text: # Question #daedf
  
  Sep 5, 2017
  
  The osmolality of the solution is 304 mOsmol/kg.
  
  #### Explanation:
  
  An osmole (Osmol) is 1 mol of particles that contribute to the osmotic pressure of a solution.
  
  The problem here is how to convert equivalents to osmoles.
  
  The point to remember is that 1 eq of anything reacts with or produces 1 eq of anything else
  
  For example,
  
  $\text{CaCl"_2 → "Ca"^"2+" + "2Cl"^"-}$
  $\text{1 mol"color(white)(mm)"1 mol"color(white)(ml)"2 mol}$
  $\text{2 eq"color(white)(mmll)"2 eq"color(white)(mml)"2 eq}$
  
  We see that $\text{2 mol Cl"^"-" = "2 eq Cl"^"-}$, but $\text{1 mol Ca"^"2+" = "2 eq Ca"^"2+}$.
  
  For ions, the rule is, $\text{1 mol" = ncolor(white)(l) "eq}$ or
  
  $\boldsymbol{\text{1 eq" = 1/n color(white)(l)"mol}}$,
  
  where $n$ is the absolute value of the charge on the ion.
  
  Now, let's use this relationship to calculate the osmolarity of the solution.
  
  Assume we have 1 L of solution.
  
  We will set up a table for easy calculation.
  
  $\boldsymbol{\underline{\text{Amt/meq"color(white)(mll)"Ion"color(white)(mll)ncolor(white)(mll)"Amt/mOsmol}}}$
  $\textcolor{w h i t e}{m m l} 145 \textcolor{w h i t e}{m m m l} \text{Na"^"+} \textcolor{w h i t e}{m l l} 1 \textcolor{w h i t e}{m m m m m} 145$
  $\textcolor{w h i t e}{m m m l l} 3 \textcolor{w h i t e}{m m m l} \text{K"^"+} \textcolor{w h i t e}{m m} 1 \textcolor{w h i t e}{m m m m m m l} 3$
  $\textcolor{w h i t e}{m m m l l} 5 \textcolor{w h i t e}{m m m l} \text{Ca"^"2+} \textcolor{w h i t e}{m} 2 \textcolor{w h i t e}{m m m m m m l} 2.5$
  $\underline{\textcolor{w h i t e}{m m l l} 153 \textcolor{w h i t e}{m m m l} \text{Cl"^"-} \textcolor{w h i t e}{m m} 1 \textcolor{w h i t e}{m m m m m} 153}$
  $\textcolor{w h i t e}{m m m m m m m m m m m l} \text{TOTAL = 303.5}$
  
  Note that there are 153 meq of cations and 153 meq of anions, as required.
  
  $\text{Osmolarity" = "303.5 mOsmol"/"1 L" = "304 mOsmol/L}$
  
  Since the solution is so dilute, its density is almost the same as that of water, and the mass of the water is approximately 1 kg.
  
  ∴ The concentration is also 304 mOsmol/kg.