C. You are asked to measure the levels of the antioxidants BHT, benzoic acid and

Question

C. You are asked to measure the levels of the antioxidants BHT, benzoic acid and ascorbic acid in a prepared meal. In order to do this the meal is first homogenized, then a 50.2g sample is freeze dried resulting in a dry weight of 10.7g. A 2.4g portion of the freeze- dried meal homogenate is dissolved in 20.0mL of water in a separating funnel. This solution is shaken with 20.0mL of octanol and left to separate into 2 layers. For each antioxidant, give an explanation for which layer (upper or lower) it primarily resides in The concentration of benzoic acid in the upper layer is found to be 0.15mg/mL. What is the total amount of benzoic acid in the initial 50.2g sample of the meal? a. b. The octanol-water partition coefficient logPow for the antioxidants BHT, benzoic acid and ascorbic acid 5.1, 1.87 and -1.85 respectively and the density of octanol is 0.82g/mL.

Explanation / Answer

a)BHT or butylated hydroxytoluene is lipophilic so it dissolves in organic liquid like octanol ,,thus goes into the octanol or organic layer.

Ascorbic acid and benzoic acid are polar compounds,so dissolves in aqueous layer

b)log Pow=octanol-water partition coefficient=[A]octanol/[A]aqueous (ratio of the concentration of A in octanol to the concentration of species A in water)

1) log Pow(benzoic acid)=1.87=[benzoic acid]o/[benzoic acid]aq

given: density of octanol=0.82g/ml(denser than water of 1g/ml) ,thus octanol forms the upper layer

[benzoic acid]o=0.15mg/ml

So, 1.87=0.15mg/ml/[benzoic acid]aq

[benzoic acid]aq=0.0802 mg/ml

Actual concentration of solution of meal prepared=2.4g/20ml=2400 mg/ml

So,fraction of benzoic acid=0.0802/2400=3.342*10^-5

mass of benzoic acid in initial 50.2g=3.342*10^-5 *50.2g=0.00167752 g=1.677 mg

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