# Question #64a93

Apr 23, 2017

$\text{Osmolarity = 280 mOsmol/L}$.

#### Explanation:

An osmole (Osmol) is 1 mol of particles that contribute to the osmotic pressure of a solution.

For example, dextrose is a nonelectrolyte.

1 mol of dextrose gives 1 mol of particles in solution. So.

$\text{1 mol dextrose = 1 Osmol dextrose}$

Thus, the osmolarity of the dextrose in your solution is

$\text{Osmolarity" = (20 color(red)(cancel(color(black)("mmol"))))/(100 color(red)(cancel(color(black)("mL")))) × (1000 color(red)(cancel(color(black)("mL"))))/"1 L" × "1 mOsmol"/(1 color(red)(cancel(color(black)("mmol")))) = "200 mOsmol/L}$

$\text{KCl}$ dissociates completely in water to form ${\text{K}}^{+}$ ions and $\text{Cl"^"-}$ ions.

Thus, each mole of $\text{KCl}$ becomes two osmoles in solution: one of ${\text{K}}^{+}$ and one of $\text{Cl"^"-}$.

The osmolarity of $\text{KCl}$ in your solution is

$\text{Osmolarity" = (4 color(red)(cancel(color(black)("mmol"))))/(100 color(red)(cancel(color(black)("mL")))) × (1000 color(red)(cancel(color(black)("mL"))))/"1 L" × "2 mOsmol"/(1 color(red)(cancel(color(black)("mmol")))) = "80 mOsmol/L}$

The total osmolarity of the solution is the sum of the individual osmolarities.

$\text{Total osmolarity" = "(200 + 80) mOsmol/L" = "280 mOsmol/L}$