# What is the osmolarity of a solution that contains #"25 g"# of urea in #"0.4163 L"# of solution?

##### 1 Answer

#### Explanation:

A solution's **osmolarity** basically tells you the number of moles of **particles that contribute to the solution's osmotic pressure** present in one liter of solution.

A particle that contributes to a solution's osmotic pressure is called an **osmole**.

Now, *urea*, **non-electrolyte**, which means that it does not dissociate into ions when dissolved in water. Simply put, every molecule of urea dissolved in solution will *not dissociate* to produce additional particles of solute.

This implies that **every mole** of urea dissolved in solution will produce **one osmole** of particles of solute.

Use the **molar mass** of urea to calculate how many moles you have in that sample

#25 color(red)(cancel(color(black)("g"))) * "1 mole urea"/(60.055color(red)(cancel(color(black)("g")))) = "0.4163 moles urea"#

Assuming that the volume of the solutionThis means that the solution's *osmolarity* will be equal to

#0.4163 color(white)(a)color(red)(cancel(color(black)("moles")))/"1 L" * "1 Osmol"/(1color(red)(cancel(color(black)("mole")))) = color(green)(|bar(ul(color(white)(a/a)color(black)("0.42 Osmol L"^(-1))color(white)(a/a)|)))#

I'll leave the answer rounded to two **sig figs**, but keep in mind that you only have one sig fig for the volume of the solution.