Author:
Jose Popoff

-Express the amount of a substance in terms of mole.

-Explain the relationship between mole and Avogadro´s number and apply it to the resolution of problems.

-Calculate the molar mass of a substance.

A mole is a measurement of the amount of substance. It is equal to 6.022 x 10^{23. }

1 mole = 6.022 x 10^{23 }

This concept is easy to grasp if you relate it to the "dozen" used to express an amount of 12. So, just like a dozen eggs (for instance) represents 12 eggs, a mole of eggs would be 6.022 x 10^{23} eggs.

1 mole CO_{2} = 6.022 X 10^{23} CO_{2} molecules

1 mole Fe = 6.022 X 10^{23 }atoms of Fe

1 mole NaCl = 6.022 X 10^{23} formula units (we use the term "formula unit" here since NaCl is an ionic

compound, therefore does not form molecules)

It is more useful, however, to express the moles of a substance in terms of its mass. The mass of one mole of a substance is called the **molar mass**. The molar mass of any substance is obtained by adding the individual masses of each component atom.

For example, the molar mass of CO_{2} is:

C ⇒ 1 (number of C atoms present in the formula) x 12.0107 g (molar mass of carbon; obtained from the periodic table.) = 12.0107 g

O ⇒ 2 (number of O atoms present in the formula) x 15.999 g (molar mass of carbon; obtained from the periodic table.) = 31.998 g

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Check out the video examples below to have a better idea on how to apply these concepts.

Tutorial