In a solution, the solute is the smaller portion that is being dissolved by the solvent, the larger portion usually in the form of H2O. Molarity is the term used to describe the solubility of the solute within the solvent in the creation of a solution.
Molarity serves as the bridge between moles and volume. It is the concentration of a solution represented as moles of solute per liter of solution:
This would mean a solution that is 0.10 M NaCl:
Although moles per liter are the traditional units for molarity, you can also use mg/mL because it is proportionally equivalent.
From the molarity formula, you can calculate volume, grams or the moles of solute.
To calculate molarity from mass (in grams, milligrams, etc.) and volume (milliliters, liters, microliters, etc.) we do the following:
PRACTICE 1: Find the molarity from 25.0 g NaCl in 500 mL solution.
STEP 1: Convert the grams given into moles given.
STEP 2: Convert milliliters into liters.
STEP 3: To find the molarity of the solution plug in the moles and liters calculated from Steps 1 and 2.
Now we must calculate the mass from volume and concentration:
PRACTICE 2: Find the grams of NaCl from 50.0 mL of 0.120 M NaCl.
STEP 1: Rearrange the molarity formula in order to isolate the moles.
STEP 2: Convert the milliliters into liters.
STEP 3: Multiply liters and molarity together to isolate the moles of the compound.
STEP 4: Convert the moles into grams.
Finally here's how you calculate the volume from mass and concentration:
PRACTICE 3: Find the volume (in mL) of 0.110 M NaCl from 2.50 moles NaCl.
STEP 1: Rearrange the molarity formula in order to isolate the liters.
STEP 2: Divide moles by molarity to isolate the liters of the compound.
STEP 3: Convert liters into millimeters.
Ionic molarity or osmolarity represents the molarity of dissolved ions in a solution. For example, if you were asked how to calculate the osmolarity of 0.200 M KNO3.
STEP 1: Break the ionic compound into its ions.
STEP 2: Now calculate the osmolarity of the solution with its equation.
Another common idea related to molarity deals with the dilution of stock solutions. In a dilution a concentrated solution is made more diluted by adding water directly to it.
Eventually you will do calculations that connect molarity to problems with density, molarity vs molality, mole fraction, mass fraction or percent.
Beyond these calculations that deal directly with the molarity formula you can bring in stoichiometry. This brings in more complex problems dealing with solution chemistry, acid base titration, pH and pOH.