Making a solution with quantity (moles!)

In order to create a solution with known quantitative numbers, we must re-visit the mole.

To quantify the amount found in a solution, the concentration is calculated by the amount of moles in a solution. Molarity or concentration is the proper terminology in identifying the amount of moles per volume.

The units for Molarity is moles/L.

Since the Molarity contains the # of moles in a specified volume,  M or Molarity can be converted into Particles, Grams, or Litres of gas through the same conversion. As in for all molar conversion, moles must be the center of the conversion and be calculated first.

Example 1.  What is the molarity of a 5.00 liter solution that was made with 10.0 moles of  KBr ?

V = 5.00L

Moles = 10.0 moles KBr

Molarity = 10.0 moles / 5.0 = 2.0M of KBr

The amount of particles found in the 5.00L or the mass of KBr in the 5.00L can be also converted as long as moles are calculated first and then further converted into the desired unit.


Example 2.  A 250 ml solution is made with 0.50 moles of NaCl.  What is the Molarity of the solution?

V = 250ml or 0.25L

Moles = 0.50moles of NaCl.
Molarity = 0.50 / 0.25 = 2.00L NaCl


Why this is important?

Calculating molarity is important in solutions or solute dissolved in a solvent. The molarity allows a specified amount of quantity found in a volume that can be further be calculated / converted into grams, particles / molecules / ions.  Molarity provides the method in knowing the exact amount of a substance to dissolve into a said volume to provide the exact concentration! Cool!