How to Use Molarity to Calculate Osmolarity

Determine how water will move by osmosis.
••• Clean water and water bubbles in blue image by Suto Norbert from Fotolia.com

Water will move across a membrane, a process known as osmosis. Find which direction the water will cross the membrane by determining the osmolarity of the solutions on either side of the membrane. According to Larry McGanhey of the College of St. Scholastica, osmolarity comes from the product of the molarity of the solution and the number of particles that result from dissolving that solution with water, known as dissociation. Find the osmolarity of two solutions to determine the direction the water will flow, as water moves across a membrane into an area with a greater osmolarity.

    Find the number of particles produced by dissolving a solute in water. Use one particle for compounds with covalent bonds, as they do not dissociate in water. For example, MgCl2 becomes three particles (Mg++ and 2 Cl-) when dissolved in water.

    Multiply the number of particles produced from dissolving the solution in water by the molarity to find the osmolarity (osmol). For instance, if your have a 1 mol solution of MgCl2: 1 x 3 = 3 osmol.

    Repeat multiplying the molarity by the number of particles for the other solution to find the osmolarity.

    Compare the osmolarities of the two solutions and note that the water will move across the membrane to the solution with the higher osmolarity.

    Things You'll Need

    • Calculator
    • Molarity of solution

Related Articles

How to Calculate Isotonicity
How to Find the Number of Representative Particles...
How to Convert Micromolar to PPM
What Is the Difference Between Active & Passive Transport...
Equation for Dissociation of Ammonia in Water
How to Compute the Freezing Point of a Mixture
What Affects the Osmolarity of a Solution?
How to Convert Water Hardness in mg/L to GPG
How to Find Mass Percentage
Why Does an Egg Shrink in Different Solutions?
How to Determine Moles in Chemistry
How to Calculate Particle Concentration
How to Convert Milligrams to Fluid Ounces
Difference Between Solubility & Molarity
How to Make Bromine & Chlorine Water
Chemistry Projects for Diffusion in Liquids
How to Neutralize Food Coloring in Water
What is Turbidity & What Does It Indicate in Microbiology?
Similarities & Differences Between Osmosis & Diffusion