How to calculate Osmolarity from Molarity?

Molarity Definition

Molarity (M) is defined as the number of moles of solute present in per liter of solution. In simple words, it tells the concentration of the solute in a solution. It is expressed by (M). It states how much moles of solute is present in the given solution.

How to Calculate Molarity

Molarity Formula:

Molarity = no. of moles of solute/liters of solution

Molarity Units:

Molarity units are “moles” which is denoted or written as (mols).


Molarity Examples

Here are a few examples :

  1. If there are 6 moles of Hydrochloric Acid (HCl) dissolves in one liter 1 Liter solvent so it becomes 6 molar HCl or 6 M HCl.
  2. If there are 0.05 moles of Sodium Chloride (NaCl) dissolves in 500 ml of a 0.1 M NaCl solution. The mole’s calculation of ions hinges with their solubility.
  3. If there are 0.1 moles of Na+ ions in one-liter solution it means it is 0.1 M NaCl aqueous solution.

 What is Osmolarity in Biology

Osmolarity is basically the degree of how many solute osmoles are existing in 1 liter of a standard solution. The units of osmolarity are “osmols” (osm). Water will always move across a membrane into the solution with the higher osmolarity.

Erstwhile Osmolarity is taken alongside with term osmolality. Both they are interrelated to the measurement of osmoles’ concentration within a solution. The primary difference between these two terms is that Osmolarity is the measurement of osmoles numbers within a liter of a solution, while Osmolarity measures the number of osmoles per kilogram (Osm/kg) of solvent. Both are written in terms of millimoles per kilogram (mmol/kg) in some instances.

Osmolarity Calculation

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How to Calculate Osmolarity from Molarity?

Here in the procedure given you can able to find out Osmolarity from Molarity. To find solutions’ osmolarity you will have to find out molarity first. For the purpose to calculate Molarity utilize the following steps and find the Molarity (M) by using its formula.

  1. Molecular weight is exhibit in Grams and due to which it is known as 1 Gram-Molecular Weight. It is Molecular weight of any sort of compound in Grams.

1 Gram. Molecular Weight. = 1 mole. 

For example, if 1 mole of Glucose = 180 grams Molecular Weight.

    2.  First of all, you have to know the exact Molecular. Weight of the solute, accurate volume of the solution, and how much solute is extant in that solution volume.

3. 1 mole of any compound comprises 6.02 x 1023  particles of that solute and this also represent the Avogadro’s Law.

1 mole of solute per liter of solution =  1 molar solution  =  1 M.

    4. To compute the Molarity of a solution, use the following equation:

                                         Amount of solute (in grams) per liter

                          M = —————————————————–

                                                       Mol. Wt. of solute

    5. After this, calculate the Osmolarity of a solution by using the following equation:


                          OSM (Osmolarity)  = M ( Molarity)  x Number of Particles of Dissociation.

     6. For example: If NaCl compound is dissolved in water it dissociates into following two Ions (Na+ and Cl) and

     7. If we dissolve MgCl2 in water it dissociates into 3 ions (Mg++ and 2 Cl) one ion of Magnesium and two ions of Chloride.

     8. Lastly, our body fluids molarity is about 0.15 M and the osmolarity is about 0.3 Osm or 300 mOsm.

     9. Some ciphers which are frequently used like:

0.9 g % means = 0.9 grams per 100ml of solution (9 grams per liter)

       0.1 g % means= 0.1 grams per 100ml (1 gram per liter)

5 % glucose solution means that 5 % of the weight of the solution is comprised of Glucose. 1 liter of water weighs is 1000 grams.

    10.  So, 0.05 x 1000 = 50 grams.

    11. Therefore a 5 % solution has 50 grams of solute dissolved in one liter.