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Unformatted text preview: ctly 12 amu. 12 g of carbon is a nice macroscopic size to measure. The bad: there was a simple relationship between the chemical
formula and the mass when we used amu, but this lost when we
switched to grams. How do we solve this problem?
The ugly: Ans: Instead of Yotta use the mole
1 amu/1.66x10-24g =1,
(or 6.02x1023amu/ 1 g)
This is an inspired choice. The
mole will make amu to gram
conversion of chemical amounts
EASY! How many atoms are in 12 g of carbon-12? 1 C − 12 atom 1 amu 12g = 6.02214x10 23 C − 12 atoms − 24 g 12 amu 1.6605388x10 Notice: 1 amu= 1.6605x10-24 g is the same thing as
6.02214x1023 amu = 1 g. KEY IDEA: instead of using 1024 particles (Yotta-particles), let’s use
6.02214x1023 particles instead. This will make the conversion from
sub-microscopic (amu masses) to macroscopic (gram masses) easy.
A mole is defined as 6.02214x1023 (Avogadro’s Number.)
(It is simple a equivalence 1 mole = 6.02x1023 things) The Convenience of Scaling The mole is just a convenient collection of objects. A dozen (12) is used for eggs, a score (20) is used in Lincoln’s
Gettysburg address, and a ream (500) is used for paper.
A mole (6.02214x1023) is a convenient amount in chemistry. The mole together with the chemical formula enables two important
1. One nuclear particle (p or n) has a mass of ~1 amu Similarly, 1 mol of nuclear particles have a mass of 1 gram! Easy conversion from individual molecules to macroscopic amounts.
Chemical Formula 2. How does it work? Mass molecules (g) Easy conversion from macroscopic mass amounts to counting
numbers. # molecules (in mol) Therefore, grams simply count (moles, i.e. collections of particles). For the same reasons: The formula mass of a substance is
numerically equal to the mass (in grams) of 1 mol of that
This mass is known as the molar mass and is simple found
from the chemical formula and the atomic masses. Mass molecules (in g) Therefore, amu’s simply count (particles). molar mass (g/mol) = formula mass (amu)
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