Calculate new freezing point of 0250 mol naphthalene in 245

Calculate new freezing point of 0.250 mol naphthalene in 2.45 mol chloroform. k_f=4.68 C and normal freezing point of chloroform=-63.5 C.

mass of chloroform = moles x molar mass

mass of chloroform = 2.45 mol x 119.38 g/mol

mass of chloroform = 292.481 g

mass of chloroform = 0.292481 kg

now

molality = moles of napthalene / mass of chloroform (kg)

molality (m) = 0.25 mol / 0.292481 kg

molality (m)= 0.854756 mol/kg

now

depression in freezing point = molality x Kf

depression in freezing point = 0.854756 x 4.68

depression in freezing point = 4 C

now

depression in freezing point = freezing point of pure solvent chloroform - freezing point of solution

-63.5 C - freezing point of solution = 4 C

freezing point of solution = -63.5 - 4 C

freezing point of solution = -67.5 C