How can I calculate osmolarity of NaCl?

2 Answers
anor277
Dec 7, 2015

This is simply twice the molarity of NaCl(aq).

Explanation:

Osmolarity is simply the concentration of all ions in solutions. It is thus the sum of sodium ion and chloride ion concentrations, inasmuch as as sodium chloride is a strong electrolyte, and dissolves to give stoichiometric Na^(+)(aq) and Cl^(-)(aq) ions.

Ernest Z.
Jan 14, 2016

You multiply the molarity of the "NaCl" by 2.

Explanation:

An osmole (Osmol) is a mole of particles that contribute to the osmotic pressure of a solution.

For example, "NaCl" dissociates completely in water to form "Na"^+ ions and "Cl"^- ions.

"NaCl(s)" → "Na"^+("aq") + "Cl"^(-)("aq")

Each ion contributes to the osmotic pressure of the solution.

Thus, each mole of "NaCl" becomes two osmoles in solution: one mole of "Na"^+ and one mole of "Cl"^-.

A solution of 1 mol/L "NaCl" has an osmolarity of 2 Osmol/L.

EXAMPLE

Calculate the osmolarity of 0.140 mol/L "NaCl".

Solution

"[NaCl] = 0.140 mol/L"

Each mole of "NaCl" becomes two osmoles.

∴ "Osmolarity" = (0.140 color(red)(cancel(color(black)("mol"))))"/L" × "2 Osmol"/(1 color(red)(cancel(color(black)("mol")))) = "0.280 Osmol/L"

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