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

To find the molecular mass of BHT, we calculate the freezing point depression, determine the molality of the solution, and then rearrange the formula to solve for the molecular mass using the mass of BHT and the mass of benzene.

Step-by-step explanation:

To determine the molecular mass of butylated hydroxytoluene (BHT), we need to use the freezing point depression principle. First, we calculate the freezing point depression (ΔTf) which is the difference between the freezing point of pure benzene and the freezing point of the solution. Since the pure benzene freezes at 5.5 °C, the depression is ΔTf = 5.5 °C - 4.880 °C = 0.620 °C.

Next, we use the formula for freezing point depression: ΔTf = i * Kf * m, where 'i' is the van't Hoff factor (for BHT, i=1 since it doesn't ionize), 'Kf' is the cryoscopic constant of benzene (5.065 °C/m), and 'm' is the molality of the solution.

After calculating molality (m = ΔTf / Kf), we find the number of moles of BHT by using the mass of BHT divided by the molar mass of BHT. Finally, to find the molar mass, we rearrange the formula to: Molar Mass of BHT = mass of BHT / (mass of benzene * m). By substituting the values into the formula, we can solve for the molecular mass of BHT.

Answer 2

Molecular mass of BHT is 204,2 g/mol

Step-by-step 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 (mole Solute)/(kgSolvent)`

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

`(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:

`(2,500g)/(0,01224 moles BHT) =` 204,2 g/mol

I hope it helps