Question

A certain substance X has a normal boiling point of 124.2 °C and a molal boiling point elevation constant K,-06-0C-kg-mol ·A solution is prepared by dissolving some urea ((N112)CO) in 650. g ofl. This solution boils at 124.7 oC, Calculate the mass of urea that was dissolved. Be sure your answer has the correct number of significant digits. 31.48 g

Answer 1

Answer:

32 g

Explanation:

The increase in the boiling point of X can be calculated using the following expression.

ΔT = Kb × b

where,

ΔT: increase in the boiling point

Kb: molal boiling point constant (0.62 °C.kg/mol) (I looked it on the web)

b: molality of the solute

ΔT = Kb × b

(124.7°C - 124.2°C) = (0.62 °C.kg/mol) × b

b = 0.81 mol/kg

The mass of X is 650 g (0.650 kg). Then, the moles of urea (solute) are:

$\frac{0.81molUrea}{1kgX} .0.650kgX=0.53molUrea$

The molar mass of urea is 60.06 g/mol. The mass of urea is:

$0.53mol.\frac{60.06g}{mol} =32g$