Answer:
51.14 g
Explanation:
When a nonvolatile compound is added to a solvent, the freezing and the boiling point are changed, a process called cryoscopy and ebullioscopy, respectively. To calculate the change in temperature, the equation is:
ΔT = K.W.i
Where K is a constant for the solvent, W is the molality, and i is the van't Hoff factor.
The molality can be calculated by:
W= m1/(M1*m2)
Where m1 is the mass of the solute (in g), M1 is the molar mass of the solute (in g), and m2 is the mass of the solvent (in kg). X is the solvent.
The van't Hoff factor relates to the particles produced when the compound dissociates. For organic compounds, such as urea, we can use i = 1.
So, for Urea, M1 = 60.0 g/mol, m1 = 40.1 g, m2 = 1100 g = 1.10 kg. So:
W = 40.1/(60*1.10)
W = 0.6076 M
3.9 = K*0.6076*1
K = 6.42 °C/M
The value of K is the same indepentend of the solute. So, for iron (III) nitrate:
M1 = 241.86 g/mol, m2 = 1.10 kg, i = 3.16, ΔT = 3.9°C
3.9 = 6.42*W*3.16
20.2872W = 3.9
W = 0.1922
0.1922 = m1/(241.86*1.10)
m1 = 51.14 g
