The freezing temperature of benzene is 5.40°c, a solution of 1.15g of napthalene in 100g of benzene has a freezing point of 4.95°c.Calculate the molecular weight of napthalene kf =5.12

Sure, here is the step by step solution:

1. First, we need to calculate the depression in freezing point, which is the difference between the freezing point of the pure solvent and the freezing point of the solution.

   ΔTf = Tf(solvent) - Tf(solution) = 5.40°C - 4.95°C = 0.45°C

2. The formula for calculating the molecular weight (M) of the solute using freezing point depression is:

   M = (Kf * w * 1000) / (W * ΔTf)

   where: Kf is the cryoscopic constant of the solvent (benzene in this case), which is given as 5.12 K kg / mol w is the weight of the solute (napthalene in this case), which is given as 1.15 g W is the weight of the solvent (benzene in this case), which is given as 100 g ΔTf is the depression in freezing point, which we calculated in the first step as 0.45°C

3. Substituting the given values into the formula, we get:

   M = (5.12 K kg / mol * 1.15 g * 1000) / (100 g * 0.45°C) = 131.2 g/mol

So, the molecular weight of napthalene is approximately 131.2 g/mol.