First off, molarity is just a way of expressing the concentration of a solution.  The molarity is the number of moles per liter of solution.  A mole is defined as 6.022 x 1023 (also called Avogadro’s constant) molecules—that’s basically a six with 23 numbers behind it!    

Secondly, every element or molecule has a molecular weight, or a mass per molecule of that compound. 
For example, sodium chloride—NaCl—has a molecular weight of 58.443 grams per mole.  This is, conveniently, also the number of grams per mole of this compound. Therefore, one mole of sodium chloride will weigh 58.443 grams.  

Finally, if you know how much of your sodium chloride is in the solution, and you know how much liquid it is dissolved in, you can find the molar concentration.  
 
Here’s an example:  
 
You have 26 grams of NaCl dissolved in 0.6 liters of water.  What is the molarity?


We know that NaCl is 58.443 grams per mole, and that we have 0.6 liters of water.  We need to find
how many moles of NaCl there are per liter of water to get the molarity.  Here is how we set the problem
up:

So the final answer is 0.742 molar (M) NaCl.

A: Hi Kelly.  That's a great question!  When I need answers to health and body related questions, one place I like to look is Discovery Health's website (health.discovery.com).  Honestly, I think they do such a good job of answering your question, I'll suggest you visit their by clicking here. 

Thanks for asking, and keep those questions comming!!

A: Thanks for the question James!  Ice floats because when water freezes (that is, when the temperature drops below 32 degrees Fahrenheit or 0 degrees Celsius) it becomes less dense than when it is in its liquid form.  That is, if you had a cup of water and a cup of ice, there would be less “stuff”—fewer water molecules—in the cup of ice than the cup of water.  The reason this happens is because of water’s hydrogen bonds.

Each molecule of water is made of one oxygen atom and two hydrogen atoms which look like this. This is why we can also write ‘water’ as ‘H2O’.

The oxygen atom of one molecule will be attracted to a hydrogen atom on another molecule.  This attraction is called a hydrogen bond, because once it is formed it is not too easy to pull the molecules far away from each other (and, of course, because it involves hydrogen!).

When the water is a liquid, these hydrogen bonds are fairly flexible, allowing
the water molecules to slide past each other.  However, when the water freezes
the hydrogen bonds become less flexible, and they hold the water molecules
farther away from each other than they would if they were liquid. Because the
molecules are held farther away from each other, there are fewer of them in a
cup than there would be in a cup of liquid water. This is what makes the ice
less dense, and is the reason why the ice floats on top of liquid water!