Answer:
The experimental molar mass of benzophenone is 182 g/m (option A)
Explanation:
ΔT = Kf . m . i
(i means the Van't Hoff factor, since benzophenone is not electrolyte, the value for i is 1)
ΔT = T° - T' (Melting temp sv pure - Melting temp sv in sl)
Kf is data (the cryoscopic constant)
m is molality (moles from solute in 1kg of solvent)
6,55°C - 3,19°C = 20,0° C/m . m
3,36 °C = 20,0 C/m . m
3,36 °C /20,0 m/C = m
0,168 = m
We have 0,168 moles of benzophenone in 1 kg of cyclohexane but we don't have 1kg, we have just 15 g so, we need the rule of three.
1000 g ______ 0,168 moles
15 g ________ (15 g . 0,168 m) / 1000 g = 0,00252 m
Now we can get the molar mass:
0,458 g of benzophenone / 0,00252 moles = 181,7 g/m
