# What are the most common questions about moles that often comes out in the exams?

##### 1 Answer

I'll try and provide some concept questions that often come up when dealing with moles. The answer will be quite long, so bear with me...

A mole is simply a way of counting atoms and molecules. Think of it like this:. let's say **cents** are the equivalent of atoms, and **dollars** are the equivalent of moles.

In the same way one dollar has *100 cents*, 1 mole has

1 dollar has

1 million dollars has

1000 trillion dollars has

One mole of *atoms*, while one mole of *molecules*.

Since one mole has

First, determine how many molecules of water are in 0.0722 moles of water

yields

Here is where molar mass comes into play. We know that one mole of oxygen weighs approximately 16.0 grams, so

Questions like this make use of mole ratios.

So, 1 mole of methane needs 2 moles of oxygen, so we could set it up like this

moles of oxygen needed.

Always think molar volume when you see STP; 1 mole of any ideal gas occupies 22.4 L at STP, so

For reaction stoichiometry, always remember that moles allow you to go from grams of one substance to grams of another by using mole ratios. Use molar masses to determine the number of moles from grams.

Here's a link to some more example problems:

http://antoine.frostburg.edu/chem/senese/101/moles/faq.shtml