Question

The mole fraction of urea (MW = 60.0g/mol) in a solution prepared by dissolving 16g of urea in 39g of H20 (MW = 18.02g/mol) is a) 0.11b) 0.13c) 0.37d) 0.58e) 9.1

Answer 1

Step 1 - What is molar fraction?

The molar fraction of a substance can be obtained by dividing its number of moles by the total number of moles in the solution (i.e., moles of solute + solvent):

`molar\text{ fraction = }\frac{number\text{ of moles of solute}}{total\text{ number of moles}}`

Step 2 - Calculating the molar fraction of urea

Let's calculate the number of moles for each substance in the solution (water and urea). In order to do so, we just have to divide their mass by their molar mass:

`\begin{gathered} for\text{ urea}\rightarrow16/60=0.26 \\ for\text{ water }\rightarrow39/18=2.16 \end{gathered}`

The molar fraction of urea can be writen thus as:

`molar\text{ fraction of urea = }\frac{0.26}{2.16\text{ + 0.26}}=(0.26)/(2.42)=0.11`

Answer: the molar fraction of urea in this solution is 0.11