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Mole Concept and Mole Conversions

We have a score of items meaning 20. Then there is the dozen to mean 12 items. The mole identifies a very large number of items.

The mole is a unit that is defined as 6.023 X 10²³ particles.

It is also equal to the formula mass of a substance expressed in grams.

For example:

1 mole of H₂O = 6.023 X 10²³ molecules of H₂O = 18 grams H₂O

This statement establishes the relationship between mole units and molecule units and the relationship between mole units and gram units.

The following are examples as to how the mole concept is applied:

Mole to gram conversion

· Determine the number of grams in 4 moles of H₂O

Formula mass H₂O = (2 x 1.0) + (1 x 16) = 18

1 mole H₂O = formula mass H₂O = 18 grams H₂O

4 moles H₂O x 18 grams / 1 mole = 72 grams H₂O

Gram to Mole conversion

· Determine the number of moles in 88 grams of CO₂

Formula Mass CO₂ = (1 x 12) + (2 x 16) = 44

1 mole of CO₂ = formula mass CO₂ = 44 grams CO₂

88 grams CO₂ x 1 mole CO₂ / 44 grams CO₂ = 2 moles CO₂

Mole to molecule conversion

· Determine the number of molecules of H₂O in 3 moles H₂O

1 mole H₂O = 6.023 X 10²³ molecules H₂O

3 moles H₂O x 6.023 X 10²³ molecules H₂O / 1 mole H₂O = 18.069 X 10²³ molecules H₂O = 1.8069 X 10²⁴ molecules H₂O

Mole to Atoms Conversion

· How many atoms are present in 17.0 mol of water?

In order to convert mols of a substance to atoms one must first convert mols to molecules

STEP 1:

Mols ----> molecules

The relationship between mols and molecules is:

1 mol of any substance = 6.023 X 10²³ molecules of that substance.

17.0 moles H₂O X 6.023 X 10²³ / 1 mole H₂O = 102.4 X 10²³ = 1.02 X 10²⁵ molecules H₂O

STEP 2:

Molecules of substance ----> total atoms

That would depend upon the formula of the substance which in this case is H₂O

The subscripts that appear right after the symbol representing an element can be interpreted as atoms of that element in one molecule of the substance.

According to the formula for H₂O:

1 molecule H₂O = 2 atoms H + 1 atom O = 3 atoms total

So once you have determined the number of molecules of H₂O from step 1 you then can use the above relationship between molecules and total atoms to determine the total atoms in the number of molecules determined in step 1

1.02 X 10²³ molecules H₂O X 3 atoms / 1 molecule H₂O = 3.06 X 10²³ atoms total

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