What is a Mole?

• To a chemist a mole is a counting unit for a substance.

• Abbreviated “mol”

• The mass of one MOLE of a pure substance is numerically equal to its ATOMIC MASS (the red number on the PT).

• We use grams to represent the unit for atomic mass.

EXAMPLES

ONE MOLE OF CARBON = 12.011 grams

ONE MOLE OF LITHIUM = 6.941 grams

ONE MOLE OF SODIUM = 22.98977 grams

ONE MOLE OF GOLD = 196.967 grams

• DO YOU GET THE IDEA?

• Calculate the mass in grams of 0.0450 moles of chromium.

• Moles Cr x grams Cr = grams Cr mole Cr

set up your conversion fraction so that mole Cr will cancel out

Sample problem(Mole to mass conversion)

• 0.0450 mol Cr X 52.00 g Cr = 2.34 g Cr

1 mol Cr

(make sure you set up your UNITS so they can cancel out)

Now you work the practice problems on page 316 of text.

11. Determine the mass in grams of each of the following:

a) 3.57 mol Al c) 3.45 mole Co

b) 42.6 mol Si d) 2.45 mol Zn

Mass to Mole Conversions

• Calcium, the fifth most abundant element on Earth, is always found combined with other elements because of its high reactivity. How many moles of calcium are in 525 grams calcium (Ca)?

mass in grams x 1 mole = number of moles

mass in grams

• 525 grams Ca x 1 mole = 13.1 moles 40.08 grams Ca

PRACTICE PROBLEMS

• 12. Determine the number of moles in each of

the following.

a) 25.5 g Ag c) 125 g Zn

b) 300.0 g S d) l.00 kg Fe

ANSWERS

• 11. a) 96.3 g Al c) 203 g Co• b) 1.20 x l03 g Si d) 1.60 x 102 Zn

• 12. a) 0.236 mol Ag c)1.91 mol Zn• b) 9.355 mol S d) 17.9 mol Fe

SO NOW YOU KNOW A MOLE

Amedeo Avagadro Was an Italian

physicist & lawyer who established that ONE MOLE of ANYTHING contains 6.02 x 10 23 representative particles.

Avagadro’s Number is

6.02 x 10 23 particles

(particles includes atoms, molecules, ions, formula units)

This is a really big number

602 000 000 000 000 000 000 000

Conversion factors:

6.02 x 10 23 representative particles 1 mole

OR

____________1 mole____________6.02 x 10 23 representative particles

moles

grams atoms

X 1/ m

olar m

ass

=

X 6.02 x 10 23 =

= 1/6.02 x 10 23 X

= molar

mas

s X

X 1/molar mass X 6.02 x 1023 =

= molar mass X 1/6.02 x 10 23 X