Answer:
The molar mass of the unknown solute is 106,9 g/m
Explanation:
Cryoscopic descent formula to solve this
ΔT = Kf . m
Be careful because units in Kfp are K/m, so let's get the ΔT degrees °C in K
3,91°C = 3,91 K
It's a difference, in the end it does not matter
For example you can have 5° C as the final temperature and as initial, 1,09 °C -- ΔT is 5 - 1.09 = 3.91
What happens in Kelvin?
5°C + 273 = 278 K
1,09° C + 273 = 274,09 K
ΔT = 278 K - 274,09 K = 3,91 K
3,91 K = 20,1 K/m * m
3,91 K / 20,1 m/K = m
0,194 = m (molality)
Molality means moles from solute in 1 kg of solvent.
1kg = 1000 g
1000 g ________ 0,194 moles
50 g _________ x
x = (50 g * 13,77 moles) / 1000 g = 9,72 *10-3 moles
Moles = mass / molar mass
Molar mass = mass / moles
Molar mass = 1,04 g / 9,72 *10-3 moles
Molar mass = 106,9 g/m
