Molarity

Solution concentration can be measured in a number of different ways, but the most commonly used is molarity (M).

Molarity is the moles of solute present in exactly 1 liter of solution.

This does NOT mean that a liter of solution is present, it is just a ratio in the same way that density is. If I know that the density of something is 2.7 g/mL it does not mean that I have 1 mL or 2.7 g. 

In the same way if I know that the molarity of a solution is 4.5 mol/L it does not mean that I have 4.5 moles or that I have 1 L of solution.

The Terms

Of course understanding the above requires you to know three terms about solutions: solute, solvent and solution.

What does it all mean?

Molarity tells how concentrated a solution is. 

So, a solution that is 3.4M (pronounced 3.4 molar) is more concentrated than one that is 2.6M.

In addition, molarity allows us to relate the volume of a solution to the amount of solute present. In other words, if I know the molarity and the volume, I can determine the amount of solute. Or, if I know the amount of solute and the molarity I can determine the volume, and, of course, if I know the amount of solute and the volume I can determine the molarity.