Question

How many moles of solute are there in the following 1.95×10^-1 m urea solution made by dissolving the urea in 500.0 g of water: ______ mol

Answer 1

0.0975 mol of solute (urea).

Step-by-step explanation:

Let's remember the formula of molality:

`Molality\text{ \lparen m\rparen=}\frac{moles\text{ of solute}}{kilograms\text{ of solvent}}=(mol)/(kg).`

As we have the mass of the solvent (water) in g but not in kg, we have to convert it. Remember that 1 kg equals 1000 g:

`500.0\text{ g }\cdot\frac{1\text{ kg}}{1000\text{ g}}=0.5\text{ kg.}`

Now, let's solve for 'moles of solute' and replace the data that we have, like this:

`\begin{gathered} moles\text{ of solute=molality}\cdot kilograms\text{ of solvent,} \\ moles\text{ of solute=1.95}\cdot10^(-1)\text{ m}\cdot0.5\text{ kg,} \\ moles\text{ of solute=0.0975 moles.} \end{gathered}`

The answer would be that we have 0.0975 mol of solute (urea) in the solution.