Molarity (moles in solutions)

1. When working with solutions it is important to know how concentrated the solution is.
2. Obviously, dropping just a pinch of sugar in some tea will be much less sweet than dumping three heaping tablespoons into the drink. The difference is the second drink is a much more concentrated sugar solution.

Same Amount of Solute in Two Different Volumes of Solvent		or	Same Volume of Solvent with Different Amounts of Solute
More Concentrated	Less Concentrated		More Concentrated	Less Concentrated

1. If you are working with acids, the concentration of the solution can tell you the difference between a substance that can be handled safely or one that can only be opened in a ventilated hood.
2. Our unit for solution concentration is MOLARITY and uses the abbreviation: M. Molarity describes how many moles are dissolved per liter of of solution not per liters of solvent.
3. It is calculated using the following formula:
   = M or (mol/L)
4. Try the following examples:
   1. What was the molarity of a solution if you took 600.0 mL of it, evaporated the water, and got 3.4 mols of solute?
   2. What is the molarity of a solution in which 1.00 grams of NaCl are dissolved in 10.0 mL of the solution?
5. Notice that molarity is moles per liter of solution, not liter of solvent. This has implications for how you will make a solution. If I handed you a pile of salt and asked you to make one liter of aqueous solution with this salt, how would you do it?

6. Let's be more specific: If I asked you to make 500.0 mL of a 3.0 M solution of NaOH. How would you do it?Click here for answer.