mole+ratios

Mole Ratios
A mole ratio is simply a ratio of one atom to another, or one compound to another. It's as simple as the ratio of boys to girls in a class, or apples to bananas in a grocery store, once you know where to look for it.

Mole ratios occur in two main places: within a molecular formula, or within a chemical formula.

In a __molecular formula__, the number of atoms gives away the ratio. For example, look at water, H 2 O.

It has two hydrogens for every water molecule, so its mole ratio of H to H 2 O is 2:1. This can be written as:

___2 H___ 1 H 2 O

What is the ratio of hydrogen to oxygen in water?

Since the formula contains 2 H's and 1 O, the ratio is 2:1, or:

__2 H___ 1 O

And sample size is irrelevant: the ratio holds true for one water molecule, or a hundred, or a billion:




 * Example:** what is the mole ratio of carbon to hydrogen in glucose, C 6 H 12 O 6 ?

Answer: since there are 6 carbons in the formula, and 12 hydrogens in the formula, the ratio is 6:12, or:

___6 C___ 12 H


 * Example:** what is the mole ratio of oxygen per molecule of glucose?



Answer: there are 6 oxygens per molecule, so the ratio is 6:1, or:

__6 O__ 1 C 6 H 12 O 6

Mole ratios can also be found in __balanced chemical equations__.

When glucose is formed from carbon dioxide and water in trees, the following chemical reaction occurs:

__6__ CO 2 + __6__ H 2 O --> C 6 H 12 O 6 + __6__ O 2

So for every glucose molecule formed, the reaction requires 6 carbon dioxide molecules:

__1 C 6 H 12 O 6 __ 6 CO 2

Or, for every 6 carbon dioxide molecules used, 6 water molecules are required.

__6 CO 2 __ 6 H 2 O

Likewise, for every glucose molecule formed, 6 oxygen molecules are released.

__1 C 6 H 12 O 6 __ 6 O 2

All of these are mole ratios.