# Question #6387d

##### 1 Answer

#### Explanation:

In order to find a solution's **osmolarity**, you need to know two things

how manyosmoles of soluteyou havethe volume of the solutionexpressed in liters

Basically, a solution's osmolarity tells you how many *osmoles* of solute you get **per liter of solution**.

#color(blue)(|bar(ul(color(white)(a/a)"osmolarity" = "osmoles of solute"/"liters of solution"color(white)(a/a)|)))#

Now, an **osmole** represents a **mole of solute particles** that contributes to the solution's *osmotic pressure*, which is the pressure needed to prevent the flow of water across a semi-permeable membrane.

Simply put, an osmole will tell you how many moles of particles you get **per mole of solute** dissolved in water.

*Calcium chloride*, ** soluble ionic compound** that dissociates completely in aqueous solution to form calcium cations,

#"CaCl"_ (color(red)(2)(aq)) -> "Ca"_ ((aq))^(2+) + color(red)(2)"Cl"_((aq))^(-)#

Notice that **one moles** of calcium chloride produces **three moles** of ions in aqueous solution

,one moleof calcium cations#1 xx "Ca"^(2+)# ,two molesof chloride anions#color(red)(2) xx "Cl"^(-)#

All three moles of ions will contribute to the osmotic pressure of the solution, so you can say that you have **osmoles** of solute particles **for every** **mole** of solute.

Now, use calcium chloride's **molar mass** to calculate ho many moles you get in that

#12.5 color(red)(cancel(color(black)("g"))) * "1 mole CaCl"_2/(111color(red)(cancel(color(black)("g")))) = "0.1126 moles CaCl"_2#

This means that the solution will contain

#0.1126 color(red)(cancel(color(black)("moles CaCl"_2))) * "3 osmoles of ions"/(1color(red)(cancel(color(black)("mole CaCl"_2)))) = "0.3378 osmoles"#

You can safely assume that the volume of water will be equivalent to the volume of the solution, which means that the osmolarity of the solution will be

#"osmolarity" = "0.3378 osmoles"/"1 L" = color(green)(|bar(ul(color(white)(a/a)"0.34 osmol L"^(-1)color(white)(a/a)|)))#

I'll leave the answer rounded to two **sig figs**, despite the fact that you only have one sig fig for the volume of water.