Question

Cuál es el punto de ebullición de una solución acuosa de urea al 20 % m/m (20g de soluto por cada 80g de solvente) , si la masa molar de urea es 60 g/mol. (Ke= 0,52 °C/m)

Answer 1

The question is: What is the boiling point of an aqueous solution of urea at 20% m / m (20g of solute for every 80g of solvent), if the molar mass of urea is 60 g / mol. (Kb = 0.52 ° C / m)

Answer: The boiling point of given aqueous solution of urea is
`2.145^(o)C`.

Step-by-step explanation:

Given: Mass of solute = 20 g

Mass of solvent = 80 g (1 g = 0.001 kg) = 0.08 kg

`K_(b) = 0.52^(o)C/m`

Molar mass of urea = 60 g

Molality is the number of moles of solute present in a kg of solvent.

Moles is the mass of a substance divided by its molar mass. So, moles of urea is calculated as follows.

`Moles = (mass)/(molar mass)\\= (20 g)/(60 g/mol)\\= 0.33 mol`

Now, molality of given solution is as follows.

`Molality = (moles)/(mass(in kg))\\= (0.33 mol)/(0.08 kg)\\= 4.125 m`

Formula used to calculate the boiling point is as follows.

`\Delta T_(b) = K_(b)m\\= 0.52^(o)C/m * 4.125 m\\= 2.145^(o)C`

Thus, we can conclude the the boiling point of given aqueous solution of urea is
`2.145^(o)C`.