Transcript *The Mole* and Avogadro*s Number

“The Mole” and
Avogadro’s
Number
6.022 x
23
10
Avogadro's Mole Clip
http://www.youtube.com/watch?v=gGRQaEsQb1I
Avogadros’ Number
Molecules and atoms are extremely
small objects - both in size and mass.
Consequently, working with them in the
laboratory requires a large collection of
them.
 How large does this collection need to
be?

Avogadros’ Number
A standard needs to be introduced. This
standard is the "mole". The mole is
based upon the carbon-12 isotope.
 Carbon 12 is the most frequently
occurring isotope of the element
Carbon (98%).

Avogadro's Number!
We ask the following question: How many carbon-12
atoms are needed to have a mass of exactly 12 g?
That number is NA - Avogadro's number.
 Careful measurements yield a value for NA =
6.0221367x10^+23.


1 mole = 6.022 x 1023 particles of any substance
Say What???
EX: if we stack 1 mole of
pennies on top of one another, how
tall would the stack be?
 The answer is it would be so tall that
the stack of pennies could reach the
sun and back almost 500 million
times!


The mole concept is no more complicated
than the more familiar concept of a dozen :
1 dozen = 12 objects.
1 dozen elephants = 12 elephants
1 dozen feathers = 12 feathers
Remember???? Dimensional Analysis!
 1 mole = 6.022x 1023 atoms of any element!

More Examples…..

1 mole of gumballs is 6.022 x 1023 gumballs

1 mole of popcorn is 6.022 x 1023 kernels of
popcorn
Who weighs more??? Obviously the gumballs, but the
quantity is the SAME for both!

This much popcorn would cover the entire US
310 miles high! Whew, that’s a lot of poppin’!
Moles and Grams

The mass in grams of 1 mole of a
substance is its “atomic mass”.

What is 1 mole of oxygen???


15.9994 grams (its atomic mass)
What is 1 mole of calcium???

40.08 grams (its atomic mass)
Moles and Grams

1 mole of Carbon weighs 12 grams.


In other words…6.022 x 1023 atoms of
Carbon weighs 12 grams.
1 mole of Chlorine weighs 35.45 grams.

In other words… 6.022 x 1023 atoms of
Chlorine weighs 35.45 grams.
NOTES! Copy these conversions.
1 mole = 6.022 x 1023 atoms
1 mole = molecular weight (in grams)
Atomic Mass Unit (amu)

This is a unit that describes the mass of a
single atom!
One single atom of Carbon has a mass of 12
atomic mass units. This is very small.
 One mole of Carbon (6.022 x 1023 atoms of Carbon)
weighs 12 grams. This is very large.

Lets remember D.A.

What is the mass of exactly 150
gumballs? 10 gumballs = 21.4 g
If you want 50 eggs, how many dozens must
you buy?
 If a football player is tackled 1.7 ft short of
the end zone, how many more yards does the
team need to get a touchdown?


150 gumballs x
21.4 g
1
10 gumballs

50 eggs x 1 dozen
1
12 eggs

1.7 ft
1
x 1 yard
3 ft
=
= 321 grams
4.2 dozen
= 0.57 yards
Lets try one together!

Determine the mass in grams of 5.50
moles if iron.
Put the original number over 1.
 Decide where the unit needs to go in the
next step to cancel out.
 Decide which conversion you will use, and
plug in the numbers.

The Answer
5.50 mol Fe x 55.85 g Fe
1
1 mol Fe
= 307 g Fe
Determine the amount of iron
present in 352 grams of Fe.
The Answer
352 grams Fe x 1 mole Fe
= 6.30 mols Fe
1
55.85 grams
Practice Problems
How many grams are in 2.50 mols of S?
2. How many grams are in 3.20 mols of Cu?
3. How many mols are present in 11 grams of
Si?
4. How many mols are present in 205 g of Hg?
5. What is the mass in grams of 0.48 mol of Pt?
1.
Solutions!
1.
2.
3.
4.
5.
80.2 g S
203 g Cu
0.39 mol Si
3.1 mol Hg
94 g Pt