Question

Butylated hydroxytoluene (BHT) is used as an antioxidant in processed foods. (It prevents fats and oils from becoming rancid.) A solution of 2.500 g of BHT in 100.0 g of benzene had a freezing point of 4.880 oC. What is molecular mass of BHT?. Kf for benzene is 5.065 oC/m

Answer 1

Answer:

Molecular mass of BHT is 204,2 g/mol

Explanation:

To answer this question you need to know that Freezing-point depression (A colligative property) is the decrease of the freezing point of a solvent on the addition of a non-volatile solute. The formula is:

ΔT = Kf m

Where ΔT is the freezing point depression (5,5°C - 4,880°C =  0,62°C

Kf that is freezing point molar constant of the solvent (5,065°C/m)

And m that is molality (moles of solute/kg of solvent). Replacing:

$m = 0,1224 \frac{mole Solute}{kgSolvent}$

Knowing you have 100,0g of solvent ≡ 0,1000 kg:

$\frac{0,1224 moles}{1 kg Solvent} *0,1000 kg$ = 0,01224 moles of solute ≡ BHT

As grams of BHT are 2,500, molecular mass of BHT is:

$\frac{2,500g}{0,01224 moles BHT} =$ 204,2 g/mol

I hope it helps