The Mole and Molar Mass

The Mole

The mole (abbreviated mol) can be defined as the number equal to the number of carbon atoms in 12.01 grams of carbon. Techniques for counting atoms very precisely have been used to

determine this number determine this number to be 6.022 x 10²³. This number is called Avogadro's number. One mole of something consists of 6.022 x 10²³ units of that substances. Just as a dozen eggs is 12 eggs, a mole of eggs is 6.022 x 10²³ eggs. And a mole of water contains 6.022 x 10²³ H₂O molecules. The table below shows a comparison of one mole samples of various elements.

KEY CONCEPT: A sample of an element with a mass equal to that element's average atomic mass expressed in grams contains 1 mol of atoms

Converting Grams <---> Moles <----> Atoms

Video for Converting Moles <=> Atoms

Video for Converting Grams <=> Moles

Practice Problems for Mole Conversions

Exercise 1

Using the periodic table, find the number of moles of each element

a) 20.4 g of barium

b) 62.8 g of cobalt

c) 2.0 x 10^-3g of strontium

Exercise 2

Using the periodic table, find the mass in grams of each of the following samples

a) 5.0 mol of potassium

b) 0.01205 mol of fluorine

c) 2.31 x 10-5 mol of manganese

Exercise 3

Using the period table, calculate the number of atoms present in each of the following

samples

a) 2.89 g of gold

b) 4.40 g of tungsten

c) 0.000259 g of platinum