Ch.4 - Chemical Quantities & Aqueous ReactionsWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds
Jules Bruno

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 Formula 

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: 

mol/l-w/vMolarity Formula

This would mean a solution that is 0.10 M NaCl: 

Understanding-MolarityUnderstanding Molarity

Although moles per liter are the traditional units for molarity, you can also use mg/mL because it is proportionally equivalent. 


Molarity Calculations

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. 

Grams-to-moles-conversionConverting from grams to molesSTEP 2: Convert milliliters into liters. 

mL-L-conversionConverting from mL to LSTEP 3: To find the molarity of the solution plug in the moles and liters calculated from Steps 1 and 2. 

Molarity-from-mass-volumeMolarity from mass and volume

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. 

Molarity-Formula-RearrangementMolarity Formula RearrangementSTEP 2: Convert the milliliters into liters. 

Volume-ConversionVolume Conversion

STEP 3: Multiply liters and molarity together to isolate the moles of the compound. 

mole-conversionConversion to moles

STEP 4: Convert the moles into grams. 

Moles-to-gramsConverting from moles to gramsFinally 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. 

Isolating-LitersIsolating Liters

STEP 2: Divide moles by molarity to isolate the liters of the compound. 

Molarity-Formula-LitersMolarity Formula and Liters

STEP 3: Convert liters into millimeters. 

Conversion-millimeters-to-litersConversion of L into mL

Osmolarity

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. 

Dissolution-Ionic-CompoundDissolution of KNO3

STEP 2: Now calculate the osmolarity of the solution with its equation. 

OsmolarityOsmolarity

Dilutions

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. 

Dilution-EquationDilution Equation

After Molarity 

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


Jules Bruno

Jules felt a void in his life after his English degree from Duke, so he started tutoring in 2007 and got a B.S. in Chemistry from FIU. He’s exceptionally skilled at making concepts dead simple and helping students in covalent bonds of knowledge.