How can I calculate osmolarity of NaCl?

2 Answers
Dec 7, 2015

Answer:

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.

Jan 14, 2016

Answer:

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"#