a scientific calculator though, as this is all you're allowed in the exams...

True, thanks for the tip.

[stonecold]

lol yeah, as vexx says, you can just do it in your head haha.....

[the.watchman]

Little tip, if you use calculator in class to do quick stoich questions, then I suggest defining a variable as Avogadro's number.
It saves me heaps of time!